Rare Variants in LAMA5 Gene associated with FLT4 and FOXC2 Mutations in Primary Lymphedema May Contribute to Severity

Mutations in the Fms-related tyrosine kinase 4 (FLT4) and forkhead box protein C2 (FOXC2) genes cause Milroy disease (MD) and lymphedema-distichiasis syndrome (LDS), respectively, but the mechanism underlying disease pathology remains unclear. Applying whole-exome sequencing to two families with MD, one LDS family, and one sporadic LDS case, we identified four rare variants in the laminin subunit alpha-5 gene (LAMA5) in subjects carrying novel and known missense FLT4 mutations and a 7-bp duplication and 1-bp insertion in FOXC2. Phenotyping was expanded in some individuals using magnetic resonance lymphangiography, indiocyanine green fluorescence lymphography, and immunofluorescent lymphatic staining of skin tissue. Skin lymphatic staining showed the existence of dermal lymphatic vasculature in the MD case. Significant lymphatic dysfunction was observed in both MD and LDS patients. In the MD patient, tortuous lymphatics in the dorsum of the foot were slowly enhanced on indocyanine green fluorescent lymphography (ICG) imaging. Dilated lymph collectors with disruption and lymph leakage were observed in the familial LDS case on magnetic resonance lymphangiography (MRL). Numerous tortuous lymph collectors were visualized along the entire length of affected lower limbs on MRL imaging, and retrograde lymph flow was observed in the lymph collectors during ICG lymphography in the isolated LDS case. The finding of rare LAMA5 variants together with FLT4 and FOXC2 mutations suggests that these mutations may be co-responsible for these disorders and most likely interfere with the function of lymphatics. Further, larger studies are needed to confirm these results.