Affecting approximately two to three of every 1,000 babies, hearing loss is the most common birth defect in the United States. About 70 percent of these cases are considered non-syndromic, meaning the hearing loss is passed down to the baby genetically without any other related conditions. However, up to 30 percent are syndromic, or associated with other birth defects that impact the structure and development of the ear and cause hearing loss.
As January is National Birth Defects Prevention Month, we’re taking a look at some of the conditions that lead to syndromic hearing loss. Through each are rare, the following are examples of syndromic birth defects commonly linked to hearing loss.
Affecting hearing ability and causing hypothyroidism, or decreased function of the thyroid gland, Pendred syndrome is a genetic disorder occurring in seven to eight out of every 100,000 newborns. The condition often results in an enlarged vestibular aqueduct, which is a malformation of the inner ear and leads to hearing loss. The hearing loss may be present at birth, or it may develop later, resulting in total deafness in some cases.
Found in one out of every 23,000 people in the U.S., Usher syndrome causes both hearing loss and visual impairment, a result of mutations of the genes responsible for hearing and vision. The hearing loss is due to a defective inner ear, while the loss in vision is attributed to degradation of the retinal cells. Usher syndrome also causes damage to the vestibular system, or the parts of the inner ear and brain responsible for controlling balance and eye movement.
Approximately one in 40,000 people has Waardenburg syndrome, which is characterized by varying degrees of hearing loss, in addition to abnormalities in pigmentation of the eyes, hair, skin, and the inner ear. The condition is present during development of the embryo, and is caused by the proliferation and migration of melanocytes, melanin-producing cells from the neural crest.
Treacher Collins syndrome
Treacher Collins syndrome is a genetic disorder that affects the development of the bones and tissue in the face and causes deformities of the ears, eyes, cheekbones, and chin. The hearing loss component is caused by defects in the three bones of the middle ear or by defects in the development of the ear canal or outer ear. Treacher Collins syndrome affects one in 50,000 people, and it recently gained national attention as it was featured in the movie Wonder.
The above are just a handful of the syndromes that can cause birth defects like hearing loss. Given how important hearing is for learning and communication during the formative years, it is crucial that babies with any such syndrome be treated for hearing loss alongside their other ailments. Understanding how such birth defects impact hearing and providing appropriate intervention from the beginning can help these children hear and improve their quality of life.