Absence of AVPR2 copy number variation in eunatremic and dysnatremic subjects in non-Hispanic Caucasian populations

Copy number variation (CNV) is increasingly recognized as a source of phenotypic variation among humans. We hypothesized that a CNV in the human arginine vasopressin receptor-2 gene (AVPR2) would be associated with serum sodium concentration based on the following lines of evidence: 1) the protein product of the AVPR2 gene is essential for renal water conservation; 2) mutations in the AVPR2 gene are associated with aberrant water balance in humans; 3) heritability of serum sodium concentration may be greater in females than in males; 4) the AVPR2 gene is X-linked; and 5) a common CNV spanning the AVPR2 gene was recently described in a non-Hispanic Caucasian population. We developed a highly reproducible assay for AVPR2 CNV. Among 279 subjects with measured serum sodium concentration in the Offspring Cohort of the Framingham Heart Study, no subjects exhibited CNV at the AVPR2 locus. Among 517 subjects in the Osteoporotic Fractures in Men Study (MrOS) - including 152 with hyponatremia and 183 with hypernatremia - no subjects with CNV at the AVPR2 locus were identified. CNV at the AVPR2 locus could not be independently confirmed, and CNV at the AVPR2 gene is unlikely to influence systemic water balance on a population-wide basis in non-Hispanic Caucasian subjects. A novel AVPR2 single nucleotide polymorphism affecting the reporter hybridization site gave rise to an artifactually low copy number signal (i.e., less than unity) in one male African American subject. Reanalysis of the original comparative genomic hybridization data revealed bona fide CNVs flanking - but not incorporating - the AVPR2 gene, consistent with our new genotyping data.