phenylketonuria (pku) a human disease characterized by mental retardation results from the
Phenylketonuria Phenylketonuria is a genetic disorder inherited from a person's parents.[1] It is due to mutations in the PAH gene, which results in low levels of the enzyme phenylalanine hydroxylase.[1] This results in the buildup of dietary phenylalanine to potentially toxic levels.[1] It is autosomal recessive, meaning that both copies of the gene must be mutated for the condition to develop.[1] There are two main types, classic PKU and variant PKU, depending on if any enzyme function remains.[1] Those with one copy of a mutated gene typically do not have symptoms.[1] Many countries have newborn screening programs for the disease.[3]
Causes of mental disorders During most of the 20th century, mental illness was believed to be caused by problematic relationships between children and their parents. This view was held well into the late 1990s, in which people still believed this child-parent relationship was a large determinant of severe mental illness, such as depression and schizophrenia. Today,[when?] the belief is held that the child-parent relationship is of small importance in terms of causing mental illness compared to biological and genetic factors[citation needed]. So, the perceived causes of mental illness have changed over time and will most likely continue to alter while more research is done in this area.[15]