A rare case of skeletal dysplasia: biallelic variant in ACAN gene.

OBJECTIVES Spondylo-epimetaphyseal dysplasia-aggregan (SEMD-ACAN) is a rare form of osteo-chondrodysplasia that includes vertebral, epiphyseal and metaphyseal dysplasia. It occurs as a result of loss-of-function mutations in the ACAN gene, which encodes aggregan protein, which is the basic component of the extracellular matrix in cartilage. It results in disproportionately short stature and skeletal abnormalities. Here, we aimed to present the fourth SEMD-ACAN report in the literature. CASE PRESENTATION A 9-year-old girl was admitted to our clinic with growth retardation. She was born from a first-degree cousin marriage with severe short stature (41 cm; -3.54 SDS). Her mother also had severe short stature. Her height was 110 cm (-4.6 SDS); she had midface hypoplasia, low-set ears, short neck, short limbs, and central obesity. Biochemical and hormonal tests were normal. Skeletal survey showed moderate platyspondylia, thoracolumbar scoliosis, lumbar lordosis, bilateral femoro-acetabular narrowing, and advanced bone age (10 years). The patient's brother was 100 cm (-3.97 SDS). He had similar but milder clinical findings. Biallelic ACAN variation (c.512C>T; p. Ala171Val) was detected in two siblings by next-generation sequencing. The parents were heterozygous carriers. Before, the heterozygous form of this variant has been reported in a 15-year-old boy with short stature, advanced bone age, and dysmorphic features. CONCLUSIONS SEMD-ACAN is a rare genetic condition that affects bone growth and development and can cause physical and developmental abnormalities. This article highlights the importance of considering genetic testing in characteristic symptoms associated with SEMD-ACAN, such as severe growth retardation and skeletal abnormalities.