LETTER TO JMG The gr/gr deletion(s): a new genetic test in male infertility?

chromosome microdeletions are the most frequent genetic cause of severe oligozoospermia (,5 million spermatozoa/ml) and azoospermia (absence of sperma-tozoa in the ejaculate).1 Microdeletions associated with infertility occur in specific regions of the long arm of the Y chromosome, called azoospermia factor (AZF) regions.2 3 In 1996, three types of AZF deletion (AZFa, AZFb, and AZFc) were described by Vogt et al; however, after the complete physical map and sequence of the AZFb and AZFc regions was produced,4 it became evident that the AZFb and AZFc intervals partially overlap.5 The Y chromosome is extremely rich in repetitive sequences, organised in amplicons.6 Ampliconic sequences are characterised by sequence pairs showing nearly complete (.99.9%) nucleotide identity, organised in massive palindromes. These repeated sequence