# FAM20A Deficiency Drives Transcriptomic Dysregulation and Functional Impairment in Gingival Fibroblasts

## TL;DR

FAM20A deficiency causes abnormal gene activity and cell function in gum cells, leading to symptoms like enamel defects and gum overgrowth in a rare genetic disorder.

## Contribution

This study identifies FAM20A's role in regulating cell adhesion, proliferation, and osteogenesis in gingival fibroblasts, offering new insights into AI1G pathogenesis.

## Key findings

- RNA sequencing revealed widespread gene dysregulation in cell adhesion, proliferation, and signaling pathways in FAM20A-deficient fibroblasts.
- Functional assays showed impaired osteogenic differentiation and increased cell proliferation in FAM20A-insufficient fibroblasts.
- FAM20A insufficiency disrupts extracellular matrix interactions and contributes to gingival fibromatosis in AI1G.

## Abstract

Amelogenesis imperfecta type 1G (AI1G), also known as Enamel‐Renal‐Gingival Syndrome (ERGS), is an autosomal recessive disorder caused by variants in FAM20A, encoding a Golgi apparatus protein crucial for protein processing and secretion. AI1G presents with enamel defects, nephrocalcinosis and gingival overgrowth. Building upon our previous findings demonstrating the impact of FAM20A insufficiency on deciduous dental pulp cells, this study investigated the molecular mechanisms underlying gingival fibromatosis in AI1G. RNA sequencing of gingival fibroblasts from an AI1G patient revealed widespread differential gene expression (DEG). Gene Ontology (GO) analysis demonstrated enrichment of DEGs in biological processes related to cell adhesion, differentiation, proliferation (including positive regulation and cell division), cell cycle regulation, apoptosis and signal transduction. Pathway analysis (Reactome and KEGG) further highlighted the dysregulation of signalling pathways, including Wnt, TGF‐β, cell cycle, DNA replication, Rho GTPase signalling and extracellular matrix organisation. Functional assays confirmed these findings, revealing delayed initial attachment and spreading, impaired osteogenic differentiation (evidenced by reduced mineralization and downregulation of DLX5, OCN, RUNX2 and OPN), enhanced cell cycle progression and proliferation (increased colony size and proliferation rates, along with a shift from G0/G1 to G2/M phase) and suppressed apoptosis in FAM20A‐insufficient fibroblasts. These results suggest that FAM20A plays a critical role in regulating fundamental processes in gingival fibroblasts, and its insufficiency contributes to the gingival fibromatosis phenotype observed in AI1G through the disruption of cell adhesion, differentiation, proliferation and apoptosis. This study proposes novel insights into the pathogenesis of AI1G and highlights potential therapeutic targets for this complex disorder.

FAM20A variants cause AI1G, marked by enamel defects, gingival overgrowth and ectopic calcifications. RNA sequencing of patient‐derived gingival fibroblasts showed dysregulated genes in adhesion, proliferation and signalling pathways. Functional assays revealed increased cell proliferation, impaired ECM interactions and osteogenesis, suggesting FAM20A dysfunction disrupts tissue remodelling and contributes to tooth eruption failure.