Molecular Genetic And Clinical Study Of A Chinese Family With Congenital Fibrosis Of The Extraocular Muscles

Objective1. To identify the chromosomal location of candidate gene by linkage analysis in this CFEOM family.2. To sequence the candidate gene KIF21A to reveal potentail mutation in this Chinese CFEOM family.3. To report the clinical characteristics of a familial with CFEOM1.4. To investigate the oculomotor nucleus of magnetic resonance imaging (MRI) in the affected individuals.Methods1.Total DNA in the peripheral blood leukoeytes of the patients were extracted with a standard protoeal. The polymorphic DNA mierosatellite markers D125345, D12S59, D12S331and D12S1048were analyzed to assess linkage to the dominant CFEOM1region; and D16S3063, D16S689, D16S3026and D16S3121were analyzed to assess CFEOM3region on the chromosome.The allele sizes were determined by ABI3730-avant genetic analyses by using the Genescan analysis V3.7and Genetyper V3.7softwares.Two Point analyses of these markers were calculated by using the MLINK program of LINKAGE software (version5.1).Gene mutation in exon8,20and21of KIF21A was determined after PCR and gene sequencing of these exons.2.Disease histories of patients were recorded. Ophthalmologic examination included corrected visualacuity, force of levator palpebrae superioris,eye movement,ocular position and forced duction testing.3.This prospective study of imaging on three patients from the family with CFEOM1. Magnetic resonance imaging (MRI) of the ocularmotor nerves at the brainstem was performed following the3D-TSE sequence.Results1.Linkage analyses were done for the CFEOM family with markers at chlomosome12around the CFEOM1locus and chlomosome16around the CFEOM3locus. Linkage analysis showed linkage between the phenotype with markers D12S345and D12S59. The highest LOD score was2.71for D12S345and D12S59. DNA sequencing analysis from all affected individuals in this CFEOM family revealed a heterozygous C→T transition at nucleotide2860of KIF21A, which would have resulted in a substitution of the arginine residue by a trptophan residue at codon954.2.The genetic trait of this pedigree was autosomal dominant inheritance and met CFEOM1criterion.There were12family members with8cases suffering from CFEOM1. All affected individuals had bilateral congenital blepharoptosis, head-tilt, chin lift and primary gaze fixed in a hypotropic position.The vertical and horizontal position of eyes and restriction of eye movement were different among affected individuals. Some patients had aberrant innervation and juvenile canities. One case was unilaterally affected.some patients had one eye in orthoptic position with presence of ptosis.3.Magnetic resonance imaging (MRI) revealed severe hypoplasia of ocular(CN3) in patients(Ⅱ:5,Ⅱ:9,Ⅲ:5) of congenital fibrosis.Absence of the right abducens nerve(CN6) was also noted on two patients(Ⅱ:5,Ⅲ:5).Conclusions1.Linkage analysis of this CFEOM family suggested the linkage of the polymorphic microsatellite markers at chromosome12around CFEOMI1locus. The maximun LOD score was2.71for D12S345and D12S59.2.DNA sequencing analysis identified a2860C→T change in exon21, resulting in a tryptophan substitution for argininein codon954of KIF21A.3.We identified a Chinese autosomal dominant inheritance of CFEOM1family in a family of12members including8affected individuals in three generations.4.Imaging of cranial nerves by MRI not only demonstrate pathology of ocularmotor nerves, but also provide much more important information about the embryonic developmental relations between the CNs and their targets EOMs.Direct MRI of CNs was of value for the diagnosis of CFEOM.