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Mutations in a non-coding gene associated with intellectual disability

Colored ribbons that represent the molecular structure of a large collection of proteins and RNAs.

Enlarge / The spliceosome is a large complex of proteins and RNAs. (credit: NCBI)

Almost 1,500 genes have been implicated in intellectual disabilities; yet for most people with such disabilities, genetic causes remain unknown. Perhaps this is in part because geneticists have been focusing on the wrong stretches of DNA when they go searching. To rectify this, Ernest Turro—a biostatistician who focuses on genetics, genomics, and molecular diagnostics—used whole genome sequencing data from the 100,000 Genomes Project to search for areas associated with intellectual disabilities.

His lab found a genetic association that is the most common one yet to be associated with neurodevelopmental abnormality. And the gene they identified doesn’t even make a protein.

Trouble with the spliceosome

Most genes include instructions for how to make proteins. That’s true. And yet human genes are not arranged linearly—or rather, they are arranged linearly, but not contiguously. A gene containing the instructions for which amino acids to string together to make a particular protein—hemoglobin, insulin, serotonin, albumin, estrogen, whatever protein you like—is modular. It contains part of the amino acid sequence, then it has a chunk of DNA that is largely irrelevant to that sequence, then a bit more of the protein’s sequence, then another chunk of random DNA, back and forth until the end of the protein. It’s as if each of these prose paragraphs were separated by a string of unrelated letters (but not a meaningful paragraph from a different article).

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Chemical tweaks to a toad hallucinogen turns it into a potential drug

Image of the face of a large toad.

Enlarge / The Colorado River toad, also known as the Sonoran Desert Toad. (credit: Mark Newman)

It is becoming increasingly accepted that classic psychedelics like LSD, psilocybin, ayahuasca, and mescaline can act as antidepressants and anti-anxiety treatments in addition to causing hallucinations. They act by binding to a serotonin receptor. But there are 14 known types of serotonin receptors, and most of the research into these compounds has focused on only one of them—the one these molecules like, called 5-HT2A. (5-HT, short for 5-hydroxytryptamine, is the chemical name for serotonin.)

The Colorado River toad (Incilius alvarius), also known as the Sonoran Desert toad, secretes a psychedelic compound that likes to bind to a different serotonin receptor subtype called 5-HT1A. And that difference may be the key to developing an entirely distinct class of antidepressants.

Uncovering novel biology

Like other psychedelics, the one the toad produces decreases depression and anxiety and induces meaningful and spiritually significant experiences. It has been used clinically to treat vets with post-traumatic stress disorder and is being developed as a treatment for other neurological disorders and drug abuse. 5-HT1A is a validated therapeutic target, as approved drugs, including the antidepressant Viibryd and the anti-anxiety med Buspar, bind to it. But little is known about how psychedelics engage with this receptor and which effects it mediates, so Daniel Wacker’s lab decided to look into it.

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