2009 Vienna - European Society of Human Genetics

Molecular and biochemical basis of disease
SSCP or DHPLC and then by sequencing. Forty-two patients (40%, 8
group A, 34 group B) underwent surgical miectomy, 32 (30%, 19 group
A, 13 group B) had heart failure requiring transplantation, 8 (8%, 6
group A, 2 group B) died suddenly and 23 (22%, 8 group A, 15 group
B) were outpatients.
We identified 21 mutations in group A (51%) and 24 in group B (38%).
The detection rate for SSCP/DHPLC was 21/59 mutations (36%), while
by sequencing was 24/46 (52%). Twenty-five mutations were not previously
reported. Four variants occurred in group A (10 patients) and
group B (4 patients). They were associated with different outcomes
and age at onset.
No significant differences in genetic causes were found between childhood-
and adulthood-onset HCM or between patients with diverse outcomes.
Although most patients had a severe HCM that could explain
this lack of differences, a wide genome approach should be useful to
detect potential genetic modifiers.
P16.24
Complex sarcomeric genetic status is not an important modifier
of disease severity in MYBPC associated hypertrophic
cardiomyopathy
M. van Tienhoven, Y. M. Hoedemaekers, M. Michels, F. J. ten Cate, D. F. Majoor–Krakauer,
D. J. J. Halley, D. Dooijes;
Erasmus Medical Center, Rotterdam, The Netherlands.
Background: Hypertrophic cardiomyopathy (HCM) is a genetically heterogeneous
disorder with a high degree of inter- and intrafamilial variability
in clinical expression. Mutations in more than 11 genes, mostly
encoding sarcomeric proteins, are known to cause HCM. Variability in
clinical expression is thought to be caused by the action of currently
unknown modifying factors. Current consensus partially explains the
variability in clinical expression by the effect of additional, secondary,
mutations in sarcomeric genes.
To analyse whether a complex HCM genotype is an important modifier
of disease severity in HCM we completely analysed 11 HCM genes in
a large cohort, homogeneous with respect to primary HCM causing
mutation.
Methods: We analysed the complete coding regions of MYH7, MYB-
PC3, MYL2, MYL3, TNNT2, TNNI3, TNNC1, ACTC1, TMP1, TCAP
and CSRP3 in a large cohort of patients with a truncating MYBPC3
mutation as primary HCM defect. The patients from the cohort were
clinically diagnosed as either having a ‘mild’ (no cardiac complaints,
IVS200 chromosomes).
Furthermore, we identified 4 known SNPs/variants previously
reported as mutations for HCM. Our DNA resequencing array appears
to date as the most rapid and cost-effective technology for mutation
screening in HCM. Further improvement of the software may detect
small insertions/deletions in the future. The HCM-array provides a first
attempt of high throughput sequencing methodology which will further
develop and probably become the method of choice for routine molecular
diagnosis of heterogeneous disorders such as HCM.
P16.26
Haploinsufficiency of MYBPC3 as the genetic cause of
sarcomeric hypertrophic cardiomyopathy
L. Pezzoli 1 , D. Marchetti 1 , A. Iacovoni 2 , C. Simon 2 , D. Barachetti 1 , A. R. Lincesso
1 , S. Pentiricci 2 , P. Ferrazzi 2 , M. Iascone 1 ;
1 Genetica Molecolare - USSD Lab. Genetica Medica, Ospedali Riuniti, Bergamo,
Italy, 2 Dipartimento Cardiovascolare, Ospedali Riuniti, Bergamo, Italy.
Hypertrophic cardiomyopathy (HCM, OMIM#192600) is an inherited
myocardial disease that shows a large genetic and allelic heterogeneity.
Over 300 mutations spread among several genes encoding myofilament,
calcium-handling and mitochondrial proteins have been identified.
The most common form is sarcomeric HCM, with hundreds of
disease-associated mutations found in more than 8 genes. Mutations
in MYH7 (β-myosin heavy chain) and MYBPC3 (myosin-binding protein
C) are responsible of about 60% of all HCM cases. The observation
that most variants found in sarcomeric genes are missense mutations
led to the proposal of dominant negative action as the pathogenic
mechanism. Instead, MYBPC3 point mutations generate frequently
truncated protein suggesting haploinsufficiency as the cause of the
disease. We hypothesized that larger gene rearrangements not detectable
by sequencing may be found in HCM patients. We analyzed
MYBPC3 gene by MLPA in 36 patients referred to our laboratory with
clinical and histological diagnosis of HCM. All patients were negative
for MYBPC3 and MYH7 point mutations. We found in 1 patient a partial
deletion spanning from exon 28 to 34 of MYBPC3. This patient
was a 31 years old male with an obstructive HCM, requiring surgical
miectomy at the age of 25. Similar severe clinical manifestations were
found in patients with MYBPC3 missense mutation leading to truncated
proteins. The observation that the phenotype of this patient is
indistinguishable from those of patients with point mutations supports
the hypothesis that haploinsufficiency is the mechanism at the basis of
MYBPC3-associated HCM.
P16.27
Genetic diagnostic of hypertrophic cardiomyopathy using mass
spectrometry arrays and high resolution melting
V. Lanca1 , H. Oliveira1 , D. Brito2 , H. Madeira2 , M. P. Bicho1 , A. R. Fernandes1 ;
1 2 Centro de Metabolismo e Endocrinologia, Lisboa, Portugal, Centro de Cardiologia
da Universidade de Lisboa, Lisboa, Portugal.
Hypertrophic Cardiomyopathy (HCM), a relatively common genetic
myocardial disorder (about 1:500), is the most frequent cause of sudden
death in young athletes. This autosomal dominant genetic disease,
caused frequently by mutations in sarcomeric genes, is characterized
by a hypertrophied, non-dilated left ventricle. Genetic testing of
HCM-patients, valuable for diagnosis, is hampered by the multiplicity
of genes (20) and mutations (609) involved. Available genetic diagnostic
services consist in the analysis of only the most frequently mutated
genes, failing to detect a mutation in 1/3 of the probands. Coupling two
high-throughput techniques, Mass Spectroscopy Genotyping (MSG)
and High Resolution Melting (HRM), enabled us to study all the 20
HCM-associated genes, thus finding mutations in CSRP3 (missed