# Congenital myasthenic syndrome secondary to pathogenic variants in the SLC5A7 gene: report of two cases

## TL;DR

This paper reports two cases of a rare neuromuscular disorder caused by mutations in the SLC5A7 gene, highlighting its symptoms and treatment challenges.

## Contribution

The study presents the first reported cases of SLC5A7-related CMS in Latin America.

## Key findings

- Two male patients with SLC5A7 mutations exhibited apnea, hypotonia, and bulbar deficits.
- Both patients showed incomplete response to pyridostigmine treatment.
- The cases highlight central nervous system involvement in SLC5A7-related CMS.

## Abstract

Congenital Myasthenic Syndromes (CMS) are rare genetic diseases, which share as a common denominator muscle fatigability due to failure of neuromuscular transmission. A distinctive clinical feature of presynaptic CMS variants caused by defects of the synthesis of acetylcholine is the association with life-threatening episodes of apnea. One of these variants is caused by mutations in the SLC5A7 gene, which encodes the sodium-dependent HC-3 high-affinity choline transporter 1 (CHT1). To our knowledge there are no published cases of this CMS type in Latin America.

We present two cases of CHT1-CMS. Both patients were males presenting with repeated episodes of apnea, hypotonia, weakness, ptosis, mild ophthalmoparesis, and bulbar deficit. The first case also presented one isolated seizure, while the second case showed global developmental delay. Both cases, exhibited incomplete improvement with treatment with pyridostigmine.

This report emphasizes the broad incidence of CMS with episodic apnea caused by mutations in the SLC5A7 gene and the frequent association of this condition with serious manifestations of central nervous system involvement.