A revised allele frequency estimate and haplotype analysis of the DBH deficiency mutation IVS1+2T → C in African‐ and European‐Americans

Dopamine beta-hydroxylase (DBH; OMIM 223360) catalyzes the conversion of dopamine (DA) to norepinephrine (NE) in the central and peripheral nervous systems. DBH deficiency is a very rare genetic disorder characterized by severe sympathetic failure in which circulating levels ofNEandepinephrine (E)areundetectable, but DA levels are greatly elevated [Robertson et al., 1986]. The onset of symptoms occurs at birth or in early childhood and as adults all affected individuals suffer from profound postural hypotension and exercise intolerance. Only six patients from five families with the disorder, all of Western European descent, are well described in the literature [Robertson et al., 1986; Man in ’t Veld et al., 1987, 1988; Biaggioni et al., 1990; Mathias et al., 1990]. We recently reported the first putative disease-causing mutations in an analysis of the DBH locus in two unrelated patients and their families [Kim et al., 2002]. Both patients were compound heterozygotes who each carried a single copy of a T!C transition at the donor splice site of intron 1 (IVS1þ 2T!C) that resulted in an aberrantly spliced product containing a premature stop codon in an in vitro splicing assay. On the homologous chromosome, a total of three different missense mutations in the DBH gene were detected: one in patient 1 (exon 2) and two in patient 2 (exons 1and6). Themechanismbywhich these missensemutations produce a loss of DBH function is as yet unknown. In our initial analysis, we genotyped a small sample of 88 healthy European-American (EA) subjects, and found no carriers of any of the threemissensemutations [Kim et al., 2002]. However, we found two subjects heterozygous for IVS1þ2T!C, which yielded an unexpectedly high C allele frequency of 0.011 0.008. This suggested a large discrepancy between the prevalence of homozygotes for the C allele and individuals affected with DBH deficiency. One possible explanation is that these homozygotes are frequently embryonic lethal, which is consistent with the low survival rate observed inmouse embryos lackingDBH [Thomas et al., 1995]. Given our initial allele frequency estimate, these data indicated that DBH deficiency might thus be an epidemiologically significant cause of fetal demise. However, more extensive genotyping studies were clearly warranted in order to accurately estimate the frequency of DBH deficiency-related mutations in the general population.Herewe report frequencies for these mutations in a substantially larger sample of subjects of both European and African-American (AA) heritage. DNA samples from a total of 801 unrelated adults were collected in the course of several genetic studies as previously described [Zabetian et al., 2000; Kohnke et al., 2002] from the following groups: 122 AAs, 456 EAs, and223 individuals ofGermandescent.Thegroups included healthy individuals and those with psychiatric and substance-use disorders. However, none of these subjects reported severe disturbances in autonomic function and thus all were considered as controls for the purpose of this study. The EA and German population samples were combined to simplify data analysis and are abbreviated as ‘‘EA/G.’’ In order to supplement theAAsample,we includedDNAcollected froma total of 260 AA mothers and infants during an ongoing study of genetic risk factors for preterm labor. DNA from two EA patients with DBHdeficiency and their familymembers was obtained as previously reported [Kim et al., 2002]. None of the four putative disease-causing mutations (IVS1þ2T!C,V87M,D100E,D331N)weredetected in any of the 122 AA or 679 EA/G adult controls genotyped in this study. IVS1þ2T!C was also genotyped in the AA mother–infant group, and a single preterm infant was found to be heterozygous for the mutation. This suggests that the C allele frequency of IVS1þ2T!C that we initially reported in EAs [Kim et al., 2002] was Grant sponsor: NARSAD; Grant sponsor: NASA; Grant sponsor: the Nathan Blaser Shy-Drager Research Program; Grant sponsor: NIH; Grant sponsor: Tuebingen University; Grant sponsor: the US.