LAUSR

BACKGROUND Lymphedema is an abnormal accumulation of interstitial fluid within the tissues. Primary lymphedema is caused by aberrant lymphangiogenesis and it has been historically classified based on age at presentation. Although most cases are sporadic, primary lymphedema may be familial or present in association with chromosomal abnormalities and syndromic disorders. To the best of our knowledge, primary lymphedema has never been described in patients with 22q11.2 deletion syndrome. METHODS AND RESULTS We identified 4 patients with 22q11.2 deletion syndrome and primary lymphedema via our International 22q11.2 Deletion Syndrome Consortium. All patients underwent comprehensive clinical, laboratory and imaging assessments to rule out other causes of lymphedema. All patients had de novo typical deletions and family histories were negative for lymphedema. CONCLUSIONS We report the novel association of primary lymphedema with 22q11.2 deletion syndrome. Importantly, animal models demonstrated Tbx1 playing a critical role in lymphangiogenesis by reducing Vegfr3 expression in lymphatic endothelial cells. Moreover, the VEGFR3 pathway is essential for lymphangiogenesis with mutations identified in hereditary primary lymphedema. Accordingly, our findings provide a new insight into understanding cellular mechanisms of lymphangiogenesis disorders.