The genome-wide linkage screen using 400 flu-orescently labelled primers on a number of families resulted in two candidate regions for HS
susceptibility. These two regions were found on separate chromosomes indicating that HS is a genetically heterogeneous disease .
The first area of linkage was found to the long arm on chromosome 6 (band 6q25.2). Linkage was originally found in Family M with three markers after screening all affected and unaffected members. As HS can have a variable severity and age of onset the genome screen was originally performed only on the members of the family that were definitely affected. This original screen revealed a number of candidate loci where all the affected individuals shared al-leles with certain markers. Linkage analysis was then carried out with unaffected members of the family using only the previously linked markers. A number of markers were uninformative and therefore high-density markers were run in order to eliminate these regions. This eliminated all markers except for one that co-segregated with the disease and initially gave a positive LOD score of 2.2 at recombination factor (9) of 0 with D6S441. The first unlinked proximal and distal markers were used to define the boundaries of the candidate region that was between markers D6S308 and D6S1581. Geno-typing was then performed using high-density markers from the ABI High Density 5 cM panel and extra markers ordered using sequence data on the UCSC website to further define the region. Recombinants with markers D6S440 and D6S442 defined the region as a 3.74-cM region on 6q.25, with a maximum two-point LOD score of 2.83 in Family M obtained with marker D6S1577. The fluorescent markers covering this region were then run on a number of other families with HS. Only one additional family, Family 6, appeared to be linked across this region. Family 6 gave positive LOD score with all markers run, with a highest combined two-point LOD score of 4.0 with marker D6S290. New DNA samples were obtained from members of Family M, which were then used to further screen the candidate region. Recombination events occurred with individual III.6 at D6S1577 and D6S441 and with a number of individuals with D6S440, narrowing the region to only 0.53 cM. This region contained six confirmed genes and one predicted gene according to the Human Genome Browser (UCSC Genome Bioinformat-
ics). These were ESR1, SYNE-1, FLJ21269, VIP, FBX05, MTRF1L and RGS17. The predicted ex-ons for all of the genes were sequenced and possible alternative exons obtained from expressed mRNA data.
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