Lysosomal disorders. J. E. Wraith. Introduction

Transcription

1 Semin Neonatol 2002; 7: doi: /siny , available online at on Lysosomal disorders J. E. Wraith Willink Biochemical Genetics Unit, Royal Manchester Children s Hospital, Manchester, UK Key words: non-immune hydrops fetalis, dysmorphism, lysosomal enzymes, prenatal diagnosis Although most lysosomal storage disorders present in infancy or early childhood with a progressive condition often associated with dysmorphism, considerable genetic heterogeneity exists resulting in a range of illnesses that can include a dramatic neonatal presentation. Whilst some conditions present with a characteristic neonatal phenotype (e.g. Niemann Pick disease type C), the remainder present in a nonspecific way often with non-immune hydrops fetalis. Diagnosis can be helped by appropriate radiological studies and, in some patients, evidence of the storage phenomena can be seen in peripheral blood smears or bone marrow aspirates. Unfortunately, for the majority of affected patients no effective, curative, treatment is possible. New developments in therapy including enzyme replacement therapy and substrate deprivation may improve prognosis in some disorders. It is important to establish an accurate diagnosis, as prenatal testing can then be offered in future pregnancies Elsevier Science Ltd. All rights reserved. Introduction Some 50 different lysosomal disorders are known in humans (LSDs). They result from the defective function of a specific protein, which leads ultimately to the progressive accumulation within the lysosome of either undegraded substrate(s) or catabolic products that are unable to escape from this organelle. Most disorders are inherited in an autosomal recessive manner and the disease process is generally progressive and unremitting. Lysosomes are present in all nucleated cells. They form part of a complex intracellular recycling system involved in the degradation of large macromolecules. This process is achieved in a stepwise manner by removal of terminal residues by a series of lysosomal enzymes, usually exohydrolases, and the released monomeric units are either transported or diffuse out of the lysosome. Approximately 75 different lysosomal enzymes (including glucosidases, lipases, proteases and nucleases) are involved Correspondence to: Dr J. E. Wraith, Director, Willink Biochemical Genetics Unit, Royal Manchester Children s Hospital, Manchester M27 4HA, UK. Tel: ; Fax: ; ed@willink.demon.co.uk /02/$-see front matter in these degradative processes; since many of the substrates are complex lipids which are not water soluble, cofactors or activators may also be involved in enzyme-substrate interactions. Other proteins may be involved in protecting enzymes from being degraded themselves in this proteolytic environment. Lysosomal enzymes have maximum activity at an acid ph, and in the lysosome this is maintained by an energy-dependent proton pump. A useful property of these enzymes is the fact that although they are highly specific towards the structure and linkage of the terminal moiety on a complex macromolecule, the overall structure may not be important. It is therefore possible to measure lysosomal enzyme activities using a variety of relatively simple water-soluble substrates incorporating coloured or fluorescent groups. Such assays are commonly used for diagnostic studies. Defects in lysosomal enzymes, cofactors or transport proteins may all give rise to specific lysosomal storage disorders and these can be classed conveniently according to the type(s) of storage material accumulating. In many cases, because lysosomal enzymes may act on several different substrates that share the same terminal residue, a complex storage pattern may result Elsevier Science Ltd. All rights reserved.

2 76 J. E. Wraith The lysosomal disorders, like many other metabolic diseases, show a remarkably varied clinical phenotype. In some patients, the presentation may be in utero or the newborn period, whereas in others, even with the same enzyme deficiency (but probably a different genetic mutation), onset may be in late adulthood. However, for most patients the onset of symptoms is in the first months or years of life following an often unremarkable and apparently normal early development. The first signs may be some slowing of development and other neurological signs; in other patients some organomegaly or a dysmorphic facial appearance may be noted. Recognition of these clinical signs will assist in the selection of appropriate diagnostic tests. In this review those disorders that can and often do present in the neonatal period will be highlighted. A very simple classification of lysosomal storage disorders is given in Table 1, including reported neonatal presentation. For a comprehensive review of lysosomal structure and function the reader is guided to the excellent text edited by Applegarth [1]. Clinical presentation Hydrops fetalis Hydrops fetalis is known to be caused by a wide variety of fetal, placental and maternal disorders. Fetal mortality is high and it is a diagnostic challenge to ensure that those disorders associated with a recurrent risk of hydrops are identified. Table 2 lists some of the lysosomal disorders that have been associated with this presentation which have been extensively reviewed [2,3]. When faced with a hydropic fetus what features might suggest a diagnosis of a LSD? A history of recurrent episodes of non-immune hydrops fetalis is important as would be the presence of parental consanguinity. Detailed anatomical examination by ultrasound should attempt to diagnose placental and fetal abnormalities. Fetal echocardiography should be performed by an experienced operator to exclude congenital heart lesions and a fetal karyotype should be carried out to exclude aneuploidy. Cell-free fluid should be analysed for metabolite excretion (oligosaccharides and glycosaminoglycans) and a culture established for subsequent enzyme assay. Investigations on the mother are also indicated and should include maternal blood testing for antibody screening as well as serological testing for infectious disease. Fetal blood sampling has a very limited place in the diagnosis of an LSD, as the volume that can be removed is so small. It may however be indicated to check for fetal anaemia, haemoglobin variants or other causes of haemolytic disease. The fetal and neonatal mortality rate for nonimmune hydrops fetalis is very high [4] and a detailed physical and pathological examination of the placenta, fetus or neonate is essential in suspected cases of LSD. In an LSD, the placenta may appear pale and bulky to gross examination [5] and histology either by light microscopy or electron microscopy may confirm the presence of lysosomal vacuolation [6,7]. In cases where no amniotic fluid has been obtained a placental cell line from a piece of chorion should be established for subsequent enzyme analysis. Often the presence of severe hydrops makes identification of the specific dysmorphic features (see later) associated with a LSD very difficult to appreciate. In addition the fetus may be macerated or aborted at a very early stage of the pregnancy making physical examination very difficult. In those infants who survive until late into the pregnancy or who are live- born a careful physical and radiological examination is required and this is described in the next section. Dysmorphism In general, the disorders that can present with hydrops fetalis (Table 2) can also present in the newborn period with dysmorphism. Infants in the newborn period with a Hurler-like phenotype (Fig. 1) usually have mucolipidosis II (I-cell disease), infantile sialic acid storage disease or GM 1 - gangliosidosis. In mucopolysaccharidosis type I (Hurler syndrome) the physical appearance at birth is normal although other abnormalities such as inguinal herniae [8] or extensive Mongolian spots [9] may be seen in affected patients. Hepatosplenomegaly and arthrogryposis may also be detected in the affected fetus. Other disorders may have a more specific dysmorphic presentation; for example, infants with severe infantile Gaucher disease may present with a colloidian membrane [10]. Other clinical presentations Table 1 highlights other more specific presentations of which one or two deserve highlighting.

3 Lysosomal disorders 77 Table 1. Lysosomal storage disorders Disease Enzyme deficiency Storage material Screening test Diagnostic test Prenatal diagnosis Neonatal presentation MPS MPS I (Hurler, Scheie, Hurler/Scheie) MPS II (Hunter) Iduronate-2- sulphatase MPS III (Sanfilippo) IIIA Heparin-Nsulphatase IIIB N-acetylglucosaminidase IIIC Acetyl CoA Iduronidase DS, HS Urine GAGs WBC enzyme assay CVB 1 Umbilical and inguinal herniae in patients with severe phenotype [8]. Extensive Mongolian blue spots [9]. glucosamine N-acetyl transferase IIID N-acetyl-glucosamine- 6-sulphatase DS, HS Urine GAGs Plasma enzyme assay CVB 2 As MPS I HS Urine GAGs WBC enzyme assay CVB HS Urine GAGs Plasma enzyme assay CVB HS Urine GAGs WBC enzyme assay CVB HS Urine GAGs WBC enzyme assay CVB MPS IV (Morquio) IVA Galactose-6-sulphatase KS Urine GAGs WBC enzyme assay CVB Hydrops fetalis has been reported [23] IVB β-galactosidase KS Urine GAGs WBC enzyme assay CVB MPS VI (Maroteaux- Lamy) Galactosamine-4- sulphatase DS Urine GAGs WBC enzyme assay CVB 3 Endocardial fibroelastosis [13] MPS VII (Sly) β-glucuronidase HS, DS Urine GAGs WBC enzyme assay CVB Hydrops fetalis is commonest presentation also intrauterine death and spontaneous abortion [24] MPS IX Hyaluronidase HA None Cultured cells Unknown Mucolipidoses ML I (Sialidosis I) Neuraminidase SA Urine sialic acid Cultured cells Cultured cells Congenital form presents in utero hydrops, ascites, stillbirth [25] ML II (I Cell) Transferase 4 Many Urine oligos Plasma enzyme assays Cultured cells or AF Neonatal presentation common with dysmorphism, fractures and hydrops fetalis all reported [26] Continued

4 78 J. E. Wraith Table 1. Continued Disease Enzyme deficiency Storage material Screening test Diagnostic test Prenatal diagnosis Neonatal presentation ML III (pseudo-hurler) IIIA As ML II Many Urine oligos Plasma enzyme assays IIIC Transferase-δsub-unit Many Urine oligos Plasma enzyme assays Cultured cells or AF Cultured cells or AF ML IV Unknown Unknown None Histology Histology of CVB Sphingolipidoses GM 1 -gangliosidosis β-galactosidase GM 1 -gang. KS, oligos, Glycolipids GM 2 -gangliosidosis Tay-Sachs β-hexosaminidase A GM 2 -gang. Globoside, oligos Sandhoff β-hexosaminidase A GM 2 -gang. and B oligos GM 2 -gangliosidosis GM 2 activator GM 2 -gang. Corneal clouding [27] Urine oligos WBC enzyme assay CVB Common dysmorphism, organomegaly and hydrops fetalis [28] None WBC enzyme assay CVB None WBC enzyme assay CVB None Cultured cells and natural substrate Unknown Globoid cell leucodystrophy Krabbe Galacto-cerebrosidase Galactosyl- None WBC enzyme assay CVB Hypertonia, irritability and twitching [29] ceramides MLD Arylsulphatase A Sulphatides None WBC enzyme assay CVB MLD Saposin B activator (sap B) Sulphitides, GM 1 -gang, Fabry disease α-galactosidase A Galacyosylsphingolipids oligos None Sulphatide loading of cultured cells None WBC enzyme assay CVB In theory sulphatide loading of cultured cells + or DNA Gaucher disease β-glucosidase Glucoceramide None WBC enzyme assay CVB Severe type II disease can present with icthyosis [10] and organomegaly and hydrops [30] Continued

5 Lysosomal disorders 79 Table 1. Continued Disease Enzyme deficiency Storage material Screening test Diagnostic test Prenatal diagnosis Neonatal presentation Gaucher disease Saposin C As above None Unknown Unknown Farber disease Ceramidase Ceramide None WBC enzyme assay CVB Diffuse joint swelling and hoarseness can appear as early as 2 weeks of age. Hydrops also reported [31] Niemann Pick A and B Sphingomyelinase Sphingomyelin None WBC enzyme assay CVB Prolonged jaundice and hydrops reported in type A [32] Glyco-proteinoses α-mannosidosis α-mannosidase α-mannosides Urine oligos WBC enzyme assay CVB β-mannosidosis β-mannosidase β-mannosides Urine oligos WBC enzyme assay CVB Fucosidosis Fucosidase Fucosides Aspartylglucosaminuria Aspartylglucosaminidasglucosamine Aspartyl- Schindler disease α-galactosidase B N-acetylgalactosamid Urine oligos WBC enzyme assay CVB Urine oligos WBC enzyme assay CVB Urine oligos WBC enzyme assay CVB Glycogen Pompe disease α-glucosidase Glycogen ECG characteristic Lymphocyte enzyme assay Lipid Wolman disease and cholesterol ester storage disease (CESD) Acid lipase Cholesterol esters Niemann Pick C Unknown Cholesterol sphingolipids Monosaccharide aminoacids and monomers ISSD (infantile sialic CVB Cardiomyopathy can occur [12] None WBC enzyme assay CVB Hydrops fetalis [33] Filipin staining of cultured cells Cholesterol esterification studies Cultured cells (not always possible) Neonatal liver disease is common [11]. Hydrops fetalis [34] Sialic acid transporter Sialic acid Urine oligo Cultured cells AF Hydrops fetalis is common [35] acid storage disease) glucuronic Salla disease As ISSD As ISSSD As ISSD As ISSD As ISSD WBC cystine Cutured cells Cystine Cystine transporter Cystine Renal tubular disease Continued

6 80 J. E. Wraith Table 1. Continued Disease Enzyme deficiency Storage material Screening test Diagnostic test Prenatal diagnosis Neonatal presentation Cobalamin F disease Cobalamin transporter Danon disease Lamp-2 Cytoplasmic debris and glycogen Cobalamin MMA, Hcy Cultured cells Cultured cells Combined methymalonc aciduria and homocystinuria [36] None Unknown Unknown Peptides Pycnodysostosis Cathepsin K Bone proteins X-Ray Poss. DNA Poss. DNA Skeletal dysplasia [37] S-acylated proteins Ceroid lipofuscinosis (CLN, Batten s disease) CLN 1 (infantile) Palmitoyl protein thioesterase CLN 2 (late infantile) Pepstatin insensitive carboxypeptidase Saposins Histology Cutured cells and DNA Subunit C mitochondrial ATP synthase Histology Cutured cells and DNA CLN 3 (juvenile) Membrane protein As CLN 2 Histology DNA DNA CLN 4 (adult, Unknown As CLN 2 Histology Histology Unknown Kuf s disease) CLN 5 (late infantile, Finnish variant) CLN 6 (late infantile variant) CLN 7 (late infantile variant) CLN 8 (progressive epilepsy with mental retardation, EPMR) Multiple enzyme deficiencies Multiple sulphatase deficiency DNA DNA Membrane protein As CLN 2 Histology DNA DNA Unknown As CLN 2 Histology Histology Unknown Unknown Unknown Histolgy Histology Unknown Membrane protein As CLN 2 Histology Histology Unknown Multiple sulphatase enzymes Galactosialidosis Neuraminidase and β-galactosidase protective protein Sulphatides,, GAGs Oligos, sialic acid Urine GAGs WBC and Plasma Enzyme Assays CVB Dysmorphism, hydrocephalus and heart disease. Hydrops fetalis [38] Urine oligs Cultured cells Cultured cells Hydrops, oedema, proteinuria, hernias and telangiectasia common [39] DS dermatan sulphate, HS heparin sulphate, KS keratin sulphate, HA hyaluronic acid, SA sialic acid, WBC white blood cell, CVB chorion villus biopsy, AF amniotic fluid, GAGs glycosaminoglycans, Oligos oligosaccharides. 1. Low activity in CVB caution re: contamination with maternal decidua. 2. Always do fetal sexing as some aunaffected female fetuses will have very low enzyme results. 3. Difficult because of cross-reactivity from other sulphatases. 4. UDP-N-Acetylglucosamine:lysosomal enzyme N-acetylglucosaminyl-l-phosphotransferase.

7 Lysosomal disorders 81 Table 2. Hydrops fetalis as the presenting feature of LSDs Mucopolysaccharidosis type IV Mucopolysaccharidosis type VII (common) Mucolipidosis I (sialidosis I) Mucolipidosis II GM 1 gangliosidosis (common) Farber disease Gaucher disease Niemann Pick A Niemann Pick C Wolman disease Infantile sialic acid storage disease (common) Multiple sulphatase deficiency Galactosialidosis Figure 2. The gum hyperplasia that is characteristic of mucolipidosis II (I-Cell disease). Figure 1. The facial dysmorphism associated with lysosomal storage disease. In this infant the underlying diagnosis is mucolipidosis II (I-Cell disease), but this facial phenotype ( Hurler-like ) is also seen in GM 1 -gangliosidosis and infantile sialic acid storage disease. A significant number of infants with Niemann Pick disease type C (NPC) will present with a form of neonatal hepatitis [11]. In this group of patients death from liver failure can occur, but those that survive may not develop other features of the disease for many years. Cardiomyopathy in the newborn period is a rare presentation of a LSD (it is more common in infants with disorders of intermediary metabolism), but should not be overlooked. Glycogen storage disease type II (Pompe disease) [12] and mucopolysaccharidoses [13] can present in this way. Radiology The radiological abnormalities associated with LSDs are known as dysostosis multiplex [14]. These defects in remodelling are usually not present in the neonatal period but become progressively more obvious during the first year or two of life. Different radiological abnormalities may be seen in specific disorders and this is illustrated by the characteristic findings seen in mucolipidosis II (I-cell disease). This condition is caused by a failure to target lysosomal enzymes to the organelle resulting from a deficiency of mannose-6-phosphate phosphotransferase activity, the enzyme necessary for post-translational modification of the enzymes to allow them to be targeted to lysosomes. Clinically, there is usually severe dysmorphism (Fig. 1) with the additional finding of pronounced gingival hyperplasia (Fig. 2). The radiological abnormalities are present from birth and include osteopenia, periosteal cloaking, neonatal or in-utero fractures and dysharmonic epiphyseal ossification [15]. Diagnosis Before considering the specific tests required for accurate diagnosis in individual cases, it is appropriate to consider a simple test that may help the diagnostic process. Storage phenomena may be seen in peripheral blood cells (Fig. 3) or bone marrow aspirates (Fig. 4) and an ultrastructural study of these tissues can be helpful [16]. Specific diagnosis usually requires a urine and blood sample. Urinary glycosaminoglycans and oligosaccharide excretion patterns should be analysed and specific enzyme assays will be required for definitive diagnosis (Table 1). For some disorders e.g. Niemann Pick disease type C more complicated

8 82 J. E. Wraith Treatment Figure 3. A peripheral blood film showing two prominent, vacuolated lymphocytes from an infant with α-mannosidosis. For most disorders palliative care is all that can be offered and the prognosis for disorders presenting in the newborn period is particularly poor as this usually indicates a severe variant of the disease in question. Significant advances have however been made with this group of disorders [18]. These include bone marrow transplantation, direct enzyme replacement and substrate deprivation therapy. A common theme with therapy for these disorders that can affect the brain is the need for early diagnosis before the onset of irreversible damage. It is ironic that those conditions producing the most dramatic neonatal presentation may ultimately be the most treatable because of their likely earlier diagnosis. Conclusions Figure 4. A bone marrow aspirate from an infant with Niemann Pick A disease showing the characteristic foam cells. diagnostic assays on cultured skin fibroblasts have to be performed and suspected cases should be discussed with the local metabolic laboratory. Specific biochemical confirmation must be pursued in all suspected cases, as all these disorders are genetic. Prenatal testing is available for the vast majority and the method of choice is indicated in Table 1. In those patients in whom a diagnosis of an LSD is strongly suspected but initial biochemical investigations are negative, more invasive procedures such as organ biopsy may be indicated. The gold standard for diagnosis remains the demonstration of lysosomal storage at an ultrastructural level [17]. It is important to remember that some other disorders (especially if associated with hydrops fetalis) may mimic an LSD. Individually LSDs are rare. As a group, however, they have a prevalence similar to phenylketonuria in most communities [19,20] and present a complex and challenging problem. Neonatal presentation is common and although treatment for the majority remains unsatisfactory developments over the next decade are likely to result in more effective therapies as well as the possible introduction of newborn screening [21,22] for LSDs. References 1 Applegarth DA, Dimmick JF, Hall JG (eds). Organelle Diseases. London: Chapman Hall, Machin GA. Hydrops Revisited: Literature review of 1,414 Cases Published in the 1980s. Am J Med Genet 1989; 34: Stone DL, Sidransky E. Hydrops Fetalis: Lysosomal Storage Disorders In Extremis. Adv Pediatr 1999; 46: Norton ME. Nonimmune hydrops fetalis. Semin Perinatol 1994; 18: Knisely AS. The pathologist and the hydropic placenta, fetus, or infant. Semin Perinatol 1995; 19: Nelson J, Kenny B, O Hara D, Harper A, Broadhead D. Foamy changes of placental cells in probable beta glucuronidase deficiency associated with hydrops fetalis. J Clin Pathol 1993; 46: Soma H, Yamada K, Osawa H, Hata T, Oguro T, Kudo M. Identification of Gaucher cells in the chorionic villi associated with recurrent hydrops fetalis. Placenta 2000; 21: Coran AG, Eraklis AJ. Inguinal hernia in the Hurler- Hunter syndrome. Surgery 1967; 61:

9 Lysosomal disorders 83 9 Rybojad M, Moraillon I, Ogier de Baulny H, Prigent F, Morel P. Extensive Mongolian spot related to Hurler disease. Ann Dermatol Venereol 1999; 126: Finn LS, Zhang M, Chen SH, Scott CR. Severe type II Gaucher disease with ichthyosis, arthrogryposis and neuronal apoptosis: molecular and pathological analyses. Am J Med Genet 2000; 91: Jaeken J, Proesmans W, Eggermont E, Van Hoof F, Den Tandt W, Standaert L, Van Herck G, Corbeel L. Niemann- Pick type C disease and early cholestasis in three brothers. Acta Paediatr Belg 1980; 33: Lorber A, Luder AS. Very early presentation of Pompe s disease and its cross-sectional echocardiographic features. Int J Cardiol 1987; 16: Fong LV, Menahem S, Wraith JE, Chow CW. Endocardial elastosis in mucopolysaccharidosis type VI. Clin Cardiol 1987; 10: Clarke LA. Clinical diagnosis of lysosomal storage diseases. In: Ref [1], pp Herman TE, McAlister WH. Neonatal mucolipidosis II (I-cell disease) with dysharmonic epiphyseal ossification and butterfly vertebral body. J Perinatol 1996; 16: Markesbery WR, Robinson RO, Falace PV, Frye MD. Mucopolysaccharidoses; ultrastructure of leukocyte inclusions. Ann Neurol 1980; 8: Buchino JJ, Vogler C, Dimmick JE. Anatomical pathology of lysosomal storage diseases. In: Ref [1], pp Wraith JE. Advances in the treatment of lysosomal storage disease. Dev Med Child Neurol 2001; in press. 19 Miekele PJ, Hopwood JJ, Clague AE, Carey WE. Prevalence of lysosomal storage disorders. JAMA 1999; 281: Poorthuis BJ, Wevers RA, Kleijer WJ, Groener JE, de Jong JG, van Weely S, Niezer-Koning KE, van Diggelen OP. The frequency of lysosomal storage disease in the Netherlands. Hum Genet 1999; 105: Umapathysivam K, Whittle AM, Ranieri E, Bindloss C, Ravenscroft O, van Diggelen OP, Hopwood JJ, Meikle PJ. Determination of acid alpha-glucosidase protein: evaluation of a screening marker for Pompe disease and other lysosomal storage disorders. Clin Chem 2000; 46: Chamoles NA, Blanco M, Gaggioli D. Diagnosis of alpha-l-iduronidase deficiency in dried blood spots on filter paper: the possibility of newborn diagnosis. Clin Chem 2001; 47: Applegarth DA, Toone JR, Wilson RD, Yong SL, Baldwin VJ. Morquio disease presenting as hydrops fetalis and enzyme analysis of chorion villus tissue in a subsequent pregnancy. Pediatr Pathol 1987; 7: Stangenberg M, Lingman G, Roberts G, Ozand P. Mucopolysacchaidosis VII as a cause of fetal hydrops in early pregnancy. Am J Med Genet 1992; 44: Bucholz T, Molitor G, Lukong KE, Praun M, Genzel- Boroviczeny M, Freund M, Pshezhetsky AV, Schulze A. Clinical presentation of congenital sialidosis in a patient with neuraminidase gene frameshift mutation. Eur J Pediatr 2001; 160: Appelmann Z, Blumberg BD, Golabi M, Golbus MS. Nonimmune hydrops fetalis may be associated with an elevated ΔOD450 in the amniotic fluid. Obstet Gynecol 1988; 71: Merin S, Livni N, Berman ER, Yatziv S. Mucolipidosis IV: ocular, systemic, and ultrastructural findings. Invest Ophthalmol Vis Sci 1975; 14: Tasso MJ, Martinez-Gutierrez A, Carrascosa C, Vazquez S Tebar R. Gm1-gangliosidosis presenting as nonimmune hydrops fetalis: a case report. J Perinat Med 1996; 24: Krabbe s disease: clinical presentation of neurological variants. Neuropaediatrics 1984; 15(Suppl): Sharma R, Hudak ML, Perszyk AA, Premachandra BR, Li H, Mont C. Perinatal lethal form of Gaucher s disease presenting with hemosiderosis. Am J Perinatol 2000; 17: Kattner E, Schafer A, Harzer K. Hydrops fetalis: manifestation in lysosomal storage diseases including Farber disease. Eur J Pediatr 1997; 156: Kolodny EH. Niemann-Pick Disease. Curr Opin Hematol 2000; 7: Hoeg JM, Demosky SJ, Pescovitz OH, Brewer HB. Cholesteryl ester storage disease: phenotypic variants of lysosomal acid cholesteryl ester hydrolase deficiency. Am J Hum Genet 1984; 36: Maconochie IK, Chong S, Mieli-Vergani G, Lake BD, Mowat AP. Fetal ascites: an unusual presentation of Niemann-Pick disease type C. Arch Dis Child 1989; 64: Lemyre E, Russo P, Melancon SB, Gagne R, Potier M, Lambert M. Clinical spectrum of infantile free sialic acid storage disease. Am J Med Genet 1999; 82: Shih VE, Axel SM, Tewsbury JC, Watkins D, Cooper BA, Rosenblatt DS. Defective lysosomal release of vitamin B 12 (cbl F): a hereditary cobalamin metabolic disorder associated with sudden death. Am J Med Genet 1989; 33: Haagerup A, Hertz JM, Christensen MF, Binderup H, Kruse TA. Cathepsin K gene mutations and 1q21 haplotypes in a patient with pycnodyostosis in an outbred population. Eur J Hum Genet 2000; 8: Castano Suarez E, Segurado Rodriguez A, Guerra Tapia A, Simon de las Heras R, Lopez-Rios F, Coll Rosell MJ. Ichthyosis: the skin manifestation of multiple sulfatase deficiency. Pediatr Dermatol 1997; 14: Patel MS, Callahan JW, Zhang S, Chan AK, Unger S, Levin AV, Skomorowski MA, Feigenbaum AS, O Brien K, Hellmann J, Ryan G, Velsher L, Chitayat D. Early infantile galactosialidosis: prenatal presentation and postnatal follow-up. Am J Med Genet 1999; 85: