This epidemiologic study of Paget's disease of bone used data from 788 cases and 387 spouse controls to investigate the following: (1) the extent to which this disorder aggregates in families; (2) the cumulative incidence of the disease in first-degree relatives of patients throughout life; and (3) the influence of age at diagnosis (<55 versus 55+ years) and presence of bone deformity in the case on risk of Paget's disease in relatives.

A positive family history in parents or siblings was reported by 12.3% of cases and 2.1% of controls. The rate of Paget's disease was approximately seven times as high in relatives of cases as in relatives of controls, and this increased rate did not differ according to gender of case or control or gender of relatives. Cumulative incidence of Paget's disease to age 90 was much higher in relatives of cases (8.9 ± 1.0% SEM) than in relatives of controls (1.8 ± 0.9% SEM). Among relatives of cases, cumulative risk was highest when the case had both early age at diagnosis and bone deformity (20.7 ± 3.6% SEM) compared with risk when the case had early age at diagnosis but not bone deformity (10.8 ± 3.2% SEM), bone deformity but not early age at diagnosis (5.8 ± 1.3% SEM), or neither bone deformity nor early age at diagnosis (3.6 ± 0.8% SEM). Risk in siblings of cases was higher when a parent was affected (22.1 ± 8.0% SEM) than when both parents were unaffected (6.7 ± 1.1% SEM).

These findings suggest that first-degree relatives of patients with Paget's disease have increased risk of developing the disorder, especially if the affected relatives have early age at diagnosis or deforming bone disease.