The influence of the length of the human Y chromosome on spontaneous abortions. A prospective study in family lines with inherited polymorphic Y chromosomes.

Following reports indicating a close association between the presence of a long Y chromosome in males and the risk of spontaneous abortion in their female partners, the incidence of spontaneous fetal loss was investigated in four family lines whose patrilineary ancestors emigrated from France to Canada during the second half of the seventeenth century. In two of the lines the males were carriers of a Yq+, in the other two the males had a Yq- or a normal Y chromosome. Results showed that in one of family lines with a Yq+, 17/26 (65.4%) wives had 33 (2.8%) spontaneous abortions in 151 pregnancies, whereas in each of the three other family lines 7/30 (23.3%) wives aborted 8 (4.9%), 15 (7.5%) and 10 (5.7%) times in 165, 200 and 175 pregnancies respectively. The high incidence of fetal loss found in one of the family lines whose males have a long Y chromosome correlates with previous observations on the influence of Yq+ on spontaneous abortions, and draws attention to the inheritable nature of this peculiarity. However, the low incidence of miscarriages observed in the other family line carrying a Yq+ seems to indicate that long Y chromosomes are of various types and could be produced by several mechanisms. Yq- does not seem to represent an increased risk of pregnancy loss. Results also demonstrated that while a long Y chromosome may affect the viability of the zygote, it does not affect the fertility of its carrier.