Case Report: Novel Homozygous Variant Causing Isolated Hyperchloridrosis in a Chinese Child With Hyponatremia.

Isolated hyperchloridrosis (HYCHL; OMIM 143860) is a rare autosomal recessive disorder caused by biallelic mutations in the gene, which is characterized by abnormally high levels of salt in sweat that can lead to dehydration associated with low levels of sodium in the blood. To date, only four variants of the gene have been identified to be associated with HYCHL. Here, we presented a rare Chinese case of HYCHL in an infant with decreased food intake, mild diarrhea, severe dehydration, and hypovolemic shock who was hospitalized in our department three times. Laboratory tests showed hyponatremia and hypochloremia. Because of recurrent attacks, whole-exome sequencing (WES) was performed and revealed a novel homozygous missense variant c.763A>C (p.Thr255Pro) in the gene (NM_001218.5). In total 0.9% sodium chloride (NaCl) solution was orally administered until 1 year and 6 months of age. Followed up to 3 years of age, the patient showed good growth and development without similar manifestations. This study reported a novel gene mutation leading to HYCHL for the first time in China, which enriched the genotype of HYCHL and emphasized the early suspicion and identification of the rare condition to adequate treatment.