“This study shows that there are other factors that determine the course of a genetic disease, and we do not know what these are,” Dr. Carel B. Hoyng of Radboud University Medical Center in Nijmegen, the Netherlands, the study‘s senior author, told Reuters Health by phone.
STGD1 is an autosomal recessive retinal dystrophy, with visual symptoms that usually emerge in childhood or early adolescence. Patients with early onset disease have a rapid visual decline and go blind before age 50, Dr. Hoyng explained, while less frequently patients develop the disease in their 20s or in their 50s and lose vision more gradually.
“Worldwide we estimate about 500,000 are affected,” the researcher said. “It’s still what we call an orphan disease.”
He and his colleagues looked at 39 patients with STGD1 from 17 families in the new study, online July 16 in Ophthalmology. Median age difference at disease onset between siblings was 4.5 years, but five families had intersibling differences ranging from 13 to 39 years.
Disease-duration-matched best corrected visual acuity (BCVA) was also significantly variable between siblings, with differences were up to 1.1 LogMAR in the right eye and 1.08 LogMAR in the left eye.
Significant visual impairment (SVI) developed in 29 patients (55 of 78 eyes). Disease-duration-based survival time until SVI showed significant intersibling differences in 15 familes. However, size of central retinal atrophy area was comparable for most siblings.
“We found that in siblings the course of disease is very different so that faces us with a problem with designing trials,” Dr. Hoyng said.
He and his colleagues are currently involved in an international clinical trial of remofuscin (Kaitaro, Kusterdingen, Germany), an oral drug. Other treatment approaches under investigation include gene therapy and antisense oligonucleotides, according to the researcher.
“There are all kinds of trials now going on to try to find a cure. Doctors should be aware of that,” he said.