doi:10.1093/humrep/den027
Human Reproduction Vol.23, No.8 pp. 1691–1697, 2008
Advance Access publication on May 15, 2008
The relationship between meiotic recombination in human
spermatocytes and aneuploidy in sperm
F. Sun1,5, M. Mikhaail-Philips1, M. Oliver-Bonet1, E. Ko1, A. Rademaker2, P. Turek3,4 and
R.H. Martin1,6
1
Department of Medical Genetics, University of Calgary, 3330 Hospital Dr, NW, Calgary, AB, Canada T2N 4N1; 2Department of
Preventive Medicine, Northwestern University Medical School, Chicago, IL 60611-4402, USA; 3Department of Urology, University of
California San Francisco, San Francisco, CA 94143-1695, USA; 4Department of Obstetrics and Gynecology and Reproductive Sciences,
University of California San Francisco, San Francisco, CA 94143-1695, USA
5
Present address: Hefei National Laboratory for Physical Sciences, Microscale and School of Life Sciences, University of Science and
Technology of China, Hefei, Anhui 230026, People’s Republic of China
6
Correspondence address. Tel: þ1-403-220-7520; Fax: þ1-403-210-7931; E-mail: [email protected]
BACKGROUND: We have previously demonstrated that a decreased recombination frequency between human X and
Y chromosomes is associated with the production of aneuploid 24,XY sperm. This study’s aim was to determine the
relationship between recombination frequency in human pachytene spermatocytes and aneuploidy frequencies in
individual chromosomes in sperm from the same men. METHODS: Six previously fertile vasectomy reversal patients
donated testicular tissue for meiotic analysis of pachytene spermatocytes using immunocytogenetic techniques for
visualization of the synaptonemal complex and recombination sites (MLH1). Individual meiotic chromosomes were
identified with centromere-specific multicolor fluorescence in situ hybridization (FISH), and the number of MLH1
signals was recorded for individual chromosomes. An ejaculated sperm sample was obtained from each patient
2–26 months post-reversal for FISH analysis of sperm aneuploidy frequencies of chromosomes 1, 9, 13, 21, X and
Y. RESULTS: There was no significant correlation between meiotic recombination frequency and sperm aneuploidy
for any individual chromosome. Similarly, there was no correlation between aneuploid sperm and bivalents with no
recombination. CONCLUSIONS: The study provides unique data on intra-individual human recombination and
aneuploidy events. It also demonstrated for the first time that men do not have an increased frequency of sperm
aneuploidy 5–9 years post-vasectomy.
Keywords: meiotic recombination; human sperm aneuploidy; synaptonemal complex; pachytene spermatocytes; non-disjunction
Introduction
Pairing and recombination of homologous chromosomes
during meiotic prophase I are essential for chromosome segregation and the formation of haploid gametes. Improper
chromosome segregation during meiosis, i.e. non-disjunction,
results in genetically unbalanced oocytes or sperm. If these
gametes participate in fertilization, the outcome is the formation of an aneuploid embryo—the leading known cause of
pregnancy loss, mental impairment and developmental disabilities (Lamb and Hassold, 2004).
The association between meiotic recombination and aneuploidy has been well-documented in model organisms
(Koehler et al., 1996; Yuan et al., 2000; Molnar et al., 2001).
In the past several years, a number of linkage analysis
studies have demonstrated that this relationship is also important in humans. Absent or reduced levels of meiotic recombination or suboptimally positioned recombination events have
been associated with non-disjunction in both males (Hassold
et al., 1991; Lorda-Sanchez et al., 1992; Savage et al., 1998)
and females (Sherman et al., 1991; Lamb et al., 1997).
Because the sex chromosomal bivalent seems particularly susceptible to non-disjunction in human males, with the majority
of sex chromosomal aneuploidies originating from paternal
errors (Jacobs et al., 1990; MacDonald et al., 1994), we
sought to determine if a reduced recombination frequency is
associated with non-disjunction of the X and Y chromosomes
in individual sperm. Initially, we performed single sperm
PCR analysis on a normal 46,XY male to determine if there
was any alteration in the recombination frequency of aneuploid
24,XY sperm compared with unisomic sperm (23,X or 23,Y)
(Shi et al., 2001). The frequency of recombination between
the two DNA markers was 38.3% for unisomic sperm, but
there was a highly significant decrease in recombination
in aneuploid sperm (25.3%). This research was the first
# The Author 2008. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology.
All rights reserved. For Permissions, please email: [email protected]
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Sun et al.
direct evidence that altered recombination has an effect on
non-disjunction in human gametes.
Studies of infertile men have also begun to address this issue.
ICSI (Palermo et al., 1992) now allows severely infertile men
the opportunity for biological fatherhood. However, it is also
clear that there is genetic risk in using sperm from infertile
men for ICSI. We (Moosani et al., 1995; McInnes et al.,
1998) and others (Pang et al., 1999; Pfeffer et al., 1999;
Vegetti et al., 2000) have demonstrated that even karyotypically
normal infertile men have an increased frequency of aneuploid
sperm and this is particularly marked for infertile men with
non-obstructive azoospermia (Bernardini et al., 2000; Palermo
et al., 2002; Martin et al., 2003a). We are interested in understanding whether this increased frequency of aneuploidy in
infertile men is also associated with defects in meiotic recombination. Luckily, immunofluorescence methods that directly visualize important meiotic proteins now make this research possible
(Barlow and Hulten, 1998; Anderson et al., 1999; Hassold et al.,
2000; Sun et al., 2004a). Antibodies against synaptonemal
complex (SC) proteins SCP1 and SCP3 mark the transverse
and lateral elements of the SC, respectively; CREST
(Calcinosis, Raynaud’s phenomenon, Esophageal dysfunction,
Sclerodactyly, Telangiectasia) marks the centromere and mut
L homologue 1 (MLH1, a mismatch repair protein) marks
recombination foci, allowing the precise identification of recombination foci along SCs during meiotic prophase. This assay,
combined with centromere-specific multicolor fluorescence in
situ hybridization (cenM-FISH), allows analysis of recombination distributions of individual chromosomes in human germ
cells in great detail (Nietzel et al., 2001; Oliver-Bonet et al.,
2003; Sun et al., 2004b, 2006a,b). Using these techniques, we
have determined that men with non-obstructive azoospermia
have a variety of meiotic defects and a dramatic decrease in
the frequency of meiotic recombination (Gonsalves et al.,
2004; Sun et al., 2004a, 2005, 2007). These findings have
been corroborated in some laboratories (Ma et al., 2006), but
not others (Topping et al., 2006). Thus, several lines of evidence
point to a relationship between meiotic recombination and aneuploid gametes, but to date, very little research has examined the
recombination frequency in spermatogenesis and aneuploid
gametes in the same individuals.
In this study, the frequency of meiotic recombination in
specific chromosomes was examined in relation to the frequency of sperm aneuploidy for the same chromosomes in
the same individuals.
Materials and Methods
Sample collection
Testicular samples were obtained from 11 patients undergoing vasectomy reversal (University of California San Francisco, CA, USA). All
of the donors had previously fathered pregnancies. None of the men
had any medical illness nor exposure to radiation, chemotherapy or
drugs, except one donor, who used ibuprofen as required. Vasectomies
had been performed 5–9 years previously. Histological examination
showed normal spermatogenesis in all patients (ages 35– 61 years).
Testicular tissues were kept in phosphate-buffered saline (PBS;
pH 7.4) until use, and were shipped on ice to Calgary by air courier.
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We have previously demonstrated that the cold storage of testicular
tissue for 2 days has no effect on the quality of preparations or on
data on chromosome pairing or recombination (Sun et al., 2004c).
Ejaculated semen specimens were available from six of the patients
(2–26 months later); the rest declined to participate further in the
study. Samples were air-freighted on ice to Calgary. Informed
consent was obtained from all patients, and this study received
ethical approval from the institutional review boards at the University
of Calgary and the University of California San Francisco.
Fluorescence immunostaining
Slides with pachytene chromosome spreads were subjected to immunofluorescence staining as described previously (Sun et al., 2004b).
Primary antibodies against the following proteins were used: SCP1
(1:1000 dilution, a gift from P. Moens, York University), SCP3
(1:250 dilution, a gift from T. Ashley, Yale University), MLH1
(1:100 dilution, Oncogene, San Diego, CA, USA) and CREST
(1:100 dilution, a gift from M. Fritzler, University of Calgary).
These primary antibodies were detected using a cocktail of secondary
antibodies (donkey antisera) conjugated with different fluorochromes:
1-amino-4-methylcoumarin-3 acetic acid (AMCA) and Cy3 (1:100
dilution, Jackson Immunoresearch, West Grove, PA, USA), AlexaFluor 488 and AlexaFluor 555 (1:125 dilution, Molecular Probes,
Eugene, OR, USA). Primary and secondary antibodies were incubated
overnight at 378C, and for 90 min at 378C, respectively. Slides were
examined on a Zeiss Axiophot epifluorescence microscope equipped
with rhodamine, fluorescein isothiocyanate (FITC), and
4’,6-diamidino-2-phenylindole (DAPI) filters and a cooled chargedcoupled device (CCD) camera. Three fluorescent images (red, green
and blue) of the SCs, MLH1 sites and CREST locations, respectively,
were captured using Applied Imaging Cytovision 3.1 software
(Applied Imaging Corporation, Santa Clara, CA, USA). Spreads
were localized using a gridded finder slide.
Each pachytene-stage nucleus used for analysis met the following
criteria: (i) the correct numbers of bivalents (i.e. 22 autosomes and
1 sex body) were present, (ii) the SCs were not overlapped with
other SCs or bent back on themselves, allowing all foci to be scored
and (iii) background was fairly low, allowing the SCs to be distinguished from background noise and from each other. MLH1 signals
were scored if they were distinct and localized on an SC. SCs were
classified as normally synapsed if they were completely linear,
without any obvious bubbles, forks, loops or irregularities. One
hundred pachytene-stage cells were analyzed for each man, and
numbers of MLH1 foci per bivalent and the total number of foci per
autosomal complement were scored.
CenM-FISH on spermatocytes
After analysis of the captured immunofluorescence images, cenMFISH, which allows simultaneous identification of each SC, was
carried out on the same spermatocytes, and was used to identify the
chromosomes. Techniques developed by Nietzel et al. (2001) and
Oliver-Bonet et al. (2003) were modified to make use of the
microwave-decondensation/codenaturation FISH technique (Ko
et al., 2001). Cells were decondensed for 5 s in dithiothreitol (DTT)
and 30 s in 3,5-diiodosalicylic acid, lithium salt (LIS)/DTT at
medium power (550 watts). Hybridization buffer (10% dextran
sulfate, 2 standard sodium citrate (SSC), 55% formamide) was
prewarmed to 508C, added to the cenM-FISH probes and warmed at
508C until all probe was dissolved. Probes were applied to the slide,
a glass cover slip was sealed in place with rubber cement, the
probes and cells were microwave codenatured for 80 s at 1100 watts
and the slide was incubated in a humid chamber at 378C for 24 h.
A post-hybridization wash (0.4 SSC, 1% Nonidet P-40; 708C)
Human sperm aneuploidy and recombination
was carried out, streptavidin-AlexaFluor 647 (Molecular Probes) solution was applied under a plastic cover slip, and the slide was incubated at 378C for 40 min in a humid chamber. The slide was
washed, with constant agitation, for 10 min in 4 SSC, air-dried
and mounted in DAPI. Cells previously analyzed by antibody immunostaining were relocated, and six fluorescent images (blue, aqua,
green, gold, red and far red) were captured for each cell, using
Applied Imaging Cytovision 3.1 software (Applied Imaging Corporation, Santa Clara, CA, USA).
After cenM-FISH identification of each pachytene bivalent, the
images of corresponding SC spreads were analyzed for MLH1 focus
distribution. The numbers of MLH1 foci per bivalent and per SC
spread were scored in all males.
FISH on ejaculated sperm
Ejaculated sperm specimens were washed, microwave decondensed
and hybridized as described previously (Ko et al., 2001): sperm
DNA on the slides was microwave-decondensed with 10 mM DTT
(Sigma, Oakville, ON, Canada) (550 watts, 15 s), followed by
10 mM LIS (Sigma)/1 mM DTT (550 watts, 1.5 min). Slides were
rinsed, air-dried at room temperature, dehydrated in 80% methanol
at 2208C for 20 min, air-dried, and used immediately. Sex
TM
chromosome hybridizations were carried out using a Fluorogreen(Amersham, Baie d’Urfé, QC, Canada) labeled X-specific a-satellite
probe, kindly provided by E. Jabs of the Johns Hopkins University,
TM
Baltimore, MD, USA (Jabs et al., 1989), a Fluoroblue- labeled
chromosome 1-specific satellite III sequence, pUC1.77, generously
provided by H.J. Cooke of Edinburgh, Scotland (Cooke and
Hindley, 1979) and a CEP SpectrumOrange Yq probe (Vysis,
Downer’s Grove, IL, USA). Chromosome 1/9 hybridizations were
carried out using the same chromosome 1-specific satellite III
TM
sequence labeled directly with Fluorogreen , and a CEP SpectrumOrange 9 probe (Vysis). Chromosome 13/21 hybridizations used
SpectrumGreen 13 LSI and SpectrumOrange 21 LSI probes (Vysis).
cell for chromosomes 1, 9, 13 and 21, was 3.42 + 0.80,
2.01 + 0.60, 1.67 + 0.51 and 0.86 + 0.27, respectively
(Table I). In all, 600 pachytene-stage spermatocytes (100
cells for each male) were analyzed to determine the mean
MLH1 focus frequency per cell for autosomes, with an
overall mean (+SD) of 50.7 + 4.7 foci (range: 32– 63)
(Table I). On average, there was an MLH1 focus in the sex
body of 86/100 cells (range: 80– 91) (Table I). These frequencies of recombination foci in autosomes and sex chromosomes
are very similar to those in previous reports (Gonsalves et al.,
2004; Codina-Pascual et al., 2006; Sun et al., 2006b). The frequency of bivalents with 0 MLH1 foci is presented in Table II.
The sperm aneuploidy frequency for chromosomes 1, 9, 13,
21, X and Y was assessed by FISH analysis. About 10 000 spermatozoa were scored for each donor (Table III). No difference
between the disomy frequencies for XX and YY was observed
(both were 0.03%). However, the XY disomy frequency
(0.17%) was higher than the combined values of XX and YY
disomy (0.06%). The highest autosomal disomy and nullisomy
frequencies were both observed in chromosome 21.
Scoring of sperm nuclei
Slides were counted using a Zeiss Axiophot microscope fitted with
four filter sets: FITC, rhodamine/FITC, DAPI and rhodamine/
FITC/DAPI. Two same-colored signals were counted as individual
signals if they were separated by at least one signal diameter (1/2
signal diameter for the overlarge Y signal) and were of similar size,
shape and intensity. The blue chromosome 1 signal in sex chromosome hybridizations was used as an internal autosomal control to
distinguish between disomy and diploidy.
Statistical analysis
Correlations between the recombination frequency and frequencies of
aneuploidy in chromosomes were performed using Pearson and Spearman correlation analyses. One-way analysis of variance was used to
determine if chromosome 21 and the sex chromosomes had a higher
frequency of bivalents with no recombination compared with other
chromosomes. A value of P , 0.05 was considered significant.
Results
An example of pachytene SCs, with identification of individual
bivalents and cenM-FISH signals in the same cell, is shown in
Fig. 1. A total of 591 pachytene stage spreads with unambiguous cenM-FISH signals were analyzed to determine the MLH1
focus frequency for chromosomes 1, 9, 13 and 21 in the six men
who provided both testicular samples and ejaculated sperm.
On average, the mean (+SD) frequency of MLH1 foci per
Figure 1: Human pachytene spermatocyte. (upper) Synaptonemal
complex (SCs) are shown in red, centromeres in blue and mut L homologue 1 (MLH1, a mismatch repair protein) foci in yellow. (lower)
Subsequent centromere-specific multicolor FISH analysis allows
identification of individual chromosomes so that recombination
(MLH1) foci can be analyzed for each SC
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Sun et al.
Table I. Analysis of MLH1 (a mismatch repair protein) focus frequencies for chromosomes 1, 9, 13, 21 and the sex body.
Donor
Number of autosomal
MLH1 foci per cella
Number of cells with
MLH1 focus in sex body
per 100 cells
Number of MLH1 foci per cell in individual SCsb
SC1
1
2
3
4
5
6
Mean
Mean
SD
Range
53.2
49.2
49.9
49.9
50.7
51.5
50.7
4.9
4.8
5.1
4.4
3.7
5.0
4.7
37– 62
32– 60
33– 61
40– 60
38– 59
37– 63
32– 63
89
91
80
90
85
81
86
SC9
SC13
SC21
Mean
SD
Mean
SD
Mean
SD
Mean
SD
3.53
3.20
3.53
3.65
3.24
3.35
3.42
0.82
0.83
0.75
0.70
1.02
0.67
0.80
2.07
1.87
1.49
2.35
2.24
2.01
2.01
0.59
0.66
0.62
0.56
0.64
0.51
0.60
1.64
1.65
1.62
1.85
1.69
1.58
1.67
0.48
0.51
0.49
0.41
0.70
0.48
0.51
0.84
0.87
0.89
0.92
0.84
0.83
0.86
0.29
0.26
0.27
0.28
0.39
0.11
0.27
a
100 pachytene-stage spermatocytes were analyzed for each man.
100 pachytene-stage spermatocytes were analyzed to identify individual synaptonemal complexes (SCs) for donors 1– 3 and 6; 48 and 143 pachytene stage
spermatocytes were analyzed, respectively, for donors 4 and 5.
b
Table II. Number of bivalents with no MLH1 foci in SCs 1, 9, 13, 21 and
the sex body.
Donor
SC1
SC9
SC13
SC21
Sex body
1
2
3
4
5
6
0
0
0
0
1
0
0
3
0
0
0
0
1
1
1
0
11
0
5
3
4
4
24
1
10
9
20
10
7
19
Correlation analysis between the frequency of recombination foci (calculated as MLH1 focus frequency per specific
chromosome) and of sperm chromosome aneuploidy in the
same individuals was performed to examine the possibility of
a direct association between meiotic recombination and
sperm aneuploidy in humans. No significant correlation was
found between the mean frequency of cells with a sex body
containing an MLH1 focus and XX, YY or XY disomy in ejaculated sperm, nor between the mean MLH1 frequency for
chromosomes 1, 9, 13 and 21 and aneuploidy for the corresponding chromosome (P . 0.05, Pearson correlation analysis). An example of this relationship in chromosome 21
(correlation coefficient r ¼ 20.1185, P ¼ 0.8230, Pearson
correlation analysis) is shown in Fig. 2. Also, there was no significant correlation between the frequency of bivalents with no
recombination foci and the frequency of sperm aneuploidy
(P . 0.05, Spearman correlation analysis).
Chromosome 21 had a higher frequency of bivalents with no
recombination foci compared with the other autosomes (P ,
0.0001) and the sex chromosomes had a higher frequency
than any other chromosome (P , 0.0001).
Discussion
We originally observed, by both human sperm karyotype
studies (Martin and Rademaker, 1990) and FISH analysis
(Spriggs et al., 1996; Shi and Martin, 2000), that the G group
chromosomes (21 and 22) and the sex chromosomes had a significantly higher frequency of sperm aneuploidy than other
1694
chromosomes. This research was corroborated by other laboratories (Williams et al., 1993; Blanco et al., 1998). This led us to
hypothesize that the reason might be that these chromosomes
normally only have one crossover: chromosomes 21 and 22
being the smallest chromosomes and the sex chromosomes
pairing and recombining only in the pseudoautosomal region.
If this single crossover were lost, a dangerous situation
would ensue, since there would be no mechanism to ensure
proper segregation of homologous chromosomes into daughter
cells. Our first study on recombination in sex chromosomes by
single sperm typing demonstrated a decrease in recombination
in the pseudoautosomal region in sperm that had undergone
non-disjunction compared with normal sperm (Shi et al.,
2001). Furthermore, immunofluorescence analysis on pachytene cells in 10 normal men demonstrated that chromosomes
21 and 22 had a higher frequency of non-crossover bivalents
compared with other autosomes, and that the sex chromosomes
had the highest frequency of univalents overall (Sun et al.,
2006a), results that have since been corroborated (CodinaPascual et al., 2006). Thus our expectations were fulfilled—
that the chromosomes with the highest frequency of achiasmate
bivalents were the same chromosomes that had the highest
frequency of sperm aneuploidy. However, a direct association
between meiotic recombination and sperm aneuploidy in the
same individual, which would more accurately reflect how
faulty recombination effects might directly impact sperm aneuploidy, was lacking. This study provides that missing link.
In this study, the frequency of meiotic recombination in
chromosomes 1, 9, 13, 21, X and Y was compared with the
frequency of sperm aneuploidy for the same chromosomes in
six men. Of the chromosomes studied, it is clear that the sex
bivalent and chromosome 21 have the highest frequency of
bivalents with no recombination foci (Table II). However,
these same chromosomes do not have a significantly higher
frequency of aneuploidy in sperm compared with the other
chromosomes (Table III). This is puzzling, since we have
observed a higher frequency of sperm aneuploidy for the
G group and sex chromosomes in many studies in the past,
including in healthy (Martin and Rademaker, 1990; Spriggs
et al., 1996) and infertile men (Martin et al., 2003b). However,
Human sperm aneuploidy and recombination
Table III. Fluorescence in situ hybridization analysis of aneuploid spermatozoa in ejaculated samples.
Donor
Number of sperm
Sex chromosomes
Number of
% Disomy
1
2
3
4
5
6
Mean
10 015
9 999
9 999
10 001
10 004
10 005
10 004
% Nullisomy
XX
YY
XY
Total
0.03
0.00
0.02
0.05
0.04
0.05
0.03
0.05
0.02
0.02
0.03
0.01
0.02
0.03
0.29
0.04
0.09
0.11
0.15
0.32
0.17
0.37
0.06
0.13
0.19
0.20
0.39
0.23
0.21
0.21
0.10
0.53
0.31
0.27
0.27
X
4963
4997
4984
4957
5006
4968
4979
Y
4969
4966
4983
4961
4933
4956
4961
Chromosomes 1 and 9
% Disomy
1
2
3
4
5
6
Mean
10 015
10 009
9 993
9 999
10 006
10 005
10 005
% Nullisomy
1
9
1
9
0.12
0.08
0.04
0.06
0.08
0.04
0.07
0.06
0.08
0.25
0.79
0.16
0.07
0.24
0.16
0.32
0.03
0.78
0.06
0.73
0.35
0.37
0.23
0.18
1.34
0.38
0.17
0.45
Chromosomes 13 and 21
% Disomy
1
2
3
4
5
6
Mean
10 010
10 006
9 998
10 001
10 019
10 009
10 007
% Nullisomy
13
21
13
0.19
0.17
0.09
0.10
0.05
0.16
0.13
0.58
0.22
0.08
0.27
0.18
0.08
0.24
0.83
0.37
0.27
3.91
0.48
0.28
1.02
Figure 2: The relationship between the frequency of MLH1 foci per
cell and of disomy in chromosome 21 (correlation coefficient
r ¼ 20.1185, P ¼ 0.8230, Pearson correlation analysis)
these fertile vasectomy reversal patients are a more select
uniform population of proven fertility, and comparison of their
frequencies of sperm aneuploidy with previous healthy populations demonstrates a lower mean frequency of disomy for
both the sex chromosomes [0.23 versus 0.41 in previous studies
(Kinakin et al., 1997)] and chromosome 21 [0.24 versus 0.37
(McInnes et al., 1998)]. It is comforting to know that men
21
0.36
0.19
0.15
1.57
0.19
0.12
0.43
seeking vasectomy reversal do not appear to have sperm with
elevated frequencies of aneuploidy despite years of physical
obstruction of the excurrent ducts in the reproductive tract.
Codina-Pascual et al. (2005) studied infertile men and found a
relationship between a low frequency of recombination in the
sex body and the overall frequency of recombination in the autosomes. We found no such relationship, but as can been seen from
Table I, these fertile men had a uniformly high percentage of
cells with a recombination focus in the sex chromosomes,
demonstrating the normality of the meiotic process in these men.
To date, there have been no other studies comparing meiotic
recombination frequency with sperm aneuploidy frequencies in
ejaculated spermatozoa. However, Ma et al. (2006) studied one
infertile man and found that a total lack of recombination in the
meiotic sex chromosomes was mirrored by a high total sex
chromosome aneuploidy frequency in testicular sperm. Also,
a reduced recombination frequency for chromosomes 13 and
21 was associated with an increased frequency of aneuploidy
in testicular sperm. It is possible that they found a significant
association between lack of recombination and sperm aneuploidy because their one infertile patient had an exceptionally
low frequency of recombination (0% in the sex chromosomes)
coupled with a very high frequency of sex chromosome
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Sun et al.
aneuploidy (41.6%). Our values in proven fertile men were
much less extreme, with most chromosome bivalents having
at least one recombination focus. Thus, our fertile men may
not have reached the threshold required to demonstrate the
relationship between recombination and aneuploidy. Certainly,
our studies and those of others have demonstrated that infertile
men with non-obstructive azoospermia have a decreased
frequency of meiotic recombination (Gonsalves et al., 2004;
Sun et al., 2004a, 2005, 2007) and an increased risk of
aneuploidy (Palermo et al., 2002; Martin et al., 2003a).
However, although these studies compared testicular tissue
and ejaculated sperm, the comparison was not made in the
same individuals. The approach applied here provides a
unique avenue to investigate the association of human meiotic
events with aneuploidy more precisely, and has the potential
to provide important information on the basic mechanisms
underlying non-disjunction in humans and also to shed light
on the cause of the increased frequency of chromosome abnormalities in infertile men. It will be important to study infertile men
with oligozoospermia or azoospermia in a similar manner, to
determine if our hypothesis of a threshold effect on a correlation
between meiotic recombination and sperm aneuploidy exists.
Funding
R.H.M. holds the Canada Research Chair in Genetics, and the
research was funded by the Canadian Institutes of Health
Research (CIHR) grant MA7961. F.S. and M.O-B. are the recipients of a CIHR Strategic Training Fellowship in Genetics,
Child Development and Health.
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Submitted on October 15, 2007; resubmitted on November 26, 2007; accepted
on January 18, 2008
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