Biochemical Screening for Mitochondrial Dysfunction In Children with Autism Spectrum Disorders

Background:  

Mitochondrial disease has been  recognized as a recurrent but still apparently rare cause of ASD.   Oliveira et al, (2005), in population-based studies, found  that between 5 and 7% of patients with ASD had abnormal, persistent lactic acidemia.   A more recent study from this group found conclusive evidence of a mitochondrial disease in 5 of 69 patients tested (Oliveria et al., 2007). Biochemical markers identification will lead to treatment of ASD children presenting with mitochondrial dysfunction . 

Objectives:  

Despite many advances in molecular techniques, the diagnosis of mitochondrial disorders remains a major challenge, especially in the evaluation of children with autism spectrum disorders (ASD). Because muscle biopsy diagnosis of mitochondrial disease is not practical in the large ASD patient population, we developed an outpatient protocol for diagnosing mitochondrial disease using basic metabolic profiling but adhering to strict timing of sample collection. Our purpose here is to report results of this testing in 20 recently evaluated patients with regressive ASD.  

Methods:

 The protocol incorporates metabolic profiling under three conditions: A) morning fasting (patient’s overnight fasting period + 3 h), B) 4-5 h after a regular breakfast, and C) 90-120 min after lunch. Tests include urine organic acids (A, C), plasma amino acids (A, B), blood lactate (A, B, C), CMP (A, B), and CK (A). Patients with regressive ASD were referred to our clinic for metabolic testing by physician’s expert in ASD, who diagnosed ASD by one of several recognized ASD diagnostic inventories. Because the testing reported herein was undertaken as a standard diagnostic service for patients with clinical signs of metabolic disease, such as developmental regression, we have not routinely tested patients with non-regressive ASD.

Results:   

All 20 patients with regressive ASD had biochemical signs of mitochondrial disease, including, in most, increased levels of blood lactate, urine 2-ketoglutarate, and CK, and absolutely or relatively increased levels of glycine and alanine. The combined increase in alanine and glycine (p < 0.0001 vs. control for both) occurs in many types of mitochondrial complex I deficiency, which was found on muscle biopsy in all of several patients who underwent more invasive testing.  No patient was found to have a mtDNA mutation. Plasma amino acids obtained at 4h fasting was diagnostically abnormal in almost all patients. 

Conclusions:  

Developmental regression is a hallmark of many metabolic disorders, especially of mitochondrial disease in children who show acute or subacute cognitive decline after a period of normal development, as typically occurs in regressive ASD. Although, for many years, enzymatic testing of biopsy-obtained muscle tissue was considered the “gold standard” for diagnosis a mitochondrial disease, there is increasing recognition of the scientific limitations of this diagnostic approach and of the impracticability of requiring muscle biopsy for diagnosis of mitochondrial disease among large numbers of at-risk patients, such as those with regressive ASD. We have found our non-invasive diagnostic protocol with an emphasis on careful timing of sampling in relation to nutritional state to be useful in establishing that most patients with regressive ASD have a primary mitochondrial disorder.