| Category | Sub-category | Percent |
|---|---|---|
| Genetic | Unknown non-syndromatic with recessive behavior | 16.4% |
| Genetic | Connexin 26 (GJB2) | 16.4% |
| Birth Related | Other birth/pregnancy related causes | 16.3% |
| Birth Related | CMV (cytomegalovirus) | 12.5% |
| Genetic | Unknown non-syndromatic with dominant behavior | 8.4% |
| Genetic | Down Syndrome | 5.5% |
| Birth Related | Hypoxia/Anoxia (lack of oxygen) | 4.3% |
| Genetic | Pendred Syndrome | 2.8% |
| Birth Related | Hyperbilirubinemia (jaundice) | 2.5% |
| Genetic | Waardenburg Syndrome | 2.5% |
| Genetic | CHARGE Syndrome | 2.5% |
| Birth Related | Maternal Alcohol/Drug Usage | 2.0% |
| Genetic | Usher Syndrome | 1.3% |
| Birth Related | Bacterial Meningitis | 1.25% |
| Genetic | Treacher Collins Syndrome | 1.0% |
| Genetic | Non-Syndromatic - X-Linked/Mitochondrial | 0.8% |
| Genetic | Branchio-Oto-Renal Syndrome | 0.6% |
| Genetic | Stickler Syndrome | 0.6% |
| Genetic | Goldenhar Syndrome | 0.5% |
| Genetic | Other Syndromes | 0.5% |
| Birth Related | Toxoplasmosis | 0.5% |
| Birth Related | Herpes Simplex | 0.5% |
| Birth Related | Syphilis | 0.15% |
| Genetic | Crouzon Syndrome | 0.1% |
| Genetic | Jervell & Lange Syndrome | 0.1% |
| Birth Related | Rubella | 0.0% |
| Birth Related | Toxemia (pre-eclampsia) | 0.0% |
| Birth Related | Maternal Diabetes | 0.0% |
Determining the percentages is much more of an art than a science. This is because lots of information isn't known. Information is updated frequently; some data is 10-20 years old. Some data is based on very small samples of people. Some refer to "hearing loss", while others refer to "deafness". For most syndromes, there isn't much information about what percentage of affected people have hearing loss, and what percentage of them had hearing loss since birth. For more issues like this, and the rationale behind the numbers, see our boring Etiology Rationale page.
The information comes from many, many sources. The original data was all in different forms, the few that did state the percentage of congenital hearing loss did so with imprecise numbers. By far the biggest source of data was the Regional and National Summary Report of Data from the 2004-2005 Annual Survey of Deaf and Hard of Hearing Children and Youth by the Gallaudet Research Institute (December, 2005). Please note that that data was not used as a starting point (see our Etiology Rationale for more details).