Phenyl ketonuria is autosomal recessive metabolic genetic disorder characterised by the mutation in the gene of hepatic enzyme phenylalanine hydroxylase,which is an important enzyme to metabolize phenylalanine and tyrosine.Mutation in this gene causes accumulation of phenylalanine as phenyl pyruvate and tyrosine. As pheylalanine plays a major role in body’s melanin production so the infants suffering from this disease will lighter skin texture,hair and eyes than other siblings. Deit containg low amount of phenylalanine can be helpful for this disease.