Linkage mapping of a nonspecific form of X-linked mental retardation (MRX53) in a large Pakistani family

Nonspecific X-linked mental retardation is a nonprogressive, genetically heterogeneous condition that affects cognitive function in the absence of other distinctive clinical manifestations. We report here linkage data on a large Pakistani family affected by a form of X-linked nonspecific mental retardation. X chromosome genotyping of family members and linkage analysis allowed the identification of a new disease locus, MRX53. The defined critical region spans approximately 15 cM between DXS1210 and DXS1047 in Xq22.2-26. A LOD score value of 3.34 at no recombination was obtained with markers DXS1072 and DXS8081.

Linkage mapping of a new syndromic form of X-linked mental retardation, MRXS7, associated with obesity

A new syndromic form of X-linked mental retardation associated to obesity, MRXS7, has been localised to Xp11.3-Xq23 in a large Pakistani family. The ten affected males show clinical manifestations of mental retardation, obesity and hypogonadism. The family was genotyped by a set of microsatellite markers spaced at approximately 10 cM intervals on the X chromosome. Linkage to five adjacent microsatellite markers, mapping in the pericentromeric area, was established and a maximum two-point lod score of 3.86 was reached at zero recombination with marker DXS1106. Reduced recombination events around the centromere prevented precise mapping of the gene.

Alopecia universalis associated with a mutation in the human hairless gene

There are several forms of hereditary human hair loss, known collectively as alopecias, the molecular bases of which are entirely unknown. A kindred with a rare, recessively inherited type of alopecia universalis was used to search for a locus by homozygosity mapping, and linkage was established in a 6-centimorgan interval on chromosome 8p12 (the logarithm of the odds favoring linkage score was 6.19). The human homolog of a murine gene, hairless, was localized in this interval by radiation hybrid mapping, and a missense mutation was found in affected individuals. Human hairless encodes a putative single zinc finger transcription factor protein with restricted expression in the brain and skin.