Labyrinthine aplasia, microtia, and microdontia (LAMM) syndrome and FGF3 mutations

Hearing loss presents as a clinical finding in more than 400 genetic syndromes, some of which are associated with inner ear anomalies. Congenital deafness with labyrinthine aplasia (also known as Michel aplasia), microtia, and microdontia (LAMM syndrome; MIM 610706) was described in 2007 as an autosomal recessive syndrome. Mutations in FGF3 were demonstrated in affected subjects. Since the initial description, 56 individuals with LAMM syndrome from 13 unrelated families have been reported. Microdontia was the most constant finding that was present in all affected individuals. Michel aplasia was present in most cases although other severe inner ear anomalies were detected in some individuals, especially with the p.R95W mutation. Microtia typically affected the upper pinna and was associated with anteverted ears, large skin tags or lobulation. Microtia was not observed in a few cases with the p.R95W mutation. Clinical findings do not appear to involve the other systems and in particular cognitive development is not affected. Reported mutations include missense, nonsense, and small deletions leading to a frameshift suggesting that the LAMM syndrome is caused by the loss of FGF3 function. The presence of severe inner ear anomalies, complete labyrinthine aplasia in most cases, limits the usage of cochlear implants. Auditory brain stem implantation may be considered as in other cases with severe inner ear anomalies. Recognition of LAMM syndrome and detection of FGF3 mutations in a deaf individual is important because it leads to better genetic counseling and empower families to have informed reproductive decisions.