Background: Evidence is accumulating that the promoter region of the insulin-like growth factor I (IGF-I) gene polymorphism and low levels of IGF-I are associated with type 2 diabetes, cardiovascular disease and birth weight; however, the number of wild-type alleles is different in each country.
Objectives: This study aimed to examine the 737/738 marker, a cytosine-adenine repeat in the promoter region of the IGF-I gene polymorphism, and plasma IGF-I levels in Japanese infants and analyze the genetic background.
Methods: Data were collected for 15 months in Kyoto Prefectural University of Medicine. The body composition parameters of all infants were determined at birth. At 5 days after birth, we took blood samples to measure the product size of the promoter region of the IGF-I gene polymorphism and plasma IGF-I.
Results: In a population-based sample of 160 subjects, 6 different alleles and 16 genotypes were identified in the promoter region of the IGF-I gene polymorphism. The existence of a 196-bp allele has proved to result in a low plasma IGF-I level, a small head and chest circumference (p < 0.05) and no significant for premature birth, short-birth height and low-birth weight.
Conclusions: This is the first study showing the role of the promoter region of the IGF-I gene polymorphism and the level of plasma IGF-I and body composition parameters in Japanese infants. Our results suggest genetical influence on prenatal growth and serum IGF-I levels.