Exploring Genetic Subtype for Inherited Night Blindness Suggests New Approach to Testing and Coping

Published April 2018 | JAMA Ophthalmology

Complete congenital stationary night blindness (cCSNB) is a rare inherited retinal disease that inhibits normal rod cell response to light. Those affected often also have reduced visual acuity, near-sightedness, eye misalignment (strabismus) and involuntary eye shaking (nystagmus).

But in some cases, the classic night blindness (nyctalopia) symptoms do not appear during early childhood, which can mask the condition. Now a study led by Virginia Miraldi Utz, MD, along with colleagues at the University of Iowa, explores the progression of cCSNB associated with variations in the gene TRPM1, one of several known to be linked to the condition.

The team explored the medical histories of seven children born with TRPM1-associated cCSNB. They found a set of symptoms that can indicate which children should receive closer examination even though night blindness has not yet emerged.

“These findings suggest that ffERG and cCSNB genetic testing should be considered for children who present with early-onset myopia, especially in the presence of strabismus and/or nystagmus,” Miraldi Utz says. “TRPM1-associated cCSNB is a channelopathy that may present without complaints of night blindness in some children.”

In the study, no patient or parent noted nyctalopia at presentation. However, five patients eventually did experience night blindness, with two cases serious enough to disrupt activities.

There are no cures for cCSNB. However, if TRPM1 mutations are present, parents can make lifestyle modifications such as having children carry flashlights to cope with low-light environments.

“The largest implication is that we need to look very carefully at conditions that have traditionally been ‘lumped’ together, “Miraldi Utz says. “Now that we have molecular testing, we can stratify based on genotype to better understand the natural history and clinical progression of disease.”