Sinus node dysfunction: current understanding and future directions.

The sinoatrial node (SAN) is the primary pacemaker of the heart. Normal SAN function is crucial in maintaining proper cardiac rhythm and contraction. Sinus node dysfunction (SND) is due to abnormalities within the SAN, which can affect the heartbeat frequency, regularity, and the propagation of electrical pulses through the cardiac conduction system.

Further delineation of the phenotypic spectrum associated with hemizygous loss-of-function variants in NONO.

The non-POU domain containing, octamer-binding gene, NONO, is located on chromosome Xq13.1 and encodes a member of a small family of RNA and DNA binding proteins that perform a variety of tasks involved in RNA synthesis, transcriptional regulation and DNA repair. Hemizygous loss-of-function variants in NONO have been shown to cause mental retardation, X-linked, syndromic 34 in males.