Abstract
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.
Highlights
Thomsen and Becker myotonia are characterised by muscle stiffness and myotonia, which is based on an electrical instability of the muscle fiber membrane
Our results demonstrate that the proband has two entirely identical chromosomes 7, both inherited from the mother
The first observation of UPD in humans was a maternal UPD 7 in two individuals suffering from Cystic Fibrosis (FC), severe growth restriction and growth hormone deficiency, but the face was not typical of Silver Russell Syndrome (SRS) [7]
Summary
Thomsen (autosomal dominant; OMIM # 160800) and Becker (autosomal recessive; OMIM # 255700) myotonia are characterised by muscle stiffness and myotonia, which is based on an electrical instability of the muscle fiber membrane. We report the first case of Becker recessive myotonia resulting from a maternal isodisomy of the entire chromosome 7. Molecular Analysis Proband’s DNA was screened for CLCN1 mutations together with his non-consanguineous parents, after obtaining signed informed consent.
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