European Human Genetics Conference 2007 June 16 – 19, 2007 ...

Cytogenetics
P0298. Female-specific instability of pericentromeric regions in
human embryo development: the earliest clinically significant
manifestation of difference between the sexes
N. V. Kovaleva;
St. Petersburg Medical Academy of Postgraduate Studies under the Federal
Agency of Health Care and Social Development, St. Petersburg, Russian Federation.
Recent studies on the sex ratio (SR, male to female ratio) among chromosome
mosaicism carriers suggested female-specific chromosome
loss and centromere instability during early human development [1].
Mosaicism results from later gestation postzygotic formation, while formation
of a chromosome rearrangement in the first zygotic cleavage
results in nonmosaics. Purpose: Nonmosaic homologous acrocentric
rearrangements (Rea), both balanced (blRea) and unbalanced (unblRea)
mostly result from post-fertilization events [2]. Therefore, the
study on the SR in carriers of a de novo nonmosaic Rea might elucidate
when sex-specific centromere instability becomes manifest. Method:
Review of balanced and unbalanced homologous Rea cases of known
sex and mode of ascertainment identified from the literature. Results:
(1) Increased proportion of females in prenatally detected carriers of
both blRea (5M/8F) and unblRea (10M/13F). (2) Female prevalence
among postnatally ill-defined carriers of unblRea (25M/39F). (3) These
data cannot be explained by a strong intrauterine selection against
male carriers of unblRea since a female preponderance was found
among miscarried fetuses (8M/13F). (4) Female prevalence among
patients with PWS due to 45,der(15q;15q) (6M/14F). (5) Overall, there
were 54 males and 87 females in the study group (SR=0.62), significantly
different from the expected ratio of 1.06 (p=0.0023). Conclusion:
These observations indicate sex-specific centromere instability
at the earliest stage of human embryo development. It is suggested
that reactivation of the paternal X chromosome occurring in the female
zygote, might interfere with the chromatin remodeling process, thus
contributing to the increased fragility of pericentromeric regions.
[1]Kovaleva NV. AJMG 136A:401-13
[2]Robinson et al. AJHG 54:290-302
P0299. High resolution oligo array CGH analysis of challenging
samples.
S. Song, J. Collins;
Agilent Technologies Inc., Santa Clara, CA, United States.
In recent years, array-based Comparative Genomic Hybridization
(aCGH) has been refined to determine chromosomal changes at progressively
higher resolutions. This evolving technology is, however,
somewhat hampered by the large amounts of input DNA required
- a minimum of 150,000 copies of a human genome, or 0.5 µg, are
generally needed to process one aCGH microarray. The GenomePlex
Whole Genome Amplification (WGA) kit provides a rapid method for
processing biological samples of limited quantity, expanding the application
of aCGH technology to analysis of nanogram quantities of DNA.
Furthermore, this global exponential amplification method enables researchers
to representatively amplify genomic DNA from samples that
have been fragmented to an average size of less than 1 kb. This feature
may enable CGH analysis of FFPE samples that were previously
thought to be unusable due to their limited amounts of DNA and high
level of degradation. The data presented in this poster demonstrate
the high quality data that can be generated using Agilent’s high density
oligo aCGH microarrays in combination with Sigma’s GenomePlex
WGA kit. Firstly, WGA lowers the required minimum amount of starting
DNA to as little as 10 ng. In addition, the ability to amplify low molecular
weight DNA, less than 0.5-1 kb in size, is demonstrated. Finally, we
compare the performance of the GenomePlex WGA method to that
of a Phi29-based isothermal amplification method in generating high
quality aCGH data on Agilent microarrays. All aCGH testing has shown
GenomePlex amplified material to behave comparably to larger quantities
of purified genomic DNA.
101
P0300. Comparison of subtelomeric FISH, Multi-FISH and CGH
for the screening of chromosomal rearrangements in 90 patients
with unexplained mental retardation and dysmorphic features
P. Callier, L. Faivre, N. Marle, C. Thauvin, J. Guy, A. Mosca, D. Assous, F.
Huet, F. Mugneret;
Département de Génétique, CHU le Bocage, DIJON, France.
Mental retardation affect 1-3% of the general population and the aetiology
remains unknown in many cases. Conventional cytogenetics
detected rearrangements of more than 10 Mb in size. The development
of molecular cytogenetic techniques permits to identify cryptic
rearrangements, but their frequency is uncertain in patients with unexplained
mental retardation. Only few studies have been performed
to compare the potential of molecular cytogenetic techniques to detect
chromosomal rearrangements. Here we present a study including 90
patients with unexplained mental retardation and dysmorphic features
with normal high-resolution karyotypes, investigated by subtelomeric
FISH, CGH and Multi-FISH.
A total of 6/90 abnormalities were found (6.6%), including three de
novo deletions (1pter, 4pter and 3q21.1-q21.3), two de novo unbalanced
translocations [der(8)t(6;8)(p25;p23] and [der(22)t(10;22)(q26;q
13)], and one unbalanced translocation inherited from the father [der(2
)t(2;10)(q37;q26)pat]. Subtelomeric FISH evidenced 5/6 chromosomal
unbalances but could not detect the interstitial 3q21.1-q21.3 deletion.
CGH revealed 6/6 chromosomal rearrangements but did not detected
the 10qter duplication of the de novo unbalanced [der(2)t(2;10)(q37;
q26)pat] translocation. Multi-FISH did not permit to detect any chromosomal
abnormalities. Molecular cytogenetics studies with specific
BACs probes of the rearrangements are in progress to better define
the size of the chromosomal abnormalities. We compared our results
with previously published studies. This study confirmed the significant
frequency of subtelomeric rearrangements in patient with unexplained
mental retardation, dysmorphic features and demonstrates the importance
of CGH technology to detect interstitial and subtelomeric rearrangements.
P0301. Identification of prognostic chromosomal aberrations in
childhood acute lymphoblastic leukemia
R. Lasan 1 , J. Konja 2 , L. Rajic 2 , R. Feminic 2 , D. Begovic 1 ;
1 Genetics and Metabolism Division, Pediatrics Department, University Hospital
Center Zagreb, Zagreb, Croatia, 2 Pediatrics Department, University Hospital
Center Zagreb, Zagreb, Croatia.
Cytogenetic abnormalities emerge as a very important characteristic
of chilhood acute lymphoblastic leukemia (ALL) with major diagnostic
and prognostic impact.
We report bone marrow cytogenetic analysis (CTG) at the time of
diagnosis 85 children (36 females and 49 males) with de novo ALL
aged from 2 months to 15 years old. Uninformative investigations were
2.1%. Normal karyotype was detected in 40.0% (3 with constitutial
+21) cases. The analysis was performed in the period of the last five
years.
Clonal chromosomal abnormalities were present in 60% of the patients.
Changes in ploidy were found in 65.3% of abnormal cases.
The distribution of ploidy groups was: hyperdiploidy with >50 chromosomes
in 34.7% (seven of them were associated with structural chromosomal
changes), hyperdiploidy (47-50 chromosomes) in 14.2%,
pseudodiploidy in 4.1%, hypodiploidy (35-45 chromosomes) 12.2%
of the patients. The most frequently acquired numerical abnormalities
were: +4, +6, +8, +14, +17, +18, +21 and +X. Structural aberrations
were found in 34.7% of the patients. The most frequent structural aberrations
were: del(6q), del(9p), t(9;22), rearrangments of chromosome
14q, 5q and 12p (mostly like a part of complex karyotype), and
t(12;21)(p13;q22.3).
The stuctural and numerical aberrations observed in 69.5% patients
were correiated by FISH. Translocations were: t(12;21), t(9;22), t(1;12),
and one marker chromosome was identified as der (21)t(21;?). For residual
disease, interphase-FISH in combination with cell enrichment or
RT-PCR is extremely useful.
Cytogenetic investigations at diagnosis and during follow up documented
unique chromosomal aberrations which yielded diagnostic
and/or prognostic significance for each relevant patient.