Canadian College of Medical Geneticists (CCMG) Cytogenetics Examination. May 4, 2010

Transcription

1 Canadian College of Medical Geneticists (CCMG) Cytogenetics Examination May 4, 2010 Examination Length = 3 hours Total Marks = 100 (7 questions) Total Pages = 8 (including cover sheet and 2 pages of prints) Instructions: 1. Please write your candidate number on each page of your exam answer booklet. Do not use your name. 2. Please write in dark blue or black ink. Do not use pencil. 3. Questions may be answered in point form. Use tables, diagrams and drawings where appropriate. Please show all calculations. 4. Candidates are encouraged to spend no more than minutes per question to ensure completion of the entire exam. 5. All exam materials must be returned at the end of the examination. 1

2 I. TOPIC: Methodology (14 marks) Array genomic hybridization (microarray) analysis is a whole genome analysis that can identify gain and loss of genomic material at a resolution much greater than that of G-band (karyotype) analysis. A. With reference to the source or synthesis of the probes on the slide (and not to the resolution of the microarray), list three different types of microarray platforms that may be used to detect copy number changes in the human genome. (1.5 marks) B. Compare the platforms described above by listing one advantage and one disadvantage for each. (3 marks) C. Provide two reasons for referral that are suitable for microarray analysis, and two for which microarray analysis is an inappropriate technique. (2 marks) D. List three cytogenetic abnormalities that are detectable by microarray analysis, and three cytogenetic abnormalities that are not detectable by microarray analysis. (3 marks) E. In addition to the patient demographics included with a traditional cytogenetics report, list five details that should be included when reporting a copy number change detected by microarray. (2.5 marks) F. When should an imbalance detected by microarray be validated by an alternate test? What are the options for validation of an imbalance detected by microarray? (2 marks) 2

3 II. TOPIC: Prenatal Cytogenetics (15 marks) Aneuploidy is the most commonly identified chromosome abnormality in humans. A. What is the frequency of aneuploidy (1.5 marks) i) At conception ii) In first trimester fetuses iii) At live birth B. Which is the most common parent of origin in the meiotic error leading to Turner syndrome? (0.5 mark) C. i) Compare the mechanisms thought to contribute to the increased risk of trisomy 21 occurrence in both older women and younger women who have had a trisomy 21 pregnancy. (4 marks) ii) What is the recurrence risk in each of these groups? (2 marks) D. List the full name of two molecular genetic/cytogenetic techniques, other than microarray analysis, that can be used for rapid aneuploidy detection in specimens submitted for prenatal diagnosis. (2 marks) Briefly describe the basic principles of each of the two techniques you have chosen. (6 marks) III. TOPIC: Cancer Cytogenetics (15 marks) In the 2008 World Health Organization (WHO) classification of tumours of haematopoietic and lymphoid tissues, a number of entities are defined in part by recurrent, specific genetic abnormalities. Identify five recurrent genetic abnormalities in acute myeloid leukemia and five recurrent genetic abnormalities in B-lymphoblastic leukaemia/lymphoma that are categorized as distinct entities in the 2008 WHO classification. For each condition, provide the cytogenetic abnormality and the gene(s) involved in the rearrangement. Precise breakpoints are not required but the chromosome arm should be stipulated. (1.5 mark per example) 3

4 IV. TOPIC: Cytogenetic Nomenclature (12 marks) A. Write the International System for Human Cytogenetic Nomenclature, for the following descriptions: i) FISH performed on 200 interphase nuclei with a dual color, dual fusion probe exhibited the typical dual fusion hybridization pattern characteristic of the translocation (9;22) of chronic myeloid leukemia in 180 of the cells examined. (2 marks) ii) Chromosome analysis performed on cultured amniotic fluid indicates 3 metaphases of normal female karyotype and 7 of a male karyotype with a terminal deletion of the short arm of chromosome 4, from band p16.3. (2 marks) iii) A newborn male with features of Down syndrome is referred for cytogenetic analysis. The mother carries a balanced translocation between the short arm of chromosome 5, breakpoint at band p15.3 and the long arm of chromosome 21, breakpoint at band q11.2. Provide the karyotype of the infant if the rearrangement in the mother segregated in an unbalanced 2:2 manner. (2 marks) B. Provide a written description with interpretation for each of the following cytogenetic analyses. Recommendations for follow-up are not required. i) nuc ish(dxz1x2)[40]//(dxz1,dyz1)x1[160] Test performed on 200 scorable nuclei of a bone marrow sample. (2 marks) ii) nuc ish(dxz1x1,dyz1x1,d18z1x3),(rb1,d21s259)x2 Test performed on 200 amniocytes. (2 marks) iii) 46,XX,ins(7;6)(q21.11;q22.1q23.3) Test performed on cultured peripheral lymphocytes. (2 marks) 4

5 V. TOPIC: Pathophysiology of Genetic Disease (14 marks) Infertility is a condition affecting approximately 10% of the reproductive age population. A. Provide four genetic causes of male infertility that result from different pathophysiological mechanisms (2 marks). For each of these genetic causes of infertility, list i) a standard genetic test that enables the diagnosis (2 marks). ii) the pathophysiological cause of the infertility (3 marks). B. Provide four genetic causes of female infertility that result from different pathophysiological mechanisms (2 marks). For each of these genetic causes of infertility, list i) a standard genetic test that enables the diagnosis (2 marks). ii) the pathophysiological cause of the infertility (3 marks). You may provide your answer in a list or table format. VI. TOPIC: Structural Chromosome Rearrangements (16 marks) A. Describe Robertsonian translocations in humans (by words and/or diagram) and the resulting imbalance in a phenotypically normal carrier. (3 marks) B. Explain the consequences faced by the individuals who are carriers of Robertsonian translocations. (5 marks) C. What are the differences between a de novo isochromosome and a de novo homologous Robertsonian translocation in terms of: the formation (3 marks) the parent of origin (1 mark) the clinical consequences. (1 mark) You may provide your answer in a list or table format. D. What test(s) would you recommend to determine whether the translocation 15q;15q found in a phenotypically normal individual is an isochromosome or a homologous translocation? (1 mark) E. List the possible karyotype(s) of the children born to a mother with a de novo Robertsonian translocation involving the two chromosome 21's, according to the ISCN. (1 mark) F. State the most common and a relatively uncommon Robertsonian translocation in man. (1) 5

6 VII. TOPIC: Print Analysis and Interpretation (14 marks) Cytogenetic analysis was requested on a couple with recurrent pregnancy loss. Two metaphase cells from the same individual are provided, to address any chromosome twists or overlaps. Annotate one metaphase of your choice. A. Identify each individual chromosome on the print and indicate the p arm clearly by a small arrow. If an abnormality is suspected, indicate the chromosome(s) and the respective arm(s) involved. (7.5 marks) B. Provide the karyotype. Precise breakpoints are not required but the short arm or long arm should be indicated. (2.5 marks) C. Write a short interpretation of your result, including follow-up recommendations that should be made to the referring physician. (4 marks) 6

7 Image 1 7

8 Image 2 8