Tay-Sachs disease carrier screening: a 21-year experience

This paper presents the findings of a community-based carrier screening program for Tay-Sachs disease, initiated on the University of Wisconsin-Madison campus in 1978. The Madison Community Tay-Sachs Screening Program (MCTSSP) is a collaborative, interdisciplinary program that organizes and conducts periodic screening for Tay-Sachs disease (TSD) for the purpose of identifying Tay-Sachs carriers. We present and analyze data on carrier detection with regard to various demographics, including family history of TSD, ancestry, gender, medication exposure, and illness. Individuals participating in the MCTSSP between 1978 and 1999 were primarily of the target population, and the carrier rate was within the expected range (1/25). Despite aggressive publicity efforts and a well-established program, attendance at the screens has declined. A recent survey of Jewish undergraduate students at the University of Wisconsin-Madison showed poor recall of family screen history and carrier status and reinforced the perception that utilization of the Madison screening program has been low. Ways to increase awareness of and interest in carrier screening for TSD are explored.     

Role of the physician in screening for carriers of Tay-Sachs disease.

A screening test for carriers of Tay-Sachs disease has been available in Toronto for more than 6 years. In that time more than 11 000 Jewish residents have been tested. Most had requested testing after hearing about the screening program from friends or the media; few had been advised by their physicians to be tested. To sample the attitudes of physicians in Toronto towards carrier screening, we studied questionnaire responses of 42 physicians whose practices were composed largely of Jewish patients. Only 31% regularly advised their young adult Jewish patients to have a carrier screening test but 76% said they had patients who asked if they should be tested. Of the 14 (33%) who had had one or more patients with Tay-Sachs disease 6 did not advise carrier testing. There was a positive correlation between specialty training and support for the screening program. Methods for increasing physician advocacy of these programs are discussed.     

The Tay-Sachs disease gene in North American Jewish populations: geographic variations and origin.

From data collected in a North American Tay-Sachs disease (TSD) heterozygote screening program, the TSD carrier frequency among 46,304 Jewish individuals was found to be .0324 (1 in 31 individuals). This frequency is consistent with earlier estimates based on TSD incidence data. TSD carrier frequencies were then examined by single country and single region of origin in 28,029 Jews within this sample for whom such data were available for analysis. Jews with Polish and/or Russian ancestry constituted 88% of this sample and had a TSD carrier frequency of .0327. No TSD carriers were observed among the 166 Jews of Near Eastern origins. Relative to Jews of Polish and Russian origins, there was at least a twofold increase in the TSD carrier frequency in Jews of Austrian, Hungarian, and Czechoslovakian origins (P less than .005). These findings suggest that the TSD gene proliferated among the antecedents of modern Ashkenazi Jewry after the Second Diaspora (70 A.D.) and before their major migrations to regions of Poland and Russia (before 1100 A.D.).     

Identification and rapid detection of three Tay-Sachs mutations in the Moroccan Jewish population.

Infantile Tay-Sachs disease (TSD) is caused by mutations in the HEXA gene that result in the complete absence of beta-hexosaminidase A activity. It is well known that an elevated frequency of TSD mutations exists among Ashkenazi Jews. More recently it has become apparent that elevated carrier frequencies for TSD also occur in several other ethnic groups, including Moroccan Jews, a subgroup of Sephardic Jews. Elsewhere we reported an in-frame deletion of one of the two adjacent phenylalanine codons at position 304 or 305 (delta F304/305) in one HEXA allele of a Moroccan Jewish TSD patient and in three obligate carriers from six unrelated Moroccan Jewish families. We have now identified two additional mutations within exon 5 of the HEXA gene that account for the remaining TSD alleles in the patient and carriers. One of the mutations is a novel C-to-G transversion, resulting in a replacement of Tyr180 by a stop codon. The other mutation is a G-to-A transition resulting in an Arg170-to-Gln substitution. This mutation is at a CpG site in a Japanese infant with Tay-Sachs disease and was described elsewhere. Analysis of nine obligate carriers from seven unrelated families showed that four harbor the delta F304/305 mutation, two the Arg170----Gln mutation, and one the Tyr180----Stop mutation. We also have developed rapid, nonradioactive assays for the detection of each mutation, which should be helpful for carrier screening.     

Novel mutations and DNA-based screening in non-Jewish carriers of Tay-Sachs disease.

We have evaluated the feasibility of using PCR-based mutation screening for non-Jewish enzyme-defined carriers identified through Tay-Sachs disease-prevention programs. Although Tay-Sachs mutations are rare in the general population, non-Jewish individuals may be screened as spouses of Jewish carriers or as relatives of probands. In order to define a panel of alleles that might account for the majority of mutations in non-Jewish carriers, we investigated 26 independent alleles from 20 obligate carriers and 3 affected individuals. Eighteen alleles were represented by 12 previously identified mutations, 7 that were newly identified, and 1 that remains unidentified. We then investigated 46 enzyme-defined carrier alleles: 19 were pseudodeficiency alleles, and five mutations accounted for 15 other alleles. An eighth new mutation was detected among enzyme-defined carriers. Eleven alleles remain unidentified, despite the testing for 23 alleles. Some may represent false positives for the enzyme test. Our results indicate that predominant mutations, other than the two pseudodeficiency alleles (739C-->T and 745C-->T) and one disease allele (IVS9+1G-->A), do not occur in the general population. This suggests that it is not possible to define a collection of mutations that could identify an overwhelming majority of the alleles in non-Jews who may require Tay-Sachs carrier screening. We conclude that determination of carrier status by DNA analysis alone is inefficient because of the large proportion of rare alleles. Notwithstanding the possibility of false positives inherent to enzyme screening, this method remains an essential component of carrier screening in non-Jews. DNA screening can be best used as an adjunct to enzyme testing to exclude known HEXA pseudodeficiency alleles, the IVS9+1G-->A disease allele, and other mutations relevant to the subject's genetic heritage.     

The presence of two different infantile Tay-Sachs disease mutations in a Cajun population.

A study was undertaken to characterize the mutation(s) responsible for Tay-Sachs disease (TSD) in a Cajun population in southwest Louisiana and to identify the origins of these mutations. Eleven of 12 infantile TSD alleles examined in six families had the beta-hexosaminidase A (Hex A) alpha-subunit exon 11 insertion mutation that is present in approximately 70% of Ashkenazi Jewish TSD heterozygotes. The mutation in the remaining allele was a single-base transition in the donor splice site of the alpha-subunit intron 9. To determine the origins of these two mutations in the Cajun population, the TSD carrier status was enzymatically determined for 90 members of four of the six families, and extensive pedigrees were constructed for all carriers. A single ancestral couple from France was found to be common to most of the carriers of the exon 11 insertion. Pedigree data suggest that this mutation has been in the Cajun population since its founding over 2 centuries ago and that it may be widely distributed within the population. In contrast, the intron 9 mutation apparently was introduced within the last century and probably is limited to a few Louisiana families.     

Mutational analyses of Tay-Sachs disease: studies on Tay-Sachs carriers of French Canadian background living in New England.

Tay-Sachs disease (TSD) results from mutations in HEXA that cause Hex A deficiency. Heterozygote-screening programs have been applied in groups with an increased TSD incidence, such as Ashkenazi Jews and French Canadians in Quebec. These programs are complicated by benign mutations that cause apparent Hex A deficiency but not TSD. Benign mutations account for only approximately 2% of Jewish and approximately 36% of non-Jewish enzyme-defined carriers. A carrier frequency of 1/53 (n = 1,434) was found in an ongoing prospective analysis of persons of French Canadian background living in New England by using an enzyme-based assay. DNA from enzyme-defined carriers from this population was analyzed to determine the molecular basis of Hex A deficiency. Samples (36) were tested for common mutations, and samples that were negative for these were screened for uncommon or novel mutations by using SSCP analysis. Exons showing mobility shifts were sequenced, and most mutations were confirmed by restriction enzyme digestion. Known disease-causing mutations were found in nine samples (four had a 7.6-kb deletion found in 80% of French Canadian TSD alleles), and known benign mutations were found in four samples. Seven novel changes were identified, including G748A in four samples. The molecular basis of Hex A deficiency in this carrier population differs from that of French Canadian TSD patients. Screening centers should be aware of the presence of benign mutations among U.S. French Canadians or Franco-Americans.(ABSTRACT TRUNCATED AT 250 WORDS)     

Estimation of the frequency of hexosaminidase a variant alleles in the American Jewish population.

There appear to be several alleles of the hexosaminidase A (HEX A) gene that lead to different clinical syndromes. In addition to the infantile-onset Tay-Sachs disease (TSD), there is a juvenile-onset and an adult-onset form, which are also characterized by low HEX A levels. There are also apparently healthy adults with low HEX A activity. Based primarily on data from population screening for TSD carrier status, we estimate the allele frequency of the combined variant alleles for which data are available to be about 4.5 x 10(-4) and the frequency of adults showing zero HEX A levels (when tested using artificial substrate) to be about 1:67,000. The implications for population screening and prenatal diagnosis are discussed.     

Twenty-year outcome analysis of genetic screening programs for Tay-Sachs and beta-thalassemia disease carriers in high schools.

Programs for education, screening, and counseling of senior-high-school students, in populations at high risk for Tay-Sachs and beta-thalassemia diseases, have existed for >20 years in Montreal. Four process and outcome variables are reported here: (i) voluntary participation rates in the high-school cohort; (ii) uptake rates for the screening test; (iii) origin of carrier couples seeking the prenatal diagnosis option in the programs; and (iv) change in incidence of the two diseases. Between 1972 and 1992, we screened 14,844 Ashkenazi-Jewish students, identified 521 HexA-deficient carriers (frequency 1:28), reached 89% of the demographic cohort in the educational component of the program, and achieved 67% voluntary participation in the subsequent screening phase. The corresponding data for the beta-thalassemia program are 25,274 students (mainly of Mediterranean origin) representing 67% of the cohort with 61% voluntary participation in the screening phase (693 carriers; frequency 1:36). From demographic data, we deduce that virtually all the carriers identified in the high-school screening program remembered their status, had their partner tested if they did not already know they were a carrier couple, and took up the options for reproductive counseling/prenatal diagnosis. In Montreal, the current origin of all couples using prenatal diagnosis for Tay-Sachs and beta-thalassemia diseases is the corresponding genetic screening/testing program, whereas, at the beginning of the programs, it was always because there was a history of an affected person in the family. Incidence of the two diseases has fallen by 90%-95% over 20 years; the rare new cases are born (with two exceptions) outside the target communities or to nonscreened couples.     

Sandhoff disease heterozygote detection: a component of population screening for Tay-Sachs disease carriers. I. Statistical methods

Serum and leukocyte hexosaminidase profiles (total activity and percent heat-labile activity levels) in obligate Sandhoff disease (SHD) heterozygotes differ from those of obligate Tay-Sachs disease (TSD) heterozygotes and noncarrier individuals. We have developed a procedure to identify, with 95% sensitivity, carriers of the allele(s) for SHD among individuals screened in a TSD heterozygote identification program. Using multivariate statistical methods of cluster analysis and discriminant analysis on serum and leukocyte hexosaminidase profiles from 102 potential SHD carriers, a linear discriminant function to classify individuals as SHD carriers or SHD noncarriers was constructed. This function classifies the serum and leukocyte profiles from all 15 obligate SHD heterozygotes studied, as those of SHD carriers. A 95% isodensity ellipse derived from only the serum hexosaminidase profiles of the 15 SHD obligate carriers has been applied to a TSD screened sample of 37,843 Jewish and non-Jewish individuals. A potential recall rate of screened individuals for serum retests and leukocyte assays of 2.01% has been estimated. These statistical methods enhance the TSD heterozygote screening program by permitting one to detect SHD heterozygotes within the screened population.     

Elevated frequency of Tay-Sachs disease among Ashkenazic Jews unlikely by genetic drift alone

Using the steady-state distribution of recessive lethal gene the probability of finding the elevated frequency of Tay-Sachs (TSD) gene among Ashkenazic Jews is computed. For various estimated values of mutation rate and population size, this probability is found to be statistically significant. This probabiltiy, in fact, becomes even smaller if a steady influx of foreign genes into the Ashkenazic Jewish populations is considered. It is suggested that heterozygote advantage together with random genetic drift should be considered as the most probable mechansim for the elevation of TSD gene frequency among the Ashkenazic Jews.     

Teaching about cystic fibrosis carrier screening by using written and video information.

We performed two studies using only written and video materials to educate people about cystic fibrosis (CF) and carrier screening. Participants were randomized to receive written or video materials. All received a brief questionnaire. Subjects in group I (n = 238) were (1) individuals in steady relationships and their partners, (2) > or = 18 years old, and (3) not pregnant. Those who accepted free screening and were not demonstrable carriers were sent a letter explaining their results and another questionnaire. Subjects in group II (n = 108) were parents seeking well child care in a university clinic. The main outcome measures were ability to answer questions correctly about (1) health status of CF carriers and people with CF, (2) the possibility of false-negative results, and (3) for those who had screening, the implications of their own results. Written and video materials were equally effective in conveying information. Prior to screening, subjects answered an average of 86% of questions correctly. Subjects with less formal education answered fewer questions correctly; 60% of those with less than a high school education had adequate knowledge of the health consequences of having CF or being a carrier, compared with > or = 94% of college graduates. Performance improved after screening. Where neither partner was a demonstrable carrier, 88% knew their own and their partner's test results, and 90% indicated that their risk of having a child with CF was not zero. Written and video educational materials can be used without face-to-face counseling to inform most people about carrier screening and their test results. These materials may be less effective for those with lower educational backgrounds.     

Tay-Sachs disease in Moroccan Jews: deletion of a phenylalanine in the alpha-subunit of beta-hexosaminidase.

Tay-Sachs disease is an inherited lysosomal storage disorder caused by defects in the beta-hexosaminidase alpha-subunit gene. The carrier frequency for Tay-Sachs disease is significantly elevated in both the Ashkenazi Jewish and Moroccan Jewish populations but not in other Jewish groups. We have found that the mutations underlying Tay-Sachs disease in Ashkenazi and Moroccan Jews are different. Analysis of a Moroccan Jewish Tay-Sachs patient had revealed an in-frame deletion (delta F) of one of the two adjacent phenylalanine codons that are present at positions 304 and 305 in the alpha-subunit sequence. The mutation impairs the subunit assembly of beta-hexosaminidase A, resulting in an absence of enzyme activity. The Moroccan patient was found also to carry, in the other alpha-subunit allele, a different, and as yet unidentified, mutation which causes a deficit of mRNA. Analysis of obligate carriers from six unrelated Moroccan Jewish families showed that three harbor the delta F mutation, raising the possibility that this defect may be a prevalent mutation in this ethnic group.     

Hereditary heat-labile hexosaminidase B: its implication for recognizing Tay-Sachs genotypes

Two pairs of alleles, at the two loci of hexosaminidase (HEX), were found to segregate in an Arab inbred family: the normal and the mutant Tay-Sachs (TSD) alleles of HEX A, and the normal and a mutant allele of HEX B. Since the mutant HEX B is heat labile, no reliable identification of TSD genotypes can be obtained in its presence, as long as the proportions of HEX A and B are estimated by the routinely used heat-inactivation method. The genotypes may be correctly identified in such cases by separation of the two isoenzymes on ion-exchange chromatography, estimating their individual activities, and calculating the ratio between them. Of the nine genotype combinations possible with these two pairs of alleles, five have been identified in the reported family by this procedure.     

The offspring of interethnic marriage: Relations of children with paternal and maternal grandparents

Over the last decades 15 to 20 per cent of all Jewish marriages in Israel were between members of the two different ethnic groups, the Orientals and Ashkenazis. At present at least 15 per cent of the school population is of mixed ethnic origin. This article gives an account of a study involving 136 children in sixth to eighth grade belonging to this group (boys and girls, hypergamous and hypogamous marriages in equal numbers) and tries to answer questions as to their distance or proximity to either ethnic group by probing the children's knowledge about and relations with their paternal and maternal grandparents and their attitudes towards them. The results of the investigation show that there seems to be a small inclination in favour of the Ashkenazi side, but that generally the children maintain close connections with both sides of the family and the outstanding finding, given the higher status of the Ashkenazis in Israeli society, is how small the difference is in the relationship of the children with either side. It is concluded that this finding is an indication of the increasing integration within Israel"s Jewish society.     

A splicing defect due to an exon-intron junctional mutation results in abnormal beta-hexosaminidase alpha 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.     

Medical students' attitudes toward genetic testing of minors

The purpose of this study was to examine attitudes of medical students at a single university toward genetic testing in minors, defining attitudes as willingness to offer testing, and reasons for offering or not offering testing. A survey was distributed to all University of Arizona medical students (n = 428) during the 2003-2004 academic year. The survey consisted of three clinical vignettes concerning genetic testing for Huntington's disease (HD), BRCA1 breast cancer predisposition mutation, and cystic fibrosis (CF) carrier status. For each vignette, students responded to whether they would provide testing for a 7-year-old, a 17-year-old, and their reasons for each age and condition. One hundred thirty-five students (31.5%) responded to the survey. Medical students were significantly more likely to test a 7-year-old for CF carrier status (57%), than they were for a BRCA1 mutation (47%), and an HD mutation (40%). Students were significantly more likely to test a 17-year-old than a 7-year-old in each clinical scenario. Students who had completed a genetics course in medical school were significantly less likely to test a 7-year-old for a BRCA1 mutation than those who had not completed a formal course. Medical students' willingness to perform genetic testing in a minor is influenced by the type of condition, the age of the minor being tested, and the amount of genetics education received in medical school.     

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.     

Attitudes of medical staff towards the psychiatric label "schizophrenic patient" tested by an anti-stigma questionnaire

The aim of this research was to investigate the opinions and attitudes of medical staff towards schizophrenic patients. The research included three groups of examinees, 200 physicians of various specialties, 200 nurses and technicians working in Zagreb city hospitals, and 200 3rd and 4th year students of the School of Medicine in Zagreb. Previously validated anti-stigma questionnaire was used, consisting of 25 questions divided into three thematic groups, structured and adapted to the specific requirements of this study. The results were mutually compared and statistically analyzed by applying the chi 2-test. Significant difference (p < 0.01) between the answers of physicians and those of medical students was found in questions 2, 4, 5, 6, 11, 13, 15, 16, 18, 22, 23, 25, and between physicians and nurses/technicians in answers to questions 4, 15, 22, 23. Significant difference (p < 0.01) between the answers given by nurses/technicians and medical students was found in questions 10, 13, 22, 23. The results point to the existence of prejudices and stigmatizing attitudes in all three investigated groups. The most frequent reasons for stigmatizing attitude of students are based on fear and insufficient knowledge about mental patients and schizophrenia as a disease, while there are a high percentage of positive answers to the questions on rehabilitation and resocialization. The nurses/technicians also show a high degree of mistrust towards schizophrenic patients and mostly answer with "I don't know", thus presenting insufficiently formed attitudes about the mentioned problems. The physicians in their answers confirm fear, mistrust and stigmatizing attitudes towards schizophrenic patients found in general population in Croatia. The consequences of such attitudes are the low quality of life of schizophrenic patients, and slow, often incomplete, resocialization.