The Principles of Clinical Cytogenetics - Extra Materials - Springer

Cytogenetics of Infertility 257
chain configurations between the translocation quadrivalent and the X-Y bivalent (see Chapter 10).
These were not seen to any significant degree in the chromosome preparations of the men with reciprocal
translocations involving other chromosomes.
In Zuffardi and Tiepolo’s (25) review of 7277 men, the range of autosomal abnormalities was
0.6–1.6%, with an average of 1.1%. Overall, the incidence of balanced translocations was 8.9 per
1000, which is 6 times greater than the 1.4 per 1000 newborns they used as a control population. For
Robertsonian translocations, the incidence in infertile men was 10 times higher than in newborns—
5.9 per 1000 vs 0.6 per 1000 (25). For a comparison of chromosome abnormalities seen in studies of
infertile men, see Tables 6–8.
Microdeletions of the Y Chromosome
The fact that genes necessary for spermatozoa production are on the long arm of the Y chromosome
became evident in a study published in 1976 by Tiepolo and Zuffardi (27). They studied six
azoospermic males and found microdeletions at Yq11.2 that were not present in the fertile fathers and
brothers of the men. These were the first microdeletions found on the Y chromosome; they are called
microdeletions because they are not detectable by conventional cytogenetic testing (see Chapters 9
and 17). Thus, molecular or molecular cytogenetic testing is required to detect these deletions. This
deleted region was called AZF for azoospermia factor. It is now known that there are several other
genes on the long arm of the Y chromosome that are associated with faulty spermatogenesis, so the
AZF region has been subdivided as described below. It is now estimated that microdeletions of the Y
chromosome are present in 8–15% of men with nonobstructive azoospermia or severe oligozoospermia
(28,29)—that is, men with a spermatozoa count of