Gain-of-function mutations in the gene encoding the V2 vasopressin receptor (V2R) cause nephrogenic syndrome of inappropriate antidiuresis. To date, reported mutations lead to the substitution of arginine 137 by either a cysteine or leucine (R137C/ L). Here, we describe a 3-month-old hyponatremic infant found to have a phenylalanine 229 to valine (F229V) substitution in V2R. Characterization of this substitution in vitro revealed that it leads to high constitutive activity of the receptor, compatible with spontaneous antidiuresis. In contrast to R137C/L mutant receptors, F229V receptors do not undergo spontaneous desensitization, which results in sustained, high basal activity. Notably, the V2R-selective inverse agonists tolvaptan and satavaptan completely silenced the constitutive signaling activity of the F229V mutant receptor, indicating that this substitution does not lock the receptor in an irreversible active state. Thus, inverse agonists might prove to be effective therapies for treating patients with this or other spontaneously activating mutations that do not lock the V2R in its active state. These results emphasize the importance of genetic testing and the functional characterization of mutant receptors for patients with nephrogenic syndrome of inappropriate antidiuresis because the results might inform treatment decisions.

Background/Aims: Mutations in the type 2 vasopressin receptor gene (AVPR2) underlie X-linked recessive nephrogenic diabetes insipidus (NDI). Here, we report on a family with a mutation in AVPR2, c.262G>A (p.V88M). This recurrently identified mutation was previously shown to abolish AVPR2 function, yet in some affected members, urine osmolalities of up to 570 mosm/kg were observed. We detail the variable clinical phenotype and investigate its molecular basis. Methods: Retrospective analysis of clinical data and in vitro assessment of wild-type and V88M-mutant receptors. Results: Clinical data were available on 6 patients. Four of these demonstrated a substantial increase in urinary concentration after 1-desamino[8-D-arginine] vasopressin, consistent with partial NDI, while 2 did not respond. In vitro analysis revealed a reduced cell surface expression and decreased binding affinity for arginine-vasopressin of the mutant receptor, leading to blunted signaling activity. Treatment with the pharmacological chaperone SR121463 enhanced cell surface expression. Conclusion: The V88M mutation is associated with phenotypical diversity, which may be explained by the fact that both the expression level and the hormone-binding affinity are affected by the mutation. Our results provide a rational basis for treatment trials with vasopressin analogues in combination with pharmacologic chaperones in patients with this recurrently identified mutation.

Objectives To assess real‐world effectiveness, safety, and usage of erenumab in Canadian patients with episodic and chronic migraine with prior ineffective prophylactic treatments. Background In randomized controlled trials, erenumab demonstrated efficacy for migraine prevention in patients with ≤4 prior ineffective prophylactic migraine therapies. The “Migraine prevention with AimoviG: Informative Canadian real‐world study” (MAGIC) assessed real‐world effectiveness of erenumab in Canadian patients with migraine. Methods MAGIC was a prospective open‐label, observational study conducted in Canadian patients with chronic migraine (CM) and episodic migraine (EM) with two to six categories of prior ineffective prophylactic therapies. Participants were administered 70 mg or 140 mg erenumab monthly based on physician’s assessment. Migraine attacks were self‐assessed using an electronic diary and patient‐reported outcome questionnaires. The primary outcome was the proportion of subjects achieving ≥50% reduction in monthly migraine days (MMD) after the 3‐month treatment period. Results Among the 95 participants who mostly experienced two (54.7%) or three (32.6%) prior categories of ineffective prophylactic therapies and who initiated erenumab, treatment was generally safe and well tolerated; 89/95 (93.7%) participants initiated treatment with 140 mg erenumab. At week 12, 32/95 (33.7%) participants including 17/64 (26.6%) CM and 15/32 (48.4%) EM achieved ≥50% reduction in MMD while 30/86 (34.9%) participants including 19/55 (34.5%) CM and 11/31 (35.5%) EM achieved ≥50% reduction in MMD at week 24. Through patient‐reported outcome questionnaires, 62/95 (65.3%) and 45/86 (52.3%) participants reported improvement of their condition at weeks 12 and 24, respectively. Physicians observed improvement in the condition of 78/95 (82.1%) and 67/86 (77.9%) participants at weeks 12 and 24, respectively. Conclusion One‐third of patients with EM and CM achieved ≥50% MMD reduction after 3 months of erenumab treatment. This study provides real‐world evidence of erenumab effectiveness, safety, and usage for migraine prevention in adult Canadian patients with multiple prior ineffective prophylactic treatments.