2009 Vienna - European Society of Human Genetics

Molecular basis of Mendelian disorders
RNA splicing. In the second family, a substitution in intron 2 (+5g>a)
has been found with unknown effect on splicing.
P12.037
Analysis of RUNX in a Danish cohort of cleidocranial dysplasia
patients revealed two large chromosomal deletions and 14
pathogenic point mutations
L. Hansen1,2 , A. K. Riis1 , H. Hove1 , E. Lauridsen1 , H. Eiberg1 , S. Kreiborg1 ;
1 2 Copenhagen University, Copenhagen, Denmark, The Wilhelm Johannsen
Centre for Functional Genome Research, Copenhagen, Denmark.
Cleidocranial dysplasia (CCD) is an autosomal dominant inherited disease
caused by mutations in the Runt gene RUNX2 (alias CBFA1;
OMIM 600211). No other candidate genes or loci are known from family
studies. In a cohort of 19 Danish CCD patients, pathogenic RUNX2
mutations were found in 16 cases. This represents a higher mutation
detection rate than reported by similar studies (1). The mutations represent
six missense mutations, two nonsense mutations and four shift
mutations plus two large chromosomal deletions. Eight mutations were
novel and six were known mutations, and two mutations were found
in two families each. The large deletions at 6p12.3-21.1 represent 500
Kbp and 750 Kbp respectively and included exon 1 to 6 of RUNX2 and
the proximal located SUPT3H gene. The point mutations were mainly
found in the Runt domain and the nuclear leading sequence of RUNX2.
Two repeat variations were found in the poly alanine and glutamine
repeats in three cases. These were judged to be non-pathogenic that
additional functional mutations were found in the coding regions.
In total 9 different cohorts of CCD patients including this work, represent
199 families and RUNX2 mutations were found in 124 of these,
which represent 61% compared to the 84% in this study. Identification
of the two large deletions by mutation screening of CCD patients has
not been reported before and suggests that future mutation studies
must include analyses for large chromosomal deletions or duplications.
P12.038
A novel VPs13B mutation in two brothers with cohen syndrome,
cutis verticis gyrata and sensorineural deafness
A. Mégarbané 1,2 , R. Slim 3 , G. Nürnberg 4 , I. Ebermann 5 , P. Nürnberg 4 , H. J.
Bolz 5 ;
1 Unité de Génétique Médicale, Faculté de Médecine, Université Saint-Joseph,
Beirut, Lebanon, 2 Institut Jérôme Lejeune, Paris, France, 3 Departments of Human
Genetics and Obstetrics Gynecology, McGill University Health Centre,
Montreal, QC, Canada, 4 Cologne Center for Genomics and Institute for Genetics,
University of Cologne, Cologne, Germany, 5 Institute of Human Genetics,
University Hospital of Cologne, Cologne, Germany.
We have previously described a syndrome characterized by microcephaly,
cutis verticis gyrata (CVG), retinitis pigmentosa, cataracts,
hearing loss and mental retardation (MIM #605685) in a non-consanguineous
Lebanese family. In view of the rarity of the disorder and
the high rate of inbreeding in Lebanese, we assumed an autosomal
recessive trait inherited from a common ancestor. Indeed, genomewide
linkage analysis resulted in a single region on chromosome 8q22
with homozygosity by descent in the patients, comprising the Cohen
syndrome (CS) gene, VPS13B. We identified a novel homozygous
splice site mutation that activates a cryptic acceptor site in exon 52.
CVG and deafness have never been reported in CS. This may reflect
a variant of CS. Alternatively, there may be an overlap of genetic conditions:
Offspring from consanguineous parents may be homozygous
for mutations in unlinked genes. Deafness and CVG could be caused
by mutations in different loci. However, our linkage data do not suggest
another causative locus. Another mutated gene or modifier locus
may segregate in cis and be responsible for deafness and CVG, but
no deafness locus maps to our 8q22 region. In contrast, the frequent
association of CVG with mental retardation suggests that it may be a
rare manifestation of CS. The mapping approach conducted here can
serve as a paradigm in rare recessive phenotypes: The prevalence of
homozygosity for the causative mutations can also be high in families
without documented consanguinity, due to a distant common ancestor,
especially in small populations with a high rate of inbreeding.
P12.039
Large deletion comprising COL A causes aortic dissection
J. Meienberg1 , S. Neuenschwander2 , A. Patrignani2 , S. Alonso1 , E. Arnold1,3 ,
C. Henggeler1 , R. Perez1 , S. Azzarello-Burri4 , B. Steiner4 , K. Spanaus5 , S. Regenass6
, C. Giunta3 , M. Rohrbach3 , T. Carrel7 , B. Steinmann3 , W. Berger1 , G.
Matyas1 ;
1Division of Medical Molecular Genetics and Gene Diagnostics, Institute of
Medical Genetics, University of Zurich, Zurich, Switzerland, 2Functional Genomics
Center Zurich, ETH and University of Zurich, Zurich, Switzerland, 3Division of Metabolism and Molecular Pediatrics, University Children’s Hospital, Zurich,
Switzerland, 4Institute of Medical Genetics, University of Zurich, Zurich, Switzerland,
5Institute for Clinical Chemistry, University Hospital, Zurich, Switzerland,
6 7 Division of Clinical Immunology, University Hospital, Zurich, Switzerland, Clinic
for Cardiovascular Surgery, University Hospital, Berne, Switzerland.
Aortic dissection (AD) is a life-threatening condition associated with
high rates of morbidity and mortality. AD can occur non-syndromic,
e.g. in the case of familial thoracic aortic aneurysms leading to type
A dissections (TAAD), or in association with genetic syndromes, such
as Marfan syndrome (MFS) caused by FBN1 mutations, Loeys-Dietz
syndrome caused by TGFBR1 or TGFBR2 mutations, and vascular
Ehlers-Danlos syndrome (EDS IV) caused by COL3A1 mutations. Although
mutations in FBN1, TGFBR1, and TGFBR2 account for the
majority of AD cases referred to us for molecular genetic testing, we
have encountered negative genetic testing results in a large group of
patients, suggesting the involvement of other genes, e.g. COL3A1,
ACTA2 or MYH11, as the genetic cause of AD. In this study, we have
assessed the impact of COL3A1 mutations in patients with suspected
MFS in whom mutation screening in FBN1 and/or TGFBR1 and TGF-
BR2 revealed no disease-causing sequence variation. MLPA analysis
of 133 unrelated patients identified the heterozygous deletion of
the entire COL3A1 gene in one patient with abdominal AD. Subsequent
microarray analyses and sequencing of breakpoints revealed
the deletion size of 3,408,306bp. Furthermore, DNA sequencing of 29
unrelated patients identified two novel exonic COL3A1 sequence variants
(c.1105G>A and c.1854A>T). Our data not only emphasize the
importance of screening for COL3A1 mutations in comprehensive genetic
testing of AD patients with suspected MFS not fulfilling the Ghent
criteria, but also extend the molecular etiology of EDS IV by providing
hitherto unreported evidence for true haploinsufficiency of COL3A1.
P12.040
Variant phenotype in individuals with severe cYP 21 mutations
M. Kocova, V. Anastasovska, E. Sukarova-Angelovska, E. Kochova;
Pediatric Clinic, Skopje, Macedonia, The Former Yugoslav Republic of.
Congenital adrenal hyperplasia(CAH) is a common autosomal recessive
disease most frequently occurring due to mutations in the CYP
21 gene. Several “severe” mutations are reported to cause severe salt
wasting(SW) form of the disease. However, homozygous carriers of
the mutations without clinical symptoms have been described.
Aim. To analyze severe CYP 21 mutations in patients with CAH and
their relatives and to analyze genotype/phenotype correlation.
Material and methods. Sixteen children (6 boys and 10 girls) with CAH
from 12 families were diagnosed with salt wasting CAH. The diagnosis
was confirmed by high 17-OHProgesterone levels.
Molecular analysis was performed in all patients and 22 first degree
relatives with ACRS-PCR method detecting 11 frequent mutations.
Total of 66 chromosomes were analyzed, 32 in patients, and 34 in
relatives.
Results. Intron 2 splicing mutation (nucleotide 656) was the most
common (33/66=50%), followed by codon 318(exon 8) mutation
(15/66=22.9%). Complex mutations were present in two children and
two relatives. All 16 children with SW had severe mutations. However,
6 relatives were also homozygous for severe or had complex mutations
without symptoms. Prenatal diagnosis helped prompt treatment
of two newborn boys. Four of the relatives had I2 homozygous splicing
mutation. “Leaky” mutation might be an explanation in these cases.
However, the complex mutations are more difficult to explain.
Conclusion. Although severe mutations were associated with the SW
form, it is difficult to explain the homozygosity in healthy relatives. This
complicates the prenatal diagnosis and counseling. Further analysis in
individuals with no genotype/phenotype correlation is warranted.