汉族面肩肱型肌营养不良症4q35致病区域基因结构特征及其与临床表型的关系

目的 研究汉族面肩肱型肌营养不良症(FSHD)4q35致病区域基因结构特征,分析位点4qA和4qB的分布规律,探讨基因型与临床表型的关系.方法 研究对象来自52个无亲缘关系家系的62例患者及57名患者血缘亲属.低熔点胶包埋法抽提基因组DNA.同一样品分别进行EcoR Ⅰ酶切、EcoR Ⅰ/Bln Ⅰ双酶切和Hind Ⅲ酶切,脉冲电场凝胶电泳分离,p13E-11、4qA和4qB探针Southern杂交,计算致病性4qA型EcoR Ⅰ片段长度和分布、易位和嵌合体情况、4qA/4qB的频率和基因型分布及基因型-临床表型关系.结果 共榆出携带致病性4qA型EcoR Ⅰ片段患者69例,范围10～38 kb,平均值20 kb±7 kb,散发型和家族型分布差异无统计学意义(t=1.413,P>0.05);检测到3种染色体易位形式,检出率14.49%,4q→10q频率(13.04%)高于10q→4q频率(1.45%)(X2= 6.900,P<0.05);标准型患者中,4qA/4qB杂合型频率(61.40%)高于4qA/4qA纯合型频率(38.60%)(X2=5.930,P<0.05),但两型片段长度分布差异无统计学意义(t=-0.039,P>0.05),不同基因型的临床严重程度(CS评分)差异无统计学意义(H=0.693,P>0.05).结论 95.0%患者携带30 kb以下的4qA型EcoRI片段,4q-10q之间存在高频率的易位蓖组现象,4qA/4qB的杂合型频率明显高于纯合刑频率,但基因型分布对临床表型的异质性无直接影响.

Characteristics of gene structure in facioscapulohumeral muscular dystrophy -related 4q35 subtelomere and genotype-phenotype correlation in Chinese Han population

Objective To investigate the characteristics of gene structure in facioscapulohumeral muscular dystrophy (FSHD) -related 4q35 subtelomere, to analyze the distribution of 2 alleles (4qA and 4qB) distal to D4Z4 of this locus, and to further elucidate the genotype-phenotype correlation in Chinese Han FSHD patients. Methods Peripheral blood samples were collected from 52 unrelated families including 62 FSHD-affected and 57 unaffected members. Genomic DNA was extracted from the lymphocytes according to the specific procedure designed to minimize DNA shearing, then digested with EcoR Ⅰ or Hind Ⅲ, or double digested with EeoR Ⅰ and Bin Ⅰ. The cleaved DNA was separated by pulsed field electrophoresis (PFGE) and Southern blotting with the probes p13E-11,4qA, and 4qB. The size of FSHD-causing 4qA allele and its distribution was analyzed by " curve fitting". Then the characteristics of translocation and mosaicism, the frequencies of two allelic variants of chromosome 4q and their genotypes were calculated to analyze the genotype-phenotype correlation. Results It was found that 69 patients carried a short chromosome 4-type allele of 4qA origin with the length 10 - 38 kb. The mean length of these pathogenic EcoR Ⅰ/4qA arrays was 20 kb±7 kb, without significant difference between the sporadic cases and familial cases (t=1.413, P>0.05). Three different translocation types were observed with a translocation rate of 14.49%. The rate of 4q→10q translocation was 13.04%, significantly higher than that of 10q→4q translocation (1.45%, X2 = 6.900, P<0.05). Somatic mosaicism was detected in a male sporadic case and a female asymptomatic familial case. In 57 cases with standard configuration distribution, the frequency of 4qA/4qB beterozygote was 61.40%, significantly higher than that of 4qA/4qA homozygote (38.60%, (X2 = 5. 930, P<0.05 ). There were not significant differences in the repeat size distributions and assessment of clinical severity between the sporadic and familial cases (t=-0.039, P>0.05 ; H = 0.693,P>0.05). Conclusion About 95% of Chinese FSHD patients carry a pathogenic 4-type allele of 4qA origin less than 30 kb long. The frequent translocations between chromosome 4q and 10q may play an essential rote for FSHD mechanism. The frequency of 4qA/4qB heterozygote is significantly higher than that of 4qA/4qA homozygote, while the allelic variant genotypes do not contribute to modify FSHD manifestations.