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Autosomal abnormalitiesFrom time to time, men may ask for fertility treatments including IVF/ICSI when they are already known to have an autosomal defect. In these cases, genetic counselling is also required.
X-linked genetic disorders and male fertility The man has only one X chromosome. This means that an X-linked recessive disorder will be manifest in males, and that the defect will be transmitted to his daughters, but not to his sons. Kail man n's syndrome The commonest X-linked disorder in infertility practice is Kallmann's syndrome and the predominant form is X-linked recessive caused by a mutation in the KALIG-1 gene on Xp 22.3 [14]. Rarer forms of Kallmann's syndrome include an autosomal-dominant form [15]. Patients with Kallmann's syndrome have hypogonadotrophic hypogonadism and may have other clinical features, including anosmia, facial asymmetry, cleft palate, colour blindness, deafness, maldescended testes and renal abnormalities. It is important to note that some men with Kallmann's syndrome have an isolated gonadotrophin deficiency without any other phenotypic abnormalities. These patients may present de novo with infertility, which can be treated successfully by hormone replacement therapy. Androgen insensitivity: Reifenstein's syndrome The rare disorder of androgen insensitivity may first present with infertility. The condition has X-linked recessive inheritance due to a defect in the androgen receptor gene located on Xq 11-12. The phenotype varies widely, from complete testicular feminization to an apparently normal man with infertility, although the latter is rare. A structured genetic search for androgen deficiency was conducted amongst men with high testosterone and low sperm counts, but no cases were found using base pair mismatch analysis technology [16]. Several de novo mutations of the androgen receptor were noted, but in all cases, these were associated with obvious genital abnormalities such as hypospadias. It was concluded that androgen insensitivity in the infertile male in the absence of any genital abnormality is rare. Other X-disorders A case report exists of an azoospermic man with biopsy-proven spermatogenetic arrest, who was found to have a submicroscopic interstitial deletion on the Xp pseudoautosomal region in peripheral blood and skin fibroblast samples. Other genetic and chromosome examinations were entirely normal, including probing of the Yq region [17]. There is also a report about two men with azoospermia and X pseudoautosomal deletions [18]. X-linked disorders not associated with male infertility A number of rare X-linked disorders are not associated with infertility. When recessive, these appear in male babies but skip several generations and therefore family history is important. Examples of such disorders include: ? retinitis pigmentosa, a condition that affects 1 in 3,000 people, may be recessive or dominant and ? chronic granulomatous disease (CGD), a condition that predisposes to severe bacterial and fungal ? Menkes' syndrome, an X-linked recessive disturbance of copper metabolism associated with
A large number of case series of Y microdeletions have been published (Table 1) and it is clear that while microdeletions may occur in the fertile population [22], they are more prevalent in the infertile population. Microdeletions have been found in three non-overlapping regions of the Y chromosome, AZF a-b-c [23]. Several genes have been described, including RBM, DAZ, DFFRY, DBY and XXX. The most commonly reported abnormality is a microdeletion in the AZFc region which encompasses the DAZ gene. However, there is no exact correlation between DAZ deletion and the presence or absence of spermatogenesis. Table 1: Men with microdeletions (Adapted from published case series data)
Clinical implications of Y microdeletions There are no reports that men with microdeletions have any phenotypic abnormalities other than abnormal spermatogenesis [23,31,38]. As there is only one Y chromosome, it may be predicted that Y microdeletions will be transmitted to male offspring, although this is likely to be rare in the normal population because, without ICSI treatment, men with very low sperm counts are less likely to father children. Nevertheless, eight such cases have been reported (Table 2). More information is needed from father/son pairs where the son has a very low sperm count, and also about the outcome of ICSI attempts where spermatozoa have been used from men with microdeletions. Long-term follow-up of any male children is also required.
Testing for Y microdeletions Testing for microdeletions is now widespread, but the lack of a standardized methodology makes it difficult to directly compare the reported results (Table 1). Several centres have developed screening methodologies [23,26,31,44]. As there is no correlation between the histopathoiogy and deletion of DAZ, it is premature to rely on detection using specific gene probes, as this will fail to find a significant proportion of men with microdeletions. Comparing results from 28 different European laboratories, it was concluded that use of a high number of primers did not improve the accuracy of results. Recommendations are being produced for standardization [45].
There are a number of inherited disorders with severe or considerable generalized abnormalities as well as infertility (Table 3). Such patients will be well known to doctors often from childhood and any fertility problem has to be managed in the context of the care of the man as a whole and with consideration of his and his partner's ability to care for a child, should infertility treatment be successful.
Date: 2016-06-12; view: 301
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