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

Molecular and biochemical basis of disease
of Medical Genetics, Munich, Germany.
Germline mutations in mismatch repair genes, tumors with high microsatellite
instability (MSI-H) and loss of protein expression are the
hallmarks of HNPCC or Lynch-Syndrome respectively. While involvement
of somatic MLH1 promoter hypermethylation is accepted in tumorigenesis
of defferent sporadic tumors, abnormal germline MLH1
promoter methylation is controversly discussed as a disease-predisposing
mechanism for HNPCC.
To clarify the MLH1 deficiency of 94 HNPCC suspected individuals
with immunohistochemically MLH1-negative and MSI-H tumors but
without germline mutation in MLH1 or other mismatch repair genes,
we studied the methylation pattern in the MLH1 promoter region by
bisulphite conversion, methylation-specific PCR, and sequencing.
MLH1 promoter methylation in peripheral blood cells was found for
twelve patients displaying a HNPCC-phenotype with early-onset
colorectal cancer and/or multiple neoplasias. The aberrant methylation
was complete in all CpG dinucleotides analysed and displayed
allele-specifity in seven cases with a heterozygous SNP. The causality
between a new promoter mutation and methylation in-cis in one case
can not be ruled out. Peripheral blood cells as well as normal colonic
tissue, buccal mucosa, and tumor tissue available from three patients
presented the epigenetic MLH1 defect. Expression analysis revealed
monoallelic MLH1 expression and complete silencing in one case, in
another case only partial silencing was found by signal reduction of
one allele.
Our findings confirm that abnormal MLH1 promoter methylation in normal
body cells mimics HNPCC. The identification of hypermethylation
as a pathogenic pre-lesion has definitive implications on surveillance
recommendations, while the heritability of methylation is questionable
and was not found in offspring of methylation-carriers.
P0761. Hereditary Polyneuropathy with Liability to Pressure
(HNPP). Report of a case.
P Vorgia 1, E. Papadopoulou1,2 , G Amiridis 2, P Paspalaki 1, E Michailidou 1,
M Kalmanti 1;
1 2 Pediatric Department University Hospital, Iraklion Crete, Greece, Neurophysiology
Laboratory University Hospital, Iraklion Crete, Greece.
An 11 year old girl was referred for a neuropediatric consultation by
an orthopedist because of an acute right hand paresis after a minor
traumatism while playing. The severity of the traumatism could not justify
very well the paresis. The clinical evaluation revealed right ulnar
and median nerve paresis and a milder left median nerve paresis as
well. The rest of the neurological evaluation was normal. The girl was
admitted in our pediatric department for further investigations. Standard
hematological and biochemical control, VDRL, coagulation and
immunological investigations were all normal. Antibodies for Borrelia,
Mycoplasma, Rickettsias, and Hepatitis were normal. Only the title of
IgGs antibodies of Bartonella was elevated. Cerebral and Cervical
MRI were also normal, but the neurophysiological investigations were
compatible for a polyneuropathy, especially for HNPP. HNPP is an
autosomal dominant disorder characterized by recurrent entrapment
neuropathies usually after minor traumatism. Her personal medical
history was marked from an uncomplicated prematurity and asthma
well controlled but her mother suffered from a polyneuropathy the last
10 years. The clinical presentation of the patient, the positive family
history and the results of the neurophysiological investigations were
compatible for the diagnosis of HNPP. PCR analysis confirmed the
diagnosis by showing loss of PMP-22 gene. PMP-22 gene is the hallmark
of HNPP. The child has completely recovered with physiotherapy
in a month. The point of this case report is that a first peripheral nerve
paresis after a minor traumatism could hide a much more complicated
diagnosis than a trivial traumatism.
P0762. Holoprosencephaly: 10 years of genetic study on 400
patients
C. Dubourg 1,2 , L. Pasquier 3 , C. Bendavid 1 , C. Henry 4 , S. Jaillard 4 , I. Gicquel 1 ,
M. Durou 2 , V. David 1,2 , S. Odent 1,3 ;
1 UMR6061 CNRS, Rennes, France, 2 Génétique Moléculaire, CHU, Rennes,
France, 3 Génétique Médicale, CHU, Rennes, France, 4 Cytogénétique, CHU,
Rennes, France.
Holoprosencephaly (HPE) is the most common brain malformation
resulting from incomplete cleavage of the prosencephalon (1 out of
16.000 live births; 1 out of 250 conceptuses). HPE is associated with a
20
wide spectrum of craniofacial malformations ranging from lethal forms
(alobar HPE with cyclopia) to less severe forms such as lobar HPE
and normal face. The aetiology is very heterogeneous involving environmental
factors, chromosomal abnormalities and at least 7 genes.
Since 1996, our team has started to work on the wide clinical and
genetic variability of holoprosencephaly. Patient samples (foetuses
or children with normal karyotype) and clinical data (from HPE to microforms)
were collected from medical teams in France and Europe.
Systematic mutation analysis and genomic rearrangements of the five
main genes (SHH, ZIC2, SIX3, TGIF, GLI2) were performed. About
19%sequence changes were identified among 350 DNA samples.
The familial cases confirmed an extreme clinical variability. Then, microrearrangements
were detected by QMPSF, MLPA and CGH array
(particularly in foetuses) improving the rate of molecular defects to a
total of 30%. Several patients samples with 2 microdeletions and/or
duplications were identified supporting multiple-hit hypothesis involving
others genetics and/or environmental factors. We performed molecular
prenatal diagnosis four times with foetal US scan and cerebral
MRI screening. At last, we showed involvement of cerebral malformations
as Aprosencephaly/Atelencephaly linked to SIX3 mutations and
cerebellar hypoplasia to SHH gene. Pan-hypopituitarism and cleft lip/
palate were associated with GLI2. This work has improved molecular
diagnosis in Holoprosencephaly and therefore genetic counselling.
P0763. Extented neonatal screening for homocystinuria in the
Qatari population
T. I. M. M. Ben-Omran 1 , H. Gan-Schreier 2 , J. Fang-Hoffmann 2 , G. Abdoh 1 ,
N. Shahbek 1 , H. Al Rifai 1 , M. Lindner 2 , G. F. Hoffmann 2 , M. Kebbewar 3 , J.
Zschocke 3 , J. Zschocke 3 , J. Zschocke 3 ;
1 Hamad Medical Corporation, Doha, Qatar, 2 Department of Pediatrics & Institute
of Human Genetics, Heidelberg, Germany, 3 2Ruprecht-Karls-University,
Heidelberg, Germany.
Homocystinuria is an autosomal recessive disorder of methionine and
homocysteine metabolism caused by a deficiency of cystathionine βsynthase
. We previously reported that homocystinuria due to cystathionine
β-synthase deficiency is common in Qatar with an incidence of
approx. 1:3000. As determinations of methionine in dried blood spots
(DBS) proved insensitive for neonatal screening, we developed a novel
two-tear strategy. To measure total homocysteine (Hcy) in DBS, a robust,
stable HPLC method with tandem mass spectrometry detection
is described, including all practical details and analytical performance
results. For mutation analysis, DNA was extracted from DBS and common
mutations R336C and D234N in the CBS gene were tested for
only native Qatari. Both methods are suitable for processing a large
number of samples.
We have analyzed 6597 newborns from Qatar, of which 2586 were of
Qatari origin. A total of 4 neonates with homocystinuria were identified.
All showed highly elevated Hcy concentrations in DBS whilst methionine
was elevated in two neonates only. Three children were homozygous
for the common mutation R336C; follow-up sequence analysis
in the fourth patient revealed homozygosity for mutation G347S, not
previously observed in the Qatari population. Metabolic screening of
t-HCY in DBS appears to have 100 % sensitivity for the detection of
classical homocystinuria and support a very high incidence of homocystinuria
in Qatar, possibly reaching up to 1:600 and caused by a high
degree of consanguinity. Molecular neonatal screening is feasible but
metabolic screening appears to have a higher sensitivity for the detection
of homocystinuria in Qatar.
P0764. Partial hypoxanthine-guanine phosphoribosyltransferase
deficiency as Lesch-Nyhan syndrome variant - the first case
detected in Lithuania
J. Songailienė 1,2 , A. Matulevičienė 1 , J. Bierau 3 , V. Kučinskas 1,2 , L. Spaapen 3 ;
1 Centre for Medical Genetics, Vilnius University Hospital Santariškių Clinics,
Vilnius, Lithuania, 2 Department of Human and Medical Genetics, Faculty of
Medicine, Vilnius University, Vilnius, Lithuania, 3 Department of Biochemical
Genetics, Academic Hospital Maastricht, Maastricht, The Netherlands.
Lesch-Nyhan syndrome is a rare, X-linked recessive inheritable disorder
caused by a deficiency of the enzyme hypoxanthine-guanine
phosphoribosyltransferase (HPRT) (OMIM #300322). HPRT gene has
been mapped to Xq26-q27 and more than 200 mutations responsible
for this disease have been characterised. Depending on the amount
of residual enzyme activity the spectrum of the disease expression