Dr. Dharmabalan writes in IMA CGP whatssapp journal:

Cerebral palsy and mental retardation are two different conditions that each affect brain function. While some individuals with cerebral palsy may also have mental retardation, the two conditions are often incorrectly used interchangeably.

Cerebral palsy is a condition in which damage in the brain prevents a person from being able to fully control physical movements, while mental retardation refers to a condition in which a person does not have fully developed intellectual ability as compared to other people in his or her age group.

Symptoms of cerebral palsy are generally focused on physical impairments. Individuals with the condition may have difficulty controlling their limb movements may be overly loose or stiff. They may also have problems with mouth function, such as having involuntary drooling.

Mental retardation symptoms tend to be categorized primarily on general intellectual levels and typically includes an individual not being able to perform regular tasks on his or her own on an everyday basis.

Cerebral palsy is thought to possibly be caused by factors that cause brain damage to a fetus while in the womb or shortly after birth. The damage may be caused by infections, such as rubella, toxoplasmosis etc. present in the expectant mother during pregnancy; a stroke in the fetus due to clots in the placenta; exposure to toxins during pregnancy; or cases of viral encephalitis or meningitis in newborns.

The causes of mental retardation in the majority of cases are unknown. Possible causes are thought to be genetic abnormalities, such as inherited neurological or chromosomal disorders.

Cerebral palsy treatment involves muscle relaxant medications, physical therapy and surgery to improve muscle coordination.

Mental retardation treatment often consists of therapy or guidance to help the individual to do common tasks and gain confidence in order to fully perform to his or her maximum intellectual capacity.

In short: A person who is mentally retarded has a very low IQ. A person with cerebral palsy has very bad motor skill.