Early pacing in a child with Lodder-Merla syndrome and progressive sinus node dysfunction: a case report.

Background: Lodder-Merla syndrome is a rare autosomal recessive condition occasionally resulting in cardiac manifestations, including progressive sinus node dysfunction (SND). Case summary: A 1-year-and-10-month-old boy presented with seizures, severe global developmental delay, and hypotonia. Sinus pauses were noted on ECG. Genetic testing confirmed a homozygous splice-site mutation in GNB5, consistent with Lodder-Merla syndrome, and a heterozygous SPTBN4 variant. Holter monitoring initially revealed intermittent sinus pauses; subsequent testing showed marked progression. Following multidisciplinary evaluation, an epicardial VVI pacemaker was implanted, after which cardiac rhythm stabilized with reliable suppression of prolonged pauses. Discussion: Cardiac involvement in GNB5-related disorders may be overshadowed by the dominant neurodevelopmental presentation. This case highlights an important cardiovascular dimension to the syndrome. SND can be progressive and life-threatening, requiring early recognition and individualized pacing strategies. In young children with significant comorbidities, classic bradyarrhythmia symptoms may be absent, underscoring the need for a high index of suspicion and proactive rhythm surveillance to enable timely intervention.