There are many different causes of hearing loss at birth. An infant could have suffered trauma in the womb that interfered with proper development, or he could have a genetic malformation that affected the structure of his ears. Parents can also pass on certain traits to their children, called hereditary factors, which increase the likelihood of hearing loss.
How Genetic Factors Affect Hearing
Genes are coded information in the cells that instruct the body on how to grow and work. Humans inherit half of all of their genes from each of their parents and these genes dictate their height, hair color, eye color, and all of their physical traits. Since these traits are a blend of information from the parents, offspring tend to resemble—and even act like—their parents.
People who carry hearing loss factors in their genes can potentially pass them down to their offspring. A person who was born with a physical malformation in the ear could transmit that information to a developing child, while parents with a strong family history of hearing loss are more likely to pass the trait to their children.
Doctors can help parents determine the likelihood of passing on hearing loss genes in a number of ways, including:
- Family history. A specialist can examine the medical history and genetic relationships within a family to discover the potential for passing on hearing loss traits.
- Physical examination and scans. Part of pre-natal testing may involve physical and radiological testing (such as CT scans of the head or neck) to see if any physical factors could cause hearing loss in offspring.
- Molecular genetic testing. This test analyzes each parent’s DNA and the possible combinations of genetic information to detect mutations and possible manifestations of hearing complications.
Difference Between Syndromic Versus Non-Syndromic Hearing Impairment
Hereditary hearing impairments are classified in two ways: syndromic and non-syndromic. A child with syndromic hearing impairment suffers physical malformations of the ear, organ malformations, or medical conditions that affect the organ systems of the body. Syndromic hearing impairment is relatively rare, and commonly causes deafness before a child begins to speak.
Non-syndromic hearing impairment is more common by far, with over 70% of hereditary hearing loss due to non-syndromic causes. These children have no visible abnormalities of the outer ear or any physical or medical problems that affect hearing ability, although some children may have malformations in the inner ear.
Common Hereditary Hearing Disorders
When a child is conceived, hundreds of genes interact between the mother, father, and child to create the structures of the ears. There are several ways gene inheritance can affect the development of a child’s hearing, including:
- Autosomal dominant inheritance. Dominant inheritance means that one parent expresses the trait and transmits it to 50 percent of his children. Dominant-inherited hearing loss can range from mid-frequency hearing disorders to complete deafness. The most common autosomal dominant syndromic hearing loss is Waardenburg syndrome, which also causes pigment abnormalities in the skin, hair, and eyes.
- Autosomal recessive inheritance. Recessive traits are usually hidden, meaning the parents show no outward signs of the trait. However, parents with recessive genes can still transmit the gene to 25 percent of their children. Most hereditary hearing loss comes from recessive genetic traits. The most common form of autosomal recessive syndromic hearing loss is Usher syndrome, which typically causes a child to be born with hearing loss and develop eye conditions causing blindness soon after.
- X-linked inheritance. These genetic inheritances are transmitted from the mother to 50 percent of her male children. In most cases, children with X-linked recessive hearing loss will retain some hearing ability. This type of inheritance accounts for the majority of cases of Alport syndrome, a disorder that causes progressive hearing loss, kidney disorders, and vision problems.
- Mitochondrial inheritance. Mitochondrial DNA mutations increase the chances of a person contracting a variety of diseases, including diabetes mellitus and Alzheimer’s disease. Pathogenic variants in the MT-RNR1 gene have been linked to late-onset hearing loss, while variants in the MT-TS1 gene are associated with childhood hearing problems. In addition, patients with diabetes mellitus who have pathogenic variants in their DNA strands are likely to develop hearing loss after the onset of diabetes.
Children who have inherited hearing disorders can still lead healthy, active lives. Call us today to schedule a hearing testing appointment, and let us help you determine which form of treatment is right for your child.