2008 Barcelona - European Society of Human Genetics

Cytogenetics
P02.008
Reconfirmation of terminal deletions and derivative
chromosomes by mLPA subtelomeric screening
K. Wakui 1,2 , Y. Furui 3 , K. Shinogi 3 , T. Fukui 3 , R. Kawamura 1 , Y. Kinishita 1 , T.
Kosho 1,2 , T. Wada 1,2 , H. Ohashi 4 , N. Gondo 3 , S. Yokoyama 3 , H. Higashi 3 , Y.
Fukushima 1,2 ;
1 Dept Med Genet, Shinshu Univ Sch Med, Matsumoto, Japan, 2 Div Clinical and
Mol Genet, Shinshu Univ Hosp, Matsumoto, Japan, 3 Biomedical Business Div.
FALCO biosystems Ltd, Kyoto, Japan, 4 Div Clinical Genet, Saitama Children’s
Hospital, Saitama, Japan.
Multiplex Ligation-dependent Probe Amplification (MLPA) has come
into wide use for subtelomeric screening as a new molecular cytogenetic
technique . We used 2 kinds of MLPA® Kits (SALSA MLPA KIT
HUMAN TELOMER, P036B and P070, MRC-Holland) for analyzing 21
subjects of known subtelomeric imbalances which have been already
detected by G-banding . Of the 12 cases detected as additional materials
of unknown origin at one of the chromosomal end by G-banding, 9
had loss of the subtelomere of the derivative chromosome and gain of
the subtelomere of the other chromosome by MLPA, as we suspected .
But, in the rest of 3 cases, MLPA showed only gain of the subtelomere
of the other chromosomal end, but no loss of the subtelomere
of the derivative chromosome . Of the 9 cases detected as terminal
deletion by G-banding, 6 cases had only loss of the targeted subtelomere,
as we suspected . But the other 3 cases had been detected not
only loss of the targeted chromosomal end, but also gain of the other
subtelomere by MLPA . We performed the metaphase FISH analysis to
confirm the results of MLPA for the cases having discrepancies of the
results between G-banding and MLPA . When a distal part of chromosomal
arm looks smaller than the normal chromosome by G-banding,
the abnormal chromosome is often interpreted as terminal deletion .
But, it is noteworthy even shorter chromosome may be derived from
familial balanced translocation . MLPA subtelomeric screening is useful
for the precise diagnosis of structural chromosomal abnormality, and
necessary for providing genetic counseling .
P02.009
A terminal 7,1 Mb chromosome 18p deletion flanked by a 2,3
mb duplication in a phenotypically normal mother and her
microcephalic and mentally retarded son
K. H. Ørstavik 1,2 , D. Misceo 3 , H. Lybæk 4 , E. Frengen 3 , G. Houge 4 ;
1 Department of Medical Genetics, Rikshospitalet University Hospital, Oslo,
Norway, 2 Faculty Division Rikshospitalet, University of Oslo, Oslo, Norway,
3 Institute of Medical Genetics, University of Oslo, Oslo, Norway, 4 Center for
Medical Genetics and Molecular Medicine, Haukeland University Hospital,
Bergen, Norway.
Deletions of chromosome 18p are frequent and associated with broad
phenotypic variability . We report an identical and cytogenetically visible
terminal deletion in a mentally retarded microcephalic boy and his
normocephalic cognitively normal mother .
The patient was a 13 year old boy with head circumference 1 .5 cm below
the 2 .5 th centile . Height was at the 10 th centile and weight between
the 25 th and 50 th centile . Early motor milestones were unremarkable .
However, he has needed extra help at school because of problems
with concentration, behaviour, and activities requiring fine motor skills.
On examination, he had a single right palmar crease . He was microcephalic
but not otherwise dysmorphic . His mother was of normal intelligence
. She was 172 cm tall with a normal head circumference and no
dysmorphic features .
G-banded chromosome analysis revealed a terminal 18p deletion,
removing band 18p11 .3 . Array CGH analysis on Agilent 44K arrays
indicated a 7,1 Mb terminal deletion flanked by a 2,3 Mb duplication;
arr cgh 18p11 .32p11 .23(RP11-76H24->RP11-42J5)x1,18p11 .23p11 .2
2(RP11-207E16->RP11-784M9)x3 . Work is under way to determine
if the duplication is inverted . Inversion would lead to generation of a
new 18p terminus . The mother’s karyotype was identical . The maternal
grandmother had normal chromosomes . The maternal grandfather
was deceased .
Inheritance of an 18p deletion has been reported previously in seven
families . In all cases the deletion was inherited from the mother, possibly
indicating that males with 18p deletions are more likely to express
adverse phenotypic effects of this genomic imbalance. This is the first
reported family in which the mother had a normal phenotype .
P02.010
FisH analysis of replication timing of human subtelomeric
regions
I. Petković;
University Children’s Hospital Zagreb, Zagreb, Croatia.
Recent studies have shown that DNA replication timing is correlated
with transcriptional activity of genes . Synchronous replication of alleles
was demonstrated for genes with a biallelic and asynchronous
replication for those with a monoallelic mode of expression . Alteration
of replication order has been associated with aneuploidy and genetic
instability, while asynchronous replication with the formation of a deletion
. No data on replication timing of subtelomeric regions (SR) are
available so far . SRs are highly unstable and rearrangements have
been reported in ~7% of patients with mental retardation .
The objective of this study was to determine the replication timing of
human SR . The replication pattern of SR of chromosomes 5, 7, 8 and
20 was investigated using FISH method in lymphocytes of 4 healthy
donors . At least 200 cells per probe per person were studied . The replication
status of a locus was classified as unreplicated (“s”-single signal)
and replicated (“d”- doubled signal) .
The results showed that each SR had a characteristic timing of replication,
and that 20q (ss: 47.8±3.1%; dd: 18±1.8%) was the first of examined
SRs to replicate, whereas 5q (ss: 75 .9±1 .8%; dd: 4 .3±0 .5%) was
the last (p