Normal babies learn how to do many new things as they grow up. They usually learn how to sit without help around 6 months of age, and they begin learn how to walk and talk around 1 year of age. Developmental delay is diagnosed when babies do not learn new things, or they learn them late.
There are many different causes for developmental delay. Lesch-Nyhan disease is one of them. Because there are so many different causes for developmental delay, a thorough evaluation by a pediatrician or pediatric neurologist is usually required. Lesch-Nyhan disease is only suspected when developmental delay is combined with evidence for overproduction of uric acid or self-injurious behavior.