Linkage studies in a family with X-linked recessive ichthyosis employing a cloned DNA sequence from the distal short arm of the X chromosome.

Recently linkage has been described between the Duchenne muscular dystrophy (DMD) gene and a cloned DNA sequence, RC8, that detects restriction fragment length polymorphism and is derived from the distal short arm of the X chromosome. Positive lod scores between RC8 and Xg prompted us to examine the linkage relationship of RC8 to the steroid sulfatase-X-linked recessive ichthyosis (XRI) locus which is situated 15 cM proximal from Xg in the subtelomeric region of Xp. Unexpectedly, at least two crossovers were found among nine informative meioses of an informative family, suggesting that RC8 and XRI may be about 25 cM apart. This implies that the genetic distance between the Xg locus and the DMD locus may exceed 50 cM.