AZFa and candidate genes:

The size of the AZFa region is estimated to be 1Mb. The frequency of deletions in AZFa is lower than that of both AZFb and AZFc.

The important candidate genes include USP9Y (ubiquitin- specific protease 9, Y chromosome) and DBY (dead box on the Y).

USP9Y is a single copy gene that functions as a C-terminal ubiquitin hydrolase. It is ubiquitously expressed in a wide variety of tissues.

DBY is ubiquitously expressed in humans. In addition it exhibits transcripts unique to the testis. The protein it encodes is an RNA helicase. DBY is more frequently deleted than USP9Y.

The other candidate genes include UTY (ubiquitous TPR motif on the Y) and TB4Y (thymosin B4-isoform).

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