Case ReportNew phenotype and neonatal onset of sodium channel myotonia in a child with a novel mutation of SCN4A gene
Introduction
Non-dystrophic myotonias are caused by mutations in the skeletal muscle chloride (CLCN1) or sodium channels (SCN4A) genes and are mainly distinguished clinically from the dystrophic myotonias by the absence of extramuscular systemic involvement and progressive weakness [1], [2]. Both conditions are associated with stiffness episodes triggered by exercise, cold, anesthetic procedures, or ingestion of potassium salts [2]. Mutations of SCN4A gene produce a spectrum of phenotypes characterized by hyperkalemic or hypokalemic periodic paralysis, paramyotonia congenita, sodium channel myotonia, congenital myasthenic syndrome and Andersen-Tawil syndrome [3]. In the spectrum of SCN4A mutations, paramyotonia congenita is usually characterized by marked worsening of myotonia by cold, by presence of episodes of weakness and by absence of the warm up phenomenon, whereas sodium channel myotonia may have cold sensitivity, absence of episode weakness and warm up phenomenon may be present. In this report, we present an Italian patient carrying a novel mutation in SCN4A gene, with very early onset of myotonia and atypical phenotype at birth. Clinical and electromyography features of the patient and of child’s mother are described.
Section snippets
Case report
This 4-years old patient was the first female child of non-consanguineous parents. The pregnancy was complicated by polyhydramnios from 30 weeks of gestation. She was born at 40 weeks gestation via spontaneous vaginal delivery and with an Apgar score of 9/10. The measurements at birth were weight, 3.040 kg, length, 47 cm and OFC, 34 cm. At birth, the neurological examination showed diffuse stiffness predominant in lower limb and abdomen, bilateral clubfoot deformity with peripheral contractures, hip
Discussion
The diseases caused by the SCN4A mutations have diverse clinical phenotypes. Paramyotonia usually presents in the first decade of life with extreme cold sensitivity and cold or exercise induced episodic muscle stiffness and weakness, predominantly in the face and upper limbs. Our patient never displayed cold sensitivity or weakness, thereby this clinical phenotype did not fulfill the diagnostic criteria for paramyotonia congenita. She had congenital myotonia confirmed at electromyography
Acknowledgment
We would like to thank Mrs. Giuliana Soncini for her technical assistance.
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