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The CNS-hypothalamic causes for abnormalities in sperm include
* (1) Structural lesions
Structural lesion that interfere with the transport of GnRH from
the hypothalamus to the pituitary gland may result in FSH and
LH concentrations in the low-normal range along with a low circulating
testosterone concentration. As with women, these men should have
radiologic imaging to specifically rule out an anatomic lesion.
* (2) Kallman's syndrome
This is an uncommon disorder (responsible for less than 1% of
azoospermia) in which the GnRH neurons do not develop normally.
The GnRH neurons are located near the olfactory neurons (used
for the sense of smell) in early development, and the process
that causes the GnRH neurons to fail to migrate to their usual
eventual location also results in failure of migration of the
olfactory neurons. The result is a lack of GnRH effect on the
pituitary gland (hypogonadotropic hypogonadism) and anosmia (inability
to smell). The infertility caused by this syndrome is treatable
by replacement of gonadotropins or GnRH using available fertility
medications.
* (3) Substance abuse
Elicit drugs (cocaine, opioid compounds, marijuana) are thought
to primarily effect the brain's ability to communicate properly
with the testes and thereby are disruptive to spermatogenesis.
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