Barth syndrome (BTHS) is an X-linked disorder characterized by skeletal 
myopathy, neutropenia, growth delay, and cardiomyopathy. It is caused by 
mutations in the tafazzin gene (TAZ). Although early diagnosis is critical to 
prevent the progression of heart failure, this disease remains unrecognized when 
heart failure is not clinically significant. Here we report on a 13-year-old boy 
with no family history of BTHS who was diagnosed with the syndrome in the 
subclinical stage of heart failure. The clues to the diagnosis of BTHS in this 
patient were the findings of lipid storage myopathy in the skeletal muscle 
biopsy, elevated plasma brain natriuretic peptide, and the diagnosis of isolated 
noncompaction of the ventricular myocardium in echocardiography. Genetic studies 
of TAZ revealed a disease-causing mutation (p.Gly216Arg) in this patient. 
Physicians should be aware of the possibility of this disease and carry out 
genetic studies when it is considered.