The Locus Coeruleus at the Crossroads of Cognitive and Metabolic Dysfunction in Down Syndrome: A Role for Chromosome 21 Gene Dosage

Intellectual disability (ID) characterizes numerous neurodevelopmental disorders, many of which also show increased obesity and metabolic comorbidities. Traditionally investigated independently, their coexistence suggests potentially shared pathogenic mechanisms, whose molecular and neural bases remain poorly understood. Down syndrome (DS), caused by trisomy 21, offers a genetically defined model for examining how altered gene dosage may affect cognition, feeding behavior, and energy homeostasis. Understanding these relationships could illuminate both the heterogeneous DS phenotype and metabolic vulnerability across ID-associated disorders. The locus coeruleus (LC), a major noradrenergic nucleus, regulates learning, memory, and energy balance. LC abnormalities have been reported in individuals with DS and corresponding mouse models, suggesting a potential contribution to both cognitive and metabolic phenotypes. Among chromosome 21 genes, dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) is a compelling candidate. DYRK1A influences pancreatic β-cell mass and metabolic pathways while regulating neuronal development, synaptic function, and cognitive processes. Moreover, DYRK1A has been implicated in LC alterations in DS, although their functional consequences have primarily been investigated in cognition. Here, we review evidence connecting intellectual disability, obesity, LC function, and chromosome 21 gene dosage. We propose that DYRK1A-dependent changes in LC-noradrenergic signaling may contribute to cognitive impairment and potentially modify metabolic regulation in DS. Rather than assuming a single established causal pathway, this framework highlights a testable interaction between genetic dosage, neural circuitry, and environmental challenges that could explain divergent outcomes across physiological domains. Importantly, current experimental evidence more strongly supports a cognitive contribution than a direct causal role in metabolic and energy balance dysfunction.