Deciphering pathways:

The BCKDK story is exciting on two levels, even though few other families with this mutation have turned up. First, “the lesson we learned is that there are potentially treatable forms of autism that are hiding in the clinic,” Gleeson says. “This was just one example. But there have got to be other examples.”

Second, the newly identified metabolic disorder joins a select list of conditions associated with autism and epilepsy that each are triggered by high-impact mutations in a single gene. Although they tend to be uncommon, single-gene disorders have offered groundbreaking scientific insights, providing some of the first solid leads on potential biological mechanisms that underpin autism. “When you have a single gene completely knocked out, studying the biology is a lot easier,” El-Fishawy says, because it’s easier to see what’s broken. And, as Novarino puts it, if solving the complicated biology of all the causes of autism is like trying to read entire works of philosophy in a foreign language, then studying single-gene cases such as tuberous sclerosis and BCKDK deficiency is a Rosetta stone, deciphering mechanisms bit by bit. “We are trying to learn the alphabet,” she says. “Then maybe we are able to read back those books.”

Researchers have, for instance, learned a lot from tuberous sclerosis, a syndrome of benign tumors and developmental delay, with a high rate of both autism and epilepsy. (The syndrome can result from malfunctions in either of two genes, TSC1 or TSC2, but is considered a single-gene disorder because just one mutated gene can trigger it.) Research in mouse models of the condition showed that the problematic mutations ramp up a pathway known as mTOR. Based on these results, a drug that blocks mTOR activity won approval in 2010 for treating tumors in children with tuberous sclerosis. Other studies showed that a similar medicine alleviates seizures and cognitive problems in the mice. These findings led to the launch five years ago of the first clinical trials testing mTOR blockers for these problems in people with the syndrome.

The researchers studying BCKDK say they hope their work will likewise open doors to developing treatments for autism and epilepsy. “People underestimate how relevant this could be for autism as a whole,” El-Fishawy says. “Lots and lots of mutations and lots and lots of genes could all wind up leading to only a handful of pathways,” he says. The key is to tease apart what goes wrong in the brain when branched-chain amino acid levels are low — and find out whether the same biochemical processes are disrupted by other causes of autism and epilepsy in non-consanguineous populations in the U.S. and U.K. as well. The potential payoff from untangling these kinds of connections is big: “If we find a treatment that affects one pathway, it might be relevant to other types of genetic variants that are associated with autism spectrum disorder,” says Jeste, who is not involved in studying BCKDK.

For this next phase of the quest, Novarino and her colleagues have looked back to the mice for answers. In mice without a functional BCKDK gene, the branched-chain amino acids are low inside the brain, but other amino acids, such as phenylalanine and tyrosine, are elevated. That makes sense: These amino acids all compete with each other to cross from the blood into the brain. If branched-chain amino acids are missing, others are more likely to get in.

The resulting imbalance in amino acids may change neural activity in ways that contribute to both autism symptoms and seizures, Novarino says. For example, branched-chain amino acids are involved in making the chemical messenger glutamate, a molecule that excites brain cells, as well as GABA, a chemical messenger that inhibits neurons. Both are needed to maintain the brain’s signaling balance, and a leading theory implicates a disruption of that balance as a cause of autism. Over-excitable neurons can also prompt storms of abnormal electrical discharges in the brain, leading to seizures.

Novarino has been exploring these and other aspects in her lab, as well as studying social behaviors in the mutant mice and testing whether the supplement can change them. She is moving to publish new findings in the coming months.

The mice will prove to be a valuable model because their symptoms are so easily reversed with the supplement, Gleeson says. “Like a switch, we think you should be able to turn the autism and epilepsy on and off,” he says. “Then you can study how the circuits are changing, or you can study how the brain chemistry is changing.”

His team also plans to test the supplement’s effects on other mouse models of autism. “It’s kind of a crazy idea,” he says with a chuckle. “But I think we have to explore all possible avenues.” The amino acids have a calming effect, says Gleeson; he knows because he, along with his lab members, tried the supplement powder themselves before shipping it to the families overseas. But he doesn’t recommend that parents give the supplement to their children with autism who don’t have a mutation in BCKDK — there’s just not enough evidence that it will help, even if there are no known side effects.

In the meantime, Gleeson’s group is also working with collaborators on a study screening the exomes of 100 children in the U.S. who were diagnosed with autism before they developed seizures. As more genes are linked to both autism and epilepsy, Gleeson says, the field can make headway. “We can now start to predict which mutations or which genes are going to be associated with pure autism, or autism with epilepsy, or autism with epilepsy plus intellectual disability,” he says. That information could help prepare families and clinicians for problems to watch for, and potentially help predict which kinds of medications will work for them, he says.

The ultimate goal is to provide therapies that target the pathway that is dysfunctional in a particular set of individuals, Gleeson says. Those with deficiencies in amino acids would get one kind of treatment, for example, whereas others with, say, a defective sodium channel would get another.

A lot more scientific detective work lies ahead to nail down and characterize all the genetic culprits underlying autism and epilepsy, but the BCKDK story shows the potential rewards of gene hunting in the Middle East. Nobody knew what afflicted the children in the families with BCKDK mutations, let alone guessed that they had a metabolic disorder that might be treatable. “But now, we finally understand the cause,” Gleeson says.

His lab’s Middle East database now includes more than 5,300 families, and around 10 percent of the families have children with autism.

Twice a year, Gleeson still embarks on intense two-week trips through multiple Middle Eastern cities to recruit new families. On a trip to Libya in September 2013, he had a chance to thank the friend who smuggled out the blood samples. Gleeson and Kara had dinner with the man, who ran a chicken restaurant. “He was a kind and elderly gentleman,” Gleeson says.

Navigating through unfamiliar places, customs and languages — and political conflicts — is a challenge, but he says he loves it. “Getting there is the tough thing,” Gleeson says, “but once I’m there, the doctors and patients are really wonderful.”