■面肩肱肌营养不良1型(FSHD1)是常染色体显性遗传性肌营养不良的最常见形式之一,其特征是由于4q35上D4Z4重复单位缩短而导致疾病外显率可变。FSHD1的分子诊断通常通过Southern印迹法进行,这是复杂的,耗时,缺乏临床实用性。因此,在这项研究中,光学基因组作图(OGM)用于FSHD1的遗传诊断。此外,表观遗传异质性由甲基化分析确定。
■对来自同一家族的四个成员的基因组DNA样品进行全外显子组测序。OGM用于鉴定D4Z4中的结构变异,而亚硫酸氢钠测序有助于鉴定位于D4Z4阵列远端的区域中CpG位点的甲基化水平。一个多学科小组收集了临床数据,和全面的家庭分析有助于评估表型和基因型。
■全外显子组测序未发现患者中与临床表型相关的变异。OGM显示先证者是具有4个和8个D4Z4重复单元的4qA等位基因的复合杂合子,而受影响的弟弟只有一个4qA等位基因和四个D4Z4重复单元。发现先证者和她的弟弟都表现出不对称的弱点,主要涉及面部,肩带,和上臂肌肉,而弟弟的临床症状更严重。先证者的父亲,神经系统检查后发现是正常的,还携带具有八个D4Z4重复单元的4qA等位基因。未受影响的母亲表现出4qA等位基因的49个D4Z4重复单元和具有4qA等位基因的四个D4Z4重复单元的次要镶嵌模式。因此,4个D4Z4重复单元中4qA等位基因的存在强烈地表明母体种系镶嵌的发生。与无症状父母相比,有症状患者的CpG6甲基化水平较低。姐姐的临床评分和ACSS较低,CpG6甲基化水平高于弟弟。
■在这项研究中,通过OGM鉴定出两个具有表型正常父母的FSHD1兄弟姐妹。我们的发现表明,四个D4Z4重复序列的4qA等位基因是通过母体种系镶嵌遗传的。临床表型异质性受CpG6甲基化水平的影响。这项研究的结果极大地有助于FSHD1的分子诊断,也有助于了解该疾病背后的临床表型变异性。
UNASSIGNED: Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is one of the most common forms of autosomal-dominant muscular dystrophies characterized by variable disease penetrance due to shortened D4Z4 repeat units on 4q35. The molecular diagnosis of FSHD1 is usually made by Southern blotting, which is complex, time-consuming, and lacks clinical practicality. Therefore, in this study, optical genome mapping (OGM) is employed for the genetic diagnosis of FSHD1. Furthermore, epigenetic heterogeneity is determined from methylation analysis.
UNASSIGNED: Genomic DNA samples from four members of the same family were subjected to whole-exome sequencing. OGM was used to identify structural variations in D4Z4, while sodium bisulfite sequencing helped identify the methylation levels of CpG sites in a region located distally to the D4Z4 array. A multidisciplinary team collected the clinical data, and comprehensive family analyses aided in the assessment of phenotypes and genotypes.
UNASSIGNED: Whole-exome sequencing did not reveal variants related to clinical phenotypes in the patients. OGM showed that the proband was a compound heterozygote for the 4qA allele with four and eight D4Z4 repeat units, whereas the affected younger brother had only one 4qA allele with four D4Z4 repeat units. Both the proband and her younger brother were found to display asymmetric weakness predominantly involving the facial, shoulder girdle, and upper arm muscles, whereas the younger brother had more severe clinical symptoms. The proband\'s father, who was found to be normal after a neurological examination, also carried the 4qA allele with eight D4Z4 repeat units. The unaffected mother exhibited 49 D4Z4 repeat units of the 4qA allele and a minor mosaic pattern with four D4Z4 repeat units of the 4qA allele. Consequently, the presence of the 4qA allele in the four D4Z4 repeat units strongly pointed to the occurrence of maternal germline mosaicism. The CpG6 methylation levels were lower in symptomatic patients compared to those in the asymptomatic parents. The older sister had lower clinical scores and ACSS and higher CpG6 methylation levels than that of her younger brother.
UNASSIGNED: In this study, two siblings with FSHD1 with phenotypically normal parents were identified by OGM. Our findings suggest that the 4qA allele of four D4Z4 repeats was inherited through maternal germline mosaicism. The clinical phenotype heterogeneity is influenced by the CpG6 methylation levels. The results of this study greatly aid in the molecular diagnosis of FSHD1 and in also understanding the clinical phenotypic variability underlying the disease.