GENETIC HOMOGENEITY OF CARTILAGE HAIR HYPOPLASIA

Cartilage-hair hypoplasia (CHH) is an autosomal recessive metaphyseal chondrodysplasia characterized by short stature and hypoplasia of the hair. Associated pleiotropic features include deficient erythrogenesis , impaired T-cell mediated immunity, Hirschsprung's dis ease, and an i ncreased risk of malignancies. CHH is most prevalent among the Old Ord er Amish in the United States and among the Finns, but sporadic famili es have been described among many other populations. We have previousl y mapped the gene for CHH to the short arm of chromosome 9 in Finnish and Amish families. The CHH locus resides close to D9S163 within an in terval of 1.5 cM flanked by D9S165 and D9S50. In order to investigate the genetic homogeneity of CHH in various populations, we studied nine families with no genealogical connections to either Amish or Finns. N o recombinants were detected between the CHH gene and any of the three closest marker loci studied, suggesting that CHH in these families re sults from mutation(s) at the same locus as in the Amish and Finnish f amilies.