The researchers found mutations in the most common recessive deafness genes, GJB2 and GJB6, in 14 percent of pediatric patients and 1 percent of adults. Thirteen percent of the children were also carriers of single mutations, indicating that they may play some role in deafness, the authors noted. Three percent of the adults had mitochondrial DNA mutations, but none of the children did.
Explore This IssueJune 2013
Dr. Liu and his team propose a testing scenario in which children with SNHL first have tests for both GJB2/GJB6 mutations and cytomegalovirus, the most common cause of hearing loss in children, before CT scans. The researchers recommend against such testing in adults because it has very low yield, except in cases with strong family history.
Avoiding Unnecessary Tests
While GJB2 had been considered a first-line genetic test for children with SNHL prior to their study, the University of Miami researchers aimed to see how it could become part of a more efficient diagnostic strategy for their adult and pediatric clinic patients, said Dr. Liu. “This study strengthened our strategy, which is to screen for common genes first. That way, we can exclude 20 to 30 percent of cases. It’s very cost effective,” he said. Identifying children with GJB2 mutations before running other tests can in some cases prevent the need for certain non-genetic tests, especially CT scans, which also deliver high doses of radiation.
That’s because GJB2 testing can rule out genetic syndromes, which cause up to 30 percent of hearing loss cases. Without evidence of a mutation that causes faulty connexin, there’s an argument for ordering several costly non-genetic tests up front, including a CT scan, lab tests, an EKG and an eye exam, said Anil Lalwani, MD, professor and vice chair for research, chief of the division of otology, neurotology and skull base surgery and director of the cochlear implantation program in the department of otolaryngology–head and neck surgery at Columbia University in New York City. Among the more common conditions are Stickler syndrome, which involves eye and joint issues, and Waardenburg syndrome, the characteristics of which include joint and skin problems. Pendred syndrome involves the thyroid, while Usher syndrome includes blindness.
Other research groups have previously recommended delaying CT scans intended to look at ear structure until a child’s GJB2 status is known, said Craig Buchman, MD, chief of the division of otology, neurology and skull base surgery at the University of North Carolina School of Medicine in Chapel Hill (Laryngoscope: 2009;119:554-558 and 2011;121:630-635). That’s because patients with faulty connexin 26 generally have negative imaging tests, he said, so CT scans may needlessly expose children to radiation or anesthesia.