INCIDENCE OF INSULIN-DEPENDENT DIABETES-MELLITUS AMONG SARDINIAN-HERITAGE CHILDREN BORN IN LAZIO REGION, ITALY

Background The relative importance of genetic and environmental factor s in causing insulin-dependent diabetes mellitus (IDDM) is unknown. We studied this question by assessing the incidence of the disease in ch ildren, born in a region with a low incidence of IDDM (Lazio), but who se parents came from a region with high incidence (Sardinia). Methods We identified all IDDM cases that occurred between 1989 and 1994. We u sed as the denominator the number of children aged 0-14 born in Lazio of Sardinian parents to calculate incidence. We compared this rate wit h the incidences of IDDM in the populations of Lazio and Sardinia. Fin dings The age-adjusted incidence of IDDM in Sardinian-heritage childre n born and living in Lazio was 33.8 per 100 000 per year (95% CI 7.0-9 9.0) for those with two Sardinian parents, and 15.9 (8.7-26.6) for tho se with only one parent from Sardinia. The former incidence was not di fferent from that recorded in Sardinia (34.4, 31.3-37.9), but was four fold that of Lazio-heritage children (7.9, 7.1-8.8). Interpretation Ou r results show that two different ethnic groups living in the same reg ion have a fourfold difference in incidence of IDDM. Children of Sardi nian-heritage born in Lazio have the same incidence as the population of origin, which is genetically prone to the disease. Moreover, childr en with one Sardinian parent had a rate half that of Sardinians and do uble that of the indigenous population. We conclude that in a given po pulation genetic susceptibility determines the frequency of IDDM in re sponse to the environmental challenge.