Expanding the phenotypic spectrum of PROK2/PROKR2: a recall-by-genotype study

Abstract

Rare variants in prokineticin 2 pathway genes (PROK2; PROKR2), cause isolated hypogonadotropic hypogonadism (IHH) in humans, leading to pubertal failure and infertility. In addition to reproduction, this pathway is also implicated in cardiovascular, metabolic, and inflammatory regulation. The role of naturally occurring PROK2/R2 variants in the general population remains unknown. Thus, we aimed to investigate the role of PROK2/R2 variants in the overall human health. We performed a recall-by-genotype study in rare PROK2/R2 variant carriers and non-carrier controls from a large hospital dataset [Massachusetts General Brigham Biobank (MGBB)]. All recalled participants underwent medical history, physical exam, completed detailed questionnaires and laboratory evaluation including a frequently sampled intravenous glucose tolerance test. Continuous and categorical variables were analyzed with a t-test/non-parametric Wilcoxon rank sum test and a Fisher's exact test, respectively. Twenty-five rare PROKR2 variant carriers (11 males and 14 females, mean age 45.6 years ± SD 11.7) and 24 non-carrier controls (16 males and 8 females, mean age 44.8 years ± SD 10) were recruited. Male variant carriers were more likely to seek fertility evaluation compared to non-carrier controls (p = 0.03) and carriers of the founder PROKR2 (p.L173R) variant (44% of the cohort) in both sexes were more likely to be diagnosed with lower gastrointestinal phenotypes compared to controls (p = 0.02). This novel clinical association is in line with the reported role of prokineticin 2 in intestinal smooth muscle function in preclinical models. Rare heterozygous PROK2/R2 variants contribute to known reproductive and novel gastrointestinal phenotypes within a hospital-based population cohort.

Fig. 1

Recall-by-genotype enrollment pipeline. The Mass General Brigham Biobank (MGBB) (N = 65274, 29214 males and 36058 females) was used to identify PROK2/PROKR2 variant carriers and non-carrier participants. Genotyping data and exome sequencing data were available in 65,106 (29144 males and 35960 females) and 53,382 (23675 males and 29705 females) MGBB participants, respectively. A total of 546 PROK2/R2 (228 males and 318 females) variant carriers and 573 (308 males and 265 females) non-variant carrier controls were identified and contacted through the MGBB. Screening visits were scheduled and completed in 25 carriers (11 males and 14 females) and 24 non-carrier controls (16 males and 8 females)

Fig. 2

Reproductive phenotypes of PROK2/R2 male rare variant carriers and non-carrier male control. Panel A: Reproductive phenotypes of PROK2/R2 male rare variant carriers (N = 11, red) and non-carrier controls (N = 16, grey). Male carriers were more likely to undergo evaluation for fertility (p = 0.03); Panel B: Male carriers of the PROKR2 founder variant p.L173R (N = 6, red) and non-carrier controls (N = 16, grey). Male carriers of the founder variant were more likely to undergo evaluation for fertility (p = 0.04), be diagnosed with infertility (p = 0.03) and receive therapy for infertility (p = 0.04). A Fisher exact test was utilized for the statistical analysis. P values < 0.05 were considered statistically significant

Fig. 3

Clinical phenotypes across all organ systems of PROK2/R2 rare variant carriers (red), PROKR2 founder variant (p.L173R) carriers (blue) and non-carrier controls. The prevalence of diseases across different organ systems was investigated via medical histories and review of electronic medical records in PROK2/PROKR2 variant carriers (reds), PROK2 p.L172R carriers (blue), and non-carrier controls (grey). No differences were observed between the two groups when PROK2/PROKR2 carriers of all variants were analyzed. However, participants with the founder PROKR2 variant (p. L173R) demonstrated lower gastrointestinal/bowel phenotypes (N = 4, including 2 participants including inflammatory bowel disease– IBD, 1 with diverticulitis/inflammatory bowel syndrome and 1 with anal fissures) at a higher frequency (37%) compared to controls (N = 1 with prior episode of diarrhea, 4%, p value 0.02). A Fisher exact test was utilized for the statistical analysis. P values < 0.05 were considered statistically significant

Fig. 4

Glucose and insulin levels of the PROK2/R2 rare variant carriers and non-carriers controls during the frequently sampled intravenous glucose tolerance test (FSIGT). PROK2/R2 rare variant carriers (N = 17, red) and non-carrier controls (N = 15, grey) underwent a frequently sampled intravenous tolerance test (FSIGT). During the 4-hour FSIGT, baseline sampling for plasma glucose occurred at −10 and −1 min. A bolu of 0.3 g/kg of glucose was administered at time 0. At 20 min, participants received a 0.03-U/kg infusion of regular human insulin over 45 s to enhance the insulin level to better help assess the effect of insulin on glucose uptake. Variant carriers demonstrated similar glucose and insulin levels to non-carrier as calculated by the area under the curve (AUC) for glucose and insulin levels during the FSIGT