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Background: Thyroid dysfunction may have adverse effects on Fontan hemodynamics. Data on thyroid function in pediatric Fontan patients with or without protein-losing enteropathy (PLE) are limited. Methods: This retrospective multicenter study included 67 Fontan patients (median age 10.9 years; 35.8% female; 28.4% PLE) in whom thyroid function testing was performed. Results: Subclinical hypothyroidism (SHT) was present in 16 (23.9%) patients. Subjects with SHT had significantly lower systolic blood pressure (p = 0.014) and body weight z-score (p = 0.006), were in a worse New York Heart Association (NYHA) functional class (p = 0.004), were more often pacing dependent (p = 0.007), and were more likely to have PLE (p = 0.033, 8/19 (42.1%) patients). Serum thyroid stimulating hormone (TSH) levels were significantly higher in patients with NYHA class ≥ II (p = 0.005), significant atrioventricular valve regurgitation (p = 0.023), elevated serum natriuretic peptides (p = 0.031), and in those with PLE (p = 0.002). Patients with active PLE had significantly higher TSH levels than those in remission (p = 0.003). A strong inverse relationship was found between lower free triiodothyronine (fT3) levels and natriuretic peptides (r: −0.599, p = 0.040). Using binary logistic regression analysis we found that worse NYHA class was an independent predictor of SHT (OR 4.2; 95% CI 1.1–16.1, p = 0.036). Conclusions: Subclinical thyroid dysfunction is common in Fontan, particularly in patients with hemodynamic derangements and PLE. Future studies are needed to address the prognostic implications of thyroid dysfunction in the Fontan population.

Isolated long-chain 3-keto-acyl CoA thiolase (LCKAT) deficiency is a rare long-chain fatty acid oxidation disorder caused by mutations in HADHB. LCKAT is part of a multi-enzyme complex called the mitochondrial trifunctional protein (MTP) which catalyzes the last three steps in the long-chain fatty acid oxidation. Until now, only three cases of isolated LCKAT deficiency have been described. All patients developed a severe cardiomyopathy and died before the age of 7 weeks. Here, we describe a newborn with isolated LCKAT deficiency, presenting with neonatal-onset cardiomyopathy, rhabdomyolysis, hypoglycemia and lactic acidosis. Bi-allelic 185G > A (p.Arg62His) and c1292T > C (p.Phe431Ser) mutations were found in HADHB. Enzymatic analysis in both lymphocytes and cultured fibroblasts revealed LCKAT deficiency with a normal long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD, also part of MTP) enzyme activity. Clinically, the patient showed recurrent cardiomyopathy, which was monitored by speckle tracking echocardiography. Subsequent treatment with special low-fat formula, low in long chain triglycerides (LCT) and supplemented with medium chain triglycerides (MCT) and ketone body therapy in (sodium-D,L-3-hydroxybutyrate) was well tolerated and resulted in improved carnitine profiles and cardiac function. Resveratrol, a natural polyphenol that has been shown to increase fatty acid oxidation, was also considered as a potential treatment option but showed no in vitro benefits in the patient's fibroblasts. Even though our patient deceased at the age of 13 months, early diagnosis and prompt initiation of dietary management with addition of sodium-D,L-3-hydroxybutyrate may have contributed to improved cardiac function and a much longer survival when compared to the previously reported cases of isolated LCKAT-deficiency.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is rarely diagnosed in childhood. We describe the case of a 9-year-old girl with genetically confirmed ARVC who presented with syncope, ventricular arrhythmia, and biventricular myocardial dysfunction. This case highlights the need for development of pediatric ARVC diagnosis criteria specific for pediatric patients and discusses potential diagnostic improvement using echocardiographic deformation imaging. (Level of Difficulty: Beginner.)