Paris Conference (1971): Standardization in Human Cytogenetics

Transcription

1 Special Section Cytogenet Genome Res 1972;11: : Standardization in Human Cytogenetics Sponsored by The National Foundation March of Dimes at The Hotel Frantel, Rungis Orly, France September 2-4, 1971 Conference Scientific Editors: John L. Hamerton, D.Sc. Patricia A. Jacobs, D.Sc. Harold P. Klinger, M.D., Ph.D. Assistant Editor: Edwin S. Geffner, M.S. Contents Introduction 317 Recommended Changes in Chicago Conference Nomenclature 317 Chromosome Banding Techniques 320 Methods and Terminology 320 Characterization of Chromosomes by Fluorescent Banding Techniques 323 Characterization of Chromosomes by Other Banding Techniques 328 Proposed Chromosome Band Nomenclature 332 Identification of Chromosome Landmarks and Bands 332 Designating Structural Chromosome Abnormalities by Breakage Points and Band Composition 338 Examples 343 Marker Chromosomes 350 Derivative and Recombinant Chromosomes 350 Identification of Human Male Meiotic Chromosomes 353 Chromosome Measurements 357 Autoradiography 357 References 359 Signatories PARIS CONFERENCE (1971): Standardization in Human Cytogeneticsl Introduction

2 Technical developments have made possible the identification of each of the human chromosomes. Establishing a standardized system of nomenclature to describe the chromosomes and chromosome regions revealed by the various new techniques therefore seemed desirable. Consequently, a group of workers concerned with human cytogenetics met in September, 1971, on the occasion of the Fourth International Congress of Human Genetics, Paris, to agree upon a uniform system of human chromosome identification. Their objective was extended by the appointment of a Standing Committee, which met in Edinburgh in January, 1972, and proposed a standardized system of designating not only individual chromosomes but also chromosome regions and bands. This proposal was subsequently accepted by the signatories of this report and has been embodied into it. The recommendations in this report, if adopted by the majority of investigators, should greatly improve communication in the field of human cytogenetics and thereby increase the value of information obtained in the next few years. Recommended Changes in Chicago Conference Nomenclature Usage of + and Signs The + or signs should be placed before the appropriate symbol where they mean additional or missing whole chromosomes. They should be placed after a symbol where an increase or decrease in length is meant. 1 In text, this report should be referred to as:. In references, this report should be listed as: : Standardization in Human Cytogenetics. Birth Defects: Original Article Series, VIII: 7, The National Foundation, New York. Reprinted with the courtesy of The National Foundation, New York (Dr. Daniel Bergsma, Editor, Birth Defects Series). Request reprints from: The National Foundation March of Dimes, 1275 Mamaroneck Avenue, White Plains NY (USA). 318 Examples 47, XY,+G 45, XY,-21 46, XY, lq+ 47, XY,+14p+ 45, XX,-D-G,+t(DqGq) 46, XY,-5,-12,+t(5pl2p),+t(5ql2q) 46, XX,-13,+t(13q21q) Male karyotype with 47 chromosomes, including an additional G-group chromosome. Male karyotype with 45 chromosomes and missing one chromosome No. 21. Male karyotype with 46 chromosomes, showing an increase in the length of the long arm of one chromosome No. 1. Male karyotype with 47 chromosomes, including an additional chromosome No. 14 which has an increase in the length of its short arm. Female karyotype with a balanced Robertsonian translocation between a D- and a G-group chromosome. Male karyotype with two translocations involving interchange of both whole arms of chromosomes Nos. 5 and 12. The breaks have occurred at or very near the centromere, and no information is available as to which centromere is included in either product.

3 Female karyotype with an unbalanced Robertsonian translocation between chromosomes Nos. 13 and 21; the long arm of chromosome No. 21 is present in triplicate. If desired, balanced Robertsonian translocations, as well as whole-arm translocations, may be recorded in briefer form; e.g., 45, XX,-D,-G,+t(DqGq) may be shortened to 45, XX, t(dqgq). Unbal- 319 anced karyotypes, however, should be written out completely, as in the last example above. Length Changes of Secondary Constrictions Increases or decreases in the length of secondary constrictions, or negatively staining regions, should be distinguished from increases or decreases in arm length owing to other structural alterations by placing the symbol h between the symbol for the arm and the + or sign. Examples 46, XY,16qh+ Male karyotype with 46 chromosomes, showing an increase in length of the secondary constriction on the long arm of chromosome No , XY,13ph- Male karyotype with 46 chromosomes, showing a decrease in the length of the negatively staining region on the short arm of chromosome No. 13. Structurally Abnormal Chromosomes All symbols for rearrangements are to be placed before the designation of the chromosome or chromosomes involved, and the rearranged chromosome or chromosomes always should be placed in parentheses. Examples 46, XX, r(18) Female karyotype with 46 chromosomes, including a ring chromosome No , X, i(xq) Female karyotype with 46 chromosomes, including one normal X chromosome and one chromosome represented by an isochromosome for the long arm of the X. 46, X, dic(y) Karyotype with 46 chromosomes, one X chromosome, and a dicentric Y chromosome. Abbreviating Lengthy Descriptions In the interests of clarity, complex rearrangements necessitating lengthy descriptions in the Chicago Conference nomenclature should be written out in full and in accord with that system the first time they are used in a report. At the discretion of the authors, an abbreviated version of the nomenclature might then be used subsequently, providing it is clearly defined immediately after the complete notation. Special Terminology In studies of interphase chromatin morphology, the terms X-chromatin (= X-body, Barr body) and Y-chromatin (= Y-body) should be used. The terms (chromosome) variant and inherited (chromosome) variant are recommended for use in situations where deviations from the norm of chromosome morphology are observed. Chromosome Banding Techniques Methods and Terminology

4 Several different technical procedures have been reported which produce banding patterns along the metaphase chromosomes. Although the biochemical basis of the various staining reactions is obscure, most of these procedures give similar cytologic results. In this report, the different staining patterns have been assigned provisional names based 321 either on the operational procedures used to obtain the patterns or on previously employed designations which have since come into general use. Methods which demonstrate constitutive heterochromatin are designated as C-staining methods, and the term C-band is used to describe a unit of chromatin stained by these methods (Fig. 1). The methods first published for demonstrating bands along the chromosomes were those that used quinacrine mustard or quinacrine dihydrochloride to produce a fluorescent banding pattern. These methods are named Q-staining methods and the resulting bands, Q-bands (Fig. 2). Other techniques which demonstrate bands along the chromosomes use the Giemsa dye mixture as the staining agent; they are generally termed G-staíníng methods and the resulting bands, G-bands (Fig. 3). One of the techniques using the Giemsa reagent, however, gives patterns which are opposite in staining r m M il > % 19 20! 5 í Mm I 9 ** ⅝⅝ I* « ii ä n ι * ** M $ ⅝.Jb X Y Fig. 1. The human karyotype: C-banding (courtesy of Dr. F. Ruddle). 322 intensity to those obtained by the G-staining methods. This technique is called the reversestaining Giemsa method (R-staining method) and the resulting bands, R-bands (Fig. 4). A band is defined here as a part of a chromosome which is clearly distinguishable from its adjacent segments by appearing darker or lighter with the Q-, G-, R-, or C-staining methods. Bands that stain darkly with one method may stain lightly with other methods. The chromosomes

5 are visualized as consisting of a continuous series of light and dark bands, so that by definition there are no interbands. ÊÈÈ; fl ÆÊÊ < ^» < ⅛ ⅞PP ^p⅛l IB ^⅝^ * _ *. A mm» II i m m t ji wm l * - ⅜» 1 If.. < :« ⅜»- -⅝ ⅛. D E * *» -*»- X Y F G F⅛. 2α. The human karyotype: Q-banding showing type A features (courtesy of Dr. K. Patau). 323 Characterization of Chromosomes by Fluorescent Banding Techniques The description to be given of the human somatic karyotype is based on the fluorescent staining pattern. Because most laboratories are not equipped for densitometry, the description has been confined to visually recognizable patterns; these have been confirmed, however, by comparison with the densitometric results of Caspersson et al. (1971). Identification of chromosomes on the basis of length, centromeric index, autoradio-graphic characteristics, and location of secondary constrictions, as outlined Fig. 2b. The human karyotype: Q-banding showing type B features (courtesy of Drs. C. Lin and I. Uchida). 324 in the Chicago Conference (1966) report, is retained in the present description. This applies to chromosomes Nos. 1 to 5, 9, 13 to 18, and the Y (X chromosomes in numbers greater than one can be identified by their late-replicating behavior). The numbers assigned to the remaining autosomes are based on their fluorescent banding patterns as given by Caspersson et al. (1971).

6 The designation of the additional chromosome associated with Down s syndrome has been retained as No. 21, although it is now known to be smaller than the No. 22. In the description that follows only major fluorescent bands will be referred to, even though in some cells these may appear to consist of several smaller bands. Faintly fluorescing bands are not referred to except when they are of special significance; generally, it may be assumed that they separate the major fluorescent bands or are located at the ends of the chromosome arms. In the description, diagnostic features indicated by A are those seen in fluorescent metaphases of fair technical quality (Fig. 2a), whereas those indicated by B are usually visible only in cells of good quality (Fig. 2b). When these details are not included in the text, the banding pattern is identical to that described under A. Features which may vary in fluorescent intensity or length or both between individuals and between homologs are indicated by C. The terms distal and proximal refer to the position of a band in respect to the centromere; centric means the area occupied by the centromere. Some mitoses show considerable nonuniformity in that the homologous chromosomes may differ greatly in overall fluorescence and relative length. Identification must be based, therefore, on the fluorescent banding patterns of the individual chromosome rather than on its overall intensity. However, intensity may serve as a secondary criterion, if due allowance is made for nonuniformity. The following terms will be used to indicate the approximate intensity of fluorescence: negative no or almost no fluorescence pale as on distal lp medium as the two broad bands on 9q intense as the distal half of 13q brilliant as on distal Yq No. 1 The long arm is that previously defined as the arm with a proximal secondary constriction. 325 A p: Distal, pale segment grading to a proximal, medium fluorescent segment. q: Central, intense band. Proximal, negative secondary constriction. B p: Proximal, medium fluorescent segment; divisible into two bands. q: Five medium fluorescent bands; central one most prominent. C q: Negative secondary constriction variable in length. 2 A Medium fluorescence along the whole length. B p: Four medium fluorescent bands; two central ones often appear as a single segment. q: Two central bands, sometimes accompanied by another two, all of medium fluorescence. Additional bands can be seen sometimes. A Single pale band in center of each arm separating medium fluorescent segments. Distal, medium fluorescent segment; longer in q than in p. B Single pale band at end of each arm; longer in p than in q. C q: Proximal band of variable fluorescence. A Medium fluorescence along the whole length. B p: Single central, medium fluorescent band. q: Proximal, intense band. Distal, pale band. C Intense centric band. A q: Central, long, medium fluorescent segment. Distal, pale segment. B p: Single medium fluorescent band; shorter and brighter than

7 on 4p. q: Distal, pale segment; divisible into a proximal, pale band and a distal, medium one. 326 No. 6 A p: Central, pale band separating medium fluorescent segments. q: Medium fluorescence along entire length. B q: Four medium fluorescent bands. No. 7 A p: Distal, short, medium fluorescent band. q: Two central, intense bands. Distal, medium fluorescent band. B p: Proximal, medium fluorescent band. No. 8 A Medium fluorescence along the whole length; q brighter than p. B p: Two evenly spaced, medium fluorescent bands. q: Two medium fluorescent bands in distal half; brighter than those on p. No. 9 A q: Proximal, negative segment corresponding to the secondary constriction. Two evenly spaced, medium fluorescent bands distal to the negative segment. B p: Central, medium fluorescent band. C q: Proximal, negative band (secondary constriction) variable in length. No. 10 A p: Medium fluorescence. q: Three evenly spaced bands; the most proximal one intense and the others medium in fluorescence. No. 11 A p: Medium fluorescence; longer than 12p. q: Short medium fluorescent band adjacent to the centromere; separated by a negative band from a more distal, medium fluorescent segment. No. 12 A p: Medium fluorescence; shorter than lip. q: Medium fluorescent band adjacent to the centromere; separated by a short, negative band from a more distal, me- 327 dium fluorescent segment. Distal segment longer than that of llq. N 13 A B C N 14 o A q: Distal half intense. q: Distal half intense; divisible into two bands.

8 p: Satellites and/or short arms with variable fluorescence. q: Proximal, intense band. q: Proximal half intense. Distal half pale; medium fluorescent band close to the distal end. C p: Satellites and/or short arms with variable fluorescence. No. 15 A q: Proximal half medium in fluorescence. Distal half pale; less fluorescent than either 13q or 14q. C p: Satellites and/or short arms with variable fluorescence. No. 16 A p: Medium fluorescence, less fluorescent than q. q: Proximal, negative segment corresponding to the secondary constriction. Distal to it, a medium fluorescent segment. C q: Negative secondary constriction variable in length. No. 17 A p: Overall pale fluorescence. q: Two segments of similar length; proximal one pale and distal one medium in fluorescence. B q: Narrow negative band separating proximal and distal segments. No. 18 A p: Overall medium fluorescence. q: Medium fluorescence; brighter than p. B q: Two bands of medium intensity; proximal one longer and brighter than distal one. No. 19 A Most weakly fluorescent chromosome in the karyotype. Short, proximal fluorescent bands on both arms; pale when compared to the whole karyotype. B Fluorescent band longer and brighter on p than on q. 328 No. 20 A Overall pale fluorescence; p medium and q pale in fluores cence. No. 21 A q: Proximal, intense segment. Distal, pale segment. C p: Satellites and/or short arms with variable fluorescence. No. 22 A Overall pale fluorescence. B q: Narrow, pale band in center of arm. C p: Satellites and/or short arms with variable fluorescence. X A p: Proximal, pale segment. Central, medium fluorescent band. q: Proximal, pale segment. Distal to it, a medium fluorescent band. B q: Three evenly spaced, medium fluorescent bands; most proximal one brightest. A p: Overall pale fluorescence. q: Proximal segment pale. Distal segment brilliant.

9 C q: The brilliant fluorescent segment on the end of q may vary in length and may be subdivided into two or more bands. The normal variation in length of the chromosome is associated with variation in length of the brilliant segment. Characterization of Chromosomes by Other Banding Techniques C-bands The banding patterns obtained with the various C-staining methods1 do not permit individual identification of each chromosome of the human somatic-cell complement. In this sense, C- bands are not strictly comparable to those obtained with the Q-,2 G-,;5 or R-staining methods.4 Used in 1 Pardue and Gall (1970); Arrighi and Hsu (1971); Chen and Ruddle (1971). 2 Caspersson et al. (1971). 3 Drets and Shaw (1971); Dutrillaux et al. (1971); Finaz and de Grouchy (1971, 1972); Patil et al. (1971); Schnedl (1971); Sumner et al. (1971); Seabright (1972); Wang and Federoff (1972). 4 Dutrillaux and Lejeune (1971). 329 conjunction with these techniques, however, the C-staining methods provide much useful information on the type and localization of chromatin throughout the complement. They are particularly valuable in such specialized studies as the characterization of male meiotic chromosomes, as will be described at the end of this report. In the following description, the C-bands are defined by their length and position along the chromosomes. The depth, or intensity, of staining is not taken into consideration. Unless otherwise indicated, the C-band corresponds in position to the centromeric region. No. 1 No. 2 No 3-8 No. 9 No. 10 No. 11 No. 12 No. 13 No No. 16 No. 17 No. 18 No X Y Large, extends from centromere into q. Small. Medium. Large, extends from centromere into q. Medium. Medium, but larger than on Nos. 10 or 12. Medium. Medium, but sometimes bipartite. Medium.

10 Large, extends from centromere into q. Medium. Medium, but larger than on No. 17. Medium. Medium. Very small band at centromere; large band on distal end of q. The C-bands on chromosomes Nos. 1, 9, and 16 and the large distal band on the Yq are all associated with obvious morphologic variability. G- and R-bands The banding patterns obtained with the G- and R-staining methods correspond with those obtained by Q-staining, except for the following chromosome segments (h = secondary constriction): Q-bandG-bandR-band C-band lqh negative qh negative qh negative distal Yq brilliant variable variable Bands which appear light, or unstained, with G-staining in general stain darkly with the R-band technique. The only exception is the 9qh, which appears lightly stained with both methods. As a rule, neither the G- nor R-staining methods clearly demonstrate those Q-bands which vary in length or intensity and which appear near the centromeres of chromosomes Nos. 3, 4, 13-15, 21, and 22. Morphologic variability in satellite size or density is reflected by variation in the size and staining intensity of the Q-, G-, R-, and C-bands. ιnι- Π-Ü-il ïï II í I⅞ i - -# lå-ii-u X Y Fig. 3. The human karyotype: G-banding (courtesy of Dr. H.J. Evans). 331 ft In ⅜ J f *? II Û Mm. æ3

11 ẁ w ii ïi 9i ⅝ 9 * si II 12 &í δ l IB * È -X- Y human karyotype: R-banding (courtesy of Dr. B. Dutrillaux). 332 However, none of these banding methods can distinguish late from early replicating X chromosomes. Proposed Chromosome Band Nomenclature Identification of Chromosome Landmarks and Bands Each chromosome in the human somatic-cell complement is considered to consist of a continuous series of bands, with no unhanded areas. The bands are allocated to various regions along the chromosome arms and delimited by specific chromosome landmarks. The bands and the regions they belong to are identified by numbers, with the centromere serving as the point of reference for the numbering scheme. Definitions The definition of a band has been given earlier as a part of a chromosome clearly distinguishable from adjacent parts by virtue of its lighter or darker staining intensity. A chromosome landmark is defined as a consistent and distinct morphologic feature that is an important diagnostic aid in identifying a chromosome. Landmarks include the ends of the chromosome arms, the centromere, and certain bands. A region is defined as any area of a chromosome lying between two adjacent landmarks. Designation of Arms, Regions and Bands The symbols p and q are retained to designate, respectively, the short and long arms of each chromosome. Regions and bands are numbered consecutively from the centromere outwards along each chromosome arm. Thus the two regions adjacent to the centromere are labeled 1 in each arm, the next, more distal regions, 2, and so on. A band used as a landmark is considered as belonging entirely to the region distal to the landmark and is accorded the band number of 1 in that region. A band bisected by the centromere is considered as two bands, each being labeled as band 1, in region 1, of the appropriate chromosome arm. In designating a particular band, four items are required: the chromosome number, the arm symbol, the region number, and the band number within that region. These items are given in order without spacing or 333 Table 1

12 Bands Serving as Landmarks which Divide the Chromosomes into Cytologically Defined Regions. The omission of an entire chromosome or a chromosome arm indicates that either both arms or the arm in question consists of only one region, delimited by the centromere and the end of the chromosome arm. Chromo- Number Landmarks some of (the numbers in parentheses are the region and band No. Arm regions numbers as shown in Fig. 5) 1 p 3 Proximal band of medium intensity (21), median band of medium intensity (31) q 4 Proximal negative band (21) distal to variable region, 2 P 2 q 3 3 P 2 q 2 4 q 3 5 q 3 6 P 2 7 q 2 P 2 q 3 8 P 2 9 q 2 P 2 q 3 10 q 2 11 q 2 12 q 2 13 q 3 14 q 3 15 q 2 16 q 2 17 q 2 18 q 2 21 q 2 X P 2 q 2 median intense band (31), distal medium band (41) Median negative band (21) Proximal negative band (21), distal negative band (31) Median negative band (21) Median negative band (21) Proximal negative band (21), distal negative band (31) Median band of medium intensity (21), distal negative band (31) Median negative band (21) Median negative band (21) Distal medium band (21) Proximal medium band (21), median band of medium intensity (31) Median negative band (21) Median band of medium intensity (21) Median intense band (21) Median band of medium intensity (21), distal band of medium intensity (31) Proximal intense band (21) Median negative band (21) Median band of medium intensity (21) Median intense band (21), distal intense band (31) Proximal intense band (21), distal medium band (31) Median intense band (21) Median band of medium intensity (21) Proximal negative band (21) Median

13 negative band (21) Median intense band (21) Proximal medium band (21) Proximal medium band (21) Q F⅛. 5. Diagrammatic representation of chromosome bands as observed with the Q-, G-, and R- staining methods; centromere representative of Q-staining method only P ¾ q (i } r \

14 Y X Negative or pale staining Q and G bands Positive R bands Positive Q and G bands Negative R bands Variable bands 336 punctuation. For example, lp33 indicates chromosome No. 1, short arm, region 3, band 3. Diagrammatic Representation of Landmarks and Bands The chromosome banding diagram shown in Fig. 5 is based on the patterns observed in different cells stained with either the Q-, G-, or R-band technique; the cells were not stained sequentially with two or more of these techniques. As indicated earlier, the banding patterns obtained with these staining methods agree sufficiently to allow the construction of a single diagram representative of all three techniques, although the position of the centromere has been indicated on the basis of the Q-band technique only. The diagram is not based on measurements of the length and position of the chromosome bands; however, the relative band sizes and distributions can be taken to be approximately correct. The bands are designated on the basis of their midpoints and not by their margins. No attempt has been made to indicate the intensity of fluorescence or staining, because this will vary with different techniques. Intensity has been taken into consideration, however, in determining which bands should serve as landmarks on each chromosome, apart from the centromere and chrom-atid ends, in order to divide the chromosome into natural, easily recognizable morphologic regions. (A list of these bands used in constructing Fig. 5 is provided in Table 1.) The C-staining method has not been taken into consideration in the preparation of this diagram. Subdivision of an Existing Landmark or Band In the event that a band serving as a landmark requires subdivision, all sub-bands derived from it should retain the original region and band number of that landmark (Fig. 6a). This rule is to be followed even if subdivision should cause one or more sub-bands to lie in an adjacent region. Whenever an existing band is to be subdivided, a decimal point should be placed after the original band designation followed by the number assigned to each sub-band. The sub-bands are numbered sequentially from the centromere outward. For example, if the original band lp33 were subdivided into three equal or unequal sub-bands, the sub-bands would be labeled lp33.1, lp33.2, and lp33.3, sub-band 33.1 being proximal and 33.3 distal to the centromere (Fig. 6b). Where the designation of the original band is in doubt, the decimal point should be followed by a question mark (?) and then the proposed sub-band number, e.g., Ip33.?l. Finally, if a sub-band is to be subdivided, additional digits 337 REGION BAND A NO. NO. B (al I I I33-31 I 312 F

15 _1 1 1 B Fig. 6a. Example illustrating the convention for numbering the subdivisions of a landmark bridging two regions: (A) the original landmark (band 31); (B) the subdivision of band 31 into three equal bands 31.1, 31.2, and 31.3; (C) alternatively, the subdivision of band 31 into three unequal bands; (D) further subdivision of band 31.3 into three equal bands 33.31, 33.32, and Fig. 6b. Example illustrating the convention for numbering the subdivisions of a band within a region: (A) the original band 33; (B) three equal bands 33.1, 33.2, and 33.3; (C) alternatively, the subdivision of band 33 into three unequal bands; (D) further subdivision of band 33.1 into three equal bands 33.11, 33.12, and but no further punctuation should be used; e.g., sub-band lp33.1 might be further subdivided into lp33.11, lp33.12, etc. (see Fig. 6). Designating Structural Chromosome Abnormalities by Breakage Points and Band Composition Two systems for designating structural abnormalities are presented. One is a short system in which the nature of the rearrangement and the break point or points are identified by the bands (or regions) in which the breaks occur. Because of the conventions built into this system, the band composition of the abnormal chromosomes present can be readily inferred from the information provided in the symbolic description. The other is a detailed system which, besides identifying the type of rearrangement, defines each abnormal chromosome present in terms of its band composition. The two systems are not mutually exclusive and can be used to complement each other. The notation used to identify the rearrangement and the method of specifying the break points are common to both systems and will be presented first. Specification of Chromosome Rearrangements Single and three-letter designations as adopted at the Chicago Conference are used to specify rearranged (i.e., structurally altered) chromosomes. Immediately following the symbol identifying the type of rearrangement, the number of the chromosome involved in the change is specified within parentheses, e.g., r(18); inv(2). If two or more chromosomes have been altered, a semicolon (;) is used to separate their designations. If one of the rearranged chromosomes is a sex chromosome, then it should be listed first; otherwise the chromosome having the lowest chromosome number is always specified first, e.g., t(x;3), t(2;5). The only exception to this rule involves certain three-break rearrangements in which part of one chromosome is inserted at a point of breakage in another chromosome. In this event, the receptor chromosome is specified first, regardless of whether it is a sex chromosome or whether its number is higher or lower than that of the donor chromosome. For translocations involving three separate chromosomes, the rule is still followed that the sex chromosome or the autosome with the lowest number is specified first. The chromosome listed next is the one which receives a segment from the first chromosome, and the chromosome speci- 339 Table 2 Nomenclature Symbols Additional to those Recommended by the Chicago Conference (1966).

16 del deletion der derivative chromosome dup duplication ins insertion inv ins inverted insertion rep reciprocal translocation1 rec recombinant chromosome rob Robertsonian translocation1 ( centric fusion ) tan tandem translocation1 ter terminal or end (pter = end of short arm; qter = end of long arm) : break (no reunion, as in a terminal deletion) :: break and join from to 1 Optional, where it is desired to be more precise than provided by the use of t as recommended by the Chicago Conference. 340 fied last is the one which donates a segment to the first listed chromosome. Some additional designations are required in the present nomenclature to identify rearrangements. These are listed in Table 2 and explained below. Deletions: The abbreviation del is used to designate a chromosome deletion. Translocations: The use of the semicolon for differentiating balanced from unbalanced translocations is abandoned in the present nomenclature. All translocations are specified by the symbol t. If the type of translocation, i.e., Robertsonian, reciprocal, or tandem, is to be emphasized, t may be replaced with rob, rep, or tan, respectively. (The symbol rep is used for reciprocal translocations to avoid confusion with rec, which is used to designate a recombinant chromosome.) Translocations resulting in a dicentric chromosome are designated by tdic. However, a dicentric generated by an internal rearrangement within the chromosome is indicated simply by die. Three-break Rearrangements: These may involve one, two, or three chromosomes. Rearrangements involving three or more chromosomes will be referred to as complex translocations. Several terms have been employed in the cytogenetic literature for three-break rearrangements involving one or two chromosomes: these include shift, insertion, and transposition. In this report all three-break rearrangements involving one or two chromosomes are referred to as insertions since they result from the excision of a segment following two breaks in one chromosome arm and its insertion at a point of breakage in either the same arm, the opposite arm of the same chromosome, or in another chromosome. The order of the bands on the inserted segment in relation to the centromere at the new site may be the same as at the original site (direct insertion) or may be reversed (inverted insertion). The abbreviation ins is used to indicate a direct insertion and inv ins to indicate an inverted insertion. Specification of Break Points The location of any given break is specified by the band in which that break has occurred. Since it is not possible at present to define band interfaces accurately, a break suspected at an interface between two bands is identified arbitrarily by the higher of the two band numbers, i.e., the number of the band more distal to the centromere.

17 341 A given break may sometimes appear to be located in either of two consecutive bands. A similar situation may occur when breaks at or near an interface between two bands are studied with two or more techniques. In this event, the break can be specified by both band numbers separated by the word or; e.g., lq23or24, indicating a break in either band lq23 or band lq24. If a break can be localized to a region but not to a particular band, only the region number should be specified; e.g., lpl, instead of lpllorl2orl3. If the break point can be assigned only to two adjacent regions, both suspected regions should be specified, e.g., lq2or3. Short System In this system structurally altered chromosomes are defined only by their break points. The break points are specified within parentheses immediately following the designation of the type of rearrangement and the chromosome(s) involved as described earlier. The break points are identified by band designations as just outlined but without specifying the chromosome number. For example, del(l)(q21) defines a terminal deletion in the long arm of chromosome No. 1 resulting from a break at band lq21. Two-break Rearrangements: When both arms of a single chromosome are involved in a twobreak rearrangement, the break point in the short arm is always specified before the break point in the long arm; e.g., inv(2)(p21q31) defines a pericentric inversion in chromosome No. 2 with break points in bands 2p21 and 2q31. When the two breaks occur within the same arm, the break point more proximal to the centromere is specified first; e.g., inv(2)(pl3p23) defines a paracentric inversion in the short arm of chromosome No. 2 with break points in bands 2pl3 and 2p23. Three-break Rearrangements: When an insertion within a single chromosome occurs, the break point at which the chromosome segment is inserted is always specified first. The remaining break points are specified in the same way as in a two-break rearrangement, i.e., the more proximal break point of the inserted segment is specified next and the more distal one last. Proximal and distal refer here to the positions of the break points following the rearrangement and not necessarily their original positions. For example, inv ins(2)(ql3p23pl3) defines an inverted insertion in chromosome No. 2 of the short-arm segment lying between bands 2pl3 and 2p23 into the long arm at band 2ql3. Because the insertion is inverted, band 2p23 is now proximal and 2pl3 distal to the centromere. 342 Rearrangements Affecting Two or More Chromosomes: The break points are specified in the same order as the chromosomes involved are specified, and a semicolon is used to separate the break points (punctuation is never used to separate break points in the same chromosome). For example, rcp(2;5)(q21;q31) defines a reciprocal translocation between the long arms of chromosomes Nos. 2 and 5, with break points at bands 2q21 and 5q31. Detailed System In this system structurally altered chromosomes are defined by their band composition. The conventions used in the short system are retained in the present system, except that an abbreviated description of the band composition of the rearranged chromosome or chromosomes is specified within the final pair of parentheses, instead of only the break points. Additional Symbols: A single colon (:) is used to indicate a chromosome break and a double colon (::) to indicate break and join. In order to avoid an unwieldy description, an arrow (- > ), meaning from to, is employed. The end of a chromosome arm may be designated either by its band designation or by the symbol ter, meaning terminal, preceded by the arm

18 designation; e.g., pter indicates end of short arm and qter, end of long arm. When it is necessary to indicate the centromere, the abbreviation cen should be used. Designating the Band Composition of a Chromosome: The description starts at the end of the short arm and proceeds through to the end of the long arm, with the bands being identified in the order in which they occur in the rearranged chromosome. If the rearrangement is confined to a single chromosome, the chromosome number is not repeated in the band description. If more than one chromosome is involved, however, the bands and chromatid ends are identified with the appropriate chromosome number. If, owing to a rearrangement, no short-arm segment is present at the end of either arm, the description of the structurally rearranged chromosome starts at the end of the long-arm segment with the lowest chromosome number. Where more than one chromosome is involved, the chromosome descriptions are presented in the same numerical order as the chromosomes involved in the rearrangement. In the special case of an unbalanced reciprocal translocation between the long arm of one chromosome and the short arm of another, the derivative chromosome carrying the centro- 343 mere belonging to the chromosome with the lower chromosome number is described first. Examples In all the examples presented in this section the short-system designation is shown first and the detailed-system designation second, followed by a brief explanation of the latter. Isochromosomes 46, X, i(xq) 46, X, i(x)(qter cen qter) Break points in this type of rearrangement are at or close to the centromere and cannot be specified. The designation indicates that both entire long arms of the X chromosome are present and separated by the centromere. Terminal Deletions 46, XX, del(l)(q21) 46, XX, del(l)(pter- > q21:) The single colon (:) indicates a break at band lq21 and deletion of the long-arm segment distal to it. The remaining chromosome consists of the entire short arm of chromosome No. 1 and part of the long arm lying between the centromere and band lq21. Interstitial Deletions 46, XX, del(l)(q21q31) 46, XX, del(l)(pter q21::q31 qter) The double colon (::) indicates breakage and union of bands lq21 and lq31 in the long arm of chromosome No. 1. The segment lying between these bands has been deleted. 344 Paracentric Inversions 46, XY, inv(2)(pl3p24) 46, XY, inv(2)(pter- > p24::pl3 p24::pl3- > qter) Breakage and union have occurred at bands 2pl3 and 2p24 in the short arm of chromosome No. 2. The segment lying between these bands is still present but inverted, as indicated by the reverse order of the bands with respect to the centromere in this segment of the rearranged chromosome. Pericentric Inversions

19 46, XY, inv(2)(p21q31) 46, X Y, inv(2)(pter- > p21:: q3 l p21:: q31 qter) Breakage and union have occurred at band 2p21 in the short arm and 2q31 in the long arm of chromosome No. 2. The segment lying between these bands is inverted. Ring Chromosomes 46, XY, r(2)(p21q31) 46, XY, r(2)(p21 q31) Breakage has occurred at band 2p21 in the short arm and 2q31 in the long arm of chromosome No. 2. With deletion of the segments distal to these bands, the broken ends have joined to form a ring chromosome. Note the omission of the colon or double colon. Dicentric Chromosomes 46, X, dic(y)(ql2) 46, X, dic(y)(pter ql2::ql2 ρter) Breakage and union has occurred at band Yql2 on sister chromatids to form a dicentric Y chromosome. 345 Reciprocal Translocations 46, XY, t(2;5)(q21;q31) 46, XY, t(2;5)(2pter 2q21: :5q31 5qter;5pter 5q31: :2q21- > 2qter) Breakage and union have occurred at bands 2q21 and 5q31 in the long arms of chromosomes Nos. 2 and 5 respectively. The segments distal to these bands have been exchanged between the two chromosomes. Note that the derivative chromosome with the lowest number (i.e., No. 2) is designated first. 46, XY, t(2;5)(pl2;q31) 46, XY, t(2;5)(2qter 2pl2::5q31-*5qter;5pter- > 5q31::2ρl2- -2pter) Breakage and union have occurred at band 2pl2 in the short arm and band 5q31 in the long arm of chromosomes Nos. 2 and 5 respectively. The segments distal to these bands have been exchanged between the two chromosomes. Note that the derivative chromosome bearing the No. 2 centromere has no terminal short-arm segment and, therefore, its description starts with the long-arm end having the lowest number (i.e., 2qter). Robertsonian Translocations 45, XX, t(13;14)(pll;qll) 45, XX, t(13;14)(13qter 13pll::14qll 14qter) Breakage and union have occurred at band 13pll in the short arm and band 14qll in the long arm of chromosomes Nos. 13 and 14 respectively. The segment distal to band 14qll has been translocated onto chromosome No. 13 at band 13pll. The rest of chromosome No. 14, with its centromere, has been lost, along with the original segment distal to 13pll, i.e., 13pter -13pll. 45, XX, t(13ql4q) 45, XX, t(13;14)(13qter- > cen- > 14qter) Breakage has occurred at or near the centromere in chromosomes Nos. 13 and 14. The rearranged chromosome has the long arms of both chromosomes separated by a centromere whose origin might have been either chromosome. Both short arms have been lost , XX, tdic(13;14)(pll;pll)

20 45, XX, tdic(13;14)(13qter- > 13pll::14pll 14qter) Breakage and union have occurred at bands 13pll and 14pll in the short arms of chromosomes Nos. 13 and 14 respectively. The segments distal to these bands have been deleted, and the remaining segments have joined at the break points in the short arms to form a dicentric translocation chromosome. Direct Insertions within a Chromosome 46, XY, ins(2)(pl3q21q31) 46, XY, ins(2)(pter- > pl3::q31- > q21::ρl3- > q21::q31 ρter) Breakage and union have occurred at band 2pl3 in the short arm and bands 2q21 and 2q31 in the long arm of chromosome No. 2. The long-arm segment between 2q21 and 2q31 has been inserted into the short arm at band 2pl3. The original orientation of the inserted segment has been maintained in its new position; i.e., 2q21 remains more proximal to the centromere than 2q31. Inverted Insertions within a Chromosome 46, XY, inv ins(2)(pl2q31q21) 46, XY, inv ins(2)(pter ρl3: :q21 q31: :pl3 q21: :q31- qter) Breakage and union have occurred at the same bands as in the previous example and the insertion is the same except that the inserted segment has been inverted; i.e., 2q21 in the inserted segment is now more distal to the centromere than 2q31. The orientation of the bands within the segment has thus been reversed with respect to the centromere. Direct Insertions between Two Chromosomes 46, XY, ins(5;2)(pl4;q22q32) 46, XY, ins(5;2)(5pter- > 5ρl4::2q32- > 2q22::5ρl4- > 5qter;2pter- > 2q22::2q32 2qter) Breakage and union have occurred at band 5pl4 in the short arm and bands 2q22 and 2q32 in the long arm of chromosomes Nos. 5 and respectively. The segment between 2q22 and 2q32 has been inserted into the short arm of chromosome No. 5 at band 5pl4. The original orientation of the inserted segment has been maintained in its new position; i.e., 2q22 remains more proximal to the centromere than 2q32. Note that the receptor chromosome is specified first. Inverted Insertions between Two Chromosomes 46, XY, inv ins(5;2)(pl4;q32q22) 46, XY, invins(5;2)(5pter 5ρl4::2q22 2q32::5pl4 5qter;2pter 2q22::2q32- > 2qter) Breakage and union have occurred at the same bands as in the previous example and the insertion is the same except that the inserted segment has been inverted; i.e., 2q22 is now more distal to the centromere of the recipient chromosome than 2q32. Complex Translocations 46, XX, t(2;5 ;7)(p21 ;q23 ;q22) 46, XX, t(2;5;7)(2qter 2ρ21::7q22- -7qter;5pter 5q23::2ρ21- > 2pter;7pter- -7q22: :5q23- > 5qter) Breakage and union have occurred at band 2p21 in the short arm of chromosome No. 2 and at bands 5q23 and 7q22 in the long arms of chromosomes Nos. 5 and 7 respectively. The segment of chromosome No. 2 distal to 2p21 has been translocated onto chromosome No. 5 at 5q23; the segment of chromosome No. 5 distal to 5q23 has been translocated onto chromosome No. 7 at 7q22; and the segment of chromosome No. 7 distal to 7q22 has been translocated onto chromosome No. 2 at 2p21. Note that the chromosome specified first is the one with the lowest

21 number; the chromosome specified next is the one receiving a segment from the first one listed, and the chromosome specified last is the one donating a segment to the first chromosome listed. Four-Break Rearrangements There are a very large number of possible four-break rearrangements. These can be described using the conventions outlined here. A single 348 B -Oder(2) q21 JL *iíγ der (5) -o--o- Fig. 7. Pachytene diagram of a t(2;5)(q21;q31) reciprocal translocation heterozygote used to specify the disjunctional possibilities and derivative chromosome combinations given in Table 3. Letters A, B, C, and D designate whole segments extending from chromosome ends (telomeres) to break points. Bands delimiting break points, only approximately to size, are shown. 349 Table 3 Designation of Unbalanced Karyotypes. Use of der Symbol to Designate Unbalanced Karyotypes Derived by Segregation in a Reciprocal Translocation Hetero-zygote. Based on the Pachytene Diagram in Fig. 7. Disjunction Unbalanced Karyotype of zygote resulting from an unbalanced gamete (segregation) gamete fertilized by a normal gamete Adjacent ABCB AD CD Adjacent ABAD CBCD ABAB AD AD CBCB CD CD 3:1** AB CB AD CB CD AB CD AD CB AD CD 46, XX, der(5), t(2;5)(q21;q31)mat 46, XY, der(2), t(2;5)(q21;q31)mat 46, XY,-5,+der(2))t(2;5)(q21 ;q3 l)mat 46, XY,-2,+der(5), t(2;5)(q21 ;q3 l)mat 46, XX,+2,-5

22 46, XY,-2,-5,+der(2),+der(2), t(2;5)(q21 ;q3 l)mat 46.XY,-2,-5,+der(5),+der(5), t(2;5)(q21 ;q3 l)mat 46, XX,-2,+5 47, XX,+der(5), t(2;5)(q21 ;q3 l)mat 45, XY,-2,-5,+der(2), t(2;5)(q21 ;q3 l)mat 47, XX,- 2)+der(2),+der(5), t(2;5)(q21 ;q3 l)mat 45, XY,-5 47, XY,+der(2), t(2;5)(q21 ;q3 l)mat 45, XX,-2,-5,+der(5), t(2;5)(q21 ;q3 l)mat 47, XX,- 5,+der(2),+der(5), t(2;5)(q21 ;3 l)mat 45, XX,-2 * Adjacent-2 disjunction minimally results in the first two unbalanced gametic types shown (AB AD, CB CD). Crossing-over in the interstitial segments between centromeres and points of exchange is necessary for the origin of the remaining four types. ** A further eight segregational types can occur at All if there is crossing-over in the interstitial segments, making a total of 12 types of gametes with three chromosomes derived from the translocation quadrivalent. 350 example from a known case is illustrated here to indicate how such rearrangements can be handled: double reciprocal translocation involving three chromosomes. 46, XX, t(l;3)(3;9)(pl2;pl3q25;q22) 46, XX, t(l;3)(3;9)(3pter 3pl3::lpl2 lqter;lpter- > lpl2::3pl3 3q25: :9q22-9qter;9pter 9q22: :3q25 3qter) Breakage and union have occurred at bands lpl2 and 3pl3 in the short arms of chromosomes Nos. 1 and 3 respectively and at bands 3q25 and 9q22 in the long arms of chromosomes Nos. 3 and 9 respectively. The segments distal to lpl2 and 3pl3 have been exchanged, as have the segments distal to 3q25 and 9q22. Marker Chromosomes A marker chromosome of completely unknown origin should be designated by the original Chicago Conference symbol mar. If part of the chromosome can be identified with one of the banding techniques, a question mark (?) and the + and signs may be used with the short system to designate the karyotype. For example, 46, XX, t(12;?)(ql5;?) defines a karyotype that includes a rearranged chromosome No. 12 in which the segment of the long arm distal to band 12ql5 could not be identified. If such a marker happened to be longer or shorter than the chromosome from which it had been derived, this could be recorded by specifying the arm and the direction of the change in length. For example, 46, XX, t(12q+;?)(ql5;?) defines a karyotype that includes a rearranged chromosome No. 12 with a longer-than-normal long arm owing to attachment of an unknown segment distal to band 12ql5. Derivative and Recombinant Chromosomes A derivative chromosome is one of the structurally rearranged chromosomes generated by a single rearrangement involving two or more chromosomes. The term is necessary if the short system is to be used (1) because a designation in that system symbolizes the rearrangement as such and not the chromosomes generated by the rearrangement, 351 although these nevertheless can be identified from the symbolic designation, and (2) in order to designate unbalanced karyotypes among offspring of structural heterozygotes which may include any one, or any combination, of the derivative chromosomes.

23 A recombinant chromosome is a structurally rearranged chromosome with a new segmental composition resulting from meiotic crossing-over between a displaced segment and its normally located counterpart in certain types of structural heterozygotes. Whereas derivative chromosomes are products of the original rearrangement and segregate at meiosis without further change, recombinant chromosomes arise de novo during gametogenesis in appropriate structural heterozygotes as predictable consequences of crossing-over in a displaced segment. Derivative chromosomes are designated by the abbreviation der and recombinant chromosomes by rec. In both cases the chromosome number is specified within parentheses immediately following the appropriate abbreviation. The chromosome number used is that which indicates the origin of the centromere of the particular derivative or recombinant chromosome. As an illustration of the way derivative chromosomes can be expressed, a balanced reciprocal translocation between chromosomes Nos. 2 and 5, specifically, 46, XX, t(2;5)(q21;q31), has been assumed and is represented by the pachytene diagram in Fig. 7. The derivative chromosomes from such a translocation would be designated der(2) and der(5). Table 3 gives the possible unbalanced gametes resulting from adjacent-1 and adjacent-2 disjunctions and also from 4 of the 12 possible 3-to-l disjunctions, together with the recommended designations of the karyotypes resulting from syngamy between each unbalanced gametic type and a normal gamete. The full karyotype designation need be written only once in any given publication and then can be abbreviated. A suggested abbreviation for the first designated karyotype in Table 3, for example, would be 46, XX, der(5)mat. Recombinant chromosomes inevitably will be rare. Examples are most likely to originate from crossing-over in inversion or insertion heterozygotes. To exemplify the method of designating these chromosomes, a peri-centric inversion of chromosome No. 2, specifically, 46, XX, inv(2)(p21q31), has been assumed and is shown diagrammatically in Fig. 8. In this case crossing-over results in a duplication (dup) of 2p in one recombinant chromosome and of 2q in the other. The respective karyotypes could be 352 originai m I 22 y P21 p22 j p16 q24 i q32 q31 No. 2 INVERSION!nv(2)(p21q31) rec(2)dup p,inv(2)(p21q31) RECOMBINANTS (Crossing over Hi O as shown) q32 4 i p16