GENETIC CAUSES OF MALE INFERTILITY
Plaseska-Karanfilska D1,*, Noveski P1, Plaseski T2,
Maleva I1, Madjunkova S1, Moneva Z1
*Corresponding Author: Professor Dr. Dijana Plaseska-Karanfilska, Research Centre for Genetic
Engineering and Biotechnology “Georgi D. Efremov,” Macedonian Academy of Sciences and Arts, Krste
Misirkov 2, Skopje 1000, Republic of Macedonia; Tel: +389(0)2 3235410; Fax: +389 (0)2 3115434; E-mail:
dijana@manu.edu.mk
page: 31
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INTRODUCTION
Infertility is a major health problem today,
affecting about 15.0% of couples trying to have a
child. Impaired fertility of the male is causative in
20.0% of infertile couples and contributory in up
to another 30.0-40.0%. Infertility already affects
about 5.0-7.0% of the general male population and
may further increase in the future, considering the
apparent trend of declining sperm count in industrialized
countries. Despite enormous progress in
the understanding of human reproductive physiology,
the underlying cause of male infertility remains
undefined in about 50.0% of cases, which
are referred to as idiopathic infertility [1]. Most
idiopathic cases are likely to be of genetic origin
because the number of genes involved in human
spermatogenesis is probably over 1 thousands. At
present, only a few of the genes implicated in the
processes of testis determination, testis descent
and spermatogenesis have routine clinical importance.
These include the cystic fibrosis transmembrane
conductance regulator (CFTR) gene, whose
mutations cause cystic fibrosis and absence of vas
deferens and the androgen receptor (AR) gene, whose mutations cause the androgen insensitivity
syndrome and spermatogenic damage.
Common Genetic Causes of Male Infertility.
Chromosomal anomalies and microdeletions of the
azoospermia factor (AZF) regions of the Y chromosome
are the only commonly known genetic causes
of spermatogenic failure. The frequency of these
two genetic anomalies increases with the severity of
the spermatogenic defect, reaching up to an overall
30.0% (15.0% karyotype abnormalities and 15.0%
of AZF microdeletions) in azoospermic men.
Sex chromosome aneuploidies, such as
47,XXY (Klinefelter’s syndrome), 47,XYY and
46,XX males are the most common chromosome
anomalies occurring at birth and in the population
of infertile males [2]. Klinefelter’s syndrome is a
form of primary testicular failure with a high prevalence
in infertile men, up to 5.0% in severe oligozoospermia
and 10.0% in azoospermia.
Y chromosome microdeletions represent the
etiological factor of 10.0-15.0% of idiopathic azoospermia
and severe oligozoospermia [3]. The frequency
of AZF deletions in infertile men ranges from
5.0 to 20.0% in worldwide surveys [4]. Y chromosome
microdeletions are found almost exclusively
in patients with azoospermia or severe oligozoospermia
[5]. The prevalence of Y chromosome microdeletions
in the infertile males from the Republic
of Macedonia is 6.4%, in patients with azoospermia
16.7% and 2.8% in those with severe oligozoosper-mia [6]. Deletions most frequently involve the AZFc
region, less frequently the AZFb region, and only
rarely the AZFa region. The most frequent deletions
in Macedonian males are AZFc deletions, while AZFa
deletions have not been detected [7,8].
Partial deletions within the AZFc region (gr/
gr and b2/b3) that remove smaller portions of the
AZFc region (1.6 and 1.8 Mb) are much more common
and are present at various frequencies in different
Y chromosome haplogroups [9]. While the
association of the complete AZFc deletion with
spermatogenic failure is well established, the role
of partial AZFc deletions on spermatogenesis and
male infertility is still controversial.
In addition to deletions, different duplications at
the AZFc region have been reported. Duplications
can occur on a chromosome with a partial AZFc deletion
and generate a chromosome with four DAZ
genes, but lacking some sequence tagged site (STS)
markers [10,11]. Recently, an AZFc partial duplication
has been shown to be a risk factor for male
infertility in Taiwan [12].
Screening for Common Genetic Causes of
Male Infertility by Quantitative Fluorescent-
Polymerase Chain Reaction. Screening for chromosomal
abnormalities is usually done by cytogenetic
analysis and for AZF deletions by polymerase
chain reaction (PCR) analysis of several STSs in the
three AZF regions. Recently, we described a multiplex
quantitative fluorescent (QF)-PCR method that
allows simultaneous detection of the most common
genetic causes of male infertility, i.e., sex chromosomal
aneuploidies and AZFc and AZFb deletions,
and some potential risk factors such as partial AZFc
deletions/duplications and AR CAG repeats [8].
This multiplex QF-PCR analysis was shown to be
a rapid, simple, reliable and inexpensive method
that can be used as a first-step genetic analysis in
infertile patients. Recently, we presented a modified
system, where we have included additional markers
in the AZFa and AZFb region, as well as a marker
for determination of the X/chromosome 3 ratio [13].
Our results showed that Klinefelter’s syndrome
and complete AZFc deletions are the most common
genetic causes of azoospermia. Partial AZFc deletions
as well as AZFc duplications were present in
both infertile and fertile men. They may represent a
risk factor for male infertility when present on certain
Y chromosomal backgrounds.
Gene Polymorphisms and Male Infertility.
Analysis of Y chromosome haplogroups, defined
by single nucleotide polymorphisms (SNPs), has
become a standard approach for studying the origin
of human populations and measuring the variability
among them. A few groups have studied the
possible association of Y chromosome haplogroups
with male infertility and Y chromosome microdeletions,
but conflicting results have been published.
Some recent studies suggested that a Y chromosome
background is an important factor that affects partial
AZFc deletion formation and its contribution to
spermatogenic failure [14].
We have used a hierarchical analysis of 28 SNP
markers by multiplex PCR followed by single base
extension reactions using a multiplex SNaPshot
kit to determine the Y chromosome haplogroups
in men from our country [15]. Our initial results
showed slight differences in the distribution of the
Y chromosome haplogroups such as higher frequency
of the R1a haplogroup in infertile patients with
a milder phenotype in comparison with those with
azoospermia and severe oligozoospermia and fertile
controls.
We have studied in detail the Y chromosomal
background of different Y chromosome deletions
detected in men from our country. Several different
Y chromosome haplogroups were determined
in men with complete AZFc (b2/b4) deletions and
gr/gr deletions. All infertile males with b2/b3 deletion
belong to the Hgr E3b1 anomaly, while the only
fertile man with this deletion falls within the Hgr
N3 anomaly. Most of the men with the b2/b4 duplication,
both infertile and fertile, were identified as
Hgr R1a, but the frequency of this Hgr was higher
in infertile men. There was also a difference in the
distribution of the Y chromosome haplogroups in
males with the b2/b3 duplication.
The analysis of polymorphisms in genes involved
in spermatogenesis represents one of the
most exciting areas of research in genetics of male
infertility [16]. Polymorphisms in these genes are
considered potential risk factors that may contribute
to the severity of spermatogenic failure.
Polymorphisms in different genes [CAG repeats in
AR and DNA polymerase g (POLG) genes, C677T
mutation in 5-methylenetetrahydrofolate reductase
(MTHFR), A260G and A386G in the DAZL gene,
different polymorphisms in FSHR, ERa, protamine 1 and 2, etc.] have been studied for possible association
with male infertility but many of them have
presented contradictory results. It is likely that only
polymorphisms in association with a specific genetic
background and/or with environmental factors
can lead to spermatogenic impairment. We have also
studied the possible association of several different
polymorphisms with male infertility. There was no
association between the POLG polymorphism and
infertility in Macedonian men [17]. We found a significantly
higher percentage of long CAG repeats
in patients with mild oligozoospermia indicating
the possible association of CAG repeat numbers in
exon 1 of the AR gene and mild oligozoospermia
[18]. Our preliminary results suggest that there is no
association between the MTHFR C677T, MTHFR
A1298C, MTR A2756G and MTRR A66G polymorphisms
and male infertility. Of the nine SNPs
evaluated in eight different genes (FASLG, JMJDIA,
LOC203413, TEX15, BRDT, OR2W3, INSR and
TAS2R38), we found significant association for three
SNPs (rs5911500 in the LOC203413, rs3088232 in
the BRDT and rs11204546 in the OR2W3 genes, respectively)
[19].
Copy number variations (CNVs) represent an
important source of genetic diversity with remarkable
differences between individuals. Copy number
variations can cause spermatogenic failure by their
increased number or specific distribution that could
result in defective recombination, meiotic failure
and loss of germ cells. Copy number variations
might also affect the activity of genes important for
spermatogenesis. The first study that investigated
CNVs in patients with severe oligozoospermia and
Sertoly cell only syndrome (SCOS) was published
only recently [20]. This study provided a number
of candidate genes, possibly causing or being risk
factors for, spermatogenic failure. Using array
CGH analysis we have also identified several CNVs
(UGT2B17 gene on chr4 q13.2; STEAP2 gene on
chr7 q21.13; TPTE gene on chr21 p11.2-11.1 and
H2BFWT on chrX q22.2) that might be associated
with impaired spermatogenesis and male infertility.
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