A 1 year old child is brought to you with delayed milestones. On examination you note that the child is very fair with hypopigmented hair and blue eye. He has also got eczemas. The child was also very irritable. What is your diagnosis?

This child is suffering from Phenylketonuria. Here there is inability to conve phenylalanine to tyrosine due to phenylalanine hydroxylase deficiency. The decreased pigmentation in this condition is due to reduced melanin formation. The treatment is a diet low in phenylalanine with tyrosine supplementation. Delay in initiation of treatment will lead to mental retardation. Ref: Essential revision notes for MRCP by Philip A Kalra, Edition 3, Page - 322 ; Harrison, Edition 17, Page - 2470