Marfan Syndrome: Mosaic Case Study Jenny Greatwood

Marfan Syndrome Autosomal dominant disease. Prevalence of ~ 1:5,000 - 1:10,000. Disorder of connective tissue which primarily affects the skeletal, ocular and cardiovascular systems.

Screening strategy for Marfan Syndrome 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. DHPLC SEQUENCING SEQUENCING

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.

Sequencing PG NG- positive control However the mutation could not be seen convincingly on direct sequencing.

Sequencing 2 Alternative primers were used to exclude the possibility of a primer binding site polymorphism but the mutation was still not clear on direct sequencing.

DHPLC Shift in exon 26 was clearly visible on dHPLC in the proband.

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.

The mutation is clearly visible in both forward and reverse. Chris Mattocks from the NGRL took the sequencing data and using genotyper found that the mutation was an estimated 50% mosaic. NG- positive control The mutation is clearly visible in both forward and reverse.

Helen White also of the NGRL designed a pyrosequencing assay to determine the extend of the mosaicism. The father of the proband was 100% WT. The proband dosage showed 60% WT and 40% mutant

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