Amelogenesis Imperfecta in Patients With Hypercalcemia Due to GNA11 Mutations

Objectives: In this study, we aimed to determine whether Familial Hypercalcemia Hypocalciuria 2 (FHH2) is a cause of Amelogensis Imperfecta (AI).
Methods: Dental examination of patients with FHH2
We diagnosed hypomineralized amelogenesis imperfecta in the affected individuals of two unrelated families with FHH2. This manifested by high susceptibility to caries and enamel wear.

Dental tissue studies of FHH2 teeth
First, we collected and prepared deciduous teeth from 2 FHH2 patients and age-matched controls. We performed several techniques to study the microanatomy of the dental tissues (SEM, Synchrotron beam ID19 , EDS, Raman micro-spectroscopy). Second, we studied the expression of GNA11/Gna11 in the human and mouse tooth germ via scRNAseq atlas. Third, we investigated more in depth the expression of Gna11/Gα11 in the mouse tooth germ (RT-qPCR, RNA Scope, Western blot, immunohistochemistry).
Results: SEM analysis showed slightly more “tapered” enamel prisms in FHH2 teeth and abnormal dentin. EDS showed a significant difference in mineralization of both enamel and dentin (lower Ca/P ratio for both tissues in the FHH2 teeth compared to control). Synchrotron acquisitions revealed punctual patches of demineralization following no set pattern in the FHH2 enamel.

Single-cell transcriptome atlas analysis of human and murine tooth germ revealed that GNA11/Gna11 was expressed at all stages of amelogenesis. We performed RT-qPCR and western blot analyses on molar and incisor germs from WT mice, showing robust Gna11/Gα11 expression. We next performed RNA Scope and immunofluorescence on OCT-included frontal and sagittal postnatal tooth germ sections. We found Gna11/Gα11 expression in both ameloblasts and odontoblasts.
Conclusions: This study shows that variants in GNA11 responsible for hypercalcemia, are a novel cause of AI. Multiproxy analyses of primary teeth affected by FHH2 revealed abnormal mineralization of enamel and dentin. In addition, combined molecular and protein analyses confirmed the expression of Gna11/Gα11 in the murine tooth germ, in both ameloblasts and odontoblasts.