IGF-I has a pivotal role in bone growth and could be one of the putative 
disease-modifier genes in AIS. Two SNPs in IGF-I gene promoter region were 
studied for any association with occurrence of AIS and for their effect on the 
curve severity among AIS.
METHODS: 506 AIS girls (Cobb>20 degrees) and 227 age-matched Chinese girls were 
recruited. The spine (L2-L4) and hip BMD of the subjects were measured by DXA. A 
subgroup of AIS patients (N=340) who were followed-up to skeletal maturity and 
the maximum Cobb's angle was recorded. Two SNPs were genotyped by PCR-RFLP 
(rs5742612 and rs2288377). The chi-square test and one-way ANOVA were used to 
test the association between genotypes and quantitative parameters, 
respectively.
RESULTS: No association was between the genotypes and the occurrence of AIS and 
the BMD of the spine and hip. The allelic frequency of T allele was 0.69 in AIS 
and control. However, the Cobb's angle was higher in patients with the 
homozygous T allele (Mean Cobb's angle: 38.1 degrees in TT vs 35.9 degrees in TC 
vs 33.2 degrees in CC group; p=0.04).
DISCUSSION: Interestingly, IGF-I polymorphism affects the curve severity of AIS 
though it was not associated with onset of AIS per se. It indicates that IGF-I 
may be a disease modifying gene. The importance of IGF-I in skeletal growth 
makes it a good candidate gene which would play a role in the documented 
association of rapid growth with curve progression in AIS.