The University of Geneva (UNIGE) team propose that taurine supplementation could stabilise retinal damage caused by retinopathy as well as treat heart disease linked to a mutation of the SLC6A6 gene.
“These results are exceptional, because it’s the first time a food supplement given orally has been used to treat the retina and the heart successfully,” says Stylianos Antonarakis, study team member and emeritus professor in UNIGE’s faculty of medicine.
“Our goal now is to detect new-borns affected by the condition at an early stage so they can be treated from birth with a taurine supplement and potentially prevent the onset of symptoms.
Taurine is the most abundant amino acid in the retina, important in photoreceptor survival and protection from oxidative stress and light damage. It is perhaps best known as a dietary supplement found in large quantities in energy drinks.
SLC6A6 gene mutations
The scientists focused on the SLC6A6 gene, which encodes a transporter protein that carries taurine to the retina and cardiac muscle to aid in function.
When there are pathogenic mutations of the SLC6A6 gene, an individual will suffer from a lack of taurine and will gradually lose his sight until he becomes blind within a few years and develops a weak heart.
Along with scientists from Pakistan, the tam looked at the genomes of 500 Pakistani families who had ill and healthy children in order to identify as many genes as possible that cause these conditions.
One family interested the researchers. Here, two healthy parents had four children in which the 15-year-old boy had lost his sight and the 4-year-old girl was gradually losing her sight but could make out shapes and colours.
Echocardiography showed the two children also had mild hypokinetic cardiomyopathy with systolic dysfunction.
After identifying the conditions as linked to a taurine transport defect caused by a SLC6A6 gene mutation, the team began taurine oral supplementation treatment at 100 milligrams per kilogram per day (mg/kg/day) in tablet form.
“We gave 100mg per kg of taurine daily to the children to be continued over the long-term, and organised regular ophthalmologic and cardiac monitoring sessions in Pakistan”, explains Emmanuelle Ranza, a doctor and geneticist at University Hospitals Geneva (HUG) and UNIGE
“In three days, the taurine levels in their blood jumped from 6 to 85 micromols per litre (μmol/l), reaching normal thresholds.
“After two years, the cardiomyopathy had completely disappeared in both children,” Dr Ranza adds.
“In addition, the degeneration in the girl’s sight was brought to a halt, and there was even an improvement, meaning she could move around by herself.
“Unfortunately, this development was not possible for the boy, who had already lost his entire retina.”
Researchers estimate that there are approximately 6,000 babies worldwide who might suffer from the same SLC6A6-related disease, and around 300 in Europe and North America.
“Our goal now is to detect new-borns affected by the condition at an early stage so they can be treated from birth with a taurine supplement and potentially prevent the onset of symptoms,” adds Antonarakis.
The geneticists also aim to continue to identify new genes that cause recessive diseases, especially since they now have proof that some of them can be treated effectively.
“This study emphasizes the contribution of each novel Mendelian gene in the understanding of disease etiology and provides the opportunity to investigate nutritional or pharmaceutical therapy for severe Mendelian disorders due to the large family of 423 transporter-encoding genes,” the study concludes.
“In addition, the identification of novel genes for autosomal recessive disorders provides the opportunity for carrier detection in the extended pedigree and family planning.”
Source: Human Molecular Genetics
Published online ahead of print: doi.org/10.1093/hmg/ddz303
“Taurine treatment of retinal degeneration and cardiomyopathy in a consanguineous family with SLC6A6 taurine transporter deficiency.”
Authors: Muhammad Ansar et al