According to wikipedia:

The androgen receptor (AR), also known as NR3C4, is activated by the binding of testosterone or dihydrotestosterone, where it plays a critical role in the forming of primary and secondary male sex characteristics. Hare et al. found that male-to-female transsexuals were found to have longer repetitions of the gene, which reduced its effectiveness at binding testosterone.[18]

So maybe the amount of testosterone would be normal but it would have less effect?