Autism and phenylketonuria.

Doctors looked at 243 kids who have PKU, a metabolic disorder. They wanted to know how many also meet criteria for autism.

All babies in the group had a heel-prick blood test soon after birth. Some started the special low-protein diet right away. Others began the diet months later because they were born before screening was routine.

Zero early-screened, early-treated PKU kids had autism. Autism only showed up in 2 of the 35 late-diagnosed cases. That is about 6 percent.

The finding says timing matters. Quick diet control seems to protect the brain from the high phenylalanine that can mimic autism traits.

Zwaigenbaum et al. (2003) ran a similar case series the same year. They found two preschoolers sent for autism testing who really had muscular dystrophy. Both papers warn: treat metabolic or muscle disease first, then reassess behavior.

Boswell et al. (2023) pooled 25 studies and saw no reliable blood difference in tryptophan-kynurenine markers for autism. Sabrina’s PKU data fit that null picture once diet keeps phenylalanine low.

Esteban-Figuerola et al. (2019) meta-analysis shows autistic kids often eat too little calcium, vitamin D, and protein. Sabrina’s work adds a metabolic reason: untreated PKU itself, not the diet, may add to autism risk.

If you assess a child for autism, always check the newborn-screening record. Late-detected PKU can look like ASD: poor eye contact, odd tone, repetitive moves. A simple blood spot test and diet change can drop phenylalanine within days. After metabolic control, re-run your ADOS. You may see the social and language gains you thought needed 20 hours of ABA. Early referral to genetics or metabolic clinic saves time, money, and brain.