Identification of two novel aquaporin-2 mutations in a Thai girl with congenital nephrogenic diabetes insipidus.

OBJECTIVE

To describe a Thai girl with congenital nephrogenic diabetes insipidus (NDI) and perform mutation analysis of the AQP2 gene.

DESIGN

Case report.

PATIENT: A 6-year old girl with a history of failure to thrive, polydipsia and polyuria was studied. Polyuria and polydipsia were observed within the first few months of life. Despite normal serum osmolality and electrolyte, the result of water deprivation test was compatible with a diagnosis of NDI.

METHODS

The entire coding regions of the AQP2 gene were assessed by polymerase chain reaction and sequencing analysis. The presence of mutations was also confirmed by restriction enzyme digestion analysis.

RESULTS

Two heterozygous novel missense mutations were identified. Both were located in exon 1; a guanine-to-thymine substitution at nucleotide position 3 (c.3G-->T) inherited from her mother and a guanine-to-adenine at position 85 (c.85G-->A) inherited from her father, resulting in a methionine to isoleucine at codon 1 (p.M1I) and glycine to serine at codon 29 (p.G29S), respectively. These mutations have never been previously described and were not detected in 100 ethnic-matched unaffected control chromosomes.

CONCLUSION

We report two novel mutations of the AQP2 gene, p.M1I and p.G29S, associated with autosomal recessive congenital NDI. This study expands the genotypic spectrum of AQP2 mutations and emphasizes an important role of genetic testing for definite diagnosis and genetic counseling.