A COMPOUND-HETEROZYGOTE MUTATIONS IN PATIENTS
WITH AUTOSOMAL-DOMINANT MARFAN SYNDROME
Cibulkova P.1, 2, Richterova R.1, 2, Dvorakova M.1, 2, Krenkova R.1 , 2, Augste E.1, 2
1Laboratory of Medical Genetics - Department of Molecular Biology, AGEL Laboratories, Novy Jicin, Czech Republic
2Education and Research Institute AGEL, Prostejov, Czech Republic
OBJECTIVES
METHODS
Marfan syndrome (MFS) is known as an autosomal dominant genetic
disorder caused by mutation in FBN1 gene (15q15-q21.1.), resulting in
defective glycoprotein fibrillin-1. The prevalence of MFS has been estimated
at 1/5 000, and more then 25% of patients represent sporadic case.
It is a multisystem connective tissue disease, mainly involving the
cardiovascular, ocular and skeletal systems. The most serious of them is
aortic root dilation and dissection. However, there is a wide range of clinical
variability both within and between families with Marfan syndrome as well as
in individuals.
We describe four cases of rare compound-heterozygous mutations in FBN1
gene.
We performed molecular analysis of all exons of FBN1 gene in order to
identify pathogenic mutations in unrelated patients with clinical diagnosis of
MFS.
• DNA was isolated from peripheral blood (Qiagen)
• 750 patients were analyzed by SSCP
• 350 patients were analyzed by NGS (Junior 454, Roche)
• all samples were also performed by MLPA (MRC-Holland)
• all detected sequence variants were subjected to in silico predictions for
its effect on protein function
• all potentially clinically relevant changes were confirmed by Sanger
sequencing
FAMILY 1
FAMILY 2
Proband 1´s features: aorta dilatation and dissection, scoliosis, pectus excavatum, joint
hypermobility, wrist and thumb sign, facial features.
Found sequence variants:
c.2953G>A (p.Gly985Arg) and c.7852G>A (p.Gly2618Arg)
Proband 2´s features: aorta dilatation, scoliosis, flat feet, pectus excavatum, joint
hypermobility, facial features.
Found sequence variants:
c.2956G>A (p.Ala986Thr) and c.7099G>T (p.Gly2367*)
1) c.2953G>A (p.Gly985Arg) - de novo
1) c.2956G>A (p.Ala986Thr)
Pathogenicity clues
2
1/2
Align GVGD
class C65 (pathogenic)
SIFT
1
Align GVGD
class C0 (benign)
deleterious
SIFT
tolerated
Mutation taster
disease causing mutation
Mutation taster
disease causing mutation
PolyPhen-2
probably damaging
PolyPhen-2
possibly damaging /
benign
1
1
Databases
1
ClinVar
/
Databases
Uniprot
possibly pathogenic
ClinVar
uncertain significance
dbSNP
/
Uniprot
/
HGMD
disease causing mutation
dbSNP
uncertain significance /
likely benign
HGMD
disease causing mutation?
1
1/2
2) c.7852G>A (p.Gly2618Arg)
Proband 1
We detected two mutations in FBN1 gene which
are probably responsible for Marfan syndrome.
Pathogenicity clues
Pathogenicity clues
Align GVGD
C15 (likely benign)
SIFT
deleterious
Mutation taster
disease causing mutation
PolyPhen-2
probably damaging
Databases
ClinVar
uncertain significance
Uniprot
possibly pathogenic
dbSNP
likely pathogenic
HGMD
/
2) c.7099G>T (p.Gly2367*) - de novo
Pathogenicity clues
The proband 2 is a carrier of compoundheterozygot sequence variations. Paternal
mutation (1) is associated with light phenotype
and relationship with MFS is unknown.
Diagnosis of MFS was confirmed due to de
novo mutation with STOP codon (2).
Align GVGD
STOP codon
SIFT
STOP codon
Mutation taster
STOP codon
PolyPhen-2
STOP codon
Databases
ClinVar
/
Uniprot
/
dbSNP
/
HGMD
/
FAMILY 3
FAMILY 4
Proband 3´s features: reduced upper segment, wrist and thumb sign, pectus excavatum,
joint hypermobility, arachnodactyly, ectopia lentis, mitral valve prolapse.
Found sequence variants:
c.6331T>C (p.Cys2111Arg) and c.6577G>A (p.Gly2193Lys)
Proband 4´s features: arachnodactyly, joint hypermobility and ectopia lentis, mitral valve
prolapse.
Found sequence variants:
c.2088C>G (p.Cys696Trp) and c.3509G>A (p.Arg1170His)
1) c.6331T>C (p.Cys2111Arg) - de novo
1) c.2088C>G (p.Cys696Trp)
Pathogenicity clues
2
2
1/2
The proband 3 is a little boy and clinical signs
are not yet clear. One mutation (1) is definitely
associated with MFS. The second sequence
change (2) isn´t described as clearly
pathogenic. This paternal variation has also
proband´s healthy brother.
Align GVGD
class C0 (benign)
SIFT
Pathogenicity clues
1/2
Align GVGD
class C65 (pathogenic)
deleterious
SIFT
deleterious
Mutation taster
disease causing mutation
Mutation taster
disease causing mutation
PolyPhen-2
possibly damaging /
benign
PolyPhen-2
probably damaging
1/2
1/2
Databases
Databases
ClinVar
/
ClinVar
/
Uniprot
/
Uniprot
possibly pathogenic
dbSNP
/
dbSNP
/
HGMD
HGMD
disease causing mutation
disease causing mutation
(Shprintzen-Goldberg sy.)
1/2
2) c.6577G>A (p.Gly2193Lys)
2) c.3509G>A (p.Arg1170His)
Pathogenicity clues
Pathogenicity clues
Align GVGD
class C0 (benign)
Align GVGD
class C0 (benign)
SIFT
tolerated
SIFT
tolerated
Mutation taster
disease causing mutation
Mutation taster
disease causing mutation
PolyPhen-2
possibly damaging /
benign
PolyPhen-2
benign
Databases
ClinVar
/
Uniprot
/
dbSNP
uncertain significance
HGMD
/
Databases
The proband 4 is from family where both
mutations are in the one FBN1 allele that was
inherited across three generations.
ClinVar
uncertain significance
Uniprot
possibly pathogenic
dbSNP
pathogenic
HGMD
disease causing mutation?
RESULTS and CONCLUSION
We are reported four cases with compound-heterozygous MFS. This shows on incomplete dominance of detected FBN1 mutations. The phenotypes of proband´s
heterozygous family members are light, did not cause the complete MFS and they do not meet the Ghent clinical criteria for MFS. They have not been previously
tested or suspected of MFS. The phenotypes of the compound-heterozygous probands are more severe and have required cardiovascular, surgical or
ophthalmological solutions early in childhood, but not leading to lethally affected individual.