BSPED2022 Poster Presentations Pituitary and Growth 1 (6 abstracts)
Understanding the molecular basis of short stature in six patients with pathogenic variants in HMGA2
Avinaash Maharaj 1 , Emily Cottrell 1 , Hermine van Duyvenvoorde 2 , Christiaan de Bruin 3 , Sjoerd Joustra 3 , Sarina Kant 3 , Danielle van der Kaay 4 , María Inmaculada Castilla de Cortázar Larrea 5 , Ahmed Massoud 6 , Louise Metherell 1 , Vivian Hwa 7 , Sabine Hombach-Klonisch 8 , Thomas Klonisch 8 & Helen Storr 1
1William Harvey Research Institute, London, United Kingdom; 2Laboratory for Diagnostic Genome Analysis (LDGA), Leiden, Netherlands; 3Leiden University Medical Center, Leiden, Netherlands; 4Erasmus MC, Rotterdam, Netherlands; 5Technologico de Monterrey, Monterrey, Mexico; 6HCA Healthcare UK, London, United Kingdom; 7Cincinnati Center for Growth Disorders, Cincinnati, USA; 8University of Manitoba, Manitoba, Canada
Background: Silver-Russell syndrome (SRS) is a unique disorder characterised by characteristic features and growth restriction due to 11p15 LOM or upd(7)Mat in ~60% cases. Monogenic defects are a rare cause of SRS and HMGA2 mutations have been identified in 4 cases to date. The function of HMGA2 is poorly understood.
Objectives: Assess the clinical phenotypes of 6 new patients with novel heterozygous HMGA2 defects and evaluate the molecular impact of the variants.
Methods: Pathogenicity prediction was conducted using a combination of computational platforms (SIFT, PolyPhen-2, Mutation Taster). Single nucleotide substitutions were generated by mutagenesis of an N-terminal FLAG tagged-HMGA2 cDNA. Frameshift constructs were customized to recapitulate reading frame extensions and generation of prolonged proteins. The variants were expressed in HEK293T cells and HMGA2 expression/nuclear localisation were assessed by immunoblotting whole cell lysates and nuclear/cytoplasmic fractions. Nuclear translocation of wild type and variant constructs were examined by confocal microscopy.
Results: Six patients from the UK, Netherlands and Mexico with variable height SDS (range -3.2 to -3.9) and IGF-I SDS (range from -1.9 to +4.4) were found to have deleterious variants in HMGA2 with differing functional impacts: c.49G>T and c.52C>T stop gain variants leading to the introduction of a premature stop codon/early truncations, c.166A>G a missense variant predicted to alter the DNA binding domain and c.144delC, c.145delA and c.299dup frameshift variants leading to the generation of prolonged proteins. Phenotypic features were highly variable with little genotype-phenotype correlation. Expression of variant constructs in mammalian cells revealed detectable HMGA2 protein for all variants except the 2 truncations. Immunoblotting of nuclear fractions showed markedly reduced HMGA2 with the exception of c.166A>G, which demonstrated a subtle reduction. These findings were recapitulated by immunofluorescence.
Conclusions: We report a series of six patients with novel pathogenic variants in HMGA2. These cases presented with short stature and a spectrum of clinical features revealing the wide phenotypic, biochemical and genetic landscape of this rare syndrome. Functional characterisation revealed abnormal protein expression and nuclear localisation providing novel insights into the molecular basis of SRS pathogenesis.
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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