2008 Barcelona - European Society of Human Genetics

Molecular and biochemical basis of disease
ABCC8 mutations in 64 children with CHI
Form of CHI diffuse focal atypical unknown total
homozygous 3 0 0 1 4
compound heterozygous 7 0 0 0 7
heterozygous 10 9 0 4 23
no mutation 18 1 1 8 28
total 38 10 1 13 62
P05.027
Homozygousity mapping of congenital hyperinsulinism of
infancy (cHi) in italian patients
A. Gessi 1 , M. Proverbio 1 , E. Mangano 1 , R. Spinelli 2 , M. Bove 3 , P. Sogno Valin 3 ,
S. Di Candia 3 , I. Zamproni 4 , S. Mora 4 , L. Bosio 3 , M. Caruso 5 , A. Salvatoni 6 , G.
Chiumello 3 , C. Battaglia 1 ;
1 Department of Science and Biomedical Technologies (DiSTeB) , University of
Milan, Milan, Italy, 2 Institute of Biomedical Technologies (ITB-CNR), Segrate,
Italy, 3 Department of Pediatrics, Endocrine Unit, IRCCS San Raffaele Scientific
Institute, Vita Salute San Raffaele University, Milan, Italy, 4 Laboratory of Pediatric
Endocrinology and BoNetwork, San Raffaele Scientific Institute, Milan, Italy,
5 Department of Pediatrics, University of Catania., Catania, Italy, 6 Department of
Clinical and Biological Science (DSCB) , Pediatric Clinic, University of Insubria,
Varese, Italy.
Congenital hyperinsulinism of infancy (CHI) is a heterogeneous disorder
due to genetic mutations 80% of which are found in genes encoding
both subunits of pancreatic KATP channel ABCC8 and KCNJ11 .
Other causative genes have been identified but, up-to-date, in 30% of
patients the genetic basis of CHI has yet to be determined, suggesting
additional locus heterogeneity .
SNP microarrays have improved the possibility for autozygousity mapping
of rare disorders with founder mutations, in order to identify disease
susceptibility loci .
In our study we have performed a genome wide SNP mapping in twenty
two CHI probands and their families using Affymetrix GeneChip®
250K Human Mapping arrays . Using a complex computational approach,
we identified long contiguous stretches of copy number neutral-homozygous
loci (autozygousity) on chromosomes 1, 5, 7, and 8,
both in consanguineous and in non consanguineous families . Three
patients, two of which carried a causative mutation on ABCC8/KCNJ11
genes, showed a wide common region of homozygousity on chromosome
11p15 . Additionally, two probands shared stretches of homozygousity
on chromosomes 4, 6, 10 ,11 and 18 .
Moreover, one patient, negative for ABCC8/KCNJ11 gene mutations,
showed a homozygous region of 79Mb on chromosome 4 containing
the causative gene HADH . Direct sequencing of the coding region of
HADH gene showed a homozygous C to T transition in exon 6 leading
to a premature stop of the synthetized protein.Further refinement of
other candidate regions by microsatellites marker analysis and linkage
analysis will be necessary to map other disease loci in CHI families .
P05.028
congenital Nephrotic syndrome (cNs) caused by a complex
genotype in the Nephrin gene (NPHs1) revealing 2 novel
mutations
E. Fylaktou 1 , S. Megremis 1 , A. Mitsioni 2 , C. Stefanidis 2 , S. Kitsiou - Tzeli 1 , E.
Kanavakis 1 , J. Traeger - Synodinos 1 ;
1 Medical Genetics, Athens University, “Aghia Sofia” Children´s Hospital, Athens,
Greece, 2 Department of Pediatrics Nephrology “P. A. Kyriakou” Children´s Hospital,
Athens, Greece.
Nephrotic syndrome (NS) is characterized by gross proteinuria, hypoalbumenia,
edema and hyperlipidemia, which in CNS manifest in utero
or within 3 months after birth . Inherited impairments of the glomerular
filtration barrier are an important cause of NS, and in CNS and infantile
NS ~60% of cases are caused by mutations in 4 genes: Nephrin
(NPHS1), Podocin (NPHS2), Laminin-β2 (LAMB2) and Wilm’s Tumor
suppressor gene (WT1). In a newborn with clinical findings compatible
with CNS, and his parents, the 27 exons of the NPHS1 gene and
8 exons of the NPHS2 gene were subject to direct DNA sequencing
analysis and mutation detection analysis (Surveyor mutation detection
kit, Transgenomic, Elancourt, France) . No mutations were found in the
NPHS2 gene . However, the proband was found to have three heterozygous
mutations in NPHS1: c .1096A>C (p .S366R) in exon9, c .649_
650delGT (p .Cys217fsX) in exon6 and c .791C>G (p .P264R) in exon7 .
The mother was found to be heterozygous for c .1096A>C (p .S366R)
while the father was heterozygous for the novel c .649_650delGT,
the known c .791C>G (p .P264R) and additionally a novel c .1619C>A
(p .A540E) in exon12 . In-silico analysis (SIFT, http://blocks .fhcrc .org/
sift/SIFT .html, polyphen, http://genetics .bwh .harvard .edu/pph) indicated
that p.A540E is not pathological, which is confirmed since the unaffected
father also carries c .649_650delGT (p .Cys217fsX) in exon6 and
c .791C>G (p .P264R) in exon7 . The novel 2bp deletion is predicted to
cause a premature termination codon, and since it is apparently incis
to the previously described c .791C>G mutation, presumably the
deletion mutation has the over-riding impact on the expression of the
phenotype .
P05.029
Creatine deficiency syndromes in Spain: enzymatic and
molecular genetic studies
P. Alcaide 1,2 , A. Ribes 3,4 , A. Arias 3,4 , R. Artuch 5,4 , J. Campistol 5,4 , B. Merinero 1,2 ,
M. Ugarte 1,2 , P. Rodríguez-Pombo 1,2 ;
1 Centro de Biología Molecular Severo Ochoa. Dpto Biología Molecular . Universidad
Autónoma de Madrid, Madrid, Spain, 2 CIBERER, Madrid, Spain, 3 Instituto
de Bioquímica Clínica, Barcelona, Spain, 4 CIBERER, Barcelona, Spain, 5 Hospital
San Joan de Deu, Barcelona, Spain.
Creatine deficiency syndromes (CDS) are a group of underdiagnosed
inborn errors caused by defects in the biosynthesis of creatine or its
transporter . The two defects affecting biosynthesis, namely arginineglycine
amidinotransferase (AGAT) and guanidinoacetate methyltransferase
(GAMT) are autosomal recessive traits, whereas the creatine
transporter (CRTR) is an X-linked disorder .
We present the results of a collaborative CDS prospective screening
based on abnormal metabolite excretion or decreased creatine signal
in brain MRS in a cohort of patients with mental retardation (MR) and/
or suspected metabolic disorder . Three GAMT and nine CRTR cases
were selected. Confirmatory diagnosis was assessed by measuring
GAMT activity or creatine uptake in fibroblasts using MS/MS methods.
Direct sequencing analysis of GAMT and SLC6A8 genes was carried
out .
In two of the three potential GAMT patients, deficient activity was
confirmed in fibroblasts (T (p .Q106X) and c .407C>T
(p .T136M), both in heterozygous fashion . Four out of the nine CRTR
cases selected (two from the same family) presented a deficient creatine
transport in fibroblasts. Mutational analysis of SLC6A8 gene led
us to identify three nucleotide changes, two of them novel: c .1210G>C
(p.A404P); c.1079-1081delTCT (p.F360del). All changes identified in
both genes fulfilled several criteria to be considered as pathogenic
mutations .
Our results confirm the presence of CDS patients in a broad population
of neurological patients including those with MR of unknown aetiology
highlighting the importance of screening for these potentially treatable
disorders .
P05.030
two novel mutations in the CYP A gene causing congenital
Adrenal Hyperplasia and severe Hypertension in a 46,XY Female
Patient
S. Kofman-Alfaro 1 , N. Nájera 1 , N. Garibay 2 , G. Queipo 1 ;
1 Hospital General de Mexico, Facultad de Medicina Universidad Nacional
Autónoma de México SDEIPTID.05-1, Mexico City, Mexico, 2 Endocrinology
Department, Hospital Infantil de México Federico Gómez, Mexico City, Mexico.
In the steroidogenic pathway, cholesterol is converted to pregnenolone
which can be processed to either mineralocorticoids in adrenal glands
or to sex steroids in the gonads. This effect is due to a 17α-hydroxylation
and 17, 20-lyase activity respectively . The microsomal enzyme
cytochrome 450c17 has a deep impact in the progress of the steroidogenic
pathway because it has both 17α-hidroxilase and 17, 20-lyase
enzymes activities . Mutations in the CYP17A1 gene cause 17α-hidroxilase
deficiency (17OHD), an unusual form of Congenital Adrenal
Hyperplasia (CAH) . This anomaly occurs in 1/50000 newborns and
it accounts for nearly 1% of the CAH cases . Classical adrenal and
gonadal phenotype of the complete 17OHD includes hypertension and
hypokalemia, secondary to massive overproduction of the 17-deoxysteroid,
11-deoxycorticosterone (DOC) and corticosterone in patients
with a 46,XY female phenotype . Nevertheless, there is considerable
variation in the clinical and biochemical features of 17OHD . Approxi-