Mucopolysaccharidosis

The presented pathology is from a liver needle biopsy from an 11-month-old female infant born to non-consanguineous parents. Her prenatal ultrasound demonstrated thick nuchal folds. The karyotype obtained from an amniocentesis was normal. She was diagnosed with hepatosplenomegaly at 3 months of age and underwent a series of tests that were nondiagnostic. Hypotonia and developmental delay were noted at 4 months of age. At age 10 months, she was referred to our hospital for a liver biopsy. At that time, she was noted to have coarse facial features, and radiographs of the spine showed several beaked vertebrae and spatula-shaped ribs (dysostosis multiplex). Hematoxylin-eosin-stained sections of the liver biopsy showed diffuse vacuolization of the hepatocyte cytoplasm, some of which contained fibrillary-like material (Figure 1). Toluidine blue failed to stain any material. Periodic acid-Schiff staining (before diastase treatment) showed abundant cytoplasmic glycogen (Figure 2) that was dissolved by diastase. Electron microscopy showed dilated lysosomes in hepatocytes and Kupffer cells and no lipid (Figure 3). At higher magnification, the storage material predominantly had a loose fibrillary structure (Figure 4). The urinalysis, performed after the liver biopsy, was positive for keratan sulfate.

What is your diagnosis?

Pathologic Diagnosis: Gangliosidosis Type 1

Landing et al1 established gangliosidosis type 1 (GM1) as an entity in 1964. It is an autosomal recessive disorder caused by an inherited deficiency of β-galactosidase. Two diseases with human β-galactosidase deficiency have been recognized: GMl, a neurodegenerative disorder with bone and visceral involvement, and Morquio disease, a form of mucopolysaccharidosis with generalized bone disease without central nervous system involvement. Originally, they were considered as 2 separate diseases, but molecular analysis has found an allelic mutation of the same gene with diverse phenotypic expression.

The enzyme β-galactosidase has catalytic activity toward glycoconjugated substrates that contain a β-galactosidic linkage. The storage material that accumulates in the cells from patients with this deficiency includes ganglioside GMl, oligosaccharides derived from glycoproteins, and keratan sulfate. In patients with GMl, there is accumulation of GMl ganglioside predominantly in the brain. In visceral organs and specifically in the liver, the storage material is a keratosulfate-like oligosaccharide.2 Patients with GMl type 1 (infantile form) present in early infancy with developmental delay. Later, signs of severe brain damage become apparent. They may have macular cherry-red spots and corneal clouding. Hepatosplenomegaly is a constant sign. In typical cases, dysmorphism (coarse facial features, among others) and generalized skeletal dysplasia are present and progressive.

The diagnosis can be suspected on the basis of chemical analysis of the urinary mucopolysaccharides and the demonstration of excessive excretion of keratan sulfate. Enzymatic assays on cultured fibroblasts or on solid organs provide a definitive diagnosis. In the GMl infantile form, β-galactosidase activity is almost completely absent. Histologically, a distinct form of hepatic storage material was described in the liver of patients with GMl by Petrelli et aP and is illustrated in this case. Most of the hepatocytes are distended by vacuoles that occupy the majority of the cytoplasm. Periodic acid-Schiff staining shows abundant glycogen outside the vacuoles, and no residual periodic acid-Schiff-positive, diastase-resistant material is detected. The negative staining for toluidine blue may be a result of the loss of the acid mucopolysaccharides contained in the cytoplasmic vacuoles from histologie fixation and processing. Alternatively, the specific type of mucopolysaccharide that accumulates in GMl is not sensitive to the common histochemical stains used to detect acid mucopolysaccharides. Electron microscopy is extremely useful in the diagnostic workup, and certain features can be diagnostic of GMl. Despite the striking vacuolization of the hepatocytes on hematoxylin-eosin staining, under the electron microscope, it is evident that the storage material is not lipid. Electron microscopy confirms an increased amount of glycogen deposits, although this does not represent the storage material. The intracytoplasmic structures in which the stored material accumulates are enlarged lysosomes that contain a characteristic, finely fibrillary material. These changes involve both the hepatocytes and Kupffer cells. In some cases, lysosomal dense rounded masses that are considered typical of GMl may be identified.4 Other authors report that typical membranous concentric bodies of gangliosides are seen by electron microscopy.5 Membranous concentric bodies are most typically found in the neurons. Kupffer cells in the liver and histiocytes in other visceral organs, however, most frequently contain numerous vacuoles of different sizes bounded by a single membrane, in which some are empty and others contain fibrillary material.6

Currently, biochemical and enzymatic assays are the gold standard for the diagnosis and subtyping of metabolic storage diseases. The histologie and electron microscopic findings of the infantile type of GMl can provide a presumptive diagnosis. Definitive diagnosis, however, is made by enzyme analysis of leukocytes, fibroblasts, or amniocytes. Due to the extreme rarity of this disease, the features of the liver biopsy may represent a challenge to the pathologist.

In this patient, the enzymatic assays for the full lysosomal enzyme panel in plasma and leukocytes demonstrated very low activity of β-galactosidase (0.0 and 1.0 nmol/h/mg protein, respectively). The diagnosis of GMl was established over Morquio type B based on the clinical findings of central nervous system involvement.

References

1. Landing BH, Silvcrman FN, Craig JM, et al. Familial neurovisceral lipidosis. Am I Dis Child 1964;108:503-522.

2. Suzuki K. Cerebral GM1 gangliosidosis: chemical pathology of visceral organs. Science. 1968;1 59:1471-1472.

3. Petrelli M, Blair JD. The liver in GM1 gangliosidosis type 1 and 2. Arch Pathol. 1975)99:111-116.

4. Phillips JM, Poucell S, Patterson J, Valencia P. The Liver: An Atlas and Text of Ultrastructural Pathology. New York, NY: Raven Press; 1987:252.

5. Gilbert-Barness E, Barness LA. Metabolic Diseases: Foundations of Clinical Management, Genetics and Pathology. South Natick, Mass: Eaton Publishing Co; 2000:361-364.

6. Suzuki Y, Sakuraba H, Oshima A. β-Galactosidase deficiency (β galacfasidosis): GM1 and Morquio B disease. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The Metabolic and Molecular Bases of Inherited Disease. 8th. ed. New York, NY: McGraw-Hill; 2001:2799.

Moueen Bu-Ghanim, MD; Claude Sansaricq, MD, PhD; Ronald Gordon, PhD; Raffaella A. Morotti, MD

Accepted for publication June 3, 2004.

From the Departments of Pathology (Drs Bu-Chanim, Cordon, and Morotti) and Human Genetic and Metabolic Disease (Dr Sansaricq), Mount Sinai Hospital, Mount Sinai School of Medicine, New York, NY.

The authors have no relevant financial interest in the products or companies described in this article.

Corresponding author: Raffaella A. Morotti, MD, Department of Pathology, One Gustave L. Levy Pl, Box 1194, New York, NY (e-mail: Raffaella.Morotti@msnyuhealth.org).

Reprints not available from the authors.

Copyright College of American Pathologists Nov 2004
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