During his research into the DFNA9 syndrome, Kemperman came across a genetic abnormality which had not previously been seen outside of America. In addition to the usual mutation P51S, he also discovered the G88E mutation. The hearing of patients with the DFNA9 syndrome deteriorates from midlife onwards. People with this abnormality also suffer from balance disorders.
Kemperman worked together with patients from Dutch families in which hearing impairment was inherited. The most extensive study was with patients with BOR syndrome (Branchio-oto-renal syndrome). In this study Kemperman investigated people from six different families, some of which had been followed for more than 30 years. As well as hearing loss, patients with BOR syndrome suffer from infections in the throat, kidney abnormalities and external ear abnormalities. Kemperman discovered that the syndrome also causes inner ear abnormalities and that the hearing loss increases with age.
The researcher also investigated the first family in the Netherlands with the DFNA20/26 syndrome. In this syndrome the hearing already starts to deteriorate at a young age. The high frequencies are damaged first and later the middle and low frequencies. The clinical picture of the Dutch family was worse than that described in the literature. Kemperman carried out gene matching research to identify the gene concerned. Although he did not find the responsible mutation, the possibilities for candidate genes were reduced. Kemperman's colleagues have since described the gene in question.
Finally, Kemperman investigated patients with DFNB1. This form of hearing impairment often starts at a young age. The hearing impairment is caused by mutations in the underlying GJB2 gene, which cause errors in the protein connexin26. The 35delG mutation is the most prevalent form in the countries surrounding the Netherlands. Kemperman confirmed that this mutation is also the most prevalent mutation for DFNB1 in the Netherlands.
This information about the clinical pictures of the four syndromes can help physicians to better inform patients about the progression of the disease. They can also use it to recognise the clinical picture in new patients at an earlier stage.
The research was funded by the Netherlands Organisation for Scientific Research.