ALAS2 is a rate-limiting enzyme in the Hb biosynthetic pathway and expressed specifically in erythroid cells. The compound dinucleotide repeat, (CA)5T(GC)2(AC)4GTA(CA)23 (GA)3CA(GA)8,within intron 7
of the human ALAS2 gene has been used as a polymorphic marker for the sideroblastic anemia syndromes and an index marker for linkage mapping.So the purpose of our study is to investigate the
distribution characteristics of this polymorphism and its relationship to the aerobic endurance in northern Han nationality Chinese.
For the case-control studies, 123 northern Han elite long-distance running athletes ,including 62 male and 61 female,vs.134 normal northern university students controls,including 70 male and 64
female, were genotyped by using the genescan and sequencing methods.
（1）Ten genotypes，157 bp、162 bp、164 bp、166 bp、168 bp、170 bp、172 bp、174 bp、176 bp、178bp、180 bp，were observed in the subjects.
（2）When 166 bp length genotype were used as the cut point，the distribution frequency of ≤166bp length genotype was significantly highter in athletes than in controls.
The result reveals that the compound dinucleotide repeat polymorphism of the ALAS2 gene is associated with the aerobic endurance capacity in northern Han nationality Chinese.And the ≤166bp length
genotype can be the genetic marker for selecting elite long-distance runners.