Genetic association and characterization ofFSTL5in isolated clubfoot

Abstract

Talipes equinovarus (clubfoot, TEV) is a congenital rotational foot deformity occurring in 1 per 1000 births with increased prevalence in males compared to females. The genetic etiology of isolated clubfoot (iTEV) remains unclear. Using a genome-wide association study, we identified a locus within FSTL5, encoding follistatin-like 5, significantly associated with iTEV. FSTL5 is an uncharacterized gene whose potential role in embryonic and post-natal development were previously unstudied. Utilizing multiple model systems, we found that Fstl5 was expressed during later stages of embryonic hindlimb development, and, in mice, expression was restricted to the condensing cartilage anlage destined to form the limb skeleton. In the post-natal growth plate, Fstl5 was specifically expressed in pre-hypertrophic chondrocytes. As Fstl5 knock-out rats displayed no gross malformations, we engineered a conditional transgenic mouse line (Fstl5LSL) to over-express Fstl5 in skeletal osteochondroprogenitors. We observed that hindlimbs were slightly shorter and that bone mineral density was reduced in adult male, but not female, Prrx1-cre;Fstl5LSL mice compared to control. No overt clubfoot-like deformity was observed in Prrx1-cre;Fstl5LSL mice, suggesting FSTL5 may function in other cell types to contribute to iTEV pathogenesis. Interrogating published mouse embryonic single-cell expression data showed Fstl5 was expressed in cell lineage sub-clusters whose transcriptomes were associated with neural system development. Moreover, our results suggest lineage-specific expression of the Fstl genes correlates with their divergent roles as modulators of TGF-ß and BMP signaling. Results from this study associate FSTL5 with iTEV and suggest a potential sexually dimorphic role for Fstl5 in vivo.

Follistatin-Like Proteins: Structure, Functions and Biomedical Importance

“…Results from a recent study associate variation of FSTL5 expression in prehypertrophic chondrocytes with lower limb malformations and congenital rotational foot deformity [99].…”

Pediatric Foot: Development, Variants, and Related Pathology

“…43 Most commonly, it is an isolated disorder considered to have a complex and poorly understood genetic component that is likely impacted by a spectrum of genetic loci. 44 The prenatal development of congenital clubfoot remains poorly understood. On clinical exam, plantar flexion is observed at the ankle, hindfoot varus, forefoot adduction, and inversion.…”

Genotype-phenotype correlation in clubfoot (talipes equinovarus)

“…Yet, the association between isolated CTEV and SNPs in proximity to NCOR2 / ZNF664 , FOXN3 , MMP7 / TMEM123 or SORCS1 genes was determined in discovery and replication datasets 78. Another GWAS indicated rs76973778 SNP located in the intron of FSTL5 gene as the associated variant both in the discovery and replication cohorts but animal studies showed no developmental abnormalities in rats heterozygous or homozygous for Fstl5 79…”