Objective: To identify the genetic locus for X-linked nonsyndromic high myopia in a large Chinese family.
Methods: Phenotypic information and DNA samples were collected from 19 individuals in a Chinese family; 7 had high myopia and 12 were unaffected. We performed a linkage scan on the X chromosome and sequenced several candidate genes.
Results: High myopia in this family, presenting since early childhood and ranging from -6.00 to -15.00 diopters of sphere, is consistent with an X-linked recessive trait. The presence of a normal optic disc and the absence of color visual defects and other systemic abnormalities indicated that high myopia in this family is nonsyndromic. Our linkage analysis mapped the disease locus to Xq28, a 6.1-cM region between DXS8069 and Xqter, with 2-point logarithm of odds scores greater than 2.0 for 5 markers and a maximum logarithm of odds score of 3.59 at θ = 0 for 2 markers. Sequence analysis of coding and adjacent intronic regions of GPR50, PRRG3, CNGA2, and BGN did not identify any potential causative mutation.
Conclusions: Nonsyndromic high myopia in a Chinese family was mapped to the MYP1 region, which confirmed and refined this region for high myopia. In addition, our results suggest that color visual defects and optic disc hypoplasia are not necessary signs of high myopia attributed to the MYP1 region.
Clinical relevance: MYP1 is a common and the best locus for positional cloning of the gene responsible for high myopia. Our results suggest that MYP1 is also responsible for nonsyndromic high myopia.