Duchenne and Becker muscular dystrophy (DMD/BMD) are commonly inherited muscle disorders. We report a 31-year-old male who had muscle symptoms with left-right differences and intellectual disability. He was diagnosed with BMD at age 15 primarily based on muscle biopsy findings. A few years later, DMD gene analysis revealed that he was a heterozygous carrier of a normal copy of the gene and a mutated copy with an exon 45–54 deletion, which is expected to result in an out-of-frame mutation. A karyotype analysis was compatible with XXY Klinefelter's syndrome. The analysis of X-chromosome inactivation (XCI) using his skeletal muscle sample revealed a skewed XCI pattern. This is the first reported case of a symptomatic male carrier of DMD caused by skewed XCI in Klinefelter's syndrome with a genetically proven heterozygous mutation of the DMD gene. The skewed XCI pattern could also explain the left-right differences in skeletal muscle symptoms observed in this patient.

Duchenne 和 Becker 肌营养不良症 (DMD/BMD) 是常见的遗传性肌肉疾病。我们报告了一名 31 岁男性，他有左右差异和智力障碍的肌肉症状。他在 15 岁时被诊断出患有 BMD，主要是根据肌肉活检结果。几年后，DMD基因分析显示，他是基因正常拷贝和外显子45-54缺失突变拷贝的杂合携带者，预计会导致框外突变。核型分析符合 XXY Klinefelter 综合征。使用他的骨骼肌样本对 X 染色体失活 (XCI) 进行的分析揭示了一个倾斜的 XCI 模式。这是首例报告的有症状的男性 DMD 携带者病例，该病例由 Klinefelter 综合征中的偏斜 XCI 引起，具有经基因证实的DMD基因杂合突变。倾斜的 XCI 模式也可以解释在该患者中观察到的骨骼肌症状的左右差异。