Congenital Fibrosis Of The Extraocular Muscles In Chinese Families: Clinical Phenotype, Linkage Mapping, And Mutation Identification Of KIF21A

PURPOSE. Congenital fibrosis of the extraocular muscles (CFEOM) is a hereditary ocular-motility disorder characterized by non-progressive restrictive ophthalmoplegia and ptosis.The study was conducted to delineate the clinical phenotype and genetic features of Chinese CFEOM families and sporadic cases. Linkage mapping and identification of the the known hotspot regions of mutation in exon 8,20,21 of KIF21A were performed in three Chinese families (Family YT, XT, ZZH) presenting with autosomal dominant CFEOM. The spectrum of mutations in KIF21A among Chinese CFEOM families and the genotype—phenotype correlations were analyzed.METHODS. Clinical and genetic studies were performed to determine their form of CFEOM. Ophthalmologic examinations were recorded by a digital camera and blood samples were obtained from the participants in the three families with informed consent. The genomic DNA were extracted from peripheral blood leukocytes according to the standard methods of protocal. Genotyping and Linkage studies were conducted using the following polymorphic DNA microsatellite markers from the FEOM1, FEOM3 regions: D12S345, D12S59, D12S331, D12S1048 were analyzed to assess linkage to the dominant FEOM1 region; D16S3063, D16S689, D16S3026, D16S3121 were analyzed to assess linkage to the dominant FEOM3 region. The markers were amplified by PCR and the products were separated on 6% denaturing polyacrylamide gels. Haplotypes were constructed manually according to the pattern of the bands visualized by silver stain. Two—point lod scores were calculated with the subroutine Mlink of the Linkage package. Mutation detection was conducted by PCR amplification of the exons 21,20,8 of KIF21A and flanking intron-exon boundaries from genomic DNA of each proband in the three families. The amplicons were subjected to bidirectional direct DNA sequencing on an ABI 3730 DNA sequencer. To further establish the pathogenicity of the mutations, the participating family members and 100 unrelated individuals were screened for a mutation by direct sequencing and SSCP as well if the mutation was detected in a proband.RESULTS. 1. Haplotype analysis revealed that pedigree XT was linked to the FEOM1 loci and not consistent with linkage to the FEOM3 loci with a maximum lod score of 2.24 at D12S331 (theta=0, 100% penetrance). Pedigree YT is very small and therefore although it was consistent with linkage to the FEOM1 loci with a maximum lod score of 0.28 at D12S331, D12S59 (theta=0, 95% penetrance) and consistent with linkage with reduced penetrance to the FEOM3 loci with a maximum lod score of 0 at D16S3026 (theta=0, 95% penetrance), this was only because there were not sufficient affected family members to rule out consistency. Pedigree ZZH is consistent with linkage to both the FEOM1...