Myosin 5B deficiency

Myosin 5B deficiency causes microvillus inclusion disease. It is a severe autosomal recessive disease caused by a myosin 5B (MYO5B) mutation and characterised by malabsorption and diarrhoea.48

The prevalence of myosin 5B is unknown, but at least 200 cases have been reported in Europe.49 Patients present with chronic, watery, life-threatening diarrhoea, usually beginning in the first hours or days of life, although it may sometimes start around 3 or 4 months of age. Infants with myosin 5B deficiency have failure to thrive, developmental delay, liver and kidney problems, and osteoporosis. Some develop cholestasis, leading to cirrhosis.


Diagnosis is confirmed by molecular and genetic testing.

48. Jayawardena D, Alrefai WA, Dudeja PK, Gill RK. Recent advances in understanding and managing malabsorption: focus on microvillus inclusion disease. F1000Res 2019;8.

49. Microvillus inclusion disease. In: Reference GH, ed.: U.S. National Library of Medicine; 2014.