Molecular Genetics Of Hereditary Diseases. High Myopia And Eye Research

Objective To analyze the linkage status between Chinese high myopia families with the known high myopia loci. To perform clinical and genetic study for two X-linked high myopia families.Methods To collect resources of high myopia and allied inherited ocular diseases by inquiring family history and ophthalmologic examinations, including visual acuity, refraction, anterior and posterior segments of eye, axial length and IOP. Eletroretinogram (ERG), fundus fluorescein angiography (FFA), dark adaptation and visual field are taken when high myopia allied ocular disorders are considered. Five to eight ml venous bloods are drawn from research subjects and genomic DNA extracted. All data are entered into data bank. Micro-satellite marker within MYP2 (18p11.31), MYP3 (12q21-23), MYP4 (7q36) and MYP5 (17q21-22) are selected for linkage analysis. Genescan and Genetyper softwares are applied for deciding genotypes. Linkage package is used to calculate Lod scores. X linked recessive (XR) family HM-ZJH is diagnosed as complete congenital stationary night blindness (CSNB 1) by clinical investigation. The disease-causing gene is mapped to Xp11.4 by linkage analysis. Mutation was screened by PCR (Polymerase Chain Reaction, PCR) of the candidate gene exons and flanked introns. The PCR products are directly sequenced. XR family HM-LG is diagnosed as incomplete congenital stationary night blindness (CSNB2) by clinical investigation. Sequence changes of CACNA1F are analysed by PCR and direct sequencing of amplicans.Results Twenty-one big families (19 Autosomal dominant and 2 X-linked recessive) with high myopia are collected. Lod scores of all markers for 4 autosomal dominant high myopia families (HM-FAN, HM-NM, HM-ZLX和HM-LH) are less than 1. ERG tests of patient in CSNB1 family HM-ZJH show a typical pattern of negative waveform of mixed cone-rod response; diminished Ops; flat rod response and near normal cone responses. The maximum lod score is 2.23 (θ=0.0) at DXS8035. A missense mutation A772C (T258P) in exon 2 of NYX gene is identified in all affected patients and all female carriers are heterozygous. This mutation is not found in normal family members of this family nor it is found among 110 unrelated normal controls. ERG tests of patients in CSNB2 family HM-ZJH show a typical pattern of negative waveform of mixed cone-rod response; partially diminished Ops; significantly reduced rod response and cone responses. Eight nucleotide changes are found in CACNA1F.Conclusion The most common inheritance mode in familial high myopia is autosomal dominant pattern. MYP2, MYP3, MYP4 and MYP5 are not linked to selected Chinese high myopia families (HM-FAN, HM-NM, HM-ZLX and HM-LH). A novel mutation of NYX gene with Threonine to Proline change is responsible for this Chinese CSNB1 family. Nucleotide changes of CACNA1F revealed in this study are not related to this Chinese CSNB2 family.