Every third individual is a carrier of a recessive inherited eye disease, according to a paradigm-breaking Hadassah study published recently in Proceedings of the National Academy of Sciences of the United States of America.

Inherited retinal diseases (IRDs) are the leading cause of sight loss in 16-64 year olds. The most common IRDs are retinitis pigmentosa (RP), Stargardt disease, Usher syndrome and achromatopsia. Most IRD sufferers become blind in their fifties or sixties.

Hadassah molecular ophthalmology Professor Dror Sharon and researcher Mor Hanany, in collaboration with Prof. Carlo Rivolta from Switzerland, developed a pipeline that calculates the numbers of carriers of IRDs and how many of those will suffer vision impairment.

“In the past, genetic mutations were thought to be rare,” says Prof. Sharon. “Today we know that every human carries recessive mutations for one disease or another. The debate is over how many mutations each individual carries. While I can’t be exact, it seems each one of us carries between 10 and 100 mutations in our genome.”

In 2018, Hanany, Sharon and colleagues from the Israeli Inherited Retinal Disease Consortium (IIRDC) carried out similar research in Israel, published in the European Journal of Human Genetics. They examined genetic data from some 2,000 families and found one in four Israelis is likely to be a carrier. That rises to one in every two among Jerusalem’s Arabs.

Encouraged by the success of that research, Hanany, Rivolta and Sharon looked at a much broader population. In their just-published article, they examined genetic sequences from 183,000 people in six population groups around the world – two in Asia and Europe and one each in Africa and Latin American countries.

Their results show that at least 36 percent of the world’s population or 2.7-billion people are carriers, of which 5.5 million are expected to have IRDs. They created a database containing over 250,000 sequence variants in 187 known IRD genes, 10,000 of the variants were determined as disease-causing mutations. A sequence variant is any sequence change compared to the reference genomic sequence as determined by the human genome project and a mutation is a variance that can cause disease.

The algorithm and its findings are significant for large bodies like the World Health Organization and pharmaceutical companies, to hospitals and individuals.

International health organizations can plan based on regional and national statistics. Preventive measures can be taken such as preimplantation genetic testing prior to in-vitro fertilization (IVF) to try to eradicate hereditary diseases.

“For me, the biggest contribution will be in genetic counseling,” says Hanany. “Couples will ask their counselor ‘what are the chances that our children will have disease X?’ Now they’ll be able to calculate the probability far more accurately.”

Other can edit the Hadassah pipeline and apply it to inherited diseases throughout the body.