gene is on one of the autosomes there is a 50% chance of an affected individual
passing this on to each offspring. Males and females are equally affected. The primary
and permanent dentitions are generally both involved, although the permanent
dentition may be the more severely affected of the two (828HFig. 13.24). There is a wide
range of presentations (phenotypes). The enamel may be thin and hard with normal
translucency but may be difficult to discern on radiographs because of its limited
thickness. In some cases the enamel may be both hypoplastic and hypomineralized, in
which case the enamel is thin and discoloured with a loss of normal translucency.
Some patients may have enamel of normal thickness which is poorly mineralized, and
yet others may have enamel of normal thickness which lacks the normal translucency
and is therefore regarded as showing features of hypomaturation. Occasionally, subtle
enamel defects may only be identified on histopathological examination of extracted
teeth. In some families taurodontism is seen. Anterior open bite may occur in
autosomal dominant amelogenesis imperfecta as well as in other inheritance patterns.
The mechanism producing the sometimes associated anterior open bite has not yet
been elucidated.
Aetiology
The enamelin gene on chromosome 4 has been shown to be mutated in some families
with autosomal dominant amelogenesis imperfecta. Other genes involved in normal
enamel formation have been implicated in autosomal dominant amelogenesis
imperfecta. Patients with tricho-dento-osseous syndrome, an autosomal dominant
syndrome characterized by amelogenesis imperfecta with taurodontism as well as
curly hair and bone changes, have been found to have mutations in the DLX3 gene on
chromosome 17.
Autosomal recessive amelogenesis imperfecta
Autosomal recessive conditions are typically seen when there is parental
consanguinity, so that that the parents may be first cousins (829HFig. 13.25). There may be
cultural reasons for this or, alternatively, consanguinity may be seen in isolated
communities with little outside contact and where there is consequently a limited gene
pool. In other recessive conditions, such as cystic fibrosis, these restrictions do not
apply and the relative prevalence of the condition is related to the frequency of gene
carriers in the population. Where the parents are close relatives, both carrier adults
will be unaffected but there will be a one in four chance of offspring inheriting two
copies of the mutant gene.
Autosomal recessive mutations causing amelogenesis imperfecta seem to be
uncommon apart from Polynesia, where, presumably, the mutation is relatively
common. Such individuals may have enamel hypoplasia and/or enamel
hypomineralization and the designator 'pigmented enamel' has been applied. A gene
on chromosome 2 has been linked to autosomal recessive amelogenesis imperfecta
associated with ocular defects.
X-linked amelogenesis imperfecta
X-linked amelogenesis imperfecta is characterized by a difference in the appearance
of the teeth of affected males and females. The majority of families studied to date