Genetic hearing loss

Some hearing impairments can be hereditary.

Parents and grandparents are usually the first to notice hearing loss, as they spend most of their time with the child. However, you should pay particular attention if your baby does not react to sudden and loud noises (by moving, crying, etc.), does not wake up from loud noises, does not turn its head in the direction of your voice or does not imitate sounds on its own. These could be the first signs that your baby is suffering from hearing loss.

If you ever suspect that your child may be hard of hearing, consult your family doctor. They can then refer you to an ear, nose and throat specialist if necessary. However, not every hearing loss has to be chronic. This is because in the vast majority of cases, the hearing loss is temporary. The children then usually have a tympanic effusion, i.e. an accumulation of fluid behind the ear or a blockage caused by earwax. Temporary hearing loss can often be remedied with medication or minor surgery.

Some children suffer from hearing loss of the inner ear, which is chronic. However, most children are not completely deaf. Children can be fitted with a hearing aid from the age of 3 months. Early detection of hearing loss as well as hearing aids and special programs can improve the existing hearing spectrum. Your child will make noticeable progress and get a head start in their language development.

How can I have a genetic hearing loss diagnosed in my child?
Whereas in the past we had to rely solely on hearing tests and the family history of the affected children, today there are modern laboratory tests to detect genetic hearing loss, such as in the case of Waardenburg syndrome. During these examinations, for example, a mouth swab is taken from the child. The samples are examined and analyzed using molecular biology. Typical genes that indicate hearing loss can thus be identified. This special laboratory test is available from us.
With a rate of 0.3%, hearing loss and deafness are the most common congenital diseases. Genetic defects play an important role in congenital hearing loss. Of course, there are also other reasons that can lead to hearing loss and deafness during a lifetime.
The most common distinction between hearing loss is syndromic and non-syndromic hearing loss.
Approximately 70% of congenital hearing impairments are non-syndromic. In 80% of these cases, autosomal recessive genes are responsible for the hearing loss and in 20% autosomal dominant genes. In less than 2% of cases, a defect in the mitochondria or X chromosomes is responsible.
If hearing loss is syndromic, the causes lie in other abnormalities. 15-30% of cases of inherited hearing loss are syndromic.

More than 400 syndromes are known and can be categorized as follows:
Syndromes resulting from cytogenetic or chromosomal abnormalities
Syndromes transmitted by classical monogenetic or Mendelian inheritance
syndromes that result from multifactorial influences and ultimately
Syndromes that result from a mixture of genetic and external factors.
It is normal for syndromes to manifest themselves in different ways. They are mild to severe and occur in combination. They also differ from person to person, and mutations can even occur within a family. One example of variation within a family is the inheritance of Waardenburg syndrome. Within a family, affected individuals exhibit an unusually wide bridge of the nose, which is caused by a misalignment of the eyes, white forelocks, a different coloration of the iris of the eyes and hearing loss. Others from the same family may just have an unusually wide bridge of the nose.

How do genes work?
Genes are like a blueprint for the formation of proteins. Proteins are the building blocks for simply everything: hair, eyes, ears, heart, lungs, etc. Each child inherits 50% of the genes of one parent and 50% of the genes of the other. If the inherited genes are defective, a disease such as hearing loss or deafness can be passed on. Hearing disorders are inherited in four ways:
Autosomal dominant inheritance: A rare allele passed on by a heterozygous parent is sufficient to inherit a hearing disorder. Heterozygosity means that a gene is present twice. Once as a normal gene and once as a mutated gene, two types of germ cells can be created. One germ cell will carry the mutated form and the other germ cell will carry the normal form. The chance of inheriting a disorder from a parent with autosomal dominant genes is therefore 50%. Women and men are equally affected.
Autosomal recessive inheritance: This inheritance is characterized by the fact that both parents are heterozygous carriers of the mutated gene but have no disorders. The defective gene is replaced by the normal gene. Affected parents (A/a) can produce two types of gametes. One is the mutated form (a) and the other is the normal form (A). This results in the following possible combinations: (A/A), (A/a), (a/A) and (a/a). Only children with the combination (a/a), i.e. who have both mutated forms, are affected by a disorder. The chance is therefore 25%.
X-chromosomal inheritance: A man has one X and one Y chromosome and a woman only two X chromosomes. Every woman inherits one X chromosome from her mother and one from her father. Males inherit an X chromosome from their mother and a Y chromosome from their father. As a rule, only one of the woman’s two X chromosomes is active. So if one X chromosome is defective, this can be compensated for by the second. This is why men who only have one X chromosome and cannot compensate for a defective X chromosome are more susceptible to hereditary diseases than women.
Mitochondrial inheritance: Mitochondria are small power plants in the cells that have their own DNA. Sperm cells do not contain mitochondria, so only the mitochondria of the egg cell can be inherited. The resulting hereditary pattern is interesting, as only affected mothers (sperm does not contain mitochondria) can pass on hereditary diseases to the next generation.
In the last decade, modern molecular biology and genetics have contributed to a better understanding of the inner ear. Research has identified a large number of genes that are responsible for the inheritance of hearing loss and deafness. The GJB2 mutation is particularly noteworthy. It is one of the most common causes of congenital hearing loss. The GJB2 mutation is a recessive disorder, as deafness only occurs in cases that have two copies of the mutation (one from each parent). If only one mutated copy is inherited, the affected person is a carrier but not deaf. Thanks to extensive research into the GJB2 mutation, affected parents can be informed about the risk of fathering a deaf child.

Literature
Apaydin F., Bereketoglu M., Turan O., Hribar K., Maassen M. M., Günhan Ö. Zenner H.P. , Pfister M. Waardenburg syndrome: a heterogeneous disease with variable penetrance ENT (2004) Mar 52:533-537.
Pfister M., Akylidiz S., Gunhan O., Maassen M.M., Rodriguez Jorge J., Zenner H.P., Apaydin F. A patient database application for Hereditary Deafness Epidemiology and Clinical Research (H.E.A.R.): an effort for standardization in multiple languages Eur Arch Otolaryngol 2003 (260) 2, 81-85.