Molecular investigation and long-term clinical progress in Greek Cypriot families with recessive distal renal tubular acidosis and sensorineural deafness due to mutations in the ATP6V1B1 gene.
The spectrum of distal renal tubular acidosis (dRTA) includes a genetically heterogeneous group of inherited conditions of both autosomal-dominant and recessive mode of inheritance. The basic defect is linked to the renal part of acid-base homeostasis, which is partly achieved by the regulated luminal secretion of H+ at the apical surface of the alpha-intercalated cells of renal collecting ducts. This is coupled to bicarbonate reabsorption with chloride counter transport across the basolateral membranes. Here, we describe the molecular findings of the first two Greek Cypriot families with recessive dRTA and the long-term clinical findings in four of five affected members. DNA linkage analysis with four polymorphic markers flanking the ATP6V1B1 gene on chromosome 2 gave evidence for positive linkage; direct DNA analysis by automated DNA sequencing revealed that patients in one family were homozygous for mutation 229+1G>T (IVS7+1G>T) and that patients in the second family were compound heterozygous for 229+1G>T and R157C. The mutations were found on four different haplotypes. Both the mutations were previously reported in patients of Turkish origin. Three known polymorphic variants were also identified. The five patients demonstrated the whole clinical spectrum of the disease including death in infancy, failure to thrive, rickets, nephrocalcinosis, nephrolithiasis, and episodes of hypokalemic paralysis. Some of the family members are now in their mid 30s and late 20s, and nephrolithiasis with recurrent renal colics is their main problem. Renal function has remained normal. In conclusion, early diagnosis in infancy and prompt treatment with alkali and potassium supplements is of great benefit to the patient with dRTA and ensures normal growth. The identification of responsible mutations facilitates antenatal or postnatal diagnosis in concerned families and improves the prognosis.