Pittsburgh ? An autistic boy died after receiving an unproven treatment that some people believe may cure the neurological and developmental disorder.

Officials said they do not know for sure what killed Abubakar Tariq Nadama, 5, who died Tuesday after suffering a heart attack following his third treatment of chelation therapy at a suburban medical clinic.

The staff at his doctor’s office performed CPR on the boy, but he was later pronounced dead in a hospital. More tests would be needed to determine the cause of death, said Deputy Coroner Larry Barr.

Chelation (pronounced key-LAY-tion) is often used in patients with sickle cell anemia, lead poisoning or other maladies. Its use dates to the 1940s.

Some people believe autism can be linked to a mercury-containing preservative once commonly used in childhood vaccines. Chelation therapy has been advocated as a remedy because it causes heavy metals to leave the body through urine.

The boy was undergoing the therapy at the Advanced Integrative Medicine Center in Portersville, about 35 miles northwest of Pittsburgh. Neither the boy’s doctor, Roy E. Kerry, nor a representative from the center returned a call for comment Thursday.

State police also were investigating.

The boy’s mother, Marwa Nadama, said she did not blame the therapy, but was waiting for results of an autopsy.