Inborn errors in metabolism

In 1909, A.E. Garrod described certain hereditary diseases which cause certain defects in metabolism. The three diseases, namely (i) alcaptonuria, (ii) phenylketonuria and (iii) albinism result due to block in the metabolism where phenylalanine is broken down and utilized. These were discussed in Mutations : 2.  Biochemical Level (Biochemical and Microbial Genetics) in some detail.