Editors' ChoiceAutism

A New Risk Factor for Autism?

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Science Translational Medicine  23 May 2012:
Vol. 4, Issue 135, pp. 135ec92
DOI: 10.1126/scitranslmed.3004314

As parents, we often have big dreams for our children’s future. However, when parents are told their child has autism—a neurodevelopmental disorder characterized by social, cognitive, and communication difficulties—the questions they ask are: Will my child speak? Will I be able to have a close relationship with my child? Will my child be able to live independently as an adult? A recent U.S. Centers for Disease Control and Prevention report estimates that in 2008, 1 in 88 children received the diagnosis of autism, and that the incidence of autism diagnosis is on the rise. In response to this growing public health concern, scientists have been searching for the causes of autism and ways to prevent and treat this disease.

A recent study identified a deletion of exon 2 in the gene encoding trimethyllysine hydroxylase epsilon (TMLHE) in a proband with autism. This gene maps to the X chromosome and encodes the first enzyme in the carnitine biosynthesis pathway. In new work, Celestine-Soper et al. now investigate the possible association of nondysmorphic (milder end of spectrum) autism with TMLHE mutations. They used a PCR assay to study 3813 DNA samples from simplex (one affected male) and multiplex (male-male affected sibling pairs) families and compared them with 8787 DNA samples from related unaffected fathers and unrelated healthy male controls. TMLHE deficiency was 2.85-fold more frequent in probands from multiplex families as compared with controls (P = 0.023). Six of seven autistic male siblings of probands in these families had the deletion, suggesting that TMLHE deficiency is a risk factor in some cases of nondysmorphic autism (meta-analysis P = 0.0037). This association was not observed in simplex families.

Although further replication studies are needed to confirm these findings, the new work suggests that defects in carnitine metabolism may somehow be involved in an increased risk for autism. A big question posed by the authors is whether the risk for autism may be modified by dietary intake of carnitine—a nutrient mostly found in red meat and eggs—during the first few years of life, when children may not consume adequate amounts of these foods. Although much more work is needed, the study by Celestino-Soper et al. provides a new target for autism researchers to start investigating.

P. B. S. Celestino-Soper et al., A common X-linked inborn error of carnitine biosynthesis may be a risk factor for nondysmorphic autism. Proc. Natl. Acad. Sci. U.S.A., 7 May 2012 (10.1073/pnas.1120210109). [Abstract]

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