The hallmark of BTHS is a combination of dilated
cardiomyopathy with endocardial fibroelastosis, neutropenia with severe
infections, and skeletal myopathy with muscle weakness, sparing the
extraocular and bulbar muscles. Onset of cardiomyopathy may be precipitous
and the response to standard congestive heart failure treatment variable.
The degree of myeloic dysfunction ranges from chronic severe neutropenia to
sporadic episodes of neutropenia. Phenotypic expression of BTHS is variable.
Forms with late onset and milder courses have been described, as have severe
forms with lethal noncompaction of the left ventricular myocardium. Fasting
ketone production is normal, but mild lactacidosis and hypoglycemia have
been observed in some patients. One case report described rapid
deterioration with l-carnitine; the patient subsequently showed
dramatic improvement of cardiac function, growth, and neutrophil count with
large doses of pantothenic acid. Before the advent of transplantation
medicine, affected males died of cardiac failure or septic complications in
infancy or early childhood. Now, survival for more than 7 years following
heart transplantation has been reported.