Objective:To investigate the association of a(TA)n dinucleotide repeat polymorphism with unknown aetiology hypomenorrhea.Methods:100 normal menstruation person(control group) and 100 hypomenorrhea patients(case group)were recruited.they all came from southen-western China.The(TA)n dinucleotide repeat in ERa gene upstream hypervariable region were purifed

cloned and sequence analysed.we observe the ERa gene(TA)n dinucleotide repeat polymorphism distribution in the two groups.Results:All samples exhibted 7 different alleles.The(TA)n dinucleotide repeats were 11~17

The most prevalent allele was TA14 repeat in control group.The distribution of the different alleles of the(TA)n dinucleotide repeat sequence in the group and control group has significant difference(χ2=13.412

P =0.037).Fisher’s exact test was applied to compare the frequency of each a1lele between two groups.The frenquency of the TA13 allele was found to be significantly greater in hypomenorrhea group(P =0.006)

and the frenquency of the TA15 allele was less in the group(P =0.033).Conclusion:A(TA)n dinucleotide repeat sequence which is in ERa gene upstream hypervariable region was associated with unknown aetiology hypomenorrhea.The TA13 allele was found to be associated with unknown aetiology hypomenorrhea and may be a risk factor;whereas TA15 allele may be a protective factor for patients.