Timothy syndrome type 1

Timothy syndrome type 1 (TS1), also known as classic Timothy syndrome, is an extremely rare and severe multisystem disorder caused by a specific gain-of-function mutation (p.Gly406Arg) in exon 8A of the CACNA1C gene, which encodes the alpha-1 subunit of the L-type calcium channel Cav1.2. This calcium channel plays a critical role in electrical signaling throughout the body, and the mutation leads to prolonged calcium influx affecting multiple organ systems. The hallmark cardiac feature is markedly prolonged QT interval (long QT syndrome type 8), which predisposes affected individuals to life-threatening ventricular arrhythmias, particularly 2:1 functional atrioventricular block, ventricular tachycardia, and ventricular fibrillation. Structural heart defects, including patent ductus arteriosus, patent foramen ovale, ventricular septal defects, and hypertrophic cardiomyopathy, are frequently observed. Beyond the heart, Timothy syndrome type 1 affects the nervous system, immune system, and other organs. Many affected children exhibit features of autism spectrum disorder, intellectual disability, seizures, and developmental delays. Syndactyly (webbing of the fingers and/or toes), typically cutaneous syndactyly of the hands and feet, is a characteristic physical finding that helps distinguish this condition clinically. Other features may include recurrent infections due to immune dysfunction, hypoglycemia, and hypothermia. Facial features can include a flat nasal bridge, thin upper lip, and round face. The prognosis for Timothy syndrome type 1 is poor, with a high rate of sudden cardiac death in early childhood; the average age of death has been reported at approximately 2.5 years, though survival varies. Treatment is primarily supportive and focused on managing cardiac arrhythmias. Beta-blockers, mexiletine, and other antiarrhythmic medications may be used, and some patients require implantable cardioverter-defibrillators (ICDs) or pacemakers. Surgical correction of structural heart defects and syndactyly may also be necessary. There is currently no cure, and management requires a multidisciplinary team including cardiologists, neurologists, and developmental specialists.

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