Abstract
Mutations in SLC4A1, encoding the chloride-bicarbonate exchanger known as anion exchanger 1, have been reported as the sole genetic cause of autosomal dominant distal renal tubular acidosis (dRTA). This disorder is extremely rare and most patients show no clinical symptoms during childhood. Here, we report a case of an infant with early-onset autosomal dominant dRTA caused by SLC4A1 mutation p.Gly609Arg that is detected as a hot spot world widely. Despite the fact that the patient's mother and sister had the same SLC4A1 mutation, all family members presented different clinical courses. A 9-month-old boy was referred to our hospital because of insufficient body weight gain. At the initial visit, his height and weight were 68.2 cm (-1.0 SD) and 6.4 kg (-2.2SD) respectively. Metabolic acidosis with a normal serum anion gap and inappropriate alkaline urine were detected. Abdominal ultrasound indicated bilateral renal medullary high-echoic lesions which suspected nephrocalcinosis. The genetic test revealed a heterozygous mutation c.1825G > A (p.Gly609Arg) in SLC4A1 that directed his diagnosis of autosomal dominant dRTA. The genetic test was performed on the patient's family members, indicating that the same SLC4A1 mutation was detected in his mother and sister. His mother had nephrocalcinosis and metabolic acidosis at the age of 35 years. However, his sister had no clinical symptoms at the age of 6 years without any laboratory abnormalities. This familial case demonstrated that the significant heterogeneity in clinical manifestations may develop even among familial members sharing the same variant.