Mondini dysplasia is a type of inner ear malformation that is present at birth (congenital). Individuals with Mondini dysplasia have one and a half coils of the cochlea instead of the normal two coils. It may occur in one ear (unilateral) or both ears (bilateral) and can cause varying degrees of sensorineural hearing loss, although most individuals have profound hearing loss. The condition can also predispose affected individuals to recurrent meningitis.

It is caused by disruption in the embryonic development of the inner ear during the seventh week of gestation. The condition may be isolated (occurring with no other conditions or malformations) or may occur with other ear malformations or a number of syndromes.

Treatment options may include surgical repair of the defect to prevent recurrent meningitis; amplification aids for those with residual hearing; and cochlear implantation.

Mondini dysplasia usually occurs sporadically as an isolated abnormality (occurring in only one individual in a family with no other abnormalities) but it can be associated with a variety of syndromes including Klippel Feil syndrome, Pendred syndrome, DiGeorge syndrome, Wildervanck syndrome, Fountain syndrome, Johanson-Blizzard syndrome, and some chromosomal trisomies. These syndromes can be inherited in a variety of ways, but Mondini dysplasia may not occur in each affected individual.

It has also has been reported in families with congenital sensorineural hearing loss, both with autosomal dominant and presumed autosomal recessive inheritance. One study described familial nonsyndromic Mondini dysplasia in a mother, son and daughter with presumed autosomal dominant inheritance; another study described familial nonsyndromic Mondini dysplasia in a family in which transmission was most consistent with autosomal recessive inheritance.

It has also been suggested that Mondini dysplasia may be associated with substances that may harm a developing fetus when a pregnant woman is exposed (teratogens) such as thalidomide or rubella.

Being that Mondini dysplasia has been associated with a variety of conditions, inheritance patterns, and both genetic and non-genetic causes, it appears to be inherited in some cases, with the inheritance pattern being dependent upon the underlying cause of the condition in each individual or family.

Genetic testing may be available for Mondini dysplasia if it is associated with a specific syndrome for which genetic testing is available, or if a mutation has previously been identified in an affected individual in the family. Unfortunately, for many cases of isolated Mondini dysplasia, there is no clinical genetic testing available.