PROPOSED CAUSE OF MARKED VASOPRESSIN RESISTANCE IN A FEMALE WITH AN X-LINKED RECESSIVE V2 RECEPTOR ABNORMALITY

Almost all cases of congenital nephrogenic diabetes insipidus (NDI) are transmitted in an X-linked recessive manner by an asymptomatic carrier female to her affected son. Severe symptomatic NDI has not previously been reported in a female with X-linked recessive NDI. Each of the three members of this family has an abnormal V-2 receptor gene, which results in truncation of the V-2 receptor beginning at arginine-337. This prematurely terminates the receptor at the carboxy-terminal tail and very likely disrupts receptor function. The son has an abnormal V-2 receptor gene on his X-chromosome, whereas the mother and daughter have one normal and one abnormal gene for the V-2 receptor. The infusion of desmopressin into the mother and son reveals a total lack of antidiuretic response, whereas the daughter increases urinary osmolality normally. The plasma factor VIII concentration after the infusion of desmopressin in the son does not rise, whereas the mother and daughter have half of the normal factor VIII response, similar to asymptomatic female carriers of NDI. These responses to desmopressin in daughter and son are those of a typical carrier female and male affected with NDI. In contrast, the mother acts as an NDI patient when the urine concentration is measured, but acts as a carrier in terms of the factor VIII response to desmopressin. We postulate that the renal tubular cells of the mother demonstrate extreme lyonization of X-chromosome inactivation, whereas in the tissue that subserves the hematological response to desmopressin, X-chromosome inactivation followed a more typically random distribution.