New genetic approaches in congenital heart disease

Congenital heart disease (CHD) is the most frequent congenital disorder in
newborns, affecting 7 out of 1000 live births . Until recently most children
with CHD died during childhood. Due to the remarkable advances in prenatal
diagnosis, in surgical as well as perioperative techniques, and close follow-up
including modern imaging modalities, mortality has substantially declined.
Today, more than 90% of children born with CHD reach adulthood.
Causes of CHD are often divided into genetic versus non-genetic categories.
Well-recognized and studied non-genetic causes of CHD include infections (e.g.
rubella), environmental teratogens (e.g. dioxins) and maternal intoxications
(e.g. alcohol, thalidomide). With respect to genetic causes, a number of
genetic studies have uncovered gene defects that are unequivocally related to
risk for CHD (reviewed in ). However, in contrast to other cardiac disorders
such as the cardiomyopathies and the primary electrical disorders, progress in
uncovering the genetic underpinnings of CHD has been slow and, with few
exceptions, classical genetic approaches such as linkage analysis have largely
failed. This is likely due to several factors. The lethality of the disease (in
particular in the past) meant that there were only very few families that were
large enough for classical linkage studies. Furthermore, the inheritance
pattern of the disease is likely more-complex then previously appreciated.
Arguments in favor of a more-complex inheritance pattern for CHD include the
large number of sporadic cases (i.e. in absence of familial aggregation), and
the fact that in case of familial aggregation, affected family members present
with heterogeneous CHD defects.
The new genetic technologies that have become available in recent years, namely
exome and genome sequencing, now provide new opportunities for gene discovery
in CHD. These new technologies now allow testing of alternative inheritance
models for the disease such as the occurrence of de novo mutations or the
homozygous/compound heterozygous inheritance of variants that occur at very low
frequency in the general population.

The objective of this study is to identify novel genes causing congenital heart
disease.

For this study patients with a severe and complex congenital heart disease and
their parents are selected. In these parent-child trios genetic research will
be conducted to identify de novo-mutations or very rare homozygous/compound
heterozygous mutations causal to the congenital heart disease. Furthermore, we
will try to identify rare variants that are shared by multiple probands. After
obtaining informed consent performing a physical exam, subjects will undergo
venous blood draw to collect and isolate DNA. Afterwards exome of whole genome
sequencing (next generation sequencing, NGS) will be used to analyze their DNA
and to identify de novo or very rare variants.These variants will be validated
with PCR and Sanger sequencing. The identified genes will be screened in
aditional probands from the CONCOR database assess the causality of the genes.
If there is convincing evidence about the possible causality of the identified
genes, they will be studied in functional and animal studied in the future.

Minimal risks are associated with participation to this study. There is the
possibility of identifying mutations in genes that are or are not related to
the congenital heart defect and will have clinical implications for the patient
or his/her parents. In this case, the unexpected findings will be discussed in
a team of experts and will be reported to the subject. This individual will
receive counseling at the out patient clinic of the Department of Clinical
Genetics AMC.

In this study we expect to identify novel genes for CHD. This work will provide
evidence for alternative inheritance patterns for these dieases, namely the
occurrence of de novo mutations and/or the occurrence of homozygosity for rare
genetic variants (recessive inheritance) in the pathogenesis of the disease.
Such data will have important implications for clinical patient care.
Importantly, as the survival of patients with CHD has improved dramatically,
nowadays CHD patients reach reproductive age and can pass on causal gene
defects to their offspring. The identification of causal genetic variants will
allow for the first time genetic counseling of CHD patients and in the future
allow for the possibility of pre-implantation genetic diagnostics for couples
who wish to become parents. New generation sequencing is emerging as a powerful
and cost-effective tool for dissecting the genetic basis of disorders that have
remained for long intractable.