X-linked retinitis pigmentosa: new map studies of XLRP2, and a possible human centromere effect.

A new large Danish family with X-linked retinitis pigmentosa was studied for linkage analysis. Carrier diagnosis was performed using full-field electro-retinogram combined with a careful fundus examination. Multipoint linkage analysis, employing DNA markers from the proximal short arm of the X chromosome and the cytogenetic centromere marker, revealed the highest location score distally to DXS255 and proximal to the ornithine carbamoyl transferase locus. In comparison with the first Danish family that we studied, the pericentromeric recombination fraction was increased; it is speculated that the observed difference in genetic distances from the centromere in the 2 Danish families is correlated with a difference in the size and location of the centromeric heterochromatin.