Uroporphyrinogen III synthase erythroid promoter mutations in adjacent GATA1 and CP2 elements cause congenital erythropoietic porphyria.

Congenital erythropoietic porphyria, an autosomal recessive inborn error of heme biosynthesis, results from the markedly deficient activity of uroporphyrinogen III synthase. Extensive mutation analyses of 40 unrelated patients only identified approximately 90% of mutant alleles. Sequencing the recently discovered erythroid-specific promoter in six patients with a single undefined allele identified four novel mutations clustered in a 20-bp region: (a) a -70T to C transition in a putative GATA-1 consensus binding element, (b) a -76G to A transition, (c) a -86C to A transversion in three unrelated patients, and (d) a -90C to A transversion in a putative CP2 binding motif. Also, a -224T to C polymorphism was present in approximately 4% of 200 unrelated Caucasian alleles. We inserted these mutant sequences into luciferase reporter constructs. When transfected into K562 erythroid cells, these constructs yielded 3 +/- 1, 54 +/- 3, 43 +/- 6, and 8 +/- 1%, respectively, of the reporter activity conferred by the wild-type promoter. Electrophoretic mobility shift assays indicated that the -70C mutation altered GATA1 binding, whereas the adjacent -76A mutation did not. Similarly, the -90C mutation altered CP2 binding, whereas the -86A mutation did not. Thus, these four pathogenic erythroid promoter mutations impaired erythroid-specific transcription, caused CEP, and identified functionally important GATA1 and CP2 transcriptional binding elements for erythroid-specific heme biosynthesis.

Fabry disease: twenty-two novel mutations in the alpha-galactosidase A gene and genotype/phenotype correlations in severely and mildly affected hemizygotes and heterozygotes.

BACKGROUND: Fabry disease, an inborn error of glycosphingolipid catabolism, results from mutations in the X-chromosomal gene encoding the lysosomal exoglycosidase, alpha-galactosidase A (alpha-Gal A; EC 3.2.1.22). The nature of the molecular lesions in the alpha-Gal A gene in 36 unrelated families was determined in order to provide precise heterozygote detection, prenatal diagnosis, and to define genotype/phenotype correlations. METHODS: Genomic DNA was isolated from affected males and/or carrier females from 36 unrelated families with Fabry disease. The entire alpha-Gal A coding region and flanking intronic sequences were analyzed by PCR amplification and solid-phase or cycle sequencing. Markers closely linked to the alpha-Gal A gene were analyzed to determine if probands with the same mutations were related. RESULTS: Twenty-two novel mutations were identified including 10 missense (P40L, W95S, S148N, C172R, M187V, N224S, W226R, A230T, D266H, N320Y), three nonsense (Y134X, C142X, W204X in two families), three splice-site defects (IVS2(+1), IVS3(+1), IVS4(+1)) and six small deletions or insertions (26delA in two families, 672ins37, 774delAC, 833insA, 1139delC, 1188insT). Of the remaining 12 families (33.3%), each had a previously identified mutation, eight of which occurred at CpG dinucleotides including R112C (two families), R112H, R227Q, R227X (three families), and R301Q. Haplotype analysis of the mutant alleles that occurred in two or three presumably unrelated families revealed that the families with the rare novel alleles (W204X and 26delA) were probably related, whereas those with mutations involving CpG dinucleotides (R112C and R227X) were not, the latter being consistent with their origins as independent mutational events. Genotype/phenotype correlations revealed that certain mutations previously found in mild variant patients also were found in classic patients. In addition, the genotypes and spectrum of phenotypic severity were determined in five heterozygotes with no family history. CONCLUSIONS: These results illustrate the molecular heterogeneity of the lesions causing Fabry disease and emphasize the fact that CpG dinucleotides constitute important hot spots for mutation in the alpha-Gal A gene. These studies also permit precise heterozygote detection and prenatal diagnosis in these families, and delineate phenotype-genotype correlations in this disease.

Uroporphyrinogen III synthase. An alternative promoter controls erythroid-specific expression in the murine gene.

Uroporphyrinogen III synthase (URO-synthase, EC 4.2.1.75) is the fourth enzyme of the heme biosynthetic pathway and is the defective enzyme in congenital erythropoietic porphyria. To investigate the erythroid-specific expression of murine URO-synthase, the cDNA and approximately 24-kilobase genomic sequences were isolated and characterized. Three alternative transcripts were identified containing different 5'-untranslated regions (5'-UTRs), but identical coding exons 2B through 10. Transcripts with 5'-UTR exon 1A alone or fused to exon 1B were ubiquitously expressed (housekeeping), whereas transcripts with 5'-UTR exon 2A were only present in erythroid cells (erythroid-specific). Analysis of the TATA-less housekeeping promoter upstream of exon 1A revealed binding sites for ubiquitously expressed transcription factors Sp1, NF1, AP1, Oct1, and NRF2. The TATA-less erythroid-specific promoter upstream of exon 2A had nine putative GATA1 erythroid enhancer binding sites. Luciferase promoter/reporter constructs transfected into NIH 3T3 and mouse erythroleukemia cells indicated that the housekeeping promoter was active in both cell lines, while the erythroid promoter was active only in erythroid cells. Site-specific mutagenesis of the first GATA1 binding site markedly reduced luciferase activity in K562 cells (<5% of wild type). Thus, housekeeping and erythroid-specific transcripts are expressed from alternative promoters of a single mouse URO-synthase gene.

Acute intermittent porphyria: novel missense mutations in the human hydroxymethylbilane synthase gene.

PURPOSE: To identify mutations in families with acute intermittent porphyria, an autosomal dominant inborn error of metabolism that results from the half-normal activity of the third enzyme in the heme biosynthetic pathway, hydroxymethylbilane synthase. METHODS: Mutations were identified by direct solid phase sequencing. RESULTS: Two novel missense mutations E80G and T78P and three previously reported mutations, R173W, G111R, and the splice site lesion, IVS1+1, were detected, each in an unrelated proband. The causality of the novel missense mutations was demonstrated by expression studies. CONCLUSION: These findings provide for the precise diagnosis of carriers in these families and further expand the molecular heterogeneity of AIP.

Identification and expression of mutations in the hydroxymethylbilane synthase gene causing acute intermittent porphyria (AIP).

BACKGROUND: Acute intermittent porphyria (AIP), an autosomal dominant inborn error, results from the half-normal activity of the heme biosynthetic enzyme hydroxymethylbilane synthase (EC 4.3.1.8; HMB-synthase). This disease is characterized by acute, life-threatening neurologic attacks that are precipitated by various drugs, hormones, and other factors. The enzymatic and/or biochemical diagnosis of AIP heterozygotes is problematic; therefore, efforts have focused on the identification of HMB-synthase mutations so that heterozygotes can be identified and educated to avoid the precipitating factors. In Spain, the occurrence of AIP has been reported, but the nature of the HMB-synthase mutations causing AIP in Spanish families has not been investigated. Molecular analysis was therefore undertaken in nine unrelated Spanish AIP patients. MATERIALS AND METHODS: Genomic DNA was isolated from affected probands and family members of nine unrelated Spanish families with AIP. The HMB-synthase gene was amplified by long-range PCR and the nucleotide sequence of each exon was determined by cycle sequencing. RESULTS: Three new mutations, a missense, M212V; a single base insertion, g4715insT; and a deletion/insertion, g7902ACT-->G, as well as five previously reported mutations (G111R, R116W, R149X R167W, and R173W) were detected in the Spanish probands. Expression of the novel missense mutation M212V in E. coli revealed that the mutation was causative, having <2% residual activity. CONCLUSIONS: These studies identified the first mutations in the HMB-synthase gene causing AIP in Spanish patients. Three of the mutations were novel, while five previously reported lesions were found in six Spanish families. These findings enable accurate identification and counseling of presymptomatic carriers in these nine unrelated Spanish AIP families and further demonstrate the genetic heterogeneity of mutations causing AIP.

Identification and characterization of hydroxymethylbilane synthase mutations causing acute intermittent porphyria: evidence for an ancestral founder of the common G111R mutation.

Acute intermittent porphyria (AIP), the most common hepatic porphyria, results from the half-normal activity of hydroxymethylbilane synthase (HMB-synthase; EC 4.3.1.8), the third enzyme in the heme biosynthetic pathway. Because life-threatening acute neurologic attacks of this autosomal dominant disease are triggered by various ecogenic factors (e.g., certain drugs, hormones, alcohol, and starvation), efforts have been directed to identify and counsel presymptomatic heterozygotes in affected families to avoid the precipitating factors. Thus, to determine the nature of the mutations causing AIP in 26 unrelated enzyme-confirmed patients from Argentina, a long-range polymerase chain reaction method was developed to amplify the entire 10-kb gene in two fragments for efficient cycle sequencing and mutation detection. Eight new mutations were identified including two missense mutations (Q34P and G335S), four small deletions (728delCT, 815delAGGA, 948delA, and 985del12), a single base insertion (666insA), and a splice site mutation (IVS12(+1)). In addition, five previously reported mutations (G111R, R173W, Q204X, R201W, and 913insC) were detected. Notably, G111R was identified in 12 of the 26 (46%) presumably unrelated propositi; however, haplotype analysis with intragenic and flanking markers indicated an ancestral founder. Expression of the two new missense mutations (Q34P and G335S) in f1 E. coli resulted in 2.5% or less of the normal expressed enzyme, confirming their defective function. Thus, eight new and five previously reported HMB-synthase mutations, including a common lesion, were detected, permitting accurate identification and counseling of presymptomatic carriers in these 26 unrelated Argentinean AIP families with this dominant porphyria.

Twenty novel mutations in the alpha-galactosidase A gene causing Fabry disease.

BACKGROUND: Fabry disease, an X-linked inborn error of glycosphingolipid catabolism, results from the deficient activity of the lysosomal exoglycohydrolase alpha-galactosidase A (EC 3.2.1.22; alpha-Gal A). The nature of the molecular lesions in the alpha-Gal A gene in 30 unrelated families was determined to provide precise heterozygote detection, prenatal diagnosis, and define genotype-phenotype correlations. MATERIALS AND METHODS: Genomic DNA was isolated from affected males and/or carrier females from 30 unrelated families with Fabry disease. The entire alpha-Gal A coding region and flanking intronic sequences were analyzed by PCR amplification and automated sequencing. RESULTS: Twenty new mutations were identified, each in a single family: C142R, G183D, S235C, W236L, D244H, P259L, M267I, I289F, Q321E, C378Y, C52X, W277X, IVS4(+4), IVS6(+2), IVS6(-1), 35del13, 256del1, 892ins1, 1176del4, and 1188del1. In the remaining 10 unrelated Fabry families, 9 previously reported mutations were detected: M42V, R112C, S148R, D165V, N215S (in 2 families), Q99X, C142X, R227X, and 1072del3. Haplotype analysis using markers closely flanking the alpha-Gal A gene indicated that the two patients with the N215S lesion were unrelated. The IVS4(+4) mutation was a rare intronic splice site mutation that causes Fabry disease. CONCLUSIONS: These studies further define the heterogeneity of mutations in the alpha-Gal A gene causing Fabry disease, permit precise heterozygote detection and prenatal diagnosis, and help delineate phenotype-genotype correlations in this disease.

Congenital erythropoietic porphyria successfully treated by allogeneic bone marrow transplantation.

The long-term biochemical and clinical effectiveness of allogenic bone marrow transplantation (BMT) was shown in a severely affected, transfusion-dependent 18-month-old female with congenital erythropoietic porphyria (CEP), an autosomal recessive inborn error of heme biosynthesis resulting from mutations in the uroporphyrinogen III synthase (URO-synthase) gene. Three years post-BMT, the recipient had normal hemoglobin, markedly reduced urinary porphyrin excretion, and no cutaneous lesions with unlimited exposure to sunlight. The patient was homoallelic for a novel URO-synthase missense mutation, G188R, that expressed less than 5% of mean normal activity in Escherichia coli, consistent with her transfusion dependency. Because the clinical severity of CEP is highly variable, ranging from nonimmune hydrops fetalis to milder, later onset forms with only cutaneous lesions, the importance of genotyping newly diagnosed infants to select severely affected patients for BMT is emphasized. In addition, the long-term effectiveness of BMT in this patient provides the rationale for future hematopoietic stem cell gene therapy in severely affected patients with CEP.

Familial porphyria cutanea tarda: characterization of seven novel uroporphyrinogen decarboxylase mutations and frequency of common hemochromatosis alleles.

Familial porphyria cutanea tarda (f-PCT) results from the half-normal activity of uroporphyrinogen decarboxylase (URO-D). Heterozygotes for this autosomal dominant trait are predisposed to photosensitive cutaneous lesions by various ecogenic factors, including iron overload and alcohol abuse. The 3.6-kb URO-D gene was completely sequenced, and a long-range PCR method was developed to amplify the entire gene for mutation analysis. Four missense mutations (M165R, L195F, N304K, and R332H), a microinsertion (g10insA), a deletion (g645Delta1053), and a novel exonic splicing defect (E314E) were identified. Expression of the L195F, N304K, and R332H polypeptides revealed significant residual activity, whereas reverse transcription-PCR and sequencing demonstrated that the E314E lesion caused abnormal splicing and exon 9 skipping. Haplotyping indicated that three of the four families with the g10insA mutation were unrelated, indicating that these microinsertions resulted from independent mutational events. Screening of nine f-PCT probands revealed that 44% were heterozygous or homozygous for the common hemochromatosis mutations, which suggests that iron overload may predispose to clinical expression. However, there was no clear correlation between f-PCT disease severity and the URO-D and/or hemochromatosis genotypes. These studies doubled the number of known f-PCT mutations, demonstrated that marked genetic heterogeneity underlies f-PCT, and permitted presymptomatic molecular diagnosis and counseling in these families to enable family members to avoid disease-precipitating factors.

Congenital erythropoietic porphyria: prolonged high-level expression and correction of the heme biosynthetic defect by retroviral-mediated gene transfer into porphyric and erythroid cells.

Congenital erythropoietic porphyria (CEP) is an autosomal recessive disorder resulting from the deficient activity of the heme biosynthetic enzyme uroporphyrinogen III synthase (UROS). Severely affected patients are transfusion dependent and have mutilating cutaneous manifestations. Successful bone marrow transplantation has proven curative, providing the rationale for stem cell gene therapy. Toward this goal, two retroviral MFG vectors containing the UROS cDNA were constructed, one with the wild-type sequence (MFG-UROS-wt) and a second with an optimized Kozak consensus sequence (MFG-UROS-K). Following transduction of CEP fibroblasts, the MFG-UROS-wt and MFG-UROS-K vectors increased the endogenous activity without selection to levels that were 18- and 5-fold greater, respectively, than the mean activity in normal fibroblasts. Notably, the MFG-UROS-wt vector expressed UROS activity in CEP fibroblasts at these high levels for over 6 months without cell toxicity. Addition of either delta-aminolevulinic acid (ALA) or ferric chloride did not affect expression of the transduced UROS gene nor did the increased concentrations of uroporphyrin isomers or porphyrin intermediates affect cell viability. Similarly, transduction of CEP lymphoblasts with the MFG-UROS-wt vector without G418 selection increased the endogenous UROS activity by 7-fold or almost 2-fold greater than that in normal lymphoblasts. Transduction of K562 erythroleukemia cells by cocultivation with the MFG-UROS-wt producer cells increased their high endogenous UROS activity by 1.6-fold without selection. Clonally isolated K562 cells expressed UROS for over 4 months at mean levels 4.7-fold greater than the endogenous activity without cell toxicity. Thus, the prolonged, high-level expression of UROS in transduced CEP fibroblasts and lymphoblasts, as well as in transduced K562 erythroid cells, demonstrated that the enzymatic defect in CEP cells could be corrected by retroviral-mediated gene therapy without selection and that the increased intracellular porphyrin intermediates were not toxic to these cells, even when porphyrin production was stimulated by supplemental ALA or iron. These in vitro studies provide the rationale for ex vivo stem cell gene therapy in severely affected patients with CEP.

Molecular genetics of congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP), an autosomal recessive inborn error of heme biosynthesis, results from the markedly deficient activity of the cytosolic enzyme, uroporphyrinogen III synthase (URO-synthase). The accumulation of the nonphysiological and pathogenic porphyrin isomers, uroporphyrin I and coproporphyrin I, leads to the clinical manifestations of CEP. Disease severity in unrelated patients is markedly heterogeneous, ranging from fetal demise or severe transfusion dependency throughout life to milder adult cases with only cutaneous photosensitivity. To date, 18 mutations causing CEP have been described in the URO-synthase gene, including single base substitutions, insertions and deletions, and splicing defects. Most mutations have been identified in one or a few unrelated families with the exception of C73R, L4F, and T228M which occurred in about 33%, 8%, and 7% of the mutant alleles studied, respectively. Prokaryotic expression of the mutant URO-synthase alleles identified those with significant residual activity, thereby permitting genotype/phenotype predictions for severe to milder phenotypes of this clinically heterogeneous disease. As successful bone marrow transplantation in severely affected patients has proven curative, current efforts are underway to develop hematopoietic stem cell gene therapy for CEP.

Molecular basis of congenital erythropoietic porphyria: mutations in the human uroporphyrinogen III synthase gene.

Congenital erythropoietic porphyria (CEP) is an autosomal recessive inborn error of metabolism that results from the markedly deficient activity of the fourth enzyme in the heme biosynthetic pathway, uroporphyrinogen III synthase (URO-synthase). To date, 17 mutations have been described including 11 missense, one nonsense, two mRNA splicing defects, one deletion and two coding region insertions. Most mutations have been identified in one or a few unrelated families with the exception of C73R and L4F which occurred in 29.6% and 9.3% of the 54 mutant alleles studied, respectively. Interestingly, analysis of the mutant alleles identified only 83% of the causative mutations, suggesting that about 20% of the mutations causing CEP lie elsewhere in the gene. Of note, mutation V82F, resulting from a G to T transversion of the last nucleotide of exon 4, caused both a missense mutation and an aberrantly spliced RNA transcript. Prokaryotic expression of the mutant URO-synthase alleles identified those with significant residual activity, thereby permitting genotype/phenotype predictions for this clinically heterogeneous disease.

Acute intermittent porphyria: a single-base deletion and a nonsense mutation in the human hydroxymethylbilane synthase gene, predicting truncations of the enzyme polypeptide.

Acute intermittent porphyria (AIP) is an autosomal-dominant inborn error of metabolism that results from the half-normal activity of the third enzyme in the heme biosynthetic pathway, hydroxymethylbilane synthase (HMB-synthase). AIP is an ecogenetic condition, since the life-threatening acute attacks are precipitated by various factors, including drugs, alcohol, fasting, and certain hormones. Biochemical diagnosis is problematic, and the identification of mutations in the HMB-synthase gene provides accurate detection of presymptomatic heterozygotes, permitting avoidance of the acute precipitating factors. By direct solid-phase sequencing, two mutations causing AIP were identified, an adenine deletion at position 629 in exon 11(629delA), which alters the reading frame and predicts premature truncation of the enzyme protein after amino acid 255, and a nonsense mutation in exon 12 (R225X). These mutations were confirmed by either restriction enzyme analysis or family studies of symptomatic patients, permitting accurate presymptomatic diagnosis of affected relatives.

Acute intermittent porphyria: identification and expression of exonic mutations in the hydroxymethylbilane synthase gene. An initiation codon missense mutation in the housekeeping transcript causes "variant acute intermittent porphyria" with normal expression of the erythroid-specific enzyme.

Acute intermittent porphyria (AIP), an autosomal dominant inborn error, results from the half-normal activity of the heme biosynthetic enzyme, hydroxymethylbilane synthase (EC 4.3.1.8). Diagnosis of AIP heterozygotes is essential to prevent acute, life-threatening neurologic attacks by avoiding various precipitating factors. Since biochemical diagnosis is problematic, the identification of hydroxymethylbilane synthase mutations has facilitated the detection of AIP heterozygotes. Molecular analyses of unrelated AIP patients revealed six exonic mutations: an initiating methionine to isoleucine substitution (M1I) in a patient with variant AIP, which precluded translation of the housekeeping, but not the erythroid-specific isozyme; four missense mutations in classical AIP patients, V93F, R116W, R201W, C247F; and a nonsense mutation W283X in a classical AIP patient, which truncated the housekeeping and erythroid-specific isozymes. Each mutation was confirmed in genomic DNA from family members. The W283X lesion was found in another unrelated AIP family. Expression of each mutation in Escherichia coli revealed that R201W, C247F, and W283X had residual activity. In vitro transcription/translation studies indicated that the M1I allele produced only the erythroid-specific enzyme, while the other mutant alleles encoded both isozymes. These mutations provide insight into the molecular pathology of classic and variant AIP and facilitate molecular diagnosis in AIP families.

Molecular basis of acute intermittent porphyria: mutations and polymorphisms in the human hydroxymethylbilane synthase gene.

Acute intermittent porphyria (AIP) is an autosomal dominant inborn error of metabolism that results from the half-normal activity of the third enzyme in the heme biosynthetic pathway, hydroxymethylbilane synthase (HMB-synthase). AIP is an ecogenetic condition, with life-threatening acute attacks precipitated by various factors including drugs, alcohol, fasting, and certain hormones. Biochemical diagnosis is problematic and the identification of mutations in the HMB-synthase gene provides accurate detection of presymptomatic heterozygotes, permitting avoidance of the acute precipitating factors. Two HMB-synthase isozymes are encoded by the HMB-synthase gene: one unique to erythroid cells and the other a housekeeping isozyme present in all cells. These two isozymes arise from a single gene by alternative splicing. The recent isolation of the cDNAs and entire genomic sequence encoding the HMB-synthase isozymes has facilitated the detection of diagnostically useful intragenic polymorphisms and disease-causing mutations. Of the 36 mutations identified to date, most caused the classic form of AIP. These mutations included small deletions and insertions, point mutations and RNA splice junction alterations and resulted in the half-normal activity of both the erythroid-specific and housekeeping isozymes. Most AIP mutations were private; however, certain mutations were frequently found in Dutch (R116W) and Swedish (W198X) AIP families. A variant form of AIP, in which patients have normal erythroid activity, but half-normal activity of the housekeeping isozyme, resulted from two mutations at the exon 1/intron 1 boundary, each altering splicing of the hepatic-specific transcript. In addition, 10 polymorphisms in the HMB-synthase gene have been identified that are useful for the diagnosis of presymptomatic AIP heterozygotes in families whose specific mutations have not been determined.

Nature and frequency of mutations in the alpha-galactosidase A gene that cause Fabry disease.

Fabry disease, an X-linked inborn error of glycosphingolipid catabolism, results from mutations in the alpha-galactosidase A (alpha-Gal A) gene at Xq22.1. To determine the nature and frequency of the molecular lesions causing the classical and milder-variant Fabry phenotypes, and for precise carrier detection in Fabry families, the alpha-Gal A transcripts or genomic sequences from unrelated Fabry hemizygotes were analyzed. In patients with the classical phenotype, 18 new mutations were identified: N34S, C56G, W162R, R227Q, R227X, D264V, D266V, S297F, D313Y, G328A, W340X, E398X, IVS2+2, IVS5 delta-2,3, 773 delta 2, 954 delta 5, 1016 delta 11, and 1123 delta 53. Unrelated asymptomatic or mildly affected patients with symptoms confined to the heart had a missense mutation, N215S, that expressed residual enzymatic activity. Related, moderately affected patients with late-onset cardiac and pulmonary manifestations had a small deletion, 1208 delta 3, that predicted the in-frame deletion of arginine 404 near the terminus of the 429 residue enzyme polypeptide. In addition, five small gene rearrangements involving exonic sequences were identified in unrelated classically affected patients. Two small deletions and one small duplication had short direct repeats at their respective breakpoint junctions and presumably resulted from slipped mispairing. A deletion occurred at a potential polymerase alpha arrest site, while the breakpoints of another deletion occurred at an inverted tetranucleotide repeat. Screening of unrelated Fabry patients with allele-specific oligonucleotides for seven mutations revealed that these were private, with the notable exception of N215S, R227Q, and R227X, which were each found in several unrelated families from different ethnic backgrounds. The CpG dinucleotide at codon 227 was the most common site of mutation, having been altered in 5% of the 148 unrelated Fabry alleles. These studies revealed that most alpha-Gal A lesions were private, that codon 227 was a mutational hot spot, and that certain mutations predicted a milder disease phenotype.

Comparison of enzyme and DNA analysis in a Tay-Sachs disease carrier screening program.

Tay-Sachs disease (GM2 gangliosidosis, type 1; TSD) is an autosomal recessive GM2 gangliosidosis resulting from the deficient activity of the lysosomal hydrolase beta-hexosaminidase A (Hex A). With a carrier frequency estimated at 1 in 25, it is a common lysosomal disorder in the Ashkenazi Jewish population. Tay-Sachs disease has provided the prototype for the prevention of severe recessive genetic diseases. Molecular analysis of the Hex A gene (HEXA) of Ashkenazi Jewish individuals affected with Tay-Sachs disease revealed that three common mutations cause the infantile and adult onset forms of the disease; a four base insertion in exon 11, a splice junction mutation in intron 12 and a point mutation in exon 7 (G269S). A study was undertaken to determine whether mutation analysis would be useful in TSD screening programs in identifying carriers and clarifying the status of individuals whose enzyme assays are inconclusive. Ashkenazi Jewish individuals who had been diagnosed as carriers, inconclusives by enzyme assay and non-carriers with low normal enzyme levels in the Mount Sinai Tay-Sachs Disease Prevention Program were examined for the presence of the three mutations using polymerase chain reaction (PCR) and allele specific oligonucleotide (ASO) hybridization. The insertion mutation was present in 29 of 34 carriers and 2 of 36 inconclusive individuals, the splice junction mutation was found in 4 of 34 carriers and the G269S mutation was found in 1 of 34 carriers. Of the 313 non-carrier individuals with normal enzyme activity in the lower normal range, one was positive for the splice junction mutation.(ABSTRACT TRUNCATED AT 250 WORDS)

Amplification of human polymorphic sites in the X-chromosomal region q21.33 to q24: DXS17, DXS87, DXS287, and alpha-galactosidase A.

Methods for the PCR amplification of five polymorphic sites in the region Xq21.33 to Xq24 were developed and used to predict heterozygosity for Fabry disease in informative families. Clones containing polymorphic sites associated with DNA segments DXS17, DXS87, and DXS287, and the alpha-galactosidase A gene were isolated from genomic libraries. Surrounding nucleotide sequences and optimal conditions for amplification of each polymorphic site were determined. These amplifiable polymorphisms provided predictions of heterozygosity for Fabry disease and should be useful for diagnostic linkage analyses in Alport syndrome, X-linked cleft palate and ankyloglossia, Pelizaeus-Merzbacher disease, and X-linked agammaglobulinemia as well as sequence-tagged sites for gene mapping.

Regional assignment of the human uroporphyrinogen III synthase (UROS) gene to chromosome 10q25.2----q26.3.

Uroporphyrinogen III synthase [UROS; hydroxymethylbilane hydro-lyase (cyclizing), EC 4.2.1.75] is the fourth enzyme in the human heme biosynthetic pathway. The recent isolation of the cDNA encoding human UROS facilitated its chromosomal localization. Human UROS sequences were specifically amplified by the polymerase chain reaction (PCR) from genomic DNA of two independent panels of human-rodent somatic cell hybrids. There was 100% concordance for the presence of the human UROS PCR product and human chromosome 10. For each of the other chromosomes, there was 19%-53% discordance with human UROS. The chromosomal assignment was confirmed by Southern hybridization analysis of DNA from somatic cell hybrids with the full-length UROS cDNA. Using human-rodent hybrids containing different portions of human chromosome 10, we assigned the UROS gene to the region 10q25.2----q26.3.