Autosomal dominant (Thomsen) and recessive (Becker) congenital myotonia are two different non dystrophic disorders, due to allelic mutations of the muscle chloride channel gene, located on chromosome 7q35. More than two thirds of the muscle chloride channel gene mutations occur independently in unique families and cause the recessive form of the disease. Becker disease is more common and severe than Thomsen disease. Here, we report on the clinical and molecular data of the first patient with maternal uniparental disomy for chromosome 7 and recessive congenital myotonia. The proband is a 15-year-old male, homozygous for a missense mutation within muscle chloride channel gene, showing few characteristic signs of the Silver Russell Syndrome.
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