Srinivasa S. Raghavan

Late-Onset Krabbe Disease (Globoid Cell Leukodystrophy): Clinical and Biochemical Features of 15 Cases

The diagnosis of late-onset variants of Krabbe disease (globoid cell leukodystrophy) has been facilitated by the recognition of galactocerebrosidase deficiency as its biochemical hallmark. Fifteen patients, ages 4-73, are presented. Signs included pes cavus, optic disc pallor, progressive spastic tetraparesis, a sensorimotor demyelinating neuropathy and hypodense lesions in the parieto-occipital periventricular white matter. Although intellect was preserved in more than half the cases, significant intrafamilial variability in mental functioning was encountered in 3 families. Bone marrow transplantation was successful in 1 13-year-old girl, but caused the death of 2 teenage twin sisters.

Identification and characterization of novel mutations of the aspartoacylase gene in non-Jewish patients with Canavan disease

Canavan disease, an inherited leukodystrophy, is caused by mutationsin the aspartoacylase (ASPA) gene. It is most common among children of Ashkenazi Jewish descent but has been diagnosed in many diverse ethnic groups.Two mutations comprise the majority of mutant alleles in Jewish patients, while mutations in the ASPA gene among non-Jewish patients are different and more diverse. In the present study, the ASPA gene was analysed in 22 unrelated non-Jewish patients with Canavan disease, and 24 different mutations were found. Of these, 14 are novel, including five missense mutations (E24G, D68A, D249V, C152W, H244R), two nonsense mutations (Q184X, E214X), three deletions (923delT, 33del13, 244delA), one insertion mutation (698insC), two sequence variations in one allele ([10T > G; 11insG]), an elimination of the stop codon (941A > G, TAG → TGG, X314W), and one splice acceptor site mutation (IVS1 − 2A > T). The E24G mutation resulted in substitution of an invariable amino acid residue (Glu) in the first esterase catalytic domain consensus sequence. The IVS1 − 2A > T mutation caused the retention of 40 nucleotides of intron 1 upstream of exon 2. The results of transient expression of the mutant ASPA cDNA containing these mutations in COS-7 cells and assays for ASPA activity of patient fibroblasts indicated that these mutations were responsible for the enzyme deficiency. In addition, patients with the novel D249V mutation manifested clinically at birth and died early. Also, patients with certain other novel mutations, including C152W, E214X, X314W, and frameshift mutations in both alleles, developed clinical manifestations at an earlier age than in classical Canavan disease.

Mucolipidosis IV: Morphology and Histochemistry of an Autopsy Case

Mucolipidosis Type IV is a rare, autosomal recessive disorder characterized by corneal opacification, mental retardation, and delayed motor milestones. Whereas lysosomal storage material has been demonstrated in biopsied tissues and leukocytes, the complete autopsy pathology, including neuropathology, is unknown. The metabolic defect remains speculative. We report the general and neuropathologic findings of the only known autopsy. In the central nervous system, neuronal loss in the cerebral cortex, basal ganglia, deep cerebellar nuclei, and brainstem nuclei was marked by astrocytosis; the cytoplasm of residual neurons had brown granules. These granules were positive with periodic acid-Schiff, Concanavalia ensiformis, and Sudan black, but not with Luxol-fast blue. Ultrastructurally, neurons contained lysosomes laden with osmiophilic, amorphous and granular material, and few lamellated membrane structures. Hepatocytes, epithelia, endothelia, chondrocytes, and tissue macrophages also stained positively with Datura stramonium and Ricinus communis-I agglutinins, with renal glomeruli also staining with peanut agglutinin; most non-neural cells contained osmiophilic granules on toluidine blue-stained, plastic embedded sections, corresponding to lamellated membrane structures. These findings complement the previously reported ocular morphology and brain and liver biochemistry performed in the same patient, and suggest that the storage material in neurons differs from that in non-neural cells. Furthermore, the underlying defect is not likely to be a deficiency of a single enzyme (i.e. a lysosomal hydrolase).

Dysmyelinogenesis in animal model of GM1 gangliosidosis

Magnetic resonance imaging (MRI), pathologic examinations, and biochemical analyses were performed on 2 different canine mutants with GM1 gangliosidosis (i.e., English Springer Spaniel and Portuguese Water Dog) and on age- and sex-matched controls. Serial MRI studies were also performed on a child with infantile-onset GM1 gangliosidosis. The affected dogs had abnormalities on MRI, including a relative increase in gray matter and an abnormal signal intensity of cerebral and cerebellar white matter observed on T2-weighted MRI. White matter changes on MRI were similar to white matter abnormalities observed in a 15-month-old boy with GM1 gangliosidosis. The weight ratio of white to gray matter from the frontal lobe was markedly reduced. Microscopic examination revealed characteristic ballooned neurons which stained lightly with Luxol-fast blue. The central cerebral and cerebellar folia white matter exhibited pallor and gliosis, while the corpus callosum and fornix stained normally with Luxol-fast blue. Axons appeared intact on Bodian staining. Ultrastructural studies revealed fewer myelinated axons in affected puppies. Total gangliosides in gray matter were elevated. Thin-layer chromatography demonstrated GM1 ganglioside as the predominant ganglioside. The amount of cerebrosides and sulfatides was reduced in the gray and white matter when compared to controls but the ratio in gray and white matter remained unchanged. Immunostaining of neutral glycolipids disclosed increased amounts of stage-specific embryonic antigen-1 glycolipid in gray matter. These findings suggest that canine models for GM1 gangliosidosis are associated with abnormal myelin development which may be similar to the human disease.

Leukocyte Sulfatidase for the Reliable Diagnosis of Metachromatic Leukodystrophy

Abstract: A simple assay technique for the determination of sulfatidase activity in leukocytes has been developed for the reliable diagnosis of metachromatic leukodystrophy (MLD). Sulfatide is tritiated in sphingosine and fatty acid by reduction with [3H]sodium borohydride in alkali in the presence of palladium chloride. This labeled natural substrate for aryl sulfatase A (AsA) is hydrolyzed by normal human leukocytes in 25 mwacetate buffer, pH 5.0, in the presence of 0.3% sodium taurodeoxycholate. The enzyme activity is greatly improved after dialysis, exhibiting better linearity with protein concentration. It is stimulated maximally by 5 mM‐MnCl2 with an apparent Km of 0.17 MM for the substrate. Patients with MLD exhibited virtually no detectable sulfatidase activity although they had residual AsA activity that was measured with the synthetic substrate, p‐nitrocatechol sulfate (NCS). Potential heterozygotes could be identified by the sulfatidase assay in instances where the NCS assay for AsA was inconclusive. Several individuals with levels of AsA activity characteristic of MLD, including a few healthy carriers and certain patients with unknown neurological diseases, were shown not to have MLD by the presence of measurable levels of sulfatidase in their leukocytes.

Mild-onset presentation of Canavan's disease associated with novel G212A point mutation in aspartoacylase gene.

We describe two sisters with a mild‐onset variant of Canavans disease who presented at age 50 and 19 months with developmental delay but without macrocephaly, hypotonia, spasticity, or seizures. Remarkably, both patients had age‐appropriate head control, gross motor development, and muscle tone. There were very mild deficits in fine motor skills, coordination, and gait. Both sisters had a history of strabismus, but otherwise vision was normal. The older child showed evidence of mild cognitive and social impairment, whereas language and behavior were normal for age in the infant. Both patients were found to be compound heterozygotes for C914A (A305E) and G212A (R71H) mutations in ASPA. Like all other known ASPA mutations, this previously unknown G212A mutation appears to have low absolute enzyme activity. Nevertheless, it is associated in these patients with an extremely benign phenotype that is highly atypical of Canavans disease. Biochemical and clinical data were evaluated using a generalized linear mixed model generated from 25 other subjects with Canavans disease. There were statistically significant differences in brain chemistry and clinical evaluations, supporting a distinct variant of Canavans disease. Future studies of ASPA enzyme structure and gene regulation in these subjects could lead to a better understanding of Canavans pathophysiology and improvements in ASPA gene therapy Ann Neurol 2006;59:428–431

Deficiency of glucosylsphingosine: -Glucosidase in Gaucher disease

Abstract A deficiency in the activity of glucosylsphingosine: β-glucosidase has been observed in Gauchers spleen tissue and skin fibroblasts. Preliminary studies indicated the presence of a material similar to glucosylsphingosine in Gauchers spleen while such a material was not detectable in normal and other pathological control spleen tissue. This is the first report of the natural occurrence of a psychosine-like material in a mammalian tissue.

Isolation and characterization of the normal canine β-galactosidase gene and its mutation in a dog model of GM1-gangliosidosis

The acid β-galactosidase cDNA of Portuguese Water dogs was isolated and sequenced. The entire coding region of the gene consists of 2004 nucleotides encoding a protein of 668 amino acids. Its encoding sequence indicates approximately 86.5% identity at the nucleotide level and about 81% identity at the amino acid level with the encoding region of the human acid β-galactosidase gene. The deduced amino acid sequence contains a 24-amino-acid putative signal sequence, six possible glycosylation sites, and seven cysteine residues. A homozygous recessive mutation, causing canine GM1-gangliosidosis, was identified at nucleotide G200→A in exon 2 resulting in an Arg60→His (mutation R60H) amino acid substitution. The mutation creates a new restriction enzyme site for Pml1. Genotyping 115 dog samples for this acid β-galactosidase gene alteration readily distinguished affected homozygous recessives (n=5), heterozygous carriers (n=50) and normal homozygotes (n=60). DNA mutation analysis provided a method more specific than enzyme assay of β-galactosidase for determination of carriers.

Oligosaccharides from placenta: early diagnosis of feline mannosidosis

High‐pressure liquid chromatography analysis of oligosaccharides from placentas allowed the diagnosis of α‐mannosidosis in three litters of kittens. The chromatography also afforded a detailed comparison of the oligosaccharide pattern and levels in placenta, liver, brain, urine and ocular fluid of the affected animals. In all cases, two series of compounds were observed, with one or two residues of N‐acetylglucosamine at the reducing terminus, respectively, and between two and nine mannose residues. This pattern is unlike that of human mannosidosis, and resembles that of ruminants, except that the major oligosaccharide contains three mannose residues instead of two.

GM2-ganglioside metabolism in cultured human skin fibroblasts: unambiguous diagnosis of GM2-gangliosidosis

The metabolism of GM2-ganglioside was studied in situ using cultured skin fibroblasts from normal individuals and patients with different forms of GM2-gangliosidosis. [3H]Sphingosine-labeled GM2 was provided in the culture medium to confluent cells in 6-cm petri dishes. After 10 days, the cells were washed free of radioactivity and harvested by trypsinization. The cellular lipids were extracted and analyzed for radioactivity in GM2 and its metabolic products. In fibroblasts from healthy subjects, 50-60% of the total cellular radioactivity was found in the neutral glycosphingolipids, ceramide, sphingomyelin and fatty acids. Degradation of the labeled GM2 progressed rapidly via GM3, ceramide dihexoside and ceramide monohexoside with a build-up of radioactivity mainly in the ceramide pool of the cell. The labeled ceramide is also reutilized for the synthesis of ceramide trihexoside, globoside and sphingomyelin or is converted to fatty acid and incorporated in ester linkages. In contrast, cells from patients with GM2-gangliosidosis representing Tay-Sachs, Sandhoff and AB variant forms of the disease did not metabolize the ingested labeled GM2-like controls. Nearly all of the radioactivity was present in the ganglioside fraction in the lipid extracts from these cells and consisted of unhydrolyzed GM2. High-performance liquid chromatographic analysis of monosialogangliosides from cells grown without added labeled GM2 in the medium indicated accumulation of endogenously synthesized GM2 in cell lines from all patients with GM2 gangliosidosis compared to healthy controls. This approach provides a reliable tool for pre- and post-natal diagnosis of all forms of GM2-gangliosidosis without ambiguity.