2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
non-consanguineous family the 5-year-old patient was examined . The
girl survived infancy problems and by 5 years had only mild ichthyosiform
skin lesions . Homozygosity for ALOX12 mutation Ala597Glu was
detected .
P05.144
investigation of cYFiP1 and cYFiP2 genes in patients with
autosomal recessive non-syndromic mental retardation
G. Guven1 , H. Kayserili2 , A. Uzumcu2 , H. Eris2 , B. Karaman2 , S. Basaran2 , O.
Uyguner2 ;
1 2 Istanbul Medical Faculty , Child Health, Istanbul, Turkey, Istanbul Medical Faculty,
Child Health, Istanbul, Turkey.
Autosomal recessive inheritance of non-syndromic mental retardation
(ARNSMR) may account for approximately 25 % of all patients with
non-syndromic mental retardation (NSMR) . Up-to-date, 12 chromosomal
loci have been mapped and only four genes have been identified
to cause ARNSMR. CYFIP1 (15q11) and CYFIP2 (5q33.3) genes,
belonging to CYFIP family by sequence similarity, interests the scientist
if any role in mental retardation due to their interactions with FMR1
protein . Suggested function of CYFIP1 in axonal growth and brain
specific editing of CYFIP2 was of our further interest to investigate
these genes in our highly selected ARNSMR families . 20 consanguineous
families with one or more affected individuals were included into
our study after through clinical check up to exclude any known syndromes
and/or chromosomal or sub-telomeric abnormalities followed
by search from fragile-X point of view . Our strategy was to perform homozygosity
mapping to CYFIP1 and CYFIP2 genes and sequence the
informatively homozygous families . Four in/delSNPs for CYFIP1 gene
and four in/del SNPs plus 2 STRs for CYFIP2 gene were selected to
be used for linkage . Presently our investigation is continuing and our
results will be presented at our poster session .
P05.145
NPHS recurrent and novel mutations in children from Greece
and cyprus with steroid-resistant nephrotic syndrome
K. Voskarides 1 , C. Makariou 1 , G. Papagregoriou 1 , N. Stergiou 2 , N. Printza 3 , E.
Alexopoulos 4 , A. Elia 5 , F. Papachristou 3 , A. Pierides 6 , E. Georgaki 2 , C. Deltas 1,7 ;
1 University of Cyprus, Nicosia, Cyprus, 2 Agia Sophia Childrens Hospital, Athens,
Greece, 3 Hippokration Hospital, Aristotle University of Thessaloniki, Thessaloniki,
Greece, 4 Aristotle University of Thessalloniki, Thessaloniki, Greece,
5 Archbishop Makarios III Hospital, Nicosia, Cyprus, 6 Hippokration Private
Hospital, Nicosia, Cyprus, 7 The Cyprus Institute of Neurology and Genetics,
Nicosia, Cyprus.
The idiopathic nephrotic syndrome occurs mainly in children, most of
whom respond well to steroid therapy, however 15-20% of these children
are steroid-resistant, frequently progressing to end-stage renal
failure . Mutations in the NPHS2 gene, encoding podocin, are an important
cause of infantile sporadic Steroid Resistant Nephrotic Syndrome
(SRNS) occurring in 2 .8-28% of the cases, depending on the studied
population . To a lesser extend, mutations in the WT1 gene are also
found in patients with SRNS. For the first time in Hellenic population,
we performed mutational analysis of the NPHS2 (including promoter
region) and WT1 (exons 8 and 9) genes, studying 18 children from
Greece and 6 from Cyprus with SRNS . For our investigation we used
a screening method based on the SURVEYOR endonuclease digestion,
which identifies and cleaves at mismatched base pairs in heteroduplexes,
followed by direct PCR-DNA sequencing . No mutation or
polymorphism was identified in exons 8 and 9 of WT1 . In the NPHS2
gene, we identified two known mutations (418delG, R229Q) and one
novel mutation (L305P), in two out of the 24 children (8 .3%), in addition
to nine known polymorphisms . Amino acid residue L305 is at the Cterminal
of the protein and is highly conserved evolutionarily, possibly
because of the functional association of this domain with nephrin and
CD2AP . Although the studied cohort was small, our investigation supports
the usefulness of the availability of a molecular diagnostic facility
for SRNS cases, in a routine clinical setting, as it assists in the correct
management of such children .
P05.146
LmX1B mutational analysis in two Nail-patella syndrome
patients: evidence for the presence of mosaicism
M. Marini 1 , A. Baban 1 , D. Maria Teresa 1 , H. Gaspar 2 , I. Mammi 3 , M. Lerone 4 , R.
Ravazzolo 1 , R. Bocciardi 1 ;
1 Molecular Genetics and Cytogenetics Unit, Genoa, Italy, 2 Istitute for Medical
Genetic, University of Zurich, Zurich, Switzerland, 3 ULSS 13 Regione Veneto
Consultorio genetico, Dolo, Italy, 4 Molecular Genetics and Cytogenetics Unit, G.
Gaslini Institute, Genoa, Italy.
Nail-patella syndrome (NPS, MIM#161200) is a rare autosomal dominat
disorder characterized by hypoplastic or absent patellae, dystrophic
nails, dysplasia of
the elbows and iliac horn, and, less frequently, ocular damage .
In the 40% of cases a glomerular defect is involved and inter- and
intra-familial expression variability is reported .
Mutations in the human LMX1B gene have been demonstrated to be
responsible for NPS in 90% of cases .
In this study we present evidence of somatic mosaicism in two cases
of NPS .
The first case is a patient carrying the c.599G>A substitution in exon
4
(Arg200Gln) . This mutation was also detectable in the healthy father
as a low height A peak superimposed to G . On the contrary, in the
patient the two peaks appeared at equal height, as expected in a heterozygote
. The second patient is heterozygous for the c .592C>T substitition
in exon 4 (Arg198Stop) . Also in this case the hypothesis of
mosaicism in the healthy father was raised by the presence of the C
and T peaks with significantly different height. These analyses were repeated
in several independent reactions with fully comparable results .
The presence of the mutated alleles in the two fathers was confirmed
by subcloning the PCR products: as expected in the hypothesis of mosaicism,
the wild-type allele-bearing colonies were significantly more
represented than the colonies with the mutated one .
To our knowledge these are the first reported cases of inheritance of a
mutated LMX1B allele in NPS patients from a mosaic parent .
P05.147
screening for melanocortin-4 receptor mutations in a cohort of
Dutch obese children
L. van den Berg1 , F. Blom1 , H. Delemarre-van de Waal2 , P. Heutink3 ;
1departments of Paediatrics and Clinical Genetics, section Medical Genomics,
VU University Medical Center, Amsterdam, The Netherlands, 2department of Paediatrics, VU University Medical Center, Amsterdam, The Netherlands,
3section Medical Genomics, VU University Medical Center, Amsterdam, The
Netherlands.
The most common monogenic form of obesity is caused by mutations
in the gene encoding the melanocortin 4 receptor (MC4R) . This receptor
integrates orexigenic and anorexigenic signals in the hypothalamus
to regulate food intake and energy expenditure . We have screened the
coding sequence and the minimal promoter region of MC4R of 221 random
patients from our VUmc center for childhood obesity . We found 18
variants in these patients, four of which were not described previously .
Two of the new variants (-1101C>T and -312T>C) are not expected to
be pathogenic because they are not evolutionary conserved in mammals
and because they are not located in predicted regulatory regions
of the gene. The new variant -705A>T may influence gene expression
because it is located in a regulatory element . This variant was found
in a 3-year-old girl with a body mass index standard deviation score
(BMI-SDS) of 3 .4 . The new variant 910C>T results in a leucine > phenylalanine
change . It was found in a 17-year-old girl with a BMI-SDS
of 3 .4 . Of the 14 known variants that we found, two have been shown
to have functional effects by others (Tyr35STOP and G231S) . In conclusion,
we detected two pathogenic mutations and several possible
pathogenic mutations in 221 random patients of our obesity clinic . We
will extend our research by screening additional patients, studying cosegregation
of mutations and obesity in families, studying phenotypic
characteristics of MC4R mutation carriers, and functional studies of
new mutations .