Abstract
Introduction
Genetic predisposition is a key causal factor in adolescent idiopathic scoliosis (AIS), which is the most common form of spinal deformity. However, common quantitative genetic effect estimates such as hereditability have not been fully evaluated and reported for this disorder. We aimed to determine the sibling recurrent risk and hereditability of AIS in first-degree relatives of 513 Chinese patients with this disorder.
Methods
Family members of 513 Chinese patients with AIS attending a scoliosis clinic were assessed. A diagnosis of AIS was made with the criteria of Cobb angle greater than 20°. The evaluation included clinical assessment and physical examination in a health screening centre by medical doctors with use of forward bending test. Any positive screening cases were referred to a scoliosis clinic for follow-up spinal radiograph. All radiographs were assessed by an orthopaedic surgeon in the scoliosis clinic. A population prevalence of scoliosis was obtained from the data of a territory-wide screening campaign. The prevalence of AIS among siblings of probands was measured both overall and divided by sex of siblings. The sibling recurrent risk (λs) was calculated for male and female siblings separately with reported population incidence of AIS.
Results
The 513 probands had 640 siblings, and 110 affected siblings were identified (17·2%, 95% CI 14·3–20·1), which was significantly higher than the disease prevalence in the general population (1·39%, p<0·0001). The prevalence of AIS was 11·3% (7·6–14·9) in male siblings and 22·2% (17·8–26·6) in female siblings. The prevalence of AIS in female siblings was significantly higher than that in male siblings (p<0·001). The average sibling recurrent risk ratio (λs) was 12·4. Overall, heritability was estimated to be 87·5%.
Conclusions
The results confirmed the prevailing impression of a strong genetic effect on risk of AIS. We provided these standard genetic aggregation estimates and hereditability of AIS for the first time. The estimates allow comparison with other complex diseases such as diabetes mellitus in term of genetic predisposition. Our findings suggest that AIS has a moderate to strong genetic predisposition and it is comparable with other complex traits.
