Tuberculosis, onychomycosis and immune deficiency in complicated Crohn's disease.

The immune system is composed of innate humoral defence and adaptive immunity. One of the key mechanisms of the innate humoral defence is through complement activation. Mutations of certain enzyme may affect the complement activation and result in decreased defence against microorganisms. Mannan-binding lectin serine protease 2 (MASP-2) mutation was associated with recurrent infections and autoimmune diseases. Tuberculosis (TB) has been linked with mannose-binding lectin and MASP-2 gene polymorphism. We report a case of a paediatric patient with MASP-2 deficiency with classical and atypical features associated with Crohn's, onychomycosis and severe cutaneous infections including TB. We also report the presence of a new mutation variant in MASP-2 reported in whole exome sequencing of our patient. © BMJ Publishing Group Limited 2019. No commercial re-use. See rights and permissions. Published by BMJ.