What causes Mondini dysplasia ?
What causes Mondini dysplasia? The underlying cause of Mondini dysplasia (MD) in most individuals appears to remain unclear. Some have suggested that retinoids (vitamin A) or other factors a fetus may be exposed to early in pregnancy have contributed to some cases of isolated MD (occurring with no other abnormalities). The potential role of these factors has created increased difficulty in determining the real cause of isolated MD. Mutations in the SLC26A4 gene cause both Pendred syndrome and DFNB4 (non-syndromic hearing loss with inner ear abnormalities), which are both associated with MD. Though mutations in the SLC26A4 gene have also been found in individuals with enlarged vestibular aqueduct (EVA) with and without MD, studies have shown there does not appear to be a relationship between isolated MD and the SLC26A4 gene. Thus hearing impairment in individuals with isolated MD may be caused by factors other than mutations in the SLC26A4 gene. More recently, a type of mutation called a microdeletion (a tiny loss of genetic material on a chromosome that may span several genes) involving the POU3F4 gene on the X chromosome was detected in some individuals with familial MD. In cases where Mondini dysplasia is associated with a specific syndrome, the cause of the syndrome in the affected individual is assumed to be related to the occurrence of MD in those cases. Syndromes that have been associated with MD include Klippel Feil syndrome, Pendred syndrome, DiGeorge syndrome, and some chromosomal trisomies.