Supplementary Material for: Clinical characteristics of pathogenic ACAN variants and 3-year response to growth hormone treatment: real-world data

Introduction
Heterozygous variants in the ACAN gene may underlie disproportionate short stature with characteristically accelerated bone age (BA) maturation and/or early-onset osteoarthritis (OA).
Methods
To describe phenotype, analyze genotype-phenotype correlations and assess the response of growth hormone (GH) treatment in children with a heterozygous ACAN variant. Thirty-six subjects (23 boys, 13 girls) with ACAN-deficiency and treated for ≥1 year with GH were identified in the Dutch National Registry of GH treatment in children.
Results
We identified 25 different heterozygous ACAN variants in 36 subjects. Median (IQR) height SDS at start of GH was -2.6 SDS (-3.2 to -2.2). Characteristic features such as disproportion, advanced BA, early-onset OA and dysmorphic features like midface hypoplasia and brachydactyly were present in the majority of children, but in ~20% no specific features were reported. Subjects with a truncating ACAN variant had a shorter height SDS compared to subjects with a non-truncating variant (-2.8 SDS and -2.1 SDS respectively, P=0.002). After 3 years of GH, height gain SDS in prepubertal children was 1.0 SDS (0.9 to 1.4). In pubertal children, height SDS remained relatively stable.
Conclusion
The phenotype of subjects with pathogenic heterozygous ACAN variants is highly variable and genetic testing for ACAN-deficiency should be considered in any child with significant short stature, even in the absence of disproportion, specific dysmorphic features or bone-age advancement. Furthermore, children with ACAN-deficiency may benefit from GH with a modest but significant response, which is sustained during 3 years of treatment.