Infantile Tay-Sachs Disease Research Articles

The Mutations in Ashkenazi Jews with Adult G M2 Gangliosidosis, the Adult Form of Tay-Sachs Disease

The adult form of Tay-Sachs disease, adult GM2 gangliosidosis, is an autosomal recessive disorder that results from mutations in the alpha chain of beta-hexosaminidase A. This disorder, like infantile Tay-Sachs disease, is more frequent in the Ashkenazi Jewish population. A point mutation in the alpha-chain gene was identified that results in the substitution of Gly with Ser in eight Ashkenazi adult GM2 gangliosidosis patients from five different families. This amino acid substitution was shown to depress drastically the catalytic activity of the alpha chain after expression in COS-1 cells. All of these patients proved to be compound heterozygotes of the allele with the Gly to Ser change and one of the two Ashkenazi infantile Tay-Sachs alleles. These findings will aid in the diagnosis and understanding of beta-hexosaminidase A deficiency disorders.

A splicing defect due to an exon-intron junctional mutation results in abnormal β-hexosaminidase α chain mRNAs in Ashkenazi Jewish patients with Tay-Sachs disease

Abnormal beta-hexosaminidase alpha chain mRNAs from an Ashkenazi Jewish patient with the classical infantile Tay-Sachs disease contained intact or truncated intron 12 sequences. Sequence analysis showed a single nucleotide transversion at the 5' donor site of intron 12 from the normal G to C. This provides the first evidence that this junctional mutation, also found independently in two other laboratories by analysis of genomic clones, results in functional abnormality. Analysis with normal and mutant oligonucleotides as probes indicated that our patient was a compound heterozygote with only one allele having the transversion. The patient studied in the other two laboratories was also a compound heterozygote. Another Ashkenazi Jewish patient was normal in this region in both alleles. Thus, the splicing defect is the underlying genetic cause in some but not all Ashkenazi Jewish patients with Tay-Sachs disease.

Ganglioside loading of cultured fibroblasts: a provocative method for the diagnosis of the G M2 gangliosidoses

Confirmation of deficient β-hexosaminidase activity in suspected cases of G M2 gangliosidosis may be difficult with available assay systems if the residual activity is high (as in many juvenile cases and genetic compounds). Hexosaminidase activity is normal in the AB-variant (activator protein deficiency), although G M2-ganglioside (G M2) catabolism is severely impaired. We therefore examined ganglioside degradation in intact fibroblasts in culture. Intracellular ganglioside levels were determined in cultured human skin fibroblasts grown in standard tissue culture medium or medium supplemented with mixed bovine brain gangliosides. Cellular uptake and catabolism of the added gangliosides were manifested by modest increases in the intracellular concentrations of gangliosides G T + G D and G M1 in all cells tested, and marked accumulation of G M2 in fibroblasts from patients with G M2 gangliosidoses. Intracellular G M2 increased five-to fifteen-fold in all of the G M2 gangliosidosis cell lines tested, including those from patients with infantile Tay—Sachs disease (TSD), Sandhoff disease, late infantile and juvenile variants of TSD with high residual enzyme activity, adult onset G M2 gangliosidosis, and the AB-variant. Significant GM2 accumulation did not occur in fibroblasts from patients with G M2 gangliosidosis grown in standard medium, or in normal fibroblasts grown in ganglioside enriched medium. Our method of ganglioside feeding employs commercially available materials and no special equipment. It should be useful for the confirmation of impaired G M2 catabolism in a variety of settings.

801 DIAGNOSIS AND CARRIER DETECTION OF TAY-SACHS DISEASE USING SULFATED FLUOROGENIC SUBSTRATES: DIRECT DETERMINATION OF HEXOSAMINIDASE A IN SERUM DURING PREGNANCY AND IN THE PRESENCE OF HEREDITARY HEATLABILE HEXOSAMINIDASE B

4-Methylumbelliferyl derivatives of β-N-acetylglucosamine-6-sulfate and β-N-acetylgalactosamine-6-sulfate were prepared by direct sulfation of the commonly used unsulfated derivatives. Both sulfated substrates were highly specific for hexosaminidase (Hex) A and in fractionated samples more than 97% of these activities was found in the Hex A fraction. The thermolability of Hex B and intermediate forms as found in subjects with hereditary heatlabile Hex B, and the increase in an intermediate Hex form as found in serum during pregnancy (Hex P), had no effect on direct determination of Hex A with the sulfated fluorogenic substrates. Serum and leukocytes from patients with infantile Tay-Sachs disease (TSD), including a TSD patient with heatlabile Hex B, had less than 2% of the respective mean activity of non-carriers. The latter patient was estimated to have 24% Hex A based on the heat inactivation method. Carrier values in serum during pregnancy and in samples with heatlabile Hex B were within the range of other carrier values and clearly separated from the respective non-carrier values. Mean carrier activities were 51-56% of the respective non-carrier means. The values of % Hex A as derived from the ratio between activities toward sulfated and unsulfated substrates were comparable to those obtained by heat inactivation excluding those with heatlabile Hex B. This helps detecting TSD genotypes and discriminates them from Sandhoff disease genotypes.

SYNTHESIS OF AN ABNORMAL GANGLIOSIDE BY SKIN FIBROBLASTS IN SANDHOFF'S DISEASE

In Sandhoff's disease, following a complete β-hexosaminidase deficiency, there is an accumulation of at least 3 different glycolipids. Upon electron microscopy, cultured fibroblasts from a patient with this condition contained a small number of lamellar inclusions. Major glycolipids in normal confluent cultured fibroblasts are ceramide trihexoside and hematoside. In 2 fibroblast lines from unrelated children with Sandhoff's disease, we detected a ganglioside with an Rf similar to GM2-ganglioside. Complete characterization has not yet been completed. Both 14C-mannosamine and 14C-glucosamine were incorporated into this lipid which thus contains sialic acid and hexosamine. On the basis of this composition, this glycolipid may represent GM2-ganglioside. This compound has never been detected in normal or pathological control fibroblasts, including infantile Tay-Sachs disease, or the other sphingolipidoses. (Supported by the Dept. Mental Hygiene, State of California and PHS Grant HD-04612.)

A clinical, biochemical and electron microscopic study of late infantile amaurotic family idiocy

A case of late infantile amaurotic family idiocy in a two and a half year old non-Jewish white boy on whom a cortical biopsy for histochemical, electron microscopic and biochemical studies was performed is presented. Since birth, the child had displayed an exaggerated extension response to sound, photophobia, and an abnormal cry. At two years of age the gait was wide-based and unsteady, and speech was still monosyllabic. Over the next six months the boy became hypertonic, paretic and demented. Ophthalmoscopic examination revealed bilateral optic atrophy but no evidence of macular degeneration or abnormal retinal pigmentation. Many of the clinical and laboratory findings were similar to those of Tay-Sachs' disease (TSD). Other clinical findings, however, were more characteristic of juvenile lipidosis. Electron microscopy showed occasional membranous cytoplasmic bodies reminiscent of those seen in TSD. Numerous pleomorphic lipid bodies and lipofuscin were also seen. The presence of the latter appears indicative of progressive lipid degradation and is similar to the picture seen in juvenile lipidosis. Chromatographic studies of the biopsied cortical tissue showed the increased ganglioside fraction to be either the major monoor disialoganglioside. Although clinically and morphologically this case appears to be a transitional link between infantile TSD and the juvenile variety of amaurotic family idiocy, biochemically the apparent increased concentration of disialoganglioside suggests that this condition represents a separate and distinct disease entity. This case illustrates the point that a meaningful nosologie delineation of amaurotic family idiocy should be based upon a combination of clinical, biochemical and morphologic criteria. Further studies along similar lines may reveal other important differences not only between, but also within, the major classes of amaurotic idiocy.

EEG findings in infantile Tay-Sachs disease

An infantile case of Tay-Sachs disease is reported. The child had a disordered EEG for his age which showed a non-focal mixed fast and slow dysrhythmia.