Assignment of the locus for hydrolethalus syndrome to a highly restricted region on 11q23-25.

Hydrolethalus syndrome is a recessively inherited lethal malformation syndrome characterized by hydrocephaly with absent midline structures of the brain, micrognathia, polydactyly, and several other abnormalities, mostly in the midline structures. Hydrolethalus syndrome was described in 1981 in Finland, where the incidence is 1:20,000. Only a few cases have been reported elsewhere, and the pathogenesis has remained unknown. Here we report the assignment of the hydrolethalus syndrome locus to chromosome 11q23-25 in Finnish families. The initial genome scan was performed using DNA samples from only 15 affected individuals. In the next step, the hydrolethalus syndrome locus was assigned to an 8.5-cM interval between markers D11S4144 and D11S1351 by linkage analysis in eight families. Finally, the critical locus could be restricted by linkage disequilibrium and haplotype analyses to a 0.5-1-cM region between markers D11S933 and D11S934. Genealogical studies performed in 40 families affected by hydrolethalus revealed no regional clustering, suggesting a relatively early introduction of the disease mutation into the Finnish population and the spreading of the mutation with the inhabitation of the late-settlement area.