Scientists believe they have discovered the gene responsible for a rare condition which makes children age up to 10 times faster than normal.
A child with progeria
Children with Hutchinson-Gilford Progeria syndrome (HGPS) usually die at around the age of 13. There is currently no cure available.
It is an extremely rare condition, estimated to affect around one in 4m children.
But the signs of the condition are very distinctive, including baldness, aged-looking skin, dwarfism, and a small face and jaw relative to head size.
Affected children also have health problems more typically associated with the elderly, such as joint stiffness, hip dislocations, cardiovascular problems, and atherosclerosis.
This is going to be very important in understanding the ageing process and this disease
Professor Peter Clayton, Great Ormond Street Hospital
French researchers say pinpointing the gene responsible for HGPS will help develop therapies for the condition, and even screening programmes which could check to see if children have the defective gene.
They focussed on the LMNA gene. Mutations of the gene have been linked to another condition called mandibulo-acral dysplasia, which shares some characteristics of HGPS.
The LMNA gene contains the "blueprints" for making two proteins called Lamin A and Lamin C.
These proteins, plus Lamin B, are woven into a kind of mesh, lining the inside of the membrane around a cell's nucleus.
When cells divide this protective mesh splits, allowing the nucleus to split in two.
As new membranes form around each of the two new nuclei, the lamins create new linings.
But if the lamin proteins do not divide properly and die prematurely, tissues cannot regenerate properly.
The researchers looked at the DNA sequences of LMNA genes from patients with HGPS.
Researchers found just one tiny abnormality - a genetic mistake in a segment of DNA which carries crucial information to a cell's protein-construction site.
The LMNA mutation appears to affect the way the relevant information is extracted from a gene so that the end of this segment is cut off.
This means the Lamin A protein is not produced properly in some cells, although it production of Lamin C does not appear to be affected.
The LMNA is a "dominant" mutation, so children who inherit a defective copy of the gene from either parent develop HGPS.
Dr Nicolas LÚvy of the H˘pital d'enfants de la Timone in Marseille, France, who led the research, said: "Without knowing what caused this type of progeria, we had little idea how we might someday treat it.
"Identifying the gene responsible for the disease is a critical step toward possible therapies."
However, he said there was a lot of research needed before their discovery could help patients.
"We don't know enough about how lamins function to think in terms of therapy yet.
"I think we'll do it in the next 10 years, but it will be difficult."
Part of the difficulty in researching the condition is the very small number affected. Dr LÚvy said more studies would be needed to confirm the team's findings.
Professor Peter Clayton, a specialist at Great Ormond Street Hospital , is one of the few UK doctors to treat a child with HGPS.
He said: "It's not immediately apparent how this would lead to treatment for HGPS which is a devastating condition.
"But ultimately, this is going to be very important in understanding the ageing process and this disease, but not at this stage in time.
"This is the beginning, rather than the end."
The research is published in Science.