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Genetic causes of male infertility

letto 6507 volte | autore: Sebastiana Pappalardo, biologa (vai al curriculum)


The frequency of chromosomal abnormalities in infertile individuals is five times higher than that found in fertile individuals.  Genetic factors are common in both men and women.  The possible causes of  the upset can be divided into three groups : (a)chromosomal alteration; (b)uni- and multi-factoral alteration of the genes. Spermatogenesis would be more disturbed by this process, as much as the exact pairing of the homologous zones of the XY pair seem to directly control the initial processes of the  I meiotic prophase, therefore sites which do not normally appear would provoke a gametogenesis  block and the arrest of the maturation of the spermatide. The result of all this is that chromosomal abnormalities or structural rearrangement can disturb the genetic control of differentiation  of the germinal cells therefore causing infertility.

(a)  Male chromosomal alteration

Numeric : presence of over numbered X or Y chromosomes
>XXY Syndrome – Klinefelter, pheno-tipically male, carriers of azoospermia and more rarely oligospermia (generally in cases of mosaichism)
>XYY Syndrome – the double Y kind – are not infertile, sometimes hypogonadism
Structural : consist mainly of the deletion of certain traits of the Y chromosome.  The severity of the problem depends on the zone affected.
>Mosaichisms: consist of the presence of many cellular lines of differing chromosomal constitution.  They are caused by a non-disjunction or the loss of a chromosome in the anaphase of a mono zygote. The variability of phenotypical effects  depends on the percentage and the distribution in organism of the various clones.
>Gene dependant infertility
In men instead, 5% of infertile males with problems of  oligo-azoospermia present with a chromosomal abnormaliaty.  It is not rare to investigate on the male karyotype with signs of azoospermia and find a Klinefelter genotype (47, XXY).The sterility in this case can be associated with the absent disactivation in the germinal cells of the extra X chromosome.

Other common causes are mosaic XY/XXY and other structural rearrangements being the movement and the inversion, that determine a mechanical arrest of meiosis because of pairing defects during prophase I

CHROMOSOMAL ALTERATION BECAUSE OF THE MALE SEXUAL CHROMOSOMES (interfere with the genetic control of  differentiation of the germinal cells) :



  • 47,XXY – Klinefelter Syndrome 1: 1000 born (azoospermia, oligospermia in the case of  mosaichism)
  • 47XYY – Double Y Syndrome 1: 1000 born (hypogonadism, fertility in genus)


DELETION (the severity varies according to the size of the affected zone)
INVERSION (the severity varies according to the size of the affected zone)
TRANSLOCATION Y – AUTOSUM (the severity varies depending on the size of the affected zone)
ISOCHROMOSOMES (the severity varies according to the size of the affected zone)

In the presence of  determinate conditions, these being azoospermia, oligoastenospermia,  idiopathic infertility, a year of sexual relations aimed at conception without a results, a batch of examinations that consist of a simple drawing of blood, give information on possible problems at a chromosomal level.

(b) Genetic alteration

Next to descriptions of  reproductive ailments caused by chromosomal abnormalities there are also those caused by genetic alteration. The genes are sub-chromosomal units, comprised of segments of DNA from where the information sets out for the correct formation of the various polypeptides; wrong messages result in abnormal end products or even missing end products. Examples  of these mechanisms are molecular disorders like Cystic Fibrosis that cause blockages of the sperm ducts resulting in obstructive azoospermia. A problem apart from the deletion of the eucromatic distal of the long arm of the Y chromosome on which a gene is mapped for the control of the spermatogenesis.  If any doubt surges as to whether a man is a carrier of such a defect, relative molecular investigations have to be effected.

    (Mutation of  a single gene)
  • MICRODELETION OF THE Y CHROMOSOME – deletion of the eucromatic distal part of the long arm of the Y chromosome on which  DAZ gene maps (loci AZF a, b, c) for the control of spermatogenesis – (Azoospermia) Prevalence of the microdeletion in infertile patients is  : 10%
  • CYSTIC FIBROSIS – a recessive autoimmune pathology where the gene is located on chromosome 7 which maps a gene for the protein CFTR- and presents about 500 mutations-(Azoospermia)

Disclaimer: the information provided on this site is designed to support, not replace, the relationship that exists between a patient/site visitor and his/her existing physician.

giovedì 20 marzo 2008

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