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