Additionally, corneal diseases of unknown origin, such as Thygeson’s superficial punctate keratitis (TSPK), or of various systemic causes, including several skin diseases, monoclonal gammopathy, enzyme-related deficiencies (tyrosinemia, lecithin-cholesterol-acyltransferase deficiency, mucopolysaccharidoses), systemic lysosomal storage diseases or cystinosis, should be incorporated into the differential diagnosis. The gene discussed is LCAT; the disease is cystinosis.