The other genetic factor thus far identified as most clearly contributing to outcome is the androgen receptor (AR), which contains a highly polymorphic CAG repeat region. A study in 47,XXY boys found that increased length of this region was inversely correlated with penile length, indicating less effective early androgen action [Zinn et al., 2005]. It is also possible that specific allelic variation of genes on the sex chromosomes may add to variation, although there is little data available looking at this specifically.
