This is a case of pellagra/ niacin deficiency. Triad of diarrhoea, dementia and dermatitis. Skin findings Affected skin lesions are initially erythematous and are associated with a burning sensation. The distribution of the cutaneous eruption is typically symmetrical and bilateral in pas of the body exposed to sun. Dorsum of the hands and feet, neck area, and a malar rash are typical areas of involvement. As the dermatitis progresses, the affected skin becomes hyperpigmented and thickened. Hanup disease: This is an autosomal recessive disorder that compromises renal and intestinal transpo of neutral amino acids. The gene for this condition, which severely depletes tryptophan (the substrate for niacin synthesis), has been found by homozygosity mapping to be located on chromosome 5p15.