Characterization of HMGA2 variants expands the spectrum of Silver-Russell syndrome

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Abstract

Silver-Russell syndrome (SRS) is a heterogeneous disorder characterized by intrauterine and postnatal growth retardation. HMGA2 variants are a rare cause of SRS and its functional role in human linear growth is unclear. Patients with suspected SRS negative for 11p15LOM/mUPD7 underwent whole-exome and/or targeted-genome sequencing. Mutant HMGA2 protein expression and nuclear localization were assessed. Two Hmga2-knockin mouse models were generated. Five clinical SRS patients harbored HMGA2 variants with differing functional impacts: 2 stop-gain nonsense variants (c.49G>T, c.52C>T), c.166A>G missense variant, and 2 frameshift variants (c.144delC, c.145delA) leading to an identical, extended-length protein. Phenotypic features were highly variable. Nuclear localization was reduced/absent for all variants except c.166A>G. Homozygous knockin mice recapitulating the c.166A>G variant (Hmga2K56E) exhibited a growth-restricted phenotype. An Hmga2Ter76-knockin mouse model lacked detectable full-length Hmga2 protein, similarly to patient 3 and 5 variants. These mice were infertile, with a pygmy phenotype. We report a heterogeneous group of individuals with SRS harboring variants in HMGA2 and describe the first Hmga2 missense knockin mouse model (Hmga2K56E) to our knowledge causing a growth-restricted phenotype. In patients with clinical features of SRS but negative genetic screening, HMGA2 should be included in next-generation sequencing testing approaches.

Authors

Avinaash V. Maharaj, Emily Cottrell, Thatchawan Thanasupawat, Sjoerd D. Joustra, Barbara Triggs-Raine, Masanobu Fujimoto, Sarina G. Kant, Danielle van der Kaay, Agnes Clement-de Boers, Alice S. Brooks, Gabriel Amador Aguirre, Irene Martín del Estal, María Inmaculada Castilla de Cortázar Larrea, Ahmed Massoud, Hermine A. van Duyvenvoorde, Christiaan De Bruin, Vivian Hwa, Thomas Klonisch, Sabine Hombach-Klonisch, Helen L. Storr