Face-recognition software has been developed that could help diagnose rare genetic conditions in children from family photographs.

The programme allows a computer to scour family snaps for facial features characteristic of conditions such as Down syndrome.

In future, it could be used to identify people born with such disorders, allowing them to be given early treatment and support.

Between 30% and 40% of rare genetic disorders are thought to involve changes in the shape of the face and skull.

However, they may not be obvious.

A majority of those with the conditions do not receive a genetic diagnosis.

The computer software employs a form of "artificial intelligence" to learn what aspects of a person's face are linked to particular conditions.

Analysing ordinary family photos, it maps the corners of the eyes, nose, mouth and other features and compares the results with a database of remembered features.

The programme automatically takes account of variations in lighting, image quality, background, pose, and facial expression.

Lead researcher Dr Christopher Nellaker, from the Medical Research Council's Functional Genomics Unit at Oxford University, said: "A doctor should in future, anywhere in the world, be able to take a smartphone picture of a patient and run the computer analysis to quickly find out which genetic disorder the person might have.

"This objective approach could help narrow the possible diagnoses, make comparisons easier and allow doctors to come to a conclusion with more certainty."

Dr Nellaker, whose research is reported in the journal eLife, added: "A diagnosis of a rare genetic disorder can be a very important step. It can provide parents with some certainty and help with genetic counselling on risks for other children or how likely a condition is to be passed on.

"A diagnosis can also improve estimates of how the disease might progress, or show which symptoms are caused by the genetic disorder and which are caused by other clinical issues that can be treated."