Digenic Inheritance of a FOXC2 Mutation and Two PIEZO1 Mutations Underlies Congenital Lymphedema in a Multigeneration Family

BACKGROUND The lymphatic system is essential for maintaining the balance of interstitial fluid in tissues and for returning protein rich fluids (lymph) to the bloodstream. Congenital lymphatic defects lead to accumulation of lymph in peripheral tissues and body cavities, termed primary lymphedema. To date, only a limited number of individual genes have been identified in association with primary lymphedema. However, variability of age of onset and severity of lymphatic abnormalities within some families suggests that multiple mutations and/or genes may be responsible, thus hampering efforts to identify individual associated genes. METHODS Whole Exome Sequencing (WES) was performed in four members of a large multigeneration family with highly variable lymphedema and followed by Sanger sequencing for identified mutations in 34 additional family members. Genotypes were correlated with clinical and lymphangioscintigraphic phenotypes. RESULTS WES uncovered two different mechanotransducer PIEZO1 mutations and one FOXC2 transcription factor mutation in various combinations. Sanger sequencing confirmed the presence/absence of the three variants in affected and unaffected family members and co-segregation of one or more variants with disease. Genetic profiles did not clearly correlate with the highly variable severity of lymphatic abnormalities. CONCLUSIONS WES in lymphedema families can uncover unexpected combinations of several lymphedema-associated mutations. These findings provide essential information for genetic counseling and reveal complex gene interactions in lymphatic developmental pathways. These can offer insights into the complex spectrum of clinical and lymphatic lymphedema phenotypes and potential targets for treatment.