ESPE Abstracts

Introduction: Recently novel approaches, through implementation of next-generation sequencing (NGS) in clinical practice for genetic evaluation of idiopathic short stature, has permitted to identify new variants of genes which modulate function of growth plate, including heterozygous mutations of the aggrecan gene. Aggrecan, a large chondroitin sulfated proteoglycan, is a major structural component of the extracellular matrix of cartilage, including growth plate, articular and intervertebral disc cartilage. We herein report five novel pathogenic variants in ACAN gene detected in five unrelated families using next-generation sequencing. Furthermore, we present the first large exonic deletion in ACAN gene in additional family, detected with array comparative genome hybridization (aCGH). Our study further expands clinical spectrum of ACAN phenotype.

Methods: Our baseline group comprised 50 children and adolescents with one inclusion criteria, i.e. height bellow -2 standard deviation scores (SDS) and five exclusion criteria: (i) growth hormone (GH) deficiency, (ii) hypothyroidism, (iii) chronic illness, (iv) defined skeletal dysplasia and/or syndrome, (v) cytogenetically detectable chromosomal abnormalities (e.g. Turner syndrome). From the baseline group we then formed a study subgroup of 16 individuals with advanced bone age and/or autosomal dominant inheritance pattern of short stature. We performed targeted or next-generation sequencing. Depending on the selection criteria (i.e., familial short stature and advanced bone age), additional array comparative genomic hybridization (aCGH) was performed.

Results: We identified 5 novel heterozygous ACAN mutations (c.301C>T, c.410_418delinsTGGA, c.2099G>A, c.7041delG, c.7069A>T) and first large exonic deletion in ACAN gene (15q26.1(89383692_89386488)x1)). Reported variants co-segregated with severe short stature phenotype in probands' respective families, except in one family member who had unexpected growth pattern with normal height (+0.1 SDS). The prevalence of ACAN defect in our study cohort is estimated to be 37.5% (6/16).

Conclusion: Our results indicate good inclusion selection criteria with high yield of ACAN positive probands. Based on our first description of the large pathogenic deletion in ACAN gene, we propose new diagnostic algorithm for aggreganopathies with inclusion genetic analysis for possible coding indels (ie., aCGH, MLPA) of ACAN gene.