Podcast recap: Andrew Jackson on how the same DNMT3A mutations behind dwarfism drive an accelerated aging syndrome
By Joy N. Ismail, PhD
In the latest episode of The Genetics Podcast, Patrick Short speaks with Dr. Andrew Jackson, Programme Leader at the MRC Human Genetics Unit within the University of Edinburgh's Institute of Genetics and Cancer. Andrew's lab studies rare growth disorders, including primordial dwarfism and microcephaly, conditions that constrain how large the brain and body become. Over roughly two decades that work has extended into aging, DNA repair, and cancer biology.
The throughline is consistent: studying the rarest monogenic conditions reveals rules that apply to everyone. The conversation centers on a finding that gain-of-function mutations in DNMT3A cause both microcephalic dwarfism and an accelerated aging syndrome. One genetic cause connecting two very different phenotypes reframes how growth and aging relate.
Growth and aging share the same biology
Andrew's group had already characterized DNMT3A gain-of-function mutations as a cause of microcephalic dwarfism, work first published in Nature Genetics about seven years ago. The link to aging came later, and from an unexpected direction.
As Andrew describes it: "Actually, it wasn't until a meeting last year when I was sat in an audience listening to talks about other progeria syndromes that the penny dropped. The processes of growth and aging are much more mechanistically linked than we'd thought." The same molecular change that limits growth also accelerates aging, which places the two processes on shared biological machinery rather than separate tracks.
Cell number sets mammalian size
A basic question runs underneath the growth work: what determines how big an animal gets? Mammals span an enormous range, from the roughly two-gram bumblebee bat to the blue whale at about 150 metric tons. Andrew's answer points to cell number rather than cell size.
"A mouse is about three thousandfold smaller than a human, and it has three thousandfold less cells. So it's cell number rather than cell size which determines mammalian size," he explains. That distinction shapes how his lab reads growth disorders. In the smallest, proportionally shrunk patients, who reach an adult stature of about one meter, or three feet, the body builds fewer cells rather than smaller ones. The same principle scales across the mammalian range, where size tracks the number of cells an animal produces during development.
Rare monogenic conditions teach fundamental biology
Andrew makes the case that rare disease is a direct route to general biology. He points to the power of single-gene conditions: a defined mutation creates a clear causal link between genotype and phenotype, which lets researchers reach questions that common, polygenic variation rarely opens up.
Human genetics also offers depth that lab models cannot match. With roughly nine billion people carrying natural variation, researchers gain access to experiments no one could design. One rare syndrome shrinks the brain to a third of its average size, close to the brain size of human ancestors two million years ago.
Discovery follows the detours
Not every finding comes from the question a lab sets out to answer. Working on Aicardi-Goutières syndrome, Andrew's group studied ribonuclease H2, the enzyme that removes ribonucleotides mistakenly incorporated into DNA. That enzyme clears more than a million ribonucleotides from the genome of every replicating cell.
The scale of that repair surprised Andrew, who had not expected ribonucleotides to be a common feature of the genome at all. Following the thread carried the lab into cancer genomics, where it helped identify the COSMIC ID4 mutational signature, a pattern of mutations in cancer whose cause had been unknown. A question about a rare neurological disorder ended up explaining a feature of tumor genomes, and tied DNA repair to how cancers accumulate damage.
The genome may not be static
The work also revises a basic assumption about the genome. "This concept that we think of ourselves as just having a single genome which is invariant through our lifetime is probably not true... We're actually a bunch of clones," Andrew says. Somatic mutations accumulate as cells divide, so the body becomes a mosaic of related but distinct genomes.
That view links growth, aging, and cancer, since each depends on how mutations arise and spread through dividing cells. The same lens that started with the smallest patients in the world now reaches into how all of us change over a lifetime.
Andrew returns often to a point about method. The field has an unusually good set of tools, but the question still leads, and the right tool follows from it. His research shows how far a single genetic cause can travel, from extreme growth disorders to the biology of aging and cancer.
Listen to the full episode below.