Expectant mothers suffering from asthma, allergies or a type of skin disease have a higher risk of giving birth to an autistic child, a study said on Monday.

Asthma, allergies and psoriasis symptoms during pregnancy - especially if diagnosed in the second trimester - doubled the risk of autism in children compared to children who were not afflicted, researchers from Kaiser Permanente in Oakland, California, said.

Autism is a mysterious condition that strikes roughly six in 1,000 children, mostly boys, and is associated with diminished social skills and an adherence to routines.

The study looked at 88,000 children belonging to the Kaiser Permanente health plan born in Northern California between 1995 and mid-1999, 420 of whom were diagnosed with autism.

The researchers said there was no statistical link between autism in children and 44 autoimmune diseases in mothers, including rheumatoid arthritis, lupus and multiple sclerosis. The exception was psoriasis, which doubled the risk of autism.

Previous research has suggested there may be a link between autoimmune disease during pregnancy and autism, because autistic children often have high levels of autoimmune response chemicals in their bloodstreams. Women make up 78 percent of patients with autoimmune diseases, where the body’s immune system attacks its own tissues.

The report, which was published in The Archives of Pediatrics and Adolescent Medicine, speculated that there may be a common underlying genetic cause to such ailments as asthma and autism.

Or, because the mother’s condition was frequently diagnosed in the second trimester, the flare-up may have caused her immune system to produce more cytokines, which are associated with inflammation and could have damaged fetal brain development.