Clues link lack of carnitine with mild autism
Although in the 1980s, experts indicated a Recommended Daily Allowance (RDA) for carnitine was not needed as the human body makes its own, we now know 1 in 350 males cannot synthesize carnitine. Its time for the RDA on carnitine to be reviewed.
Researchers are always looking for new clues to the causes of autism, with the hope of its prevention or to improve treatment. Now, at Baylor College of Medicine in Houston, Texas, Arthur Beaudet PhD, proposes the lack of carnitine, a nutrient needed for normal development of the brain, liver, heart and muscles, might trigger a mild form of autism.
Results of his research are published in the journal BioEssays. Beaudet, who is also the Henry and Emma Meyer Chair and Professor of Molecular and Human Genetics at Baylor College of Medicine, emphasizes that more research is needed to confirm his idea, but speculates that if confirmed, it could prevent 10 to 20 percent of cases of autism simply through adding carnitine to infant diets.
In 2009 in the Beaudet lab, graduate student Patricia Celestino-Soper discovered how approximately 1 in 350 males in the general population cannot synthesize their own carnitine. This is because they have an inactive copy of the TMLHE gene located on the X chromosome.
"Of the nearly 460,000 males in the United States who have TMLHE gene deficiency, only about 3 percent develop autism. The remaining 97 percent become healthy adults, although sometimes behavioral regression occurs."
Arthur L. Beaudet PhD, Departments of Molecular and Human Genetics and Pediatrics, Baylor College of Medicine, Texas Children's Hospital, Houston, Texas, USA.
Regression might be subtle as having a social smile and playfulness at 6 to 8 months, then gradually losing these behaviors. Regression can also occur later and be more dramatic. Although it is currently estimated TMLHE deficiency is only present in about 1 percent of autism cases, Beaudet believes carnitine deficiency might cause a much larger fraction than now assumed. Beaudet: "We speculate that individuals with a normal physical exam and normal brain imaging result, represent 10 to 20 percent of all cases of autism spectrum disorders — and might have in common a mechanism leading to a mild form of autism. This mechanism might involve brain carnitine deficiency."
Searching for more evidence of carnitine deficiency in mild forms of autism in males, Beaudet examined genes on the X chromosome that might possibly be involved. With colleagues, he identified how the SLC6A14 gene is linked to the transport of carnitine across the blood-brain barrier — a gene that operates differently in females. In women with no mutation in the SLC6A14 gene, healthy girls express more autism like behaviors.
How could carnitine deficiency lead to a form of autism in an apparently healthy infant? Even Beaudet believes most infants are born with adequate carnitine as "carnitine is usually delivered across the placenta, and most infants are born with adequate carnitine stores." Carnitine is abundant in breast milk, infant formulas and cow's milk, so infants will be protected from the deficiency as long as they are exclusively fed these products.
"In many cultures, when the infant is introduced to new foods between 4 and 8 months of age, the first non-milk foods are fruits, juices, cereals and vegetables, all of which contain almost no carnitine, meats are introduced later," Beaudet explains. "Eggs, dairy and meats all have more substantial amounts of carnitine. Red meats are particularly rich; 1 ounce of beef contains 2,000 times more carnitine than 1 ounce of white rice." So, when low-carnitine solid foods are added to the infant diet, that child's intake of carnitine drops in proportion to the reduction in their milk intake. This reduction in carnitine might lead to brain carnitine deficiency and autism. Many parents of children with autism spectrum disorder report picky eating, which may also reduce the amount of meat in a diet.
Beaudet and colleagues speculate both an individual's genetic makeup and environment can contribute to mild autism, as dozens of genes affect the metabolism of carnitine. Each gene might contribute in a small way to the disorder. Certain medications, minor illnesses (especially gastrointestinal conditions) and changes to a child's microbiome are all factors that can each deplete carnitine from the body.
That carnitine deficiency might be involved in mild forms of autism brings up the question of whether there should be a Recommended Daily Allowance (RDA) for carnitine in normal infant diets. In the 1980s, experts indicated that an RDA for carnitine was not necessary as the human body can make its own.
"We now know that 1 in 350 males indeed cannot synthesize carnitine. The need for an RDA for carnitine perhaps should be reviewed,"
Arthur L. Beaudet MD, Professor, Departments of Molecular and Human Genetics and Pediatrics, Baylor College of Medicine, Texas Children's Hospital, Houston, Texas, USA.
Could 10–20% of autism be prevented? We hypothesize that nonsyndromic or “essential” autism involves extreme male bias in infants who are genetically normal, but they develop deficiency of carnitine and perhaps other nutrients in the brain causing autism that may be amenable to early reversal and prevention. That brain carnitine deficiency might cause autism is suggested by reports of severe carnitine deficiency in autism and by evidence that TMLHE deficiency - a defect in carnitine biosynthesis - is a risk factor for autism. A gene on the X chromosome (SLC6A14) likely escapes random X-inactivation (a mixed epigenetic and genetic regulation) and could limit carnitine transport across the blood-brain barrier in boys when compared to girls. A mixed, common gene variant-environment hypothesis is proposed with diet, minor illnesses, microbiome, and drugs as possible risk modifiers. The hypothesis can be tested using animal models and by a trial of carnitine supplementation in siblings of probands. Perhaps the lack of any Recommended Dietary Allowance for carnitine in infants should be reviewed.
Also see the video abstract here: https://youtu.be/BuRH_jSjX5Y
The evolution of this hypothesis was supported by past grants from the Simons Foundation Autism Research Initiative, Autism Speaks #7697 and currently the National Institutes of Health Baylor College of Medicine Intellectual and Developmental Disability Research Center grant P30 HD024064.
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Jul 20, 2017 Fetal Timeline Maternal Timeline News News Archive
Animal products like meat, fish, poultry, and milk are the best sources for adding carnitine.
Generally, the redder the meat, the higher the carnitine. Dairy products contain carnitine
primarily in whey. Image credit: FitDay.com