Key result
Levothyroxine supplementation normalized thyroid function in a 13-year-old girl with severe hypothyroidism, but did not improve her sick sinus syndrome, which was linked to a heterozygous SCN5A variant.
Case Report (n=1)
Severe hypothyroidism may act as a modifying factor in the development of sick sinus syndrome in patients with SCN5A variants, highlighting the importance of genetic testing in such cases.
Levothyroxine may not resolve sick sinus syndrome despite thyroid normalization in SCN5A carriers; leaves open role of genetic testing in refractory pediatric bradycardia.
Previous studies have reported that hypothyroidism can lead to sick sinus syndrome (SSS) or other rhythm disturbances. Variants in the alpha subunit of the cardiac sodium channel (SCN5A) are known to be among the genetic causes of SSS. We encountered an adolescent patient with SSS and hypothyroidism who also harbored an SCN5A variant. The patient was a 13-year-old girl who was referred to our hospital because of bradycardia identified during a school electrocardiography screening. Clinical examination revealed severe hypothyroidism due to Hashimoto thyroiditis and SSS. After levothyroxine supplementation, her symptoms of hypothyroidism improved; however, the SSS did not. Genetic testing revealed a heterozygous variant (c.1066 G>A, p.Asp356Asn) in SCN5A. This is the first report of the coexistence of SSS due to an SCN5A variant and severe hypothyroidism in an adolescent patient. While patients with SCN5A variants exhibit phenotypic heterogeneity due to the presence of various modifiers, the presence of severe hypothyroidism may affect the development of SSS. This case highlights the importance of genetic analysis, including testing for SCN5A variants, in patients with hypothyroidism complicated by SSS or cardiac conduction disorders.
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Yamane et al. (2022) conducted a case report in Sick Sinus Syndrome and Hypothyroidism (n=1). Levothyroxine supplementation was evaluated on Improvement of sick sinus syndrome and thyroid function. Levothyroxine supplementation normalized thyroid function in a 13-year-old girl with severe hypothyroidism, but did not improve her sick sinus syndrome, which was linked to a heterozygous SCN5A variant.
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