31/45. Sandhoff's disease (GM2 gangliosidosis type 2). Histopathology and ultrastructure of the eye. Sandhoff's disease (GM2 gangliosidosis type 2) was diagnosed in an infant in whom a progressive neurologic disorder and cherry-red foveal spots developed. At autopsy, ultrastructural examination of the retina and optic nerve disclosed abundant pleomorphic storage cytosomes in all neurons of the retina, including the inner segments of the photoreceptor cells, and in glial cells of the optic nerve. Electron microscopy of the cornea showed, within the keratocytes, distended clear lysosomes that contained some fibrillogranular material and an occasional collection of lamellae. We discuss the pathogenesis of the clinical and pathologic ocular findings with regard to the inherited absence of the enzymes hexosaminidase a and B and an accumulation of the substrates, GM2 ganglioside and asialo GM2, in the nervous system (including retina and optic nerve) and globoside and other hexosamine-containing substances in the viscera (including cornea). ( info) |
32/45. Segregation of Tay-Sachs and Sandhoff alleles in a non-Jewish family. A non-Jewish family is presented in which the genes for tay-sachs disease and sandhoff disease are segregating. Individuals heterozygous for both alleles have low serum and white cell total hexosaminidase levels together with a proportion of heat-labile hexosaminidase a (HEX A) which falls in the normal range. The individuals would not be detected as carriers of tay-sachs disease or sandhoff disease in a population screening program. ( info) |
33/45. A family with combined Farber and Sandhoff, isolated Sandhoff and isolated fetal Farber disease: postnatal exclusion and prenatal diagnosis of Farber disease using lipid loading tests on intact cultured cells. An earlier described patient with combined sphingolipidoses, Farber and Sandhoff disease, had two healthy older brothers and two further sibs, one with sandhoff disease and one (a fetus) with Farber disease, showing segregation of the respective genes. The prenatal diagnosis in the latter was performed using lipid (sphingomyelin and glucosylceramide) loading tests on the cultured amniotic fluid cells. After 1-3 days of incubation the cells' lipid extract revealed radioactive ceramide to be released and highly accumulated. The deficiency in acid ceramidase was known from the patient with the combined diseases. Confirmation of the prenatal Farber diagnosis was done by similar loading tests on the fetal fibroblasts and by analysis of liver lipids of the less than 18-week-old fetus. CONCLUSION: This is the first report on the use of lipid loading tests on intact cultured cells for prenatal diagnosis of Farber disease. The postnatal diagnosis of Farber disease can also be readily made using those tests, as was shown in four further cases. ( info) |
34/45. A novel missense mutation (C522Y) is present in the beta-hexosaminidase beta-subunit gene of a Japanese patient with infantile sandhoff disease. A novel missense mutation (1565G-->A) was identified in the cDNA and genomic dna coding for the beta-hexosaminidase beta-subunit of a Japanese patient with infantile sandhoff disease. The patient was homozygous for this mutation, which should result in a cysteine-to-tyrosine substitution at codon 522. Computer-assisted analysis of this amino acid substitution predicted alteration in the secondary structure in the region of a highly conserved sequence. An immunofluorescence study revealed the accumulation of GM2 ganglioside in cultured fibroblasts from the patient with this mutation. ( info) |
35/45. Mutation analysis of a sandhoff disease patient in the Maronite community in cyprus. sandhoff disease occurs in the Christian Maronite community in cyprus, a community that established over a thousand years ago. Nowadays, this community comprises less than 1% of the whole population, and has been culturally and socially isolated. Cultured fibroblasts from a patient from this inbred group showed a beta-hexosaminidase beta subunit mRNA of apparently the normal size but of reduced quantity. A mutational analysis of cDNA obtained by polymerase chain reaction amplification of mRNA showed a deletion of A at nt 76 (counted from A of the initiation codon, ATG). The deletion results in a frame shift and a premature termination within 20 amino acids from the N-terminus of the normal mature enzyme protein. The patient was homozygous for the deletion. The 5'-end of the gene showed many discrepancies from the previously published sequence. We consider that these differences are probably polymorphisms of little functional significance, because the patient's fibroblasts generate decreased but stable mRNA and because some of these base changes were also found in the genes from control fibroblasts. An extensive evaluation of the prevalence of this mutant allele in this community is being initiated. ( info) |
36/45. Preferential beta-hexosaminidase (Hex) A (alpha beta) formation in the absence of beta-Hex B (beta beta) due to heterozygous point mutations present in beta-Hex beta-chain alleles of a motor neuron disease patient. Deficiency of the lysosomal enzyme beta-hexosaminidase b (beta-Hex B) (a homodimer, beta beta), caused by a defect in the HEX B gene encoding the beta-chain, is usually accompanied by an absence of beta-Hex A (a heterodimer, alpha beta), thereby causing sandhoff disease. However, we have earlier demonstrated the presence of partial beta-Hex A (30-50% of normal) even in the absence of beta-Hex B in an adult with motor neuron disease. The patient is a compound heterozygote with normal beta-chain message and one HEX B point mutation originating from each asymptomatic parent. Since the non-expression of beta-Hex B was post-transcriptional, we transfected COS-7 cells to understand the effect of each mutation on beta-Hex B activity. transfection of the A1367-->C mutant (maternal allele) construct produced no overexpressed beta-Hex B, indicating that the encoded Tyr456-->Ser beta-chain was non-functional. Chou-Fasman analysis predicted that the Tyr456-->Ser mutation would cause a dramatic change in beta-chain folding (which often inhibits formation of functional dimers). This explains the complete lack of beta-Hex B in the transfectants and a partial deficiency of beta-Hex A and B (50% of normal) in the patient's mother. Since immunoprecipitated beta-Hex A (alpha beta) protein from patient fibroblasts showed the presence of mature beta-chains even though there was no beta-Hex B (beta beta) protein, the mutant beta-chain inherited from the father (who has normal beta-Hex A and B) must undergo preferential association with the normal alpha-chains in the patient, thus producing only beta-Hex A. Transient expression of the A619-->G mutant (paternal allele) construct produced beta-Hex B activity comparable to the wild type (approximately 10-20-fold over mock-transfected) whereas stable expression produced normal message but no beta-Hex B activity (wild type beta-Hex B expression: only 2-fold over mock-transfected). The lack of increased beta-Hex B after stable expression of the Ile207-->Val beta-chains at a lower copy number indicates the absence of self-association at low concentrations of Ile207-->Val beta-chain. In the patient who also has a non-functional Tyr456-->Ser allele, the effective concentration of beta-chains is reduced to 50% of normal and the remaining Ile207-->Val beta-chains fail to self-associate but can still dimerize with the abundant normal alpha-chains thus producing partial beta-Hex A and no beta-Hex B. ( info) |
| The causal factors and the physiopathology of motor diarrhea are still unclear. This case report describes a 60-year-old white man with severe diarrhea for more than 10 years and minor signs of autonomic dysfunction. Extensive investigation showed that small intestinal motility and absorption were normal but that accelerated colon transit precluded water and solute absorption from the large bowel. Orthostatic hypotension, sexual dysfunction, and loss of sweating suggested dysfunction of the autonomous nervous system, which was confirmed by reduced plasma concentrations of norepinephrine and dopamine. Rectal biopsy specimens showed enlarged enteric ganglion cells filled with lipidic material. Levels of total hexosaminidase and hexosaminidase b in plasma, white blood cells, and fibroblasts were decreased, as found in sandhoff disease. The pedigree of the proband's family showed several affected and heterozygous individuals, detected by examination of total hexosaminidase and hexosaminidase b levels in plasma. Among the five homozygous subjects, three had a clinical picture of diarrhea and orthostatic hypotension since the age of 50. Therefore, hexosaminidase b deficiency should probably be regarded as a cause for dysautonomia; dysfunction of the gastrointestinal tract, manifested by motor diarrhea or esophageal dysmotility, could be the initial and prevalent presentation of dysautonomia. ( info) |
38/45. GM-2 gangliosidosis (Sandhoff's disease): two year follow-up by MRI. Two children with GM-2 gangliosidosis type 0 (Sandhoff's disease) followed up by MRI at 1.5 Tesla for 1.8 years are reported. One was presymptomatic at the first MRI examination. As her neurological status deteriorated, MRI showed low signal in bilaterally, on T2-weighted images the white matter with involvement of the optic radiations. In the second, MRI correlated well with the clinical progression of the disease, showing in the different stages involvement of thalamus and basal ganglia. There was no contrast enhancement and the grey matter remained normal. ( info) |
39/45. Molecular genetics of GM2-gangliosidosis AB variant: a novel mutation and expression in BHK cells. The GM2 activator is a hexosaminidase a-specific glycolipid-binding protein required for the lysosomal degradation of ganglioside GM2. Genetic deficiency of GM2 activator leads to a neurological disorder, an atypical form of tay-sachs disease (GM2 gangliosidosis variant AB). Here, we describe a G506 to C transversion (Arg169 to Pro) in the mRNA of an infantile patient suffering from GM2-gangliosidosis variant AB. Using the polymerase chain reaction amplification and direct-sequencing technique, we found the patient to be homozygous for the mutation, whereas the parents were, as expected, heterozygous. BHK cells transfected with a construct of mutant cDNA gave no GM2 activator protein detectable by the Western blotting technique, whereas those transfected by a wild-type cDNA construct showed a significant level of human GM2 activator protein. The substitution of proline for the normal Arg169 therefore appears to result in premature degradation of the mutant GM2 activator, either during the post-translational processing steps or after reaching the lysosome. The basis for the phenotype of GM2 gangliosidosis variant AB may therefore be either inactivation of the physiological activator function by the point mutation or instability of the mutant protein. ( info) |
40/45. Thalamic hyperdensity--is it a diagnostic marker for sandhoff disease? sandhoff disease, also known as GM2-gangliosidoses variant 0, is caused by the deficient activity of both hexosaminidase a and hexosaminidase b. We report a 15-month-old boy diagnosed with sandhoff disease by demonstrating the enzyme deficiency. The interesting finding was bilateral thalamic hyperdensity on the CT scan. The hyperdensity in all previously published cases was homogeneous and symmetric and limited to the thalamus; the cause still remains unknown. We suggest that the finding of dense thalami may be useful as a specific diagnostic criterion for the GM2-gangliosidoses and especially for sandhoff disease. ( info) |