Autosomal dominant hypercholesterolemia (ADH), one of the most frequent hereditary disorders, is characterized by an isolated elevation of LDL particles that leads to premature mortality from cardiovascular complications. It is generally assumed that mutations in the LDLR and APOB genes account for ADH. We identified one large French pedigree (HC2) and 12 additional white families with ADH in which we excluded linkage to the LDLR and APOB, implicating a new locus we named "FH3." A LOD score of 3.13 at a recombination fraction of 0 was obtained at markers D1S2892 and D1S2722. We localized the FH3 locus to a 9-cM interval at 1p34.1-p32. We tested four regional markers in another set of 12 ADH families. Positive LOD scores were obtained in three pedigrees, whereas linkage was excluded in the others. Heterogeneity tests indicated linkage to FH3 in approximately 27% of these non-LDLR/non-APOB ADH families and implied a fourth locus. Radiation hybrid mapping located four candidate genes at 1p34.1-p32, outside the critical region, showing no identity with FH3. Our results show that ADH is genetically more heterogeneous than conventionally accepted.

Mutations in the LDL receptor gene (LDLR) cause familial hypercholesterolemia (FH), a common autosomal dominant disorder. The LDLR database is a computerized tool that has been developed to provide tools to analyse the numerous mutations that have been identified in the LDLR gene. The second version of the LDLR database contains 140 new entries and the software has been modified to accommodate four new routines. The analysis of the updated data (350 mutations) gives the following informations: (i) 63% of the mutations are missense, and only 20% occur in CpG dinucleotides; (ii) although the mutations are widely distributed throughout the gene, there is an excess of mutations in exons 4 and 9, and a deficit in exons 13 and 15; (iii) the analysis of the distribution of mutations located within the ligand-binding domain shows that 74% of the mutations in this domain affect a conserved amino-acid, and that they are mostly confined in the C-terminal region of the repeats. Conversely, the same analysis in the EGF-like domain shows that 64% of the mutations in this domain affect a non-conserved amino-acid, and, that they are mostly confined in the N-terminal half of the repeats. The database is now accessible on the World Wide Web at http://www.umd.necker.fr

Mutations in the LDL receptor gene (LDLR) cause familial hypercholesterolemia (FH), one of the most frequent hereditary dominant disorders. The protein defect was identified in 1973, the gene was localized by in situ hybridization in 1985, and since, a growing number of mutations have been reported. The UMD-LDLR database is customized software that has been developed to list all mutations, and also to provide means to analyze them at the nucleotide and protein levels. The database has been recently modified to fulfill the recommendations of the Nomenclature Working Group for human gene mutations. However, in the current version, both the nomenclature and usual LDLR gene mutation names are reported since the latter are more commonly used. The software has also been modified to accommodate the splicing mutations and alleles that carry two nucleotide variations. The current version of UMD-LDLR contains 840 entries, of which 490 are new entries. Point mutations account for 90% of all mutations in the LDLR gene; the remaining are mostly major rearrangements, due to the presence of Alu sequences. Three new routines have been implemented in the software, thus giving users access to 13 sorting tools. In addition to the database, a Web site containing information about polymorphisms, major rearrangements, and promoter mutations is available. Both are accessible to the scientific community (www.umd.necker.fr) and should help groups working on LDLR to check their mutations and identify new ones, and greatly facilitate the understanding of functional classes/genotype relationships and of genotype/phenotype correlations.

Cystic fibrosis (CF) is thought to be rare in the black populations of Africa who have minimal white admixture. Only a few cases have been reported but have not been studied at the molecular level. We report the detection of CFTR mutations in three southern African black patients.One was homozygous for the 3120 + 1G-*A mutation, while the other two were compound heterozygotes each with this mutation on one chromosome. The other mutations were G1249E and a previously unreported in frame 54 bp deletion within exon 17a involving nucleotides 3196-3249 (3196del54). The 3120 + 1G->A mutation was first described in American black patients and has been shown to be a common mutation in this population (9-14% of CF chromosomes). It was also found in a black CF patient whose father, the 3120 + 1G-4A carrier, is from Cameroon.These data suggest that it is an old mutation which accounts for many of the CFTR mutations in African blacks.

The low-density lipoprotein receptor (LDLR) plays a major role in cholesterol homeostasis. Mutations in the regulatory region of the LDLR gene, although rare, have been shown to alter transcriptional activity of the gene and can cause familial hypercholesterolaemia (FH). In this study, a transition (c-->t) was identified at nucleotide position -59 within repeat 2 of the LDLR promoter in a South African FH patient of mixed ancestry. By screening 17 family members of the index case for this promoter mutation, two additional single base changes (-124c-->t and-175g-->t) were identified, located at recently described cis- acting regulatory sequences of the LDLR promoter. Both the-59c-->t and the-124c-->t transitions were identified in the normocholesterolaemic son of the index patient. Reporter plasmids containing the normal and mutant promoter fragments were constructed by directional cloning. Transcription studies using a luciferase reporter system demonstrated that the-59c-->t mutation significantly reduces promoter activity in both the presence and absence of sterols ( approximately 40% of normal activity), while the-124c-->t variant increases transcription ( approximately 160%) of the LDLR gene. The intra-familial phenotypic variability observed amongst individuals with the-59c-->t mutation can probably be ascribed to allelic interaction, suggesting that variation in the LDLR promoter region may contribute significantly to the phenotypic expression of FH-related mutations in populations where these mutations prevail.

We have developed a rapid, nonradioactive screening test enabling the simultaneous analysis of three lowdensity Iipoprotein receptor (LDLR) gene mutations (DIS4N, D206E, and V408M), which together account for familial hypercholesterolemla (FH) in -90% of the South African Afrikaner population. The assay is designed so that FH patients, negative for these founder-related mutations (found in descendants of European settlers), subsequently can be screened for unknown mutations in the mutation-rich exon 4 of the LDLR gene. Our screening assay consists of two steps: (1) multiplex allele-specific PCR amplification of exons 4 and 9, and (2) simultaneous analysis of single-and double-strand conformational polymorphisms in exon 4 by vertical electrophoresis on low crosslinked polyacrylamide gels. The simplicity, specificity, and versatility of the multiplex assay makes it an ideal system for routine screening of FH mutations in large population samples.

The South African population harbors genes that are derived from varying degrees of admixture between indigenous groups and immigrants from Europe and the East. This study represents the first direct mutation-based attempt to determine the impact of admixture from other gene pools on the familial hypercholesterolemia (FH) phenotype in the recently founded Coloured population of South Africa, a people of mixed ancestry. A cohort of 236 apparently unrelated patients with clinical features of FH was screened for a common mutation causing familial defective apolipoprotein B-100 (FDB) and seven low-density lipoprotein receptor (LDLR) gene defects known to be relatively common in South Africans with FH. Six founder-type 'South African mutations' were responsible for FH in approximately 20% of the study population, while only 1 patient tested positive for the familial defective apolipoprotein B-100 mutation R3500Q. The detection of multiple founder-type LDLR gene mutations originating from European, Indian and Jewish populations provides direct genetic evidence that Caucasoid admixture contributes significantly to the apparently high prevalence of FH in South African patients of mixed ancestry. This study contributes to our knowledge of the biological history of this unique population and illustrates the potential consequences of recent admixture in populations with different disease risks.

In South Africa, the high prevalence of familial hypercholesterolaemia (FH) among Afrikaners, Jews, and Indians as a result of founder genes is in striking contrast to its reported virtual absence in the black population in general. In this study, the molecular basis of primary hypercholesterolaemia was studied in 16 Africans diagnosed with FH. DNA analysis using three screening methods resulted in the identification of seven diVerent mutations in the coding region of the low density lipoprotein (LDLR) gene in 10 of the patients analysed. These included a 6 bp deletion (GCGATG) accounting for 28% of defective alleles, and six point mutations (D151H, R232W, R385Q, E387K, P678L, and R793Q) detected in single families. The Sotho patient with missense mutation R232W was also heterozygous for a de novo splicing defect 313+1G→A. Several silent mutations/ polymorphisms were detected in the LDLR and apolipoprotein B genes, including a base change (g→t) at nucleotide position −175 in the FP2 LDLR regulatory element. This promoter variant was detected at a significantly higher (p<0.05) frequency in FH patients compared to controls and occurred in cis with mutation E387K in one family. Analysis of four intragenic LDLR gene polymorphisms showed that the same chromosomal background was identified at this locus in the four FH patients with the 6 bp deletion. Detection of the 6 bp deletion in Xhosa, Pedi, and Tswana FH patients suggests that it is an ancient mutation predating tribal separation approximately 3000 years ago.