Hypomaturation amelogenesis imperfecta due to WDR72 mutations: a novel mutation and ultrastructural analyses of deciduous teeth

Abstract

Background: Mutations in WDR72 have been identified in autosomal recessive hypomaturation amelogenesis imperfecta (AI).

Objective: to describe a novel WDR72 mutation and report the ultrastructural enamel phenotype associated with a different WDR72 mutation.

Methods: A family segregating autosomal recessive hypomaturation AI was recruited, genomic DNA obtained and WDR72 sequenced. Four deciduous teeth from one individual with a previously published WDR72 mutation, extracted as part of clinical care, were subjected to scanning electron microscopy, energy-dispersive X-ray analysis and transverse microradiography.

Results: A novel homozygous nonsense mutation, R897X, was identified in WDR72 in a family originating from Pakistan. Ultrastructural analysis of enamel from the deciduous teeth of an AI patient with the WDR72 mutation S783X revealed energy-dispersive X-ray analysis spectra with normal carbon and nitrogen peaks, excluding retention of enamel matrix protein. However, transverse microradiography values were significantly lower for affected teeth when compared to normal teeth, consistent with reduced mineralisation. On scanning electron microscopy the enamel rod form observed was normal, yet with inter-rod enamel more prominent than in controls. This appearance was unaltered following incubation with either α-chymotrypsin or lipase.

Conclusions: The novel WDR72 mutation described brings the total reported WDR72 mutations to four. Analyses of deciduous tooth enamel in an individual with a homozygous WDR72 mutation identified changes consistent with a late failure of enamel maturation without retention of matrix proteins. The mechanisms by which intracellular WDR72 influences enamel maturation remain unknown.

Fig. 1

Clinical and radiographic phenotype, pedigree and novel WDR72 mutation. a Heavily restored lower dentition of the proband's sister aged 18 years. The visible enamel of teeth, including where restorations have failed, has a yellow/brown discolouration (arrows). b–d Radiographs of two affected individuals. Details from panoramic radiographs taken of the proband's sister when aged 8 years (b) and 20 years (c). The developing lower right second molar tooth (*) has a normal crown morphology in b, but without the expected contrast in radiodensity observed in someone without AI (inset). The same tooth (**) approximately 8 years after eruption and restoration failure is characterised by considerable enamel loss consistent with early functional failure. Both the upper and lower first permanent molar teeth (+) have required restoration with metal crowns due to functional failure. d A dental bitewing radiograph of the proband taken aged 12 years illustrating the typical post-eruptive pattern of enamel loss that starts soon after tooth eruption into the mouth. e The pedigree confirmed consanguinity (proband marked with arrow) with confirmation of the c.2728C>T mutation.

Fig. 2

Ultrastructural phenotyping of deciduous teeth. a, b EDX spectra: the C:O and Ca:P ratios were indistinguishable between control (a) and autosomal recessive hypomaturation AI (b) enamel with no N peak (between the C and O peaks) observed in either sample. c–e SEM of control (c) and AI-affected (d, e) enamel. The AI enamel rods are grossly normal but the inter-rod enamel is more obvious (pale lines marked with arrow heads) in the affected enamel compared to the controls. There is an apparent lack of enamel rod decussation in the affected enamel whereas in the control enamel there is different rod long axis orientation in the upper compared to the lower part of the image. Scale bars = 20 μm.