Study question: What is the heritability of C-reactive protein (CRP) levels in women with polycystic ovary syndrome (PCOS) and their first-degree relatives?
Summary answer: Women with PCOS and their siblings are more likely to have elevated CRP levels when both of their parents have elevated CRP. This PCOS family-based study indicates that CRP levels are likely a heritable trait.
What is known already: Previous studies have established that an elevated blood level of CRP is variably present in women with PCOS, and may be present independent of metabolic status.
Study design, size and duration: A familial based phenotyping study consisting of 81 families comprised of PCOS patients and their first-degree relatives for 305 subjects.
Participants/materials, setting and methods: Study conducted at an academic health center. An elevated CRP level was defined as >28.6 nmol/l. To account for familial clustering, generalized estimating equations with a logit link were used to model the association between elevated CRP levels in patients with PCOS and their siblings with their parental group (A = neither parent with elevated CRP; B = one parent with elevated CRP; C= both parents with elevated CRP), adjusting for gender, age and BMI of the offspring. We did additional heritability analyses by using a variance component estimation method for CRP levels, adjusting for sex, age and BMI.
Main results and the role of chance: We observed elevated CRP levels in 94% of the offspring in group C, 45% in group B and 10% in group A after adjusting for age, gender and BMI of the offspring. The median BMI of the offspring in group A, B and C were 30.0, 28.7 and 31.2 kg/m², respectively. Heritability estimates of CRP levels ranged from 0.75 to 0.83 and remained significant after excluding for type 2 diabetes mellitus. Our small sample size increases the possibility of a type 1 error.
Limitations, reasons for caution: This is a single report in an adequately powered but limited sample size study identifying the strong heritability of CRP levels. Replication in other large family cohorts is necessary.
Wider implication of the findings: These findings support the concept that there is an increased cardiovascular disease risk profile in families of women with PCOS.
Study funding/competing interest: This research was supported by National Institutes of Health grants U54HD-034449 and P50 HD044405 (A.D.). Priyathama Vellanki is supported in part by NIH/NIDDK Training Grant T32 DK007169.