LAUSR

INTRODUCTION Among children born small for gestational age, 10-15% fails to catch-up and remains short (SGA-SS). The underlying mechanisms are mostly unknown. We aim to decipher genetic aetiologies of SGA-SS within a large single-centre cohort. METHODS Out of 820 patients treated with growth hormone (GH), 256 were classified as SGA-SS (birth length and/or birth weight <-2 SD for gestational age, and life-minimum height <-2.5 SD). Those with the DNA triplet available (child and both parents) were included in the study (176/256). Targeted testing (karyotype/FISH/MLPA/specific Sanger sequencing) was performed if a specific genetic disorder was clinically suggestive. All remaining patients underwent MS-MLPA to identify Silver-Russell syndrome, and those with unknown genetic aetiology were subsequently examined using whole exome sequencing or targeted panel of 398 growth-related genes. Genetic variants were classified using ACMG guidelines. RESULTS The genetic aetiology was elucidated in 74/176 (42%) children. Of these, 12/74 (16%) had pathogenic or likely pathogenic gene variants (P/LP) affecting pituitary development (LHX4, OTX2, PROKR2, PTCH1, POU1F1), the GH-IGF-1 or IGF-2 axis (GHSR, IGFALS, IGF1R, STAT3, HMGA2), 2/74 (3%) the thyroid axis (TRHR, THRA), 17/74 (23%) the cartilaginous matrix (ACAN, various collagens, FLNB, MATN3), and 7/74 (9%) the paracrine chondrocyte regulation (FGFR3, FGFR2, NPR2). In 12/74 (16%) we revealed P/LP affecting fundamental intracellular/intranuclear processes (CDC42, KMT2D, LMNA, NSD1, PTPN11, SRCAP, SON, SOS1, SOX9, TLK2). SHOX deficiency was found in 7/74 (9%), Silver-Russell syndrome in 12/74 (16%) (11p15, UPD7), and miscellaneous chromosomal aberrations in 5/74 (7%) children. CONCLUSIONS The high diagnostic yield sheds a new light on the genetic landscape of SGA-SS, with a central role of the growth plate with substantial contributions from the GH-IGF-1 and thyroid axes and from intracellular regulation and signalling.