Developmental delay in children is related to genes to a certain extent, but not absolutely, because the causes of developmental delay in babies are very complicated, and genetic factors are only one of the aspects. First of all, the developmental delay is related to genes. If the parents of a child have mental retardation, this condition will also cause the developmental delay of the child, especially the backwardness of intelligence. If a child has trisomy 21, this can also cause developmental delays due to genes. Hypothyroidism is the second cause of developmental delay. Low thyroxine secretion in the body can cause developmental delay and slow down the metabolism of the child.