Expanding molecular basis for rasopathies - a new player? M. Ludwig1,2, C. Y. Hung1, J. L. McCauley1, J. Dallman3, E. J. Back3, I. Mihalek4, G. X. Shi5, D. A. Andres5, O. Bodamer1 1) Department of Human Genetics, University of Miami - Miller School of Medicine, Miami, Florida, USA; 2) Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria; 3) Department of Biology, University of Miami, Miami, Florida, USA; 4) Bioinformatics Institute A*STAR Singapore, Singapore; 5) Department of Molecular and Cellular Biochemistry, University of Kentucky - College of Medicine, Lexington, Kentucky, USA.

   Background: Gain-of-function mutations in 13 different genes of the ras-MAPK-pathway cause a heterogeneous group of genetic disorders known as rasopathies. The clinical phenotypes of these disorders overlap due to the shared pathway, including Costello (OMIM #218040), CFC (OMIM #115150), LEOPARD (OMIM #151100), Noonan syndrome (OMIM #163950) and others. Patient: We report a 24 month-old boy born full term via C-section following a pregnancy complicated by pre-eclampsia and polyhydraminos. Postnatally he presented with prominent overgrowth: birth weight: 5.14 kg (>97th percentile), birth length: 53.5 cm (90th percentile) and head circumference: 38.5 cm (>90th percentile). His parents are of Cuban-Hispanic descent, healthy and non-consanguineous. Physical examination at presentation revealed a phenotype reminiscent of Costello syndrome, including facial dysmorphism, severe developmental delay, muscular hypotonia, broad fingers with deep palmar and plantar creases, congenital heart defects and non-progressive hypertrophic cardiomyopathy. Methods and Results: Sanger sequencing revealed no pathogenic mutation in any of the known rasopathy genes including BRAF, CBL, HRAS, KRAS, MAP2K1, MAP2K2, NF1, NRAS, PTPN11, RAF1, SHOC2, SOS1 and SPRED1. The high density SNP microarray (Illumina HumanOmni1-Quad BeadChip, >1 million markers) showed no copy number variation. Whole exome sequencing (Illumina HiSeq2000; 82 million pass filter paired-end reads; average depth of 0.74 at 20X) revealed a de-novo missense variant in a novel gene predicted to be within the ras-MAPK-pathway. The variant was confirmed by Sanger sequencing, absent in 654 Hispanic control alleles and not reported in the SNP database (NCBI). The gene is expressed in all tissues and conserved throughout all species. The de-novo variant was introduced into PC6 cells, leading to increased MEK-ERK signaling in comparison to wild-type. This gain-of-function is characteristic for rasopathies. Conclusion: We identified a gain-of-function variant in a gene within the ras-MAPK-pathway associated with a characteristic clinical phenotype. Additional testing is ongoing to further delineate the functional consequences including a zebrafish model. Additional patients with a similar phenotype without an underlying molecular cause are currently screened for variants in this gene. Note: The name of the gene will be disclosed at the meeting.

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