Title:Microhomology-Mediated Break-Induced Replication: A Possible
Molecular Mechanism of the Formation of a Large CNV in FBN1
Gene in a Patient with Marfan Syndrome
Volume: 23
Issue: 5
Author(s): Gergely Buki, Kinga Hadzsiev and Judit Bene*
Affiliation:
- Department of Medical Genetics, Clinical Center, Medical School, University of Pécs, Pécs, Hungary
- Szentágothai Research Centre, University of Pécs, Pécs, Hungary
Keywords:
MMBIR, Marfan syndrome, FBN1 gene, CNV, genomic rearrangement, breakpoint analyses.
Abstract:
Background: Marfan syndrome (MFS) is an autosomal dominant multisystem
disorder caused by mutations in the fibrillin-1 gene (FBN1). A small portion of them is
copy number variations (CNVs), which can occur through recombination-based,
replication-based mechanisms or retrotransposition. Not many have been characterized
precisely in MFS.
Methods: A female patient with suspected Marfan syndrome was referred for genetic
testing at our institute. After systematic sequencing of FBN1, TGFBR1, and TGFBR2
genes, multiplex ligation-dependent probe amplification was applied. Long-range PCR,
subsequent Sanger sequencing with designed primers, and preliminary in silico analysis
were applied for the precise characterization of the breakpoints.
Results: Primary analysis displayed a de novo large deletion affecting exons 46 and 47
in the FBN1 gene, which resulted in the loss of the 31st and 32nd calcium-binding EGFlike
domains. Further examination of the breakpoints showed a 4916 nucleotide long
deletion localized in intronic regions. Surprisingly a ‘TG’ dinucleotide insertion was
detected at the junction. We hypothesize that the CNV formation was generated by a
rare event based on the known microhomology-mediated break-induced replication
(MMBIR).
Conclusion: An increasing number of CNVs are associated with Mendelian diseases
and other traits. Approximately 2-7% of the cases in MFS are caused by CNVs. Up to
date, hardly any model was proposed to demonstrate the formation of these genomic
rearrangements in the FBN1 gene. Hereby, with the help of previous models and
breakpoint analysis, we presented a potential mechanism (based on MMBIR) in the
formation of this large deletion.