METHODOLOGY Open Access
Selection of single blastocysts for fresh transfer
via standard morphology assessment alone and
with array CGH for good prognosis IVF patients:
results from a randomized pilot study
Zhihong Yang1
, Jiaen Liu2
, Gary S Collins3
, Shala A Salem1
, Xiaohong Liu2
, Sarah S Lyle1
, Alison C Peck1
,
E Scott Sills1*
and Rifaat D Salem1
Abstract
Background: Single embryo transfer (SET) remains underutilized as a strategy to reduce multiple gestation risk in
IVF, and its overall lower pregnancy rate underscores the need for improved techniques to select one embryo for
fresh transfer. This study explored use of comprehensive chromosomal screening by array CGH (aCGH) to provide
this advantage and improve pregnancy rate from SET.
Methods: First-time IVF patients with a good prognosis (age <35, no prior miscarriage) and normal karyotype
seeking elective SET were prospectively randomized into two groups: In Group A, embryos were selected on the
basis of morphology and comprehensive chromosomal screening via aCGH (from d5 trophectoderm biopsy) while
Group B embryos were assessed by morphology only. All patients had a single fresh blastocyst transferred on d6.
Laboratory parameters and clinical pregnancy rates were compared between the two groups.
Results: For patients in Group A (n = 55), 425 blastocysts were biopsied and analyzed via aCGH (7.7 blastocysts/
patient). Aneuploidy was detected in 191/425 (44.9%) of blastocysts in this group. For patients in Group B (n = 48),
389 blastocysts were microscopically examined (8.1 blastocysts/patient). Clinical pregnancy rate was significantly
higher in the morphology + aCGH group compared to the morphology-only group (70.9 and 45.8%, respectively;
p = 0.017); ongoing pregnancy rate for Groups A and B were 69.1 vs. 41.7%, respectively (p = 0.009). There were no
twin pregnancies.
Conclusion: Although aCGH followed by frozen embryo transfer has been used to screen at risk embryos (e.g., known
parental chromosomal translocation or history of recurrent pregnancy loss), this is the first description of aCGH fully
integrated with a clinical IVF program to select single blastocysts for fresh SET in good prognosis patients. The
observed aneuploidy rate (44.9%) among biopsied blastocysts highlights the inherent imprecision of SET when
conventional morphology is used alone. Embryos randomized to the aCGH group implanted with greater efficiency,
resulted in clinical pregnancy more often, and yielded a lower miscarriage rate than those selected without aCGH.
Additional studies are needed to verify our pilot data and confirm a role for on-site, rapid aCGH for IVF patients
contemplating fresh SET.
* Correspondence: dr.sills@prc-ivf.com
1
Division of Reproductive Endocrinology Research, Pacific Reproductive
Center, Torrance, CA 90505, USA
Full list of author information is available at the end of the article
© 2012 Yang et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly cited.
Yang et al. Molecular Cytogenetics 2012, 5:24
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Background
Multiple gestation represents the most significant complication
of assisted reproductive treatment (ART). Single
embryo transfer (SET), either elective or mandatory,
has been advocated as an effective means to avoid multiple
gestation following IVF [1-3]. Despite a welcome
trend in increased acceptance and utilization of elective
SET treatment in some groups [4], most IVF cycles continue
to involve two or more embryos for transfer. When
SET is done, selection of the single embryo or blastocyst
for transfer is typically done on the basis of morphology
[5,6]. However, since acceptable morphology alone cannot
negate the potential for chromosomal error in the
selected embryo, the transfer of one apparently “normal
looking” embryo carries considerable risk [7]. Aneuploidy
is the most common abnormality in human
embryos derived from IVF [8-15], a problem that contributes
substantially to poor IVF outcomes [16]. As other
investigators have noted, screening embryos by fluorescence
in situ hybridization (FISH) was a reasonable response
to this challenge, but the approach was limited
because it failed to screen all chromosomes at the same
time [17-21]. Conventional comparative genomic
hybridization (CGH) has been used for comprehensive
screening of aneuploidy for oocytes and embryos [19,22-
25] with cryopreservation of embryo(s) from which the
biopsy was derived. When results became available, frozen
embryo transfer (FET) was subsequently arranged so
that only euploid embryo(s) were transferred.
At present, there is no consensus on the best way to
determine the competency of the embryonic genome
during IVF. Both single nucleotide polymorphism (SNP)
array and array CGH (aCGH) have been validated as accurate
methods to achieve comprehensive chromosome
screening when biopsy is performed on d3 for fresh
transfer on d5 [26-30]. The difference in mosaicism between
embryos at d3 and d5 has led to a preference for
biopsy at the blastocyst stage when mosaicism is reduced
[31-33]. When combined with trophectoderm biopsy and
blastocyst vitrification, SNP microarray has resulted in
high implantation rate and low miscarriage rates for
some IVF patients [31]. However, experience is limited
with aCGH to select a single euploid blastocyst for fresh
transfer in the absence of known chromosomal diagnosis.
In this pilot study, we evaluated a rapid, on-site
aCGH application to select a single euploid blastocyst
for fresh transfer in good prognosis patients <35 yrs of
age, who were undergoing a first IVF attempt.
Methods
Patient sample
Following IRB approval, patients undergoing IVF at our
programs in Beijing and Los Angeles were offered enrollment
in this prospective, single-blind, pilot interventional
study to compare embryo assessment by conventional microscopy
alone or with array comparative genomic
hybridization (aCGH) performed on trophectoderm. Written
informed consent was obtained from all study participants
and all received pre-treatment counseling in
anticipation of possible incorporation of aCGH in their IVF
treatment. Patients were eligible for this study if (female)
age was <35 yrs, if there was a history of regular ovulation,
if etiology of infertility was tubal factor or male factor (or
both), and if no prior IVF treatment had been initiated.
Additionally, all study subjects were required to have a normal
intrauterine contour (confirmed by hysteroscopy), both
ovaries intact, basal serum FSH and estradiol on d2-3 at
<10 IU/l and <60 pg/ml, respectively. IVF patients whose
treatment incorporated donor gametes or frozen/thawed
embryos were excluded. A random number table was used
to determine patients in vitro laboratory management strategy
as either (1) traditional morphology assessment plus
aCGH (Group A, n= 55), or (2) conventional morphology
assessment only (Group B, n =48). Patients (but not laboratory
or clinical staff) were blinded with regard to their
randomization group. The two cohorts were mutually exclusive,
and no study patient had embryos assigned to both
laboratory groups.
Ovarian stimulation and fertilization
Before commencing gonadotropin therapy patients
underwent transvaginal ultrasound evaluation with remeasurement
of serum FSH, LH and estradiol on d3 of
the index cycle. Pituitary downregulation was achieved
with GnRH-agonist administered on d21 of the cycle immediately
preceding treatment, as previously described
[33]. Periodic transvaginal ultrasound and serum estradiol
measurements were used to track follicular growth
and thickness of endometrial lining. When ≥3 follicles
reached 19 mm mean diameter, periovulatory hCG was
administered by subcutaneous injection of recombinant
hCG (250 μg OvidrelW
, Merck Serono; Geneva, Switzerland)
with oocyte retrieval performed under transvaginal
ultrasound guidance 35-36 h later. Following removal of
all cumulus cells, ICSI was performed and normal
fertilization was verified 16-18 h after injection by presence
of two pronuclei and two polar bodies.
Embryo culture and trophectoderm biopsy
All embryos were cultured in sequential media (Vitrolife;
Göteborg, Sweden) to blastocyst stage. On d3 when
embryos were at the 6–8 cell stage, a noncontact 1.48 μ
diode laser (OCTAX Microscience GmbH; Bruckberg,
Germany) was used to create a circular 6-9 μ diameter
opening in the zona pellucida. For embryos randomized
to the aCGH group, this breach enabled biopsy of
trophectoderm (TE) on d5 rapidly. Between 3–5 herniated
TE cells were gently aspirated by pipette and,
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when necessary, freed from the blastocyst by application
of several laser pulses. Harvested TE cells were
washed in PBS and placed within a PCR tube with
2.5 μl 1x PBS as previously described [34]. A uniform
assisted hatching methodology was used for all embryos
irrespective of subsequent TE biopsy or conventional
microscopic assessment alone.
aCGH protocol
Whole genome amplification was performed on-site using
the SurePlex DNA amplification system (BlueGnome Ltd;
Cambridge, UK) in accordance with manufacturer’s guidelines,
as described elsewhere [34,35]. Briefly, samples and
control DNA (8 μl for each) were labeled with Cy3 and
Cy5 fluorophores (BlueGnome Ltd; Cambridge, UK). Labeling
time was approximately 3 h with DNA resuspended
in dexsulphate hybridization buffer and hybridized overnight
under cover slides. After washing 1x 10 min in saline
sodium citrate (SSC)/0.05% Tween-20 at room
temperature, an additional irrigation in SSC 1x 10 min
was completed at room temperature. Slides were washed
in SSC 1x 5 min at 60°C and again for 1 min at room
temperature (in SSC). Vacuum centrifuge was used to
dry microarray slides over 3 min, followed by laser scanning
at 10 μm (Agilent Technologies; Santa Clara, USA).
Microarray data were analyzed with BlueFuse software
(BlueGnome, Cambridge, UK) for chromatin loss or gain
across all 24 chromosomes. Aberrations were considered
non-artifact if ≥15 probes deviated from normal
limits as defined by the 24Sure platform. The published
accuracy rate for this aCGH technique when applied to
TE cells is 95% [35].
Blastocyst grading and selection for transfer
In both aCGH and control groups, blastocysts were
graded [36] on a 1 to 6 scale determined by degree of expansion
and hatching status, as follows: Grade 1 (early
blastocyst): blastocoele <1/2 of total embryo volume;
Grade 2 (intermediate blastocyst): blastocoele ≥1/2 of
total embryo volume; Grade 3 (full blastocyst): blastocoele
fully occupies the embryo; Grade 4 (expanded
blastocyst): blastocoele is larger than early blastocyst and
zona pellucida (ZP) demonstrates thinning; Grade 5
(hatching blastocyst): herniation of trophectoderm cells
from the ZP; and Grade 6 (hatched blastocyst): blastocyst
has escaped the ZP. For blastocysts at Grades 3 to 6, the
inner cell mass (ICM) and trophectoderm (TE) were also
graded. The ICM was graded as follows: A (many ICM
cells packed together tightly); B (several ICM cells
grouped loosely) and C (very few ICM cells). TE was
graded as follows: A (many TE cells forming multiple
epithelial layers); B (few TE cells consisting of a loose
epithelium) and C (very few large TE cells).
Fresh SET was performed on the morning of d6 under
direct ultrasound guidance for all patients. For embryos
in the aCGH group only one euploid blastocyst was
selected for transfer, based on data from the aCGH analysis.
When multiple euploid blastocysts were available
(as determined by aCGH), the best grade euploid blastocyst
was selected for transfer. Any surplus euploid blastocysts
were vitrified for later use [34]. In the non-aCGH
(control) group, a single blastocyst was selected for fresh
transfer based on morphological criteria only (e.g., no
aCGH evaluation). The surplus blastocysts with good
morphology (grade 3BB or above) were vitrified for future
FET cycles.
Outcome measures and statistical analysis
Clinical pregnancy rates were tabulated and compared
for IVF patients in both groups. Clinical pregnancy was
defined as an intrauterine gestational sac containing one
embryo which demonstrated cardiac action with rate
≥110/min [37], and pregnancies at ≥20 weeks of gestation
were classified at on-going. Differences between
groups were assessed by Chi-squared and Fisher’s exact
tests. A difference of p < 0.05 was considered statistically
significant.
Results
During the four-month study interval, a total of 188 IVF
patients met inclusion criteria and 112 volunteered for
enrollment (59.6%). Fifty six patients were randomized
to each group. Of these, some patients did not initiate
IVF due to failure to complete mandatory pre-IVF testing,
they rescheduled their IVF, or they withdrew from
treatment for personal reasons (see Figure 1). For Group
A (morphology + aCGH) and Group B (morphology
only) 55 and 48 IVF patients completed the study, respectively.
The clinical and demographic features of the
two groups were similar, as summarized in Table 1.
There were no cancellations or complications for any patient
in either study group.
For patients in Group A, 425 of 457 blastocysts were
biopsied and analyzed via array CGH (7.7 blastocysts/patient).
Biopsy could not be completed for 32 blastocysts
due to poor morphology or because they degenerated
after biopsy. This evaluation revealed aneuploidy in 191/
425 (44.9%) of blastocysts. ‘No signal’ due to amplification
failure occurred in 8 blastocysts. Among aneuploid
blastocysts, 68/191 (35.6%) had single chromosome loss
(monosomy) and 20.9% displayed single chromosome
gain (trisomy). Approximately 43% of aneuploid blastocysts
were chromosomally abnormal due to a severe,
compound genetic defect where two or more chromosomes
were affected (see Table 2). While chromosomal
abnormalities were detected in all chromosomes, disruptions
involving chromosomes 15, 16, 21, 22 and X were
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most frequently observed. Errors of chromosomes 4 and
6 were relatively uncommon. All patients in Group A
had at least one euploid blastocyst available for transfer
on d6. For patients in Group B, 389 blastocysts were
microscopically examined (8.1 blastocysts/patient).
A single embryo was selected for transfer to all patients
on d6. As shown in Table 3, the observed ongoing pregnancy
rate was significantly higher in the morphology +
aCGH group compared to the morphology-only group
(69.1 vs. 41.7%, respectively; p = 0.009). A significant difference
in clinical pregnancy rate was also noted between
the two study groups (70.9 vs. 45.8%, respectively;
p = 0.017). There were no twin pregnancies identified in
either group. A low miscarriage rate was noted for all
study patients, although this was somewhat lower in the
morphology + aCCH group than for the morphology-only
group (2.6 vs. 9.1%, respectively; p = 0.597, by Fisher’s
exact test).
Discussion
Delivery of a healthy singleton live birth is the target outcome
for all infertility treatment. Although elective SET
has emerged as the best answer to reduce the multiple
gestation rate in IVF, uncertainty about the technique itself,
low patient awareness of the process, lack of a favorable
reimbursement system, and inferior
cryopreservation success rates have hindered the uptake
of this approach [38]. The value of promoting SET was
recently underscored by a population-based cohort study
of IVF outcomes where cerebral palsy (CP) incidence
was noted among 1042 IVF singletons born after SET in
Denmark [39]. Only one of those children received a CP
diagnosis, compared with 21 CP diagnoses among IVF
singletons born after two or more embryo transfers [39].
In Canada, efforts to mandate SET gained support from
a multi-year review showing how this change in IVF
Table 1 Characteristics of patients whose embryos were
randomized to assessment by morphology with aCGH
(Group A) and blastocyst morphology only (Group B)
Group A (n = 55) Group B (n = 48)
Age (yrs) 31.2 ± 2.5 31.5 ± 2.7
Total oocytes retrieved 19.5 ± 8.2 19.3 ± 8.1
MII (mature) oocytes 16.6 ± 7.8 16.3 ± 7.6
Oocytes fertilized (2pn) 13.1 ± 6.7 12.8 ± 6.4
Day 3 embryos 12.9 ± 1.8 12.6 ± 1.9
Day 5 blastocysts 8.3 ± 2.1 8.1 ± 2.4
Notes: Total number of blastocysts in Group [A] and [B] were 457 and 389,
respectively. aCGH = array comparative genomic hybridization, MII = metaphase
II, 2pn = two pronuclei. All data reported as mean ± SD. There was no
significant difference between groups (p > 0.05) in any category.
Table 2 Detail of aCGH results derived from aneuploid
blastocysts (n = 191) in Group A
n (%)
Single chromosome loss (monosomy) 68 (35.6)
Single chromosome gain (trisomy) 40 (20.9)
Dual chromosomal abnormality 55 (28.8)
Complex chromosomal abnormality 28 (14.7)
188
112
5656
55 48
81
A B
425 389
Eligible for study entry
Enrolled and randomized
Completed study
Figure 1 Schematic for patients randomized either to embryo
assessment by standard morphology plus aCGH (A) or
morphology alone (B). Withdrawals, deferrals and drop-outs for
each group are circled in red. The total number of blastocysts
associated with each group is circled in blue.
Table 3 Comparison of laboratory findings and clinical
outcome among IVF patients undergoing SET with
embryo assessment by aCGH + morphology (Group A)
and blastocyst morphology alone (Group B)
A B p
Fresh blastocyst transfer according to
morphology assessment:
55 (100) 48 (100)
Grade 5/6 31 (56.4) 28 (58.3)
Grade 4 21 (38.2) 19 (39.6) 0.677a
Grade 3 3 (5.4) 1 (2.1)
Clinical pregnancy 39 (70.9) 22 (45.8) 0.017a
Ongoing pregnancy (≥20wks GA) 38 (69.1) 20 (41.7) 0.009a
Missed abortion 1 (2.6) 2 (9.1) 0.597b
Notes: All data reported as n (%). SET = single embryo transfer; aCGH = array
comparative genomic hybridization; GA = gestational age a
by Chi-squared test
b
by Fisher’s exact test.
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practice would prevent infant deaths and reduce serious
complications associated with multiple gestations [40].
Researchers found 17% of all NICU admissions—82
infants from 44 multiple gestations—resulted from
assisted fertility treatments, and most NICU admissions
(75 of 82 infants) were twins or triplets whose mothers
used IVF to become pregnant. Among those 75 babies
there were 6 deaths, and 5 more developed severe intraventricular
hemorrhage [40].
Given this background, IVF patients should be encouraged
to consider elective SET during pre-treatment
counseling. Except for Sweden and Belgium [41,42], all
other jurisdictions allow the decision for number of
embryos for transfer to be made by doctor and patient,
so the role of the reproductive endocrinologist in this
process is vital [38]. How the choice to have elective SET
is communicated has been shown to be an important influencing
factor as this choice is made [43]. Yet in many
clinics, if SET is offered at all, it is the patient herself
who requests this option. Confidence in chance of success
after SET, younger patient age, and first IVF treatment
appear to favor a patient asking for SET [44]. We
support the basic criteria for elective SET as proposed by
others [45], including age <37 yrs, at least two good
quality embryos available (3–5 cells on d2 or 6–9 cells
on d3; <20% fragmentation and no multinucleate blastomeres),
and no more than one previous failed treatment
cycle. Among Australian IVF patients, preference for a
healthy singleton pregnancy was predictive for elective
SET, but perception of risk of multiple gestation was not
[44]. Reporting on IVF patients in Ireland, Walsh et al.
[46] investigated pre-treatment anxiety about twins and
no association with patient age was observed. When presented
with the option of SET, good prognosis IVF
patients in Ireland agreed with this approach [47].
So why hasn’t elective SET found wider application in
clinical IVF practice? Low pregnancy rates after fresh
SET [48-51] have limited its acceptance, but this criticism
of elective SET may be offset when cumulative outcome
with subsequent frozen embryo transfer (FET)
cycles is considered [52-55]. To be sure, more IVF
patients would request elective SET if the success rate
approached that following a two embryo transfer [56]. It
is therefore understandable for both patients and clinicians
to view elective SET with skepticism unless significant
refinements in fresh embryo assessment come
forward to facilitate the selection of competent embryos.
The current study extends prior research where aCGH
was used for IVF patients with a known chromosomal
rearrangement [29,35], and is the first to apply this technology
to embryos from young, good prognosis patients
undertaking IVF for the first time. Because SET is more
frequently requested by IVF patients with a favorable
prognosis [47], and since in this setting the clinical
urgency to identify the best single embryo for transfer is
maximal, our hypothesis developed this clinical problem
into a therapeutic solution where aCGH figured prominently.
Incorporating aCGH within an IVF clinic not only
promises improved reproductive competency of each
embryo at fresh transfer, it also offers important ploidy information
regarding any supernumary (non-transferred)
embryos which may be cryopreserved for later use. At our
center, integrating aCGH with the clinical IVF program
was associated with the same extra cost typically charged
for the more limited genetic assessment gained from 5probe
FISH—less than $3000. These considerations should
be particularly welcome among patients and clinicians
contemplating elective SET, but who hesitate to make
decisions without the advantage of comprehensive
chromosomal screening. Moreover, an integrated testing
approach also removed the a priori requirement for material
to be frozen and shipped off-site for testing, followed
by arranging subsequent FET based on findings from
aCGH performed remotely. We believe that patient stress
was reduced by eliminating FET medications entirely,
while also reducing overall IVF treatment time. How
patients quantify the distinctions between fresh transfer
and FET treatment regimes is the target of ongoing study.
Our research contributes new aCGH data on embryos
from good-prognosis IVF patients, placing the limitations
of standard embryo morphology in sharp relief.
The extent of aneuploidy in early human embryos can be
extensive [11,57,58] although this rate is typically lower
in blastocysts [25]. Yet, the current study provides further
evidence of substantial genetic abnormality in apparently
normal blastocysts, including monosomy and
complex aneuploidy [7,25,59]. Our data show conventional
morphological criteria alone to be insufficiently accurate
even for young, low-risk IVF patients (see
Figure 2). Recent research on thawed blastocysts after
SNP-based comprehensive chromosomal screening and
vitrification has yielded similar results [60].
Several limitations of our investigation should be
acknowledged. First, although elective SET brings distinct
advantages for many IVF patients, the approach is
not for everyone. Indiscriminate use of elective SET for
patients with multiple failed cycles has been criticized as
inferior to a two-embryo strategy [61], and the improved
pregnancy rate noted here may not fully generalize to all
IVF patients. Additionally, this pilot study was designed
to use aCGH for selection of a single blastocyst for fresh
transfer. It is possible that embryo assessment by conventional
morphology inappropriately excludes euploid
embryos from transfer although this question was outside
the scope of our study. Hence, the relation between
chromosomal integrity and morphological grades based
on developmental stage, ICM and TE appearance,
requires further investigation with a larger sample.
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Conclusion
In this pilot study, we have shown that the prospect of a
successful IVF outcome with elective SET may be substantially
lifted if aCGH testing is integrated with the clinical
IVF program. The observed discordance between ploidy
status and morphology means embryo selection without
the benefit of information gained from aCGH would allow
the transfer of a reproductively incompetent—albeit morphologically
normal—embryo. Although these initial SET
data are encouraging, a multi-center randomized clinical
trial with a larger sample is planned to validate these preliminary
findings.
Competing interest
The authors declare that they have no competing interests.
Author details
1
Division of Reproductive Endocrinology Research, Pacific Reproductive
Center, Torrance, CA 90505, USA. 2
IVF Division, Beijing Jia En De Yun Hospital,
Beijing 100083, People's Republic of China. 3
Centre for Statistics in Medicine,
Wolfson College Annexe, University of Oxford, Oxford, UK.
A
B
-12
A
B
50µ
50µ
Figure 2 Representative aCGH data obtained from human blastocysts via trophectoderm biopsy performed on post-fertilization day 5.
While standard microscopy confirmed good morphology (Grade 5AA) for both blastocysts, ploidy status was not uniform. Using aCGH to screen
embryos before fresh transfer, normal chromosomal status (46,XX) was verified in A, but not in B (45,XY,-12).
Yang et al. Molecular Cytogenetics 2012, 5:24 Page 6 of 8
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Authors’ contributions
ZY and JL conceived the research, designed the study, and directed the
aCGH analysis. GSC was the chief statistician in charge of data analysis. SAS,
XL, ACP, ESS, and RDS were the reproductive endocrinologists with oversight
of the clinical program. SSL was the embryologist. ESS edited the manuscript
and organized the revisions. All authors read and approved the final
manuscript.
Received: 3 February 2012 Accepted: 2 May 2012
Published: 2 May 2012
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doi:10.1186/1755-8166-5-24
Cite this article as: Yang et al.: Selection of single blastocysts for fresh
transfer via standard morphology assessment alone and with array CGH
for good prognosis IVF patients: results from a randomized pilot study.
Molecular Cytogenetics 2012 5:24.
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Yang et al. Molecular Cytogenetics 2012, 5:24 Page 8 of 8
http://www.molecularcytogenetics.org/content/5/1/24