Sotos Syndrome Presenting with Neonatal Hyperinsulinaemic Hypoglycaemia, Extensive Thrombosis, and Multisystem Involvement.

Initially described as an uncommon presenting feature of Sotos syndrome (SoS), over the last decades, congenital hyperinsulinaemic hypoglycaemia (CHI) has been increasingly reported in association with this condition. The mechanism responsible for CHI in SoS is unclear. We report the case of a neonate presenting with CHI and extensive venous and arterial thrombosis associated with kidney, heart, liver, skeleton, and brain abnormalities and finally diagnosed with SoS on whole genome sequencing. Our case describes an extended phenotype associated with SoS presenting with CHI (including thrombosis and liver dysfunction) and reinforces the association of transient CHI with SoS. The case also shows that an early neonatal diagnosis of rare genetic conditions is challenging, especially in acutely unwell patients, and that in complex cases with incomplete, atypical, or overlapping phenotypes, broad genomic testing by whole exome or whole genome sequencing may be a useful diagnostic strategy.