Diagnostic approach for FSHD revisited: SMCHD1 mutations cause FSHD2 and act as modifiers of disease severity in FSHD1
Diagnostic approach for FSHD revisited: SMCHD1 mutations cause FSHD2 and act as modifiers of disease severity in FSHD1
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DOI：
10.1038/ejhg.2014.191
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发表时间：
2015-06-01
影响因子：
5.2
通讯作者：
Mueller, Clemens R.
中科院分区：
文献类型：
--
作者：
Larsen, Mirjam;Rost, Simone;Mueller, Clemens R.
面肩肱型肌营养不良症（FSHD）是一种常染色体显性遗传的肌肉疾病，具有广泛的临床变异性。染色体4q35上D4Z4大卫星重复序列的收缩是其病理生理学的分子基础。最近，在一个没有D4Z4重复收缩的患者亚组中，已经鉴定出SMCHD1基因的变体，其导致D4Z4的低甲基化，从而导致DUX4转录，这导致FSHD 2型。在这项研究中，我们通过下一代测序（NGS）筛选了55例FSHD1阴性和40例FSHD1阳性患者，这些患者来自无关家族，以寻找SMCHD1的潜在致病性变体。我们在11名索引患者中鉴定了SMCHD1的变异，包括错义、剪接位点和无义突变。我们开发了一种焦磷酸测序法来确定D4Z4重复序列阵列的甲基化状态，发现FSHD 2患者的甲基化水平显著低于健康对照和FSHD 1患者。11名SMCHD1突变携带者中有2名具有中度收缩的D4Z4等位基因，因此这些患者患有FSHD 1和2。比较患者的表型，所有FSHD 2患者受到的影响相对较轻，而FSHD 1 +2患者受到的影响比D4Z4拷贝数预期的严重得多。我们的研究结果证实了SMCHD 1突变在FSHD 2中的作用以及作为疾病严重程度的调节剂。在16.4%没有D4Z4重复收缩的表型FSHD患者中发现SMCHD1变异，FSHD 2的发生率相当高，因此我们建议在分子FSHD诊断工作流程中包括SMCHD1测序，单体型分析和甲基化分析。
Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant muscular disorder with a wide clinical variability. Contractions of the D4Z4 macrosatellite repeat on chromosome 4q35 are the molecular basis of the pathophysiology. Recently, in a subset of patients without D4Z4 repeat contractions, variants in the SMCHD1 gene have been identified that lead to hypomethylation of D4Z4 and thus DUX4 transcription, which causes FSHD type 2. In this study, we have screened 55 FSHD1-negative and 40 FSHD1-positive patients from unrelated families for potentially pathogenic variants in SMCHD1 by next-generation sequencing (NGS). We identified variants in SMCHD1 in 11 index patients, including missense, splice site and nonsense mutations. We developed a pyrosequencing assay to determine the methylation status of the D4Z4 repeat array and found significantly lower methylation levels for FSHD2 patients than for healthy controls and FSHD1 patients. Two out of eleven SMCHD1 mutation carriers had moderately contracted D4Z4 alleles thus these patients are suffering from FSHD1 and 2. Comparing the phenotype of patients, all FSHD2 patients were relatively mildly affected while patients with FSHD1+2 were much more severely affected than expected from their D4Z4 copy number. Our findings confirm the role of SMCHD1 mutations in FSHD2 and as a modifier of disease severity. With SMCHD1 variants found in 16.4% of phenotypic FSHD patients without D4Z4 repeat contractions, the incidence of FSHD2 is rather high and hence we suggest including sequencing of SMCHD1, haplotyping and methylation analysis in the workflow of molecular FSHD diagnostics.