Kwashiorkor: A childhood disease that is caused by protein deprivation. Early signs include apathy, drowsiness, and irritability. More advanced signs are poor growth, lack of stamina, loss of muscle mass, swelling, abnormal hair (sparse, thin, often streaky red or gray hair in dark-skinned children), and abnormal skin that darkens in irritated but not sun-exposed areas. An enlarged and protuberant belly is common. Kwashiorkor disables the immune system, rendering the affected individual susceptible to a host of infectious diseases. It is responsible for much illness and death among children worldwide. Also known as protein malnutrition and protein-calorie malnutrition (PCM).