Case 2 -

Mucopolysaccharidosis Type I (MPS I, Hurler Syndrome) Carole A. Vogler Cardinal Glennon Children's Hospital St. Louis, MO

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Clinical History A ten-month-old African-American boy presented with rhinorrhea and fever. The child was the product of a normal term pregnancy born to a 22-year-old G2 P2 mother. He had a history of bilateral inguinal hernias repaired at age two months. Family history was negative for developmental disease. Three half-siblings were all in good health. Physical examination showed a weight > 50th percentile, height > 10th percentile, head circumference > 95th percentile for his age. He had an abnormal facies with frontal bossing, a flat nasal bridge, and coarse features, and "spade-like" hands with short "stubby" fingers. He had no gibbus. A 1.5 cm umbilical hernia and hepatosplenomegaly were present; the liver was 6 cm below the right coastal margin and the spleen was 3 cm below the left coastal margin. He had bilateral corneal clouding. A biopsy was performed. Case 2 - Figure 1 - The conjunctival connective tissue contains numerous fibroblasts distended by what appear by light microscopy to be empty vacuoles. This extensive cytoplasmic vacolization is very suggestive of a lysosomal storage disease. (Toluidine blue) Case 2 - Figure 2 - By electron microscopy, the vacuoles distending the fibroblasts in the conjunctival stroma are surrounded by a single membrane and contain fine fibrillogranular storage material and occasional electron dense granules. This type of storage material is nonspecific but very characteristic of the mucopolysaccharidoses. It can also be seen in other lysosomal storage diseases, including mucolipidoses, mannosidosis, and sialadosis. (Uranyl acetate-lead citrate) Differential diagnosis The fibrillogranular and clear storage distending lysosomes in fibroblasts, endothelial and perineural cells in the conjunctival biopsy were diagnostic of a lysosomal storage disease (LSD). The findings were consistent with the clinical diagnosis of mucopolysaccharidosis and MPS I was subsequently confirmed by documenting deficient leukocyte α-L-iduronidase. Other diagnostic considerations based on the morphology of the stored material included mucolipidoses, mannosidosis, sialadosis, glutamyl ribose-5-phosphate storage disease and GM1 gangliosidosis. Final Diagnosis: Mucopolysaccharidosis Type I (MPS I, Hurler Syndrome) Discussion LSD affect 1/5,000 children and are a heterogeneous group of almost 50 inherited disorders. Most LSD are the result of a defect in a gene that codes for a specific lysosomal acid hydrolase but defects in a enzyme coactivator, membrane transporter, targeting mechanism for protein localization to the lysosome or intracellular vesicular trafficking can also cause LSD [1, 2] . The enzyme deficiency blocks a catabolic pathway which leads to progressive accumulation of undegraded substrate macromolecules leading to cellular and organ dysfunction. Which tissue is affected and at what age symptoms develop depends on the importance of the degradative pathway in a given tissue. LSD patients have a broad spectrum of phenotypes; most have progressive neurological degeneration overlaying a variety of musculoskeletal and visceral abnormalities. Clinical findings that warrant investigation for LSD include nonimmune fetal hydrops, progressive organomegaly, skeletal abnormalities, joint stiffness, coarse facial features, progressive dementia or loss of developmental skills and unexplained neuropathic extremity or bone pain [2]. Patients with MPS, due to deficiency of an enzyme needed for normal catabolism of glycosaminoglycans, as in this patient, present with progressive hepatosplenomegaly, bone and joint abnormalities termed dysostosis multiplex, coarse facial features, corneal clouding and developmental delay [1]. In many patients with LSD, biochemical analysis of cultured fibroblasts, leukocytes or plasma provides a diagnosis [2]. Tissue biopsy with ultrastructural evaluation can also be useful. Many metabolic diseases, including LSD, have well characterized ultrastructural alterations in the rectal mucosa, skin, conjunctiva and peripheral blood leukocytes providing criteria for diagnosis [3]. Cultured fibroblasts can have artifacts of culture that mimic lysosomal storage [4] and are not as useful of morphological evaluation as tissue samples. In some patients with morphological evidence of LSD, a specific disorder is suggested by the character of the stored material. In others, a differential diagnosis is indicated by the finding of accumulation of fibrillogranular lysosomal material, as in this case. EM has particular value in those disorders with incompletely characterized biochemical defects [5]. Early diagnosis is becoming more important for patients with LSD as effective disease-specific therapy becomes a reality for these disorders. Patients are ideally diagnosed before serious mental or physical impairments are present [2]. A newborn screening program that measures levels of the lysosomal-associated membrane protein, LAMP-1, and saposins, which are elevated in some patients with LSD, is being studied [2]. Neonatal LSD screening initiatives and protocols are being developed based on the common feature of lysosomal enlargement and increase in lysosomal proteins. Immune quantification assays of protein markers and tandem mass spectrometry for glycosphingolipid and oligosaccharide markers have been suggested for newborn screening for LSD [6, 7] . In the past decade there have been major advances in therapies for LSD. Bone marrow or hematopoietic stem cell transplantation and enzyme replacement therapy may benefit selected patients with LSD, particularly if treatment is begun early in life or if CNS symptoms are minimal [8, 9, 10] . Table 1: LSD for which disease specific therapies are being evaluated [2, 8, 9, 10] Bone marrow or hematopoetic stem cell transplantation MPS I, II, III, VI, VII α-Mannosidosis Wolman Disease Metachromatic leukodystrophy Krabbe Disease Mucolipidosis II Neuronal ceroid lipofuscinosis 1 Farber Disease Fucosidosis Niemann-Pick C Gaucher Disease Fabry Disease GM1 and GM2 gangliosidosis Enzyme replacement therapy Gaucher Disease Fabry Disease MPS I, II, VI Pompe Disease Niemann-Pick B Central to many of these therapies is the Man 6-P receptor pathway which allows enzyme in the blood to be delivered intracellularly to lysosomes where it can catabolize stored substrate. Gene therapy is likely on the horizon for LSD and holds the promise of a virtual cure by providing patients with an endogenous source of enzyme by supplying a normal copy of the gene for the deficient protein. Animal models have been very important in the evaluation of the effectiveness of such therapies for LSD [1, 9, 11, 12] . They will continue to provide important information on the safety and impact of new therapeutic strategies including new enzyme delivery methods, substrate deprivation, neural stem cell and gene therapy on LSD. Such therapies hopefully will allow more effective treatment of the skeleton and circumvent the blood-brain barrier to provide therapeutic enzyme to the CNS. References Sly WS, Enzyme replacement therapy: from concept to clinical practice, Acta Paed suppl 2002; 439: 71-78. Wilcox WR, Lysosomal storage disorders: the need for better pediatric recognition and comprehensive care. J Ped 2004; 144: S3-S14. Buchino JJ, Vogler C, Dimmick JE, Anatomical pathology of lysosomal storage diseases, in Organelle Diseases, 1997, ed DA Applegarth, JE Dimmick and JG Hall, Chapman and Hall, London. Landing BH, Ng WG, Alfi O, Donnell GN, Fibroblast culture in the diagnosis of genetic metabolic diseases: Comparative histochemical, ultrastructural and biochemical studies. Persp Ped Pathol 1979; 5: 237-262. Vogler C, Rosenberg HS, Williams JC, Butler I, Electron microscopy in the diagnosis of lysosomal storage diseases. Am J Med Genet 1987; S3: 243-255. Meikle PJ, Ranieri E, Hons BS, Simonsen H, et al, Newborn screening for lysosomal storage disorders: clinical evaluation of a two-tier strategy. Pediatr 2004;114: 909-916 Li Y, Scott R, Chamoles NA, Ghavami et al, Direct multiplex assay of lysosomal enzymes in dried blood spots for newborn screening. Clin Chem 2004; 50: 1785-1796. Wegner DA, Coppola S, Liu SL, Insights into the diagnosis and treatment of lysosomal storage diseases. Arch Neurol 2003; 60: 322-328. Desnick RJ, Schuchman EH, Enzyme replacement and enhancement therapies: lessons from lysosomal disorders. Nat Rev Genet 2002; 3: 954-966. Kakkis ED, Muenzer J, Tiller GE, Waber L et al, Enzyme-replacement therapy in mucopolysaccharidosis I. JAMA, 2001; 344: 182-188. Vogler C, Barker J, Sands MS, Levy B et al, Murine Mucopolysaccharidosis VII: Impact of therapies on the phenotype, clinical course and pathology in a model of a lysosomal storage disease. Ped Dev Pathol 2001; 4: 421-433. Kakkis E, McEntee M, Vogler C, Le S, et al, Intrathecal enzyme replacement therapy reduces lysosomal storage in the brain and meninges of the canine model of MPS I. Mol Gen Metab 2004; 83: 163-174.