Delayed Bone Age in a Child with a Novel Loss-of-Function Variant in SETBP1 Gene Sheds Light on the Potential Role of SETBP1 Protein in Skeletal Development.

INTRODUCTION: SETBP1 gene variants that decrease or eliminate protein activity have been associated with phenotypes characterized by speech apraxia and intellectual disabilities. This condition, distinctly separated from Schinzel-Giedion syndrome, is referred to as autosomal dominant mental retardation 29 (ADR29).

CASE PRESENTATION: In this report, we present the case of a 6-year-old male patient exhibiting fine and global motor skill impairments along with expressive language delay. The patient carried a novel germline, heterozygous, de novo nonsense variant in the SETBP1 gene, specifically the c.532C>T variant, which prematurely terminates protein translation at amino acid 178, p.(Gln178*), and removes more than 10% of the reference protein isoform consisting of 1,596 amino acids. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, this variant has been classified as pathogenic.

CONCLUSION: Given the limited number of ADR29 cases reported to date, it is critical to focus attention on the phenotypic features of each new individual and seek out previously undocumented defects. The clinical findings found in our patient align with current knowledge on the correlation between the genotypes characterized by loss-of-function variants in SETBP1 gene and a particular neurological phenotype. Furthermore, the presence of a severely delayed bone age in this patient, which we report for the first time, could indicate a possible indirect but significant contribution of the SETBP1 protein in bone development and maturation processes. This finding highlights the need for further investigation into the potential effects of SETBP1 gene variants on bone health and the possible involvement of the SETBP1 protein in skeletal growth and development.