Case report of a child with long QT syndrome type 14 caused by CALM1 gene mutation and literature review

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OBJECTIVE: To analyze the clinical and genetic characteristics of a patient with long QT syndrome type 14 (long QT syndrome-14, LQT14, OMIM # 616247) caused by a de novo CALM1 mutation. METHODS: The clinical data of the patient were collected, next-generation sequencing technology was used to determine the exome gene sequence of the patient, and the suspected pathogenic locus was verified by Sanger sequencing. RESULTS: A 5-year and 9-month-old girl was admitted to the hospital due to a syncopal episode. During the attack, the main symptoms were loss of consciousness, cyanosis of the face and lips, and weakness of limbs. The child had multiple seizures in the past, all of which occurred after emotional excitement and activity. She was diagnosed with epilepsy for more than 3 years, but the effect of antiepileptic treatment was not satisfactory. The electrocardiogram was normal in the past. A month ago, convulsions occurred again after exercise, and the electrocardiogram showed QTc 496 ms. The treadmill test showed a significant prolongation of QTc after exercise, and the genetic results suggested a new heterozygous variant of CALM1, c.395A>G; p. (Asp132Gly). Consequently, she was diagnosed with LQT14 and treated with propranolol. During a follow-up of 15 months, there were no seizures or syncope. CONCLUSIONS: This patient had multiple episodes of convulsions or syncope after emotional stimulation or activity, with intermittent prolongation of the QTc on routine ECG, marked prolongation of the QTc after exercise, and T-wave alternans, which differed from the LQT14 phenotype caused by the previous CALM1 mutation.

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