Identification of a novel splicing mutation and genotype-phenotype correlations in rare PLS3-related childhood-onset osteoporosis

Abstract

Background: X-linked early-onset osteoporosis, caused by mutations in plastin3 (PLS3), is an extremely rare disease characterized by low bone mineral density (BMD) and recurrent osteoporotic fractures. There is limited information on genetic and phenotypic spectrum, as well as genotype-phenotype correlations of the disease. Moreover, whether decreased PLS3 levels were also involved in osteoporosis among subjects without PLS3 pathogenic mutations remains unknown.

Methods: Whole-exome sequencing and bidirectional Sanger sequencing were performed for screening and validation of pathogenic mutations. Serum biochemical parameters and clinical information of the subjects were retrospectively collected. ELISA and online datasets were utilized to investigate the association between PLS3 expression and BMD.

Results: We identified a novel splicing mutation (c.892-2A > G) which led to the skipping of exon 9 in a family with X-linked early-onset osteoporosis. Scoliosis represents a potential new phenotype in the patients harboring PLS3 mutations, which may be corrected by brace treatment. Genotype-phenotype analysis reveals that there was no significant difference in BMD z-scores between different types of reported mutations including this study (p = 0.5). There is a marginally significant negative correlation between age and BMD z-score (p = 0.059, r = - 0.30). The conditions of osteoporosis in all patients were improved after bisphosphonates therapy, with mean BMD z-score increased from - 2.9 to - 0.57 (p < 0.0001). Serum PLS3 levels in adolescents and adults without PLS3 pathogenic mutations but representing osteoporosis were also evaluated, while no association was found between bone mineral density and PLS3 levels (p > 0.05).

Conclusions: Our findings expanded the mutation and phenotype spectrum of the rare disease and highlights the importance of early diagnosis and early treatment with bisphosphonates. More reports of cases with PLS3 mutation and function studies of the gene are warranted to understand genotype-phenotype correlations.

Keywords: Mutation; PLS3 gene; Phenotype; Primary osteoporosis; Scoliosis.

Fig. 1

Pedigree and genetic analysis of the family. a Pedigree of the family showing an X-linked recessive inheritance. b Pathogenic mutation in PLS3 confirmed by sanger sequencing. c Gel image showing the RT-PCR products of PLS3 cDNA fragments. d Schematic representation of the alternation of the PLS3 gene and PLS3 protein (e) induced by the splicing mutation

Fig. 2

Standing anteroposterior and lateral spinal radiographs of the proband. a Spinal radiographs showed lumbar compression fracture. b The proband exhibits the phenotype of scoliosis 3 months after lumbar compression fracture. c The cobb angle decreased to 15° and the proband reached skeletally mature after 5 years of brace treatment. White arrows indicated the apical vertebra

Fig. 3

Schematic representation of the previously reported deleterious mutations in PLS3 gene and corresponding protein domains. Detained information regarding location, clinical characteristics of male patients and reference were listed in Additional file 1: Table S1. CBM calmodulin-binding motif

Fig. 4

Analysis of the genotypes and phenotypes of the male patients. a Comparison of BMD z-score between different types of mutations. b The correlation between BMD z-score and age at evaluation. c BMD z-score before and after bisphosphonates therapy in affected males. d The association of the increase of BMD z-score per year and the age in the affected males underwent bisphosphonates therapy

Fig. 5

Relationship between PLS3 levels and bone mineral density. a–b Association of PLS3 concentration by ELISA in adolescents. c–e Association of PLS expression levels with bone mineral density in adults based on public datasets GSE 7429, GSE 56814 and GSE 56815