Carriers of the Complex Allele HFE c.[187C>G;340+4T>C] Have Increased Risk of Iron Overload in São Miguel Island Population (Azores, Portugal).

Iron overload is associated with acquired and genetic conditions, the most common being hereditary hemochromatosis (HH) type-I, caused by HFE mutations. Here, we conducted a hospital-based case-control study of 41 patients from the São Miguel Island (Azores, Portugal), six belonging to a family with HH type-I pseudodominant inheritance, and 35 unrelated individuals fulfilling the biochemical criteria of iron overload compatible with HH type-I. For this purpose, we analyzed the most common HFE mutations- c.845G>A [p.Cys282Tyr], c.187C>G [p.His63Asp], and c.193A>T [p.Ser65Cys]. Results revealed that the family's HH pseudodominant pattern is due to consanguineous marriage of HFE-c.845G>A carriers, and to marriage with a genetically unrelated spouse that is a -c.187G carrier. Regarding unrelated patients, six were homozygous for c.845A, and three were c.845A/c.187G compound heterozygous. We then performed sequencing of HFE exons 2, 4, 5 and their intron-flanking regions. No other mutations were observed, but we identified the -c.340+4C [IVS2+4C] splice variant in 26 (74.3%) patients. Functionally, the c.340+4C may generate alternative splicing by HFE exon 2 skipping and consequently, a protein missing the α1-domain essential for HFE/ transferrin receptor-1 interactions. Finally, we investigated HFE mutations configuration with iron overload by determining haplotypes and genotypic profiles. Results evidenced that carriers of HFE-c.187G allele also carry -c.340+4C, suggesting in-cis configuration. This data is corroborated by the association analysis where carriers of the complex allele HFE-c.[187C>G;340+4T>C] have an increased iron overload risk (RR = 2.08, 95% CI = 1.40-2.94, p<0.001). Therefore, homozygous for this complex allele are at risk of having iron overload because they will produce two altered proteins--the p.63Asp [c.187G], and the protein lacking 88 amino acids encoded by exon 2. In summary, we provide evidence that the complex allele HFE-c.[187C>G;340+4T>C] has a role, as genetic predisposition factor, on iron overload in the São Miguel population. Independent replication studies in other populations are needed to confirm this association.

HLA Class I and II profiles in São Miguel Island (Azores): genetic diversity and linkage disequilibrium.

BACKGROUND: Human leukocyte antigen (HLA) genes are characterized by high levels of polymorphism and linkage disequilibrium (LD), important characteristics to study the genetic background of human populations and their genetic structure. Here, we analyse the allele distribution and LD extent of HLA class I and II in São Miguel Island population (Azores archipelago, Portugal). FINDINGS: The sample set was composed of 106 healthy blood donors living in São Miguel Island obtained from the anonymized Azorean DNA bank. HLA class I (-A, -B and -Cw) and class II (-DRB1, -DQB1, -DPA1 and -DPB1) genotyping was performed by PCR-SSP Olerup SSP (GenoVision Inc.), according to the manufacturer's instructions.Genetic diversity values, based on the 7 loci, ranged from 0.821 both for HLA-DPA1 and -DQB1 to 0.934 for HLA-B, with a mean value of 0.846. Analysis of 5 HLA-A-Cw-B-DRB1-DQB1 haplotypes revealed that A*01-Cw*07-B*08-DRB1*03-DQB1*02 is the most frequent in São Miguel (7.9%) followed by A*24-B*08-Cw*07-DRB1*03-DQB1*02 (3.8%). In addition, even though the reports of high LD for HLA markers in worldwide populations, São Miguel islanders do not have extensive LD (average D' = 0.285). CONCLUSIONS: In summary, the results demonstrate high variability of HLA in São Miguel Island population as well as absence of genetic structure and extensive LD. The data here presented suggest that in São Miguel islanders autoimmune diseases studies will necessarily encompass a more focused analysis of HLA extended haplotypes as well as the evaluation of other non-HLA candidate genes.

Evaluation of linkage disequilibrium on the Xq13.3 region: comparison between the Azores islands and mainland Portugal.

The design of genetic studies of complex diseases is dependent on the extent and distribution of linkage disequilibrium (LD) across the genome in different populations. Here, we characterize the extent of LD in the Azores (Western, Central, and Eastern island groups) and mainland Portugal populations. LD was evaluated in the Xq13.3 region by genotyping eight STR markers spanning 20.9 Mb. Standardized multiallelic disequilibrium coefficient (D') analysis indicates that the Western group presents higher values when compared with the Central and Eastern groups. However, all island groups show values of D' lower than 0.5 and 0.33, suggesting no extensive LD in these populations. Taken together, the data show that the Azorean population presents a lower D' (0.142) than mainland Portugal (0.226). Although, both populations do not show extensive LD, the easy reconstruction of large pedigrees in the Azorean population is a valuable resource for the fine mapping of disease genes.

Azores Islands: genetic origin, gene flow and diversity pattern.

BACKGROUND: The Azores are an archipelago located in the North Atlantic Ocean (parallel 38) composed of nine islands, dispersed over three geographical groups: The Eastern group (São Miguel and Santa Maria), the Central group (Terceira, Graciosa, Pico, São Jorge and Faial) and the Western group (Flores and Corvo). Taking into consideration the geographical and settlement history differences of the archipelago, the genetic diversity pattern and the internal migration of the Azorean population were assessed, based on the analysis of 15 STR loci in 592 unrelated individuals. RESULTS: The results of this evaluation reveal that Terceira displays the highest value of gene diversity (0.7979) and Corvo the lowest (0.7717). Gene flow analysis indicates that Corvo has the lowest value for migration, 23.35, where as São Miguel and Terceira have the highest values for emigration, 108.14 and 87.66, respectively. Taken together, the data demonstrate that, despite settlement diversity, no genetic difference between the populations of the nine islands is observable today. This may be explained by internal migration. CONCLUSION: Overall, the Azorean population can be analysed as a homogeneous genetic group, which consequently, would present, possibly, the same drug-reaction profile. In terms of genomic medicine, these results will have a significant impact on the design of future genetic and pharmacogenomic studies in the Azorean population.