Featured Research

from universities, journals, and other organizations

Defective carnitine metabolism may play role in autism

May 7, 2012
Baylor College of Medicine
The deletion of part of a gene that plays a role in the synthesis of carnitine – an amino acid derivative that helps the body use fat for energy – may play a role in milder forms of autism, said a group of researchers.

The deletion of part of a gene that plays a role in the synthesis of carnitine -- an amino acid derivative that helps the body use fat for energy -- may play a role in milder forms of autism, said a group of researchers led by those at Baylor College of Medicine and Texas Children's Hospital.

Related Articles

"This is a novel inborn error of metabolism," said Dr. Arthur Beaudet, chair of molecular and human genetics at BCM and a physician at Texas Children's Hospital, and the senior author of the report that appears online in the Proceedings of the National Academy of Sciences. "How it is associated with the causes of autism is as yet unclear. However, it could point to a means of treatment or even prevention in some patients."

Deletion leads to imbalance

Beaudet and his international group of collaborators believe the gene deletion leads to an imbalance in carnitine in the body. Meat eaters receive about 75 percent of their carnitine from their diet. However, dietary carnitine levels are low in vegetarians and particularly in vegans. In most people, levels of carnitine are balanced by the body's ability to manufacture its own carnitine in the liver, kidney and brain, starting with a modified form of the amino acid lysine.

Carnitine deficiency has been identified when not enough is absorbed through the diet or because of medical treatments such as kidney dialysis. Genetic forms of carnitine deficiency also exist, which are caused when too much carnitine is excreted through the kidneys.

In this new inborn error, there is a deletion in the second exon -- the protein-coding portion of a gene -- of the TMLHE gene, which includes the genetic code for the first enzyme in the synthesis of carnitine (TMLHE stands for trimethyllysine epsilon which encodes the enzyme trimethyllysine dioxygenase).

Studies in the laboratory that identified the deletion were led by Dr. Patricia B.S. Celestino-Soper, as a graduate student in Beaudet's laboratory at BCM, and by Dr. Sara Violante, a graduate student in the laboratory of Dr. Frιdιric M. Vaz of the Academic Medical Center in Amsterdam.

Frequency of deletion

To determine the frequency of the gene deletion, Beaudet and his colleagues tested male autism patients who were the only people with the disorder in their families (simplex families) from the Simons Simplex Collection, the South Carolina Early Autism Project and Houston families. In collaboration with laboratories and researchers in Nashville, Los Angeles, Paris, New York, Toronto and Cambridge (United Kingdom), they tested affected male siblings in families with more than one male case of autism (multiplex families).

When they looked at the TMLHE genes in males affected by autism and compared them to normal controls, they found that the gene alteration is a fairly common one, occurring in as many as one in 366 males unaffected by autism. It was not significantly more common in males within families in which there is only one person with autism. However, it is nearly three times more common in families with two or more boys with autism.

No syndromic form

Beaudet said most of the affected males with the deletion did not have syndromic autism that is frequently associated with other serious diseases. In many instances, syndromic autism affects physical development as well as cognitive, which is reflected in their facial features as well as other parts of their bodies. None of the six boys affected with autism (where information was available) had the syndromic form of disease. Their intelligence quotients and cognitive scores varied, with some being far below normal and others normal.

"Most of the males we identified with the TMLHE deficiency were apparently normal as adults," said Beaudet, although detailed information on learning and behavior was not available on these "control" males. "The gene deletion is neither necessary nor sufficient in itself to cause autism."

"TMLHE deficiency itself is likely to be a weak risk factor for autism, but we need to do more studies to replicate our results," Beaudet said. He estimated that at the rates found in his study, the deficiency might be a factor in about 170 males born with autism per year in the United States. This would equate to about one-half of one percent of autism cases.

The authors from Amsterdam found major increases in some carnitine-related chemicals and absence of others in both urine and plasma. These metabolic alterations were found to be predictive of the dysfunction of the TMLHE gene and therefore can be used to identify males with this disorder.

It remains uncertain whether TMLHE deficiency is benign or causes autism by affecting the function of neurons through toxic accumulation or deficiency of a variety of chemical metabolites.

"We believe that the most attractive hypothesis at this time is that the increased risk of autism is modified by dietary intake of carnitine from birth through the first few years of life," said Beaudet.

He and his colleagues are undertaking three studies to further their understanding of the TMLHE deficiency. In one, they will attempt to replicate the findings in multiplex families. In a second, they will study carnitine levels in the cerebrospinal fluid of infants with autism -- both those who have the gene deficiency and those who do not. In a third study, they plan to begin giving boys under age 5 with autism carnitine or a related supplement and determine whether this improves the behavior of those with the TMLHE deficiency and those without.

Story Source:

The above story is based on materials provided by Baylor College of Medicine. Note: Materials may be edited for content and length.

Cite This Page:

Baylor College of Medicine. "Defective carnitine metabolism may play role in autism." ScienceDaily. ScienceDaily, 7 May 2012. <www.sciencedaily.com/releases/2012/05/120507154101.htm>.
Baylor College of Medicine. (2012, May 7). Defective carnitine metabolism may play role in autism. ScienceDaily. Retrieved January 30, 2015 from www.sciencedaily.com/releases/2012/05/120507154101.htm
Baylor College of Medicine. "Defective carnitine metabolism may play role in autism." ScienceDaily. www.sciencedaily.com/releases/2012/05/120507154101.htm (accessed January 30, 2015).

Share This

More From ScienceDaily

More Mind & Brain News

Friday, January 30, 2015

Featured Research

from universities, journals, and other organizations

Featured Videos

from AP, Reuters, AFP, and other news services

Binge-Watching TV Linked To Loneliness

Binge-Watching TV Linked To Loneliness

Newsy (Jan. 29, 2015) — Researchers at University of Texas at Austin found a link between binge-watching TV shows and feelings of loneliness and depression. Video provided by Newsy
Powered by NewsLook.com
Signs You Might Be The Passive Aggressive Friend

Signs You Might Be The Passive Aggressive Friend

BuzzFeed (Jan. 28, 2015) — "No, I&apos;m not mad. Why, are you mad?" Video provided by BuzzFeed
Powered by NewsLook.com
City Divided: A Look at Model Schools in the TDSB

City Divided: A Look at Model Schools in the TDSB

The Toronto Star (Jan. 27, 2015) — Model schools are rethinking how they engage with the community to help enhance the lives of the students and their parents. Video provided by The Toronto Star
Powered by NewsLook.com
Man Saves Pennies For 65 Years

Man Saves Pennies For 65 Years

Rooftop Comedy (Jan. 26, 2015) — A man in Texas saved every penny he found for 65 years, and this week he finally cashed them in. Bank tellers at Prosperity Bank in Slaton, Texas were shocked when Ira Keys arrived at their bank with over 500 pounds of loose pennies stored in coffee cans. After more than an hour of sorting and counting, it turned out the 81 year-old was in possession of 81,600 pennies, or $816. And he&apos;s got more at home! Video provided by Rooftop Comedy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.


Breaking News:

Strange & Offbeat Stories


Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News


Free Subscriptions

Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile

Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?

Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins