A novel mutation in collagen gene COL1A2 associated with transient regional osteoporosis.

A young man was diagnosed with transient regional osteoporosis (TRO). The genetic analysis revealed a novel de novo likely pathogenic variant in COL1A2 gene. Our hypothesis is that TRO may be a possible clinical manifestation of osteogenesis imperfecta due to a reduced bone mass and an impaired trabecular mechanical competence. INTRODUCTION: Transient regional osteoporosis (TRO) is a disease characterized by episodes of pain in the lower limbs involving the hip, knee, ankle or foot. Here, we present a clinical case of a Caucasian 25-year-old man exhibiting TRO. Based on few mild clinical findings suggestive of osteogenesis imperfecta (OI), but without a history of fragility fractures, we performed a genetic assessment to investigate this hypothesis. METHODS: Medical history was obtained from the patient and family members, including biochemical, RMI and DXA assessments. Next-generation sequencing of COL1A1, COL1A2, COL2A1, CASR, CYP19A1, CUL7, CRTAP, KAL1, LEPRE1, LRP5, PPIB and SLC9A3R1, genes involved in juvenile osteoporosis, was performed. RESULTS: We identified a novel de novo heterozygous missense variant, c.488G > A, in exon 11 of the COL1A2 gene (NM_000089.3), resulting in the putative p.Gly163Asp substitution in the N-terminal part of the helical domain of type I collagen. The variant was predicted to be damaging by the in silico prediction tools and the mutation was therefore classified as likely pathogenic. This mutation can affect skeletal health impairing bone mass and trabecular mechanical competence, inducing a disease whose features strictly evoke a TRO. CONCLUSION: The present study describes a novel de novo heterozygous missense variant in COL1A2 gene, possibly inducing a propensity to trabecular microfractures. The recurrent symptomatic bone marrow oedema episodes could be the clinical picture consistent with the hypothesis of an inherited connective tissue disorder giving bone fragility.