What is Barth syndrome?

A rare genetic disease of the mitochondria

Barth syndrome (BTHS) is a rare, life-threatening genetic disease caused by mutations in the TAFAZZIN gene on the X chromosome. Because of that X-linkage it almost exclusively affects males. Only a few hundred individuals are diagnosed worldwide, though the condition is believed to be underdiagnosed.

The TAFAZZIN gene encodes tafazzin, an enzyme that remodels cardiolipin — a lipid unique to the inner mitochondrial membrane that mitochondria need to produce energy efficiently. When tafazzin doesn't work, cells accumulate an immature form of the lipid (monolysocardiolipin) and mitochondrial energy production suffers, hitting the body's most energy-hungry tissues hardest.

How it presents

Cardiomyopathy — weakening of the heart muscle, often dilated cardiomyopathy or left-ventricular non-compaction, frequently appearing in infancy. Heart failure and arrhythmia are the leading clinical concerns.
Neutropenia — chronically or intermittently low neutrophil counts, raising the risk of serious bacterial infection.
Skeletal myopathy and fatigue — muscle weakness and profound exercise intolerance that shape daily life.
Growth delay — slowed growth in childhood, often with a later catch-up phase, along with feeding difficulties in infancy.

Severity varies widely between individuals — even within the same family — and no two courses look alike.

How it's diagnosed

The diagnostic biomarker is the monolysocardiolipin-to-cardiolipin (MLCL/CL) ratio, measurable from a dried blood spot: an elevated ratio separates Barth syndrome from controls with essentially complete accuracy, and it stays reliable even in atypical cases where individual cardiolipin species look normal. Diagnosis is confirmed by TAFAZZIN gene sequencing.

Testing access is a bottleneck. Only two laboratories worldwide are known to offer the clinical MLCL/CL assay (Amsterdam UMC, and UCLH Queen Square in London since 2023), and no newborn-screening study of the biomarker has ever been run — one reason diagnosis is often delayed and the true prevalence is uncertain.

Living with Barth syndrome

Care is multidisciplinary: cardiology (heart-failure management, and transplant in severe cases), immunology and hematology (including G-CSF for neutropenia), nutrition, and physical therapy. The first disease-specific therapy was approved in 2025 — see therapy progress for the current treatment landscape.

Learn more

Barth Syndrome Foundation ↗ — families, clinicians, and research
BSF research programs ↗
Funding index — grants open to BTHS researchers

Last updated August 7, 2026.