Tay-Sachs Disease Heterozygotes Research Articles

Common HEXB polymorphisms reduce serum HexA and HexB enzymatic activities, potentially masking Tay-Sachs disease carrier identification

A DNA-proven Tay-Sachs disease (TSD) carrier and his brother were found to have serum percent Hexosaminidase A (%HexA) enzymatic activities in the non-carrier range, while the leukocyte %HexA profiles clearly identified them as TSD heterozygotes. Both their serum HexA and HexB enzymatic activities were below reference range, suggesting inheritance of mutations in both the HEXA (α-subunit) and HEXB (β-subunit) genes. DNA sequencing revealed that both individuals, carried the common HEXA 1277_1278insTATC mutation, and two common HEXB polymorphisms: [619A>G (+) delTG]. To determine if these HEXB polymorphisms reduce HexA and HexB enzymatic activities, 69 DNA samples from subjects previously screened enzymatically in both serum and leukocytes for TSD carrier status were selected for either high, mid-range or low serum Total Hex (defined as the sum of HexA and HexB) activities and were tested for the HEXB mutations. Further, three additional TSD carriers ascertained by the atypical pattern of normal serum %HexA but carrier leukocyte %HexA, were found to have the [delTG (+) 619A>G] genotype. In addition, the frequency of the [delTG (+) 619A>G] genotype was significantly higher ( P < 0.01) in subjects with low serum HexB enzymatic activities. Given the high frequency of the [delTG (+) 619A>G] haplotype in the Ashkenazi Jewish population (approximately 10%), up to 10% of TSD carriers may have normal serum %HexA values with low total Hex. Accordingly, serum %HexA should not be the sole criterion used for carrier status determination. Where total Hex activity is reduced, further testing with leukocyte Hex profiles is indicated.

Heterozygosity for Tay-Sachs and Sandhoff diseases in non-Jewish Americans with ancestry from Ireland, Great Britain, or Italy.

Previous reports have found that non-Jewish Americans with ancestry from Ireland have an increased frequency of heterozygosity for Tay-Sachs disease (TSD), although frequency estimates are substantially different. Our goal in this study was to determine the frequency of heterozygosity for TSD and Sandhoff diseases (SD) among Irish Americans, as well as in persons of English, Scottish, and/or Welsh ancestry and in individuals with Italian heritage, who were referred for determination of their heterozygosity status and who had no known family history of TSD or SD or of heterozygosity for these conditions. Of 610 nonpregnant subjects with Irish background, 24 TSD heterozygotes were identified by biochemical testing, corresponding to a heterozygote frequency of 1 in 25 (4%; 95% CI, 1/39-1/17). In comparison, of 322 nonpregnant individuals with ancestry from England, Scotland, or Wales, two TSD heterozygotes were identified (1 in 161 or 0.62%; 95% CI, 1/328-1/45), and three TSD heterozygotes were ascertained from 436 nonpregnant individuals with Italian heritage (1 in 145 or 0.69%; 95% CI, 1/714-1/50). Samples from 21 Irish heterozygotes were analyzed for HEXA gene mutations. Two (9.5%) Irish heterozygotes had the lethal + 1 IVS-9 G --> A mutation, whereas 9 (42.8%) had a benign pseudodeficiency mutation. No mutation was found in 10 (47.6%) heterozygotes. These data allow for a frequency estimate of deleterious alleles for TSD among Irish Americans of 1 in 305 (95% CI, 1/2517-1/85) to 1 in 41 (95% CI, 1/72-1/35), depending on whether one, respectively, excludes or includes enzyme-defined heterozygotes lacking a defined deleterious mutation. Pseudodeficiency mutations were identified in both of the heterozygotes with ancestry from other countries in the British Isles, suggesting that individuals with ancestry from these countries do not have an increased rate of TSD heterozygosity. Four SD heterozygotes were found among individuals of Italian descent, a frequency of 1 in 109 (0.92%; 95% CI, 1/400-1/43). This frequency was higher than those for other populations, including those with Irish (1 in 305 or 0.33%; 95% CI, 1/252-1/85), English, Scottish, or Welsh (1 in 161 or 0.62%; 95% CI, 1/1328-1/45), or Ashkenazi Jewish (1 in 281 or 0.36%; 95% CI, 1/1361-1/96) ancestry. Individuals of Irish or Italian heritage might benefit from genetic counseling for TSD and SD, respectively.

16. Late-onset GM2 gangliosidosis and other hexosaminidase mutations among Jews

Publisher Summary This chapter discusses the late-onset G M2 gangliosidosis and other Hexosaminidase mutation among Jews. Tay-Sachs Disease (TSD) is caused by absence of β-hexosaminidase (Hex) A, following which heat inactivation method (HIM) for quantifying Hex A using the synthetic substrate 4-MUG. The interaction between Hex A and G M2 ganglioside substrate is accomplished by a nonenzymatic protein, the G M2 activator. Hex A-deficient adults have residual Hex A activity that are significantly higher in TSD patients, but significantly lower than in TSD heterozygotes. AGG is a slowly progressing neurodegenerative disorder. The patients have very low Hex A activity and usually carry the Gly269Ser mutation in compound heterozygosity with an infantile TSD mutation. Homozygotes for the Gly269Ser mutation are only mildly affected. The enzyme β-hexosaminidase (Hex) B does not degrade the G M2 ganglioside in humans, and therefore has no direct involvement in TSD. However, it is a major participant in the routine enzymatic assay for identification of TSD genotypes because Hex B, like Hex A, hydrolyzes the synthetic substrate 4-MUG, and, unlike Hex A, it is heat stabile. It is estimated that 1 in 140 Moroccans is a TSD carrier, and seven different TSD mutations in this community have been identified.

Lower frequency of Gaucher disease carriers among Tay-Sachs disease carriers.

The heterozygote frequency of Gaucher disease (GD) and Tay-Sachs disease (TSD) is distinctly high among Ashkenazi Jews (1:29 for TSD and 1:16 for GD). Two main theories have been suggested to explain this high occurrence: a founder effect with subsequent genetic drift, and a selective advantage of heterozygotes. We compared the frequency of the GD most common mutation (1226A-->G) among carriers of the common TSD mutation (+1277 TATC) with the frequency of this mutation in the general Ashkenazi population. The frequency of GD carriers among 308 TSD heterozygotes was 1:28 which is about half the expected (P = 0.03). These results indicate that carriers of both diseases do not possess additional evolutionary advantage over single mutation carriers. A reasonable interpretation of these findings is that one or both mutations have arisen relatively recently in different regions of Europe and have not yet reached genetic equilibrium.

Heterozygosity for Tay-Sachs and Sandhoff diseases among Massachusetts residents with French Canadian background.

The frequency of Tay-Sachs disease (TSD) heterozygosity is increased among French Canadians in eastern Quebec. A large proportion of the New England population has French Canadian heritage; thus, it is important to determine if they too are at increased risk for TSD heterozygosity. This prospective study was designed to assess the TSD heterozygote frequency among people with French Canadian background living in Massachusetts. A simultaneous screen for heterozygosity for Sandhoff disease, a related genetic disorder, was also undertaken. 1260 non-pregnant subjects of French Canadian background were included in the study. beta hexosaminidase activity was measured in blood samples, and results were evaluated for TSD and Sandhoff disease heterozygosity. Samples from the TSD heterozygotes were also subjected to mutation analysis. Of the 1260 samples studied, 22 (1 in 57; CI 1 in 41, 1 in 98) were identified as TSD heterozygotes by enzymatic analyses and 11 subjects (1 in 114; CI 1 in 72, 1 in 280) were identified as Sandhoff disease heterozygotes. Three of the 22 TSD heterozygotes were found to have benign pseudodeficiency mutations, resulting in a maximum TSD heterozygote frequency of 19 in 1260 (1 in 66; CI 1 in 46, 1 in 120). Together, these data provide a maximum frequency of heterozygosity for TSD or Sandhoff disease of 30 in 1260 (1 in 42; CI 1 in 31, 1 in 64) in this population. Simultaneous screening for TSD and Sandhoff disease heterozygosity by assay of beta hexosaminidases A and B activities provides a possible method for use with subjects of French Canadian background. The relevance of some of the novel mutations identified in this group needs further study. However, the comparatively high combined frequency of TSD and Sandhoff disease heterozygosity indicates a need for discussion regarding the appropriateness of carrier testing for these disorders for persons of French Canadian background in Massachusetts.

Heterozygote screening for Tay-Sachs disease

Tay-Sachs disease (TSD) is an autosomal recessive, neurodegenerative disorder caused by a deficiency of beta-hexosaminidase A activity. Mass screening for TSD heterozygotes has been routine in the Ashkenazi Jewish population since the early 1970s. Recent advances in the molecular genetics and epidemiology of TSD require a reevaluation of heterozygote screening practices. The use of DNA-based analyses for a panel of common mutations detects about 98% of TSD mutations found in the Ashkenazi Jews and about 50% of TSD mutations found in the general non-Jewish population; enzyme-based analysis has nearly 100% sensitivity for all populations. We recommend 1) that members of several ethnic groups and persons with a family history consistent with TSD be offered testing for TSD heterozygosity and 2) that assays of enzyme activity be used as the primary screening tool, with mutation analysis used as an adjunct tool in certain cases.

Heterozygosity for Tay-Sachs disease in non-Jewish Americans with ancestry from Ireland or Great Britain.

We performed a genetic epidemiological analysis of American non-Jewish people with ancestry from Ireland or Great Britain with regard to heterozgosity for Tay-Sachs disease (TSD). This study was prompted by a recent report that the frequency of heterozygosity for TSD among Irish Americans was 1 in 8, a frequency much higher than that recognised for any other population group. We identified 19 of 576 (3.3%) people of Irish background as TSD heterozygotes by the standard thermolability assay for beta-hexosaminidase A (Hex A) activity. Three of 289 people of non-Irish British Isles background (1%) were also identified as heterozygotes by biochemical testing. Specimens from the biochemically identified Irish heterozygotes were analysed for seven different Hex A alpha subunit gene mutations; three (15.8%) had a lethal +1 IVS-9 G to A mutation, previously noted to be a common mutation among TSD heterozygotes of Irish ancestry. Eight of 19 (42.1%) had one of two benign or pseudodeficiency mutations, and no mutation was found in 42.1% of the heterozygotes analysed. These data indicate that non-Jewish Americans with Irish background have a significantly increased frequency of heterozygosity at the Hex A alpha subunit gene locus, but that approximately 42% of the biochemically ascertained heterozygotes have clinically benign mutations. A pseudodeficiency mutation was identified in one of the three TSD heterozygotes of non-Irish British Isles background; no mutations were found in the other two. The data allow for a frequency estimate of deleterious alleles for TSD among Irish Americans of 1 in 192 to 1 in 52. Non-Jewish Americans with ancestry from Great Britain have a minimal, if any, increase in rate of heterozygosity at the TSD gene locus relative to the general population.

P.3.052 - First episode schizophrenia: Treatment and outcome

This chapter discusses the late-onset GM2 gangliosidosis and other Hexosaminidase mutation among Jews. Tay-Sachs Disease (TSD) is caused by absence of β-hexosaminidase (Hex) A, following which heat inactivation method (HIM) for quantifying Hex A using the synthetic substrate 4-MUG. The interaction between Hex A and GM2 ganglioside substrate is accomplished by a nonenzymatic protein, the GM2 activator. Hex A-deficient adults have residual Hex A activity that are significantly higher in TSD patients, but significantly lower than in TSD heterozygotes. AGG is a slowly progressing neurodegenerative disorder. The patients have very low Hex A activity and usually carry the Gly269Ser mutation in compound heterozygosity with an infantile TSD mutation. Homozygotes for the Gly269Ser mutation are only mildly affected. The enzyme β-hexosaminidase (Hex) B does not degrade the GM2 ganglioside in humans, and therefore has no direct involvement in TSD. However, it is a major participant in the routine enzymatic assay for identification of TSD genotypes because Hex B, like Hex A, hydrolyzes the synthetic substrate 4-MUG, and, unlike Hex A, it is heat stabile. It is estimated that 1 in 140 Moroccans is a TSD carrier, and seven different TSD mutations in this community have been identified.

Molecular basis of hexosaminidase A deficiency and pseudodeficiency in the Berks County Pennsylvania Dutch.

Following the birth of two infants with Tay-Sachs disease (TSD), a non-Jewish, Pennsylvania Dutch kindred was screened for TSD carriers using the biochemical assay. A high frequency of individuals who appeared to be TSD heterozygotes was detected (Kelly et al., 1975). Clinical and biochemical evidence suggested that the increased carrier frequency was due to at least two altered alleles for the hexosaminidase A alpha-subunit. We now report two mutant alleles in this Pennsylvania Dutch kindred, and one polymorphism. One allele, reported originally in a French TSD patient (Akli et al., 1991), is a GT-->AT transition at the donor splice-site of intron 9. The second, a C-->T transition at nucleotide 739 (Arg247Trp), has been shown by Triggs-Raine et al. (1992) to be a clinically benign "pseudodeficient" allele associated with reduced enzyme activity against artificial substrate. Finally, a polymorphism [G-->A (759)], which leaves valine at codon 253 unchanged, is described.

Marked variation in blood beta-hexosaminidase in Gaucher disease

Gaucher disease is due to a primary deficiency of acid beta-glucosidase activity and is associated with secondary elevations of several plasma/serum lysosomal enzyme activities, including beta-hexosaminidase. We analyzed plasma and serum beta-hexosaminidase A & B activities in 55 patients with enzyme-documented Gaucher disease. The mean beta-hexosaminidase activity was increased and the percent of the A isozyme decreased, consistent with earlier studies. Gaucher disease patients had 2,067 ± 1,491 nmol ml −1 h −1 units of beta-hexosaminidase activity with 51.9 ± 15.5% beta-hexosaminidase A compared to 1,086 ± 260 nmol ml −1 h −1 and 67.8 ± 4.0% beta-hexosaminidase A in normal controls and 965 ± 261 nmol ml −1 h −1 and 43.6 ± 5.5% beta-hexosaminidase A in Tay-Sachs disease heterozygotes. Contrary to previous reports, marked heterogeneity of both total plasma/serum enzyme activity and isozyme pattern was noted, as some patients had normal enzyme levels and others had severe reductions in the percent of hexosaminidase A. These data argue against the suggestions of recent studies that routine serum beta-hexosaminidase testing done in Tay-Sachs disease heterozygote detection programs can be effectively used to screen for patients with Gaucher disease.

Tay-Sachs disease heterozygote detection: use of a centrifugal analyser for automation of hexosaminidase assays with two different artificial substrates.

An assay for measuring hexosaminidase A in serum and leucocytes is described in which a centrifugal analyser is used for automation of the enzyme assays after manual heat inactivation. The...

Tay-Sachs disease: B 1 variant

This first child of non-Jewish parents had nystagmus at 4 months of age, bilateral cherry-red macular spots at 7 months of age, and hyperacusis at 8 months of age; the patient has deteriorated progressively following a clinical course typical of Tay-Sachs disease B variant. Total β- N-acetylhexosaminidase assayed with 4-methylumbelliferyl-β-glucosamine (4 MU GlcNAc) as substrate was within the normal range in plasma and cultured dermal fibroblasts and 2 3 the normal mean in leukocytes. The hexosaminidase A activity, assayed with the same substrate in plasma and cultured fibroblasts, approximated Tay-Sachs disease heterozygote levels; however, the activity of hexosaminidase A assayed with 4 MU Glc NAc-6-sulfate in the plasma, leukocytes, and cultured fibroblasts was < 8, 2, and 1%, respectively of the control mean. This female infant with the B 1 variant of Tay-Sachs disease demonstrated an earlier onset and more rapidly progressive course than was observed in 4 of the 5 previously reported patients with this Tay-Sachs disease variant.

Identification of Tay-Sachs by hexosaminidase analysis of urine and tear samples.

1. Two readily obtainable biological fluids, i.e., urine and tears, were investigated as possible substitutes for serum and leukocytes for the detection of Tay-Sachs disease (TSD) heterozygotes based on Quantitative hexosaminidase A (Hex A) determinations. 2. Hexosaminidase isoenzyme patterns were determined, by means of an automated DEAE-cellulose microcolumn procedure, for serum, urine and tear samples from normals, TSD carriers, normal pregnancies, carrier-pregnancies and TSD children. 3. Normal pregnancy and TSD carrier sera gave almost identical hexosaminidase patterns with multiple intermediate peaks. Whereas, urine and tear samples from normal pregnant women showed hexosaminidase isoenzyme patterns resembling those of normal controls. These results suggested that use of these fluids might eliminate the effect of pregnancy of the Hex A ratio which occurs when serum is used as the test fluid. In addition these fluids are most economical and simpler to obtain than a blood sample. 4. About 200 urine samples, from the various categories listed above, were analyzed for Hex A with both the heat denaturation and pH inactivation methods and the results compared with serum and leukocyte levels from many of the same individuals. With either method, the wide overlap between the urinary Hex A normal and heterozygote ranges would require retesting with leukocytes of about 30% of the subjects. These results would preclude the use of urines as a suitable fluid for the mass screening of the Ashkenazic Jewish population for TSD heterozygotes.

Automated Determination of Serum Hexosaminidase A by pH Inactivation for Detection of Tay-Sachs Disease Heterozygotes

Abstract We have automated a manual test for detection of heterozygotes of Tay-Sachs disease by assay of hexosaminidase A in serum, based on pH inactivation [Clin. Chim. Acta 43, 417 (1973)]. The same manifold is used both for the total hexosaminidase and pH-inactivation (hexosaminidase B) procedures. Automation expedites mass screening of the Ashkenazi Jewish population for carriers of the Tay-Sachs gene (prevalence rate, 1:30), because 100 or more tests can be performed daily. The mean percentage value and range (±2 SD) of hexosaminidase A for normal adults is 68.6 (58-79) and for carriers is 48.8 (39-59) with the automated pH-inactivation procedure. "Presumed carriers" (&amp;lt;53% hexosaminidase A) and individuals in the uncertain range (53 to 58%) should be retested by using leukocytes, to avoid the effect of certain physical ailments, before being labeled as carriers. The same automated system used for this assay can also be used to detect carriers of at least seven other sphingolipidoses for which artificial fluorogenic substrates are available.

Sandhoff disease: Diagnosis of heterozygous carriers by serum hexosaminidase assay

1. (1) A batch-wise fractionation of hexosaminidases with DEAE-cellulose gave consistent and reproducible results. The ratio of the A and B enzymes by this method was slightly higher than that by the heat inactivation method. 2. (2) Investigations on obligate and possible carriers of Sandhoff disease revealed a characteristic serum hexosaminidase pattern; low total hexosaminidase activity with relative preservation of component A. This was well contrasted with low activity of component A and normal total activity in Tay-Sachs disease heterozygotes.

Rapid test for the detection of tay-sachs disease heterozygotes and homozygotes by serum hexosaminidase assay

Total serum hexosaminidase activity is generally measured quantitatively by the amount of fluorescent product formed by action of its various isoenzymes on the 4-methyl-umbelliferyl-β-D-N-acetylglucosaminide substrate at pH 4.5. Only the heat labile form of the enzyme (Hex A) is inactive in fluids and tissues of Tay-Sachs children. Known carriers (parents) have serum Hex A values about sol1 2 of those found for non-carriers. Carrier detection tests, presently utilized for the mass screening of the Ashkenazi Jewish population, are based either on prolonged heat inactivation or electrophoretic separation of Hex A from its other serum isoenzymes. We found that serum Hex A can also be inactivated by 5 min incubation at pH 2.8 ± 0.05 and 37°. This finding led to a simple, rapid, quantitative assay for Hex A which was applied to 29 sera (14 normal, 8 carrier, 4 pregnancy and 3 Tay-Sachs disease). Except for the pregnancy and carrier groups, there was no overlap in serum Hex A values for any of the other categories. The results by acid pH inactivation correlated well with those obtained by the heat denaturation procedure. The greater potential of the acid inactivation method for automated systems, suitable for mass screening of carriers, is presently under development.

Detection of Tay-Sachs disease heterozygotes by assay of hexosaminidase A in serum and leukocytes

Activity of the enzyme hexosaminidase A was assayed by cellulose acetate electrophoresis in serum and leukocytes of parents of children with Tay-Sachs disease. The activity of the enzyme was lower than normal in both serum and leukocytes of the parents. The data from the serum assay were more consistent than those from the leukocyte assay. This method is applicable for the detection of heterozygous carriers of Tay-Sachs disease. Activity of the enzyme hexosaminidase A was assayed by cellulose acetate electrophoresis in serum and leukocytes of parents of children with Tay-Sachs disease. The activity of the enzyme was lower than normal in both serum and leukocytes of the parents. The data from the serum assay were more consistent than those from the leukocyte assay. This method is applicable for the detection of heterozygous carriers of Tay-Sachs disease.