Everything about Y Chromosome Microdeletion totally explained
Y chromosome microdeletion (YCM) is a family of
genetic disorders caused by missing gene(s) in the
Y chromosome. Many men with YCM exhibit no symptoms and lead normal lives. However, YCM is also known to be present in a significant number of men with reduced
fertility. Men with reduced sperm production (in up to 20% of men with reduced
sperm count, some form of YCM has been detected) varies from
oligozoospermia, significant lack of sperm, or
azoospermia, complete lack of sperm.
Various genes shown to have some correlation with
spermatogenesis in men with reduced fertility include
RBM,
DAZ,
SPGY, and
TSPY.
Cause
The mechanism of
mutation isn't different for Y-chromosome microdeletion. However, the ability to repair it differs from other chromosomes. The human Y chromosome is passed directly from father to son, and isn't protected against accumulating copying errors, whereas other chromosomes are error corrected by recombining genetic information from mother and father. This may leave
natural selection as the primary repair mechanism for the Y chromosome.
Diagnosis
Y chromosome microdeletion is currently diagnosed by extracting DNA from
leukocytes in a man's blood sample, mixing it with some of the about 300 known
genetic markers for
sequence-tagged sites (STS) on the Y chromosome, and then using
polymerase chain reaction amplification and
gel electrophoresis in order to test whether the DNA sequence corresponding to the selected markers is present in the DNA.
Such procedures can test only the integrity of a tiny part of the overall 23 million
base pair long Y chromosome, therefore the sensitivity of such tests depends on the choice and number of markers used. Present diagnostic techniques can only discover certain types of deletions and mutations on a chromosome and give therefore no complete picture of genetic causes of infertility. They can only demonstrate the presence of some defects, but not the absence of any possible genetic defect on the chromosome.
The gold standard test for genetic mutation, namely complete
DNA sequencing of a patient's Y chromosome, is still far too expensive for use in epidemiologic research or even clinical diagnostics.
Infertility
Microdeletions in the Y chromosome have been found at a much higher rate in
infertile men than in fertile controls and the correlation found may still go up as improved genetic testing techniques for the Y chromosome are developed.
Further Information
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