Context: Small for gestational age (SGA) subjects experience pre- and postnatal growth restriction, which might be influenced by polymorphisms in the IGF1 gene. The well-known -841(CA)(n)/192 bp polymorphism has been associated with birth size, cardiovascular disease, and IGF-1 levels, and is in linkage disequilibrium with the -G1245A single nucleotide polymorphism (SNP; rs35767).
Objective: To associate the -G1245A SNP with head circumference (HC) and brain sparing (a greater head compared with height SDS) in short SGA and SGA catch-up subjects.
Design: Gene association study.
Patients: We studied 635 SGA subjects out of which 439 remained short and 196 had a postnatal height >-2.00 SDS.
Measurements: The -G1245A SNP IGF1 gene polymorphism and head size.
Results: All SGA subjects had a postnatal head size below the population mean (-1.01 SDS, P<0.001). Whereas SGA catch-up subjects had a head size that was in proportion with their height, short SGA subjects displayed extensive brain sparing (HC - height: SGA CU: 0.01 versus short SGA: 1.75 SDS, P<0.001). The most severely SGA born subjects had a 0.4 SDS smaller postnatal head size and 0.6 SDS less brain sparing when carrying the -1245 A-allele in contrast to G-allele carriers (P=0.03). The association between the -G1245A SNP and head size remained significant after correction for birth weight and postnatal height SDS (P=0.03). Birth weight, birth length and postnatal height SDS were not related with the - G1245A SNP.
Conclusions: The -1245 A-allele of the IGF1 promoter SNP is associated with a small head size and less brain sparing in SGA born subjects and particularly those with the lowest birth weight.