GENETICS IN ENDOCRINOLOGY Pathophysiology, diagnosis and treatment of familial nephrogenic diabetes insipidus

For an endocrinologist, nephrogenic diabetes insipidus (NDI) is an end-organ disease, that is the antidiuretic hormone, arginine-vasopressin (AVP) is normally produced but not recognized by the kidney with an inability to concentrate urine despite elevated plasma concentrations of AVP. Polyuria with hyposthenuria and polydipsia are the cardinal clinical manifestations of the disease. For a geneticist, hereditary NDI is a rare disease with a prevalence of five per million males secondary to loss of function of the vasopressin V2 receptor, an X-linked gene, or loss of function of the water channel AQP2. These are small genes, easily sequenced, with a number of both recurrent and private mutations described as disease causing. Other inherited disorders with mild, moderate or severe inability to concentrate urine include Bartter's syndrome and cystinosis. MAGED2 mutations are responsible for a transient form of Bartter's syndrome with severe polyhydramnios. The purpose of this review is to describe classical phenotype findings that will help physicians to identify early, before dehydration episodes with hypernatremia, patients with familial NDI. A number of patients are still diagnosed late with repeated dehydration episodes and large dilations of the the urinary tract leading to a flow obstructive nephropathy with progressive deterioration of glomerular function. Families with ancestral X-linked AVPR2 mutations could be reconstructed and all female heterozygote patients identified with subsequent perinatal genetic testing to recognize affected males within 2 weeks of birth. Prevention of dehydration episodes is of critical importance in early life and beyond and decreasing solute intake will diminish total urine output.