Background. There is increased awareness regarding the co-occurrence of autism spectrum disorder (ASD) and inherited metabolic disorders (IMD), and this is crucial for the management of both diagnoses in clinical practice. We aimed firstly to report twenty-two patients with a dual diagnosis of IMD and ASD who are still being followed up in the child metabolism outpatient clinic; secondly to evaluate the time of both IMD and ASD diagnosis and the clinical progress of their metabolic disorders to underline treatable conditions.

Methods. Among the patients admitted to the Pediatric Metabolism outpatient clinic because of IMD, twentytwo of them who had a diagnosis of ASD were included in the study. Data of the patients were collected from their medical records. The most recent progress of the patients concerning their metabolic disorder was obtained from the patients` files.

Results. Six cases with Phenylketonuria, 2 cases with partial Biotinidase Deficiency, 3 cases with Cerebral Creatine Deficiency Syndrome (CCDS), 5 cases with Mucopolysaccharidosis (MPS) Type-3b, 2 cases with MPS Type-3a, 1 case with MPS Type 4, 2 cases with Hypervalinemia and 1 case with Maple Syrup Urine Disease were all diagnosed as also having ASD. The diagnoses of CCDS and MPS Type 3 were after the diagnosis of ASD. Phenylketonuria and Mucopolysaccharidosis were the most common diagnoses in our study. In addition, rare entities such as MPS Type 3b and Type 4 and Hypervalinemia were also reported to co-occur with autism.

Conclusions. Considering the co-occurrence of both disorders and implementing intervention strategies accordingly will certainly be beneficial in clinical practice and particularly in countries with a high rate of consanguinity.

Keywords: autism spectrum disorder, developmental delay, inherited metabolic disorders