Genetic variation in the promoter and 5' UTR of the copper transporter, ATP7B, in patients with Wilson disease.

ATP7B is a copper-transporting P-type ATPase defective in the copper transport disorder, Wilson disease (WND). We have sequenced the 5' UTR and promoter region of ATP7B in 37 unrelated WND patients in whom partial sequencing of the coding region and intron/exon boundaries of the gene had failed to identify one or both disease-causing mutations. Three patients were found to be heterozygous for a 15 bp deletion between nucleotides -424 and -441. This deletion had been previously identified as the most common mutation in Sardinian WND patients. Two novel single-nucleotide changes were also identified within the 5' UTR and promoter of ATP7B; however, these were found at a similar frequency in control chromosomes and are apparently normal variants. These results suggest that mutations in regulatory elements of ATP7B are uncommon in patients of European ancestry, except in Sardinia.

Localization, expression and genomic structure of the gene encoding the human serine protease testisin.

Testisin is a recently identified human serine protease expressed by premeiotic testicular germ cells and is a candidate tumor suppressor for testicular cancer. Here, we report the characterization of the gene encoding testisin, designated PRSS21, and its localization on the short arm of human chromosome 16 (16p13.3) between the microsatellite marker D16S246 and the radiation hybrid breakpoint CY23HA. We have further refined the localization to cosmid 406D6 in this interval and have established that the gene is approximately 4. 5 kb in length, and contains six exons and five intervening introns. The structure of PRSS21 is very similar to the human prostasin gene (PRSS8) which maps nearby on 16p11.2, suggesting that these genes may have evolved through gene duplication. Sequence analysis showed that the two known isoforms of testisin are generated by alternative pre-mRNA splicing. A major transcription initiation site was identified 97 nucleotides upstream of the testisin translation start and conforms to a consensus initiator element. The region surrounding the transcription initiation site lacks a TATA consensus sequence, but contains a CCAAT sequence and includes a CpG island. The 5'-flanking region contains several consensus response elements including Sp1, AP1 and several testis-specific elements. Analysis of testisin gene expression in tumor cell lines shows that testisin is not expressed in testicular tumor cells but is aberrantly expressed in some tumor cell lines of non-testis origin. These data provide the basis for identifying potential genetic alterations of PRSS21 that may underlie both testicular abnormalities and tumorigenesis.

Effects of HFE C282Y and H63D polymorphisms and polygenic background on iron stores in a large community sample of twins.

The aim of this study was to assess and to compare the role of HFE polymorphisms and other genetic factors in variation in iron stores. Blood samples were obtained from 3,375 adult male and female twins (age range 29-82 years) recruited from the Australian Twin Registry. There were 1,233 complete pairs (562 monozygotic and 571 dizygotic twins). Serum iron, transferrin, transferrin saturation with iron, and ferritin were measured, and the HFE C282Y and H63D genotypes were determined. The frequency of the C282Y allele was.072, and that of the H63D allele was.141. Significant sources of variation in the indices of iron status included age, sex, age-sex interaction, body-mass index, and both the C282Y and H63D genotypes. The iron, transferrin, and saturation values of CC and CY subjects differed significantly, but the ferritin values did not. After correction for age and body-mass index, 23% and 31% of the variance in iron, 66% and 49% of the variance in transferrin, 33% and 47% of the variance in transferrin saturation, and 47% and 47% of the variance in ferritin could be explained by additive genetic factors, for men and women, respectively. HFE C282Y and H63D variation accounted for <5% of the corrected phenotypic variance, except for saturation (12% in women and 5% in men). We conclude that HFE CY and HD heterozygotes differ in iron status from the CC and HH homozygotes and that serum transferrin saturation is more affected than is serum ferritin. There are highly significant effects of other as-yet-unidentified genes on iron stores, in addition to HFE genotype.

Genetics of hemochromatosis.

Hereditary hemochromatosis (HHC) is a common autosomal recessive disorder of iron metabolism that results in progressive iron overload and can be fatal if untreated. The hemochromatosis gene (HFE) was identified by positional cloning in 1996. Two missense mutations have been described in HFE. The majority of HHC patients are homozygous for a cysteine-to-tyrosine substitution (C282Y); however, a small number are homozygous for a histidine-to-aspartic-acid substitution (H63D) or are heterozygous for both of these mutations. Mechanisms by which C282Y and H63D may disrupt the normal functioning of HFE have been suggested, but the role of HFE in the process of normal iron metabolism has yet to be clearly defined.

Generation of a transcription map distal to HLA-F.

We have constructed a transcription map covering a 2 Mb region beginning approximately 1 Mb distal to HLA-F. Cosmids isolated from a chromsome 6 library were positioned by YAC hybridisation, STS and fingerprint analysis. Using direct cDNA selection, exon trapping, and direct genomic sequence analysis, we identified 42 potential exonic fragments in this region. Six fragments corresponded to previously characterised genes, four previously broadly mapped to this region. Five fragments were similar to known genes, eight fragments matched ESTs and 10 of the remaining 23 novel fragments, gave a positive signal on northern analysis. All cDNA fragments were mapped to the YAC and cosmid contig covering the region and with respect to other known genes and STS in this area. The distribution of the cDNA fragments indicated their organisation in three clusters around CpG islands.

The hemochromatosis 845 G-->A and 187 C-->G mutations: prevalence in non-Caucasian populations.

Hemochromatosis, the inherited disorder of iron metabolism, leads, if untreated, to progressive iron overload and premature death. The hemochromatosis gene, HFE, recently has been identified, and characterization of this gene has shown that it contains two mutations that result in amino acid substitutions-cDNA nucleotides 845 G-->A (C282Y) and 187 C-->G (H63D). Although hemochromatosis is common in Caucasians, affecting >=1/300 individuals of northern European origin, it has not been recognized in other populations. The present study used PCR and restriction-enzyme digestion to analyze the frequency of the 845 G-->A and 187 C-->G mutations in HLA-typed samples from non-Caucasian populations, comprising Australian Aboriginal, Chinese, and Pacific Islanders. Results showed that the 845 G-->A mutation was present in these populations (allele frequency 0.32%), and, furthermore, it was always seen in conjunction with HLA haplotypes common in Caucasians, suggesting that 845 G-->A may have been introduced into these populations by Caucasian admixture. 187 C-->G was present at an allele frequency of 2.68% in the two populations analyzed (Australian Aboriginal and Chinese). In the Australian Aboriginal samples, 187 C-->G was found to be associated with HLA haplotypes common in Caucasians, suggesting that it was introduced by recent admixture. In the Chinese samples analyzed, 187 C-->G was present in association with a wide variety of HLA haplotypes, showing this mutation to be widespread and likely to predate the more genetically restricted 845 G-->A mutation.

Expression of HLA-linked hemochromatosis in subjects homozygous or heterozygous for the C282Y mutation.

BACKGROUND & AIMS: In the absence of a genetic test, diagnostic criteria for hereditary hemochromatosis have been imprecise. The identification of the HFE gene and the C282Y mutation allow definition of expression of this disease and reassessment of diagnostic criteria. The aim of this study was to analyze the concordance between the genetic diagnosis and the previous clinical diagnosis in families with hemochromatosis. METHODS: Three hundred subjects were tested for the C282Y mutation and were grouped as homozygous, heterozygous, or homozygous normal. RESULTS: All adults previously diagnosed as homozygous or heterozygous for HLA-linked hereditary hemochromatosis carried at least one C282Y mutation. Two adolescents, previously thought to be homozygous, had no C282Y mutation. Of 127 subjects homozygous for the mutation, 105 met criteria for diagnosis. Iron overload was not expressed in 6.7% of homozygous men and 32.7% of homozygous women. The iron indices in 8 of 171 subjects heterozygous for the C282Y mutation were within the range previously regarded as indicative of homozygosity. Seven of these 8 carried the H63D mutation. CONCLUSIONS: In Australia, 17.3% of subjects homozygous for the C282Y mutation do not express iron overload to meet current diagnostic criteria of hemochromatosis. In subjects heterozygous for the mutation, 4.8% have iron overload in the range previously diagnosed as homozygous. Nonexpression is common, particularly in women.

Isolation and characterisation of cosmids to intervals within a 4.5Mb region at 6p21.3.

The gene responsible for hereditary haemochromatosis (HH) has recently been identified. One mutation in this gene, termed HFE, has been found in all Australian HH patients. We previously identified a predominant HH ancestral haplotype covering 4.5Mb at 6p21.3, and showed that patients with two copies of this haplotype express a more severe form of the disorder. One key question to now be resolved is why haplotype related variation in phenotypic expression of HH is present if all patients tested have the same HFE mutation. A cosmid resource covering the 4.5Mb HH ancestral haplo type region was obtained. These cosmids provide the material for the completion of a transcript map of this region, and will assist the identification of candidate modifiers of HFE expression.

Genetic variation in the COL6A1 region is associated with congenital heart defects in trisomy 21 (Down's syndrome).

Genetic variation in the COL6A1-COL6A2 gene cluster on chromosome 21 was studied in 113 controls and 58 European families (including control and family subgroups of British/Irish origin) having a child with trisomy 21. There were statistically significant differences among subgroups of trisomic children with and without congenital heart defects (CHD) in distributions of definitive, 3-RFLP haplotype classes received from their nondisjoining and disjoining parents. Haplotypes received by trisomic children with CHD from their disjoining parents were not a random sample of controls' haplotypes. Analysis of parental single-RFLP genotypes and linkage disequilibrium patterns confirmed this parent subgroup differed from a random sample of controls. There were no significant differences in parent subgroup genotype distribution at any of nine control loci distributed along chromosome 21q. This sample showed an association between genetic variation in the COL6A1 gene region and congenital heart defects in trisomy 21.

Unusual genotypes in the COL6A1 gene in parents of children with trisomy 21 and major congenital heart defects.

Collagen type VI is a candidate for a role in the pathogenesis of congenital heart defects (CHD) in Down's syndrome. Three restriction fragment length polymorphisms of the COL6A1 gene were used to determine COL6A1 genotypes in 50 families of affected children with trisomy 21 (29 with congenital heart defects and 21 without) and 37 unrelated volunteers. We found seven unusual genotypes in the parents of affected children with Down's syndrome, five being unique to the parents of children with trisomy 21 and CHD. There were no unusual genotypes associated with other chromosome 21 loci. No single COL6A1 genotype was associated with CHD. Thus, the unusual genotypes unique to parents of affected children suggest that genetic variation in the COL6A1 gene region contributes to the pathogenesis of CHD in Down's syndrome.

Meiotic crossing-over in nondisjoined chromosomes of children with trisomy 21 and a congenital heart defect.

We have used DNA polymorphisms to study meiotic crossovers of chromosome 21q in 27 nuclear families. Each family had a child with Down syndrome and a congenital heart defect. Twenty DNA polymorphisms on chromosome 21 were used to determine parental and meiotic origin of nondisjunction and to identify crossovers. Twenty-four cases were of maternal origin, and three were of paternal origin. Twenty-two unequivocal crossover events were identified. Sixteen crossovers were observed in 22 chromosome pairs nondisjoining at the second meiotic division. Fifty percent of crossover events in MI nondisjunction are detectable by molecular genetic means. Thus, the results suggest that, in this sample, each nondisjoined chromosome 21 pair has been involved in at least one crossover event.