Heritability patterns in hand osteoarthritis: the role of osteophytes

INTRODUCTION The objective of the present study was to assess heritability of clinical and radiographic features of hand osteoarthritis (OA) in affected patients and their siblings. METHODS A convenience sample of patients with clinical and radiographic hand OA and their siblings were evaluated by examination and radiography. Radiographs were scored for hand OA features by radiographic atlas. The heritability of hand OA phenotypes was assessed for clinical and radiographic measures based on anatomic locations and radiographic characteristics. Phenotypic data were transformed to reduce non-normality, if necessary. A variance components approach was used to calculate heritability. RESULTS One hundred and thirty-six probands with hand OA and their sibling(s) were enrolled. By anatomic location, the highest heritability was seen with involvement of the first interphalangeal joint (h2 = 0.63, P = 0.00004), the first carpometacarpal joint (h2 = 0.38, P = 0.01), the distal interphalangeal joints (h2 = 0.36, P = 0.02), and the proximal interphalangeal joints (h2 = 0.30, P = 0.03) with osteophytes. The number and severity of joints with osteophyte involvement was heritable overall (h2 = 0.38, P = 0.008 for number and h2 = 0.35, P = 0.01 for severity) and for all interphalangeal joints (h2 = 0.42, P = 0.004 and h2 = 0.33, P = 0.02). The severity of carpometacarpal joint involvement was also heritable (h2 = 0.53, P = 0.0006). Similar results were obtained when the analysis was limited to the Caucasian sample. CONCLUSIONS In a population with clinical and radiographic hand OA and their siblings, the presence of osteophytes was the most sensitive biomarker for hand OA heritability. Significant heritability was detected for anatomic phenotypes by joint location, severity of joint involvement with osteophytes as well as for overall number and degree of hand OA involvement. These findings are in agreement with the strong genetic predisposition for hand OA reported by others. The results support phenotyping based on severity of osteophytes and a joint-specific approach. More specific phenotypes may hold greater promise in the study of genetics in hand OA.