Assignment of the Nance-Horan syndrome to the distal short arm of the X chromosome

There are three types of X-linked cataracts recorded in Mendelian Inheritance in Man (McKusick 1988): congenital total, with posterior sutural opacities in heterozygotes: congenital, with microcornea or slight microphthalmia; and the cataract-dental syndrome or Nance-Horan (NH) syndrome. To identify a DNA marker close to the gene responsible for the NH syndrome, linkage analysis on 36 members in a three-generation pedigree including seven affected males and nine carrier females was performed using 31 DNA markers. A LOD score of 1.662 at 0=0.16 was obtained with probe 782 from locus DXS85 on Xp22.2–p22.3. Negative LOD scores were found at six loci on the short arm, one distal to DXS85, five proximal, and six probes spanning the long arm were highly negative. These results make the assignment of the locus for NH to the distal end of the short arm of the X chromosome likely.