Marfan Syndrome:Mosaic Case
Study
Jenny Greatwood
• Autosomal dominant disease.
• Prevalence of ~ 1:5,000 - 1:10,000.
• Disorder of connective tissue which primarily affects the skeletal, ocular and cardiovascular systems.
Marfan Syndrome
Screening strategy for Marfan Syndrome
DHPLCDHPLC
SEQUENCINGSEQUENCING
• Associated with mutations in the FBN1 gene on 15q21.2.
• Large gene spanning ~235kb of DNA with 65 exons.
• Scattered throughout the gene and are largely unique to individual families.
SEQUENCINGSEQUENCING
Marfan syndrome- case study
• Received PG for predictive testing
Proband NG previously tested in Holland found to have c.3250G>T p.G1084C in exon 26 of the Fibrillin 1 gene, which is of unknown clinical significance.
No clinical information given, only a pedigree of the immediate family.
However the mutation could not be seen convincingly on direct sequencing.
Sequencing
PGPG
NG- positive controlNG- positive control
Alternative primers were used to exclude the possibility of a primer binding site polymorphism but the mutation was still not clear on direct sequencing.
Sequencing 2
Shift in exon 26 was clearly visible on dHPLC in the proband.
DHPLC
• After contact with the original testing centre in Holland we found out that their testing strategy was the same.
• They had also used dHPLC and then direct sequencing using a 3100/3130.
• They said that the mutation was visible clearly on the raw sequencing data.
• ? NG mosaic – although no mention of mosaicism in Hollands report.
Chris Mattocks from the NGRL took the sequencing data and using genotyper found that the mutation was an estimated 50% mosaic.
The mutation is clearly visible in both forward and reverse.
NG- positive controlNG- positive control
The father of the proband was 100% WT. The proband dosage showed 60% WT and 40% mutant
Helen White also of the NGRL designed a pyrosequencing assay to determine the extend of the mosaicism.
Conclusion
• A case of somatic mosaicism.
• Most likely to be de novo in NG.
• The father of the proband was reported as not carrying the mutation, however we can not rule out the possibility of germ-line mosaicism.
• Although we were able to establish the extent of the mosaicism in the proband the reported mutation is still an unclassified variant.
Acknowledgements
Work carried out by:
• Esta Cross- WRGL• Nick Parkin- WRGL• Chris Mattocks- NGRL• Helen White- NGRL