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TAZ (NM_000116.3) encodes the tafazzin protein, a mitochondrial transacylase that catalyzes remodeling of cardiolipin and is expressed at high levels in cardiac and skeletal muscle. TAZ is located on chromosome Xq28 and is composed of 11 coding exons. Mutations in the TAZ gene are generally inherited in an X-linked recessive fashion in association with Barth syndrome, but with notable variable expressivity. Barth syndrome (also known as 3-methylglutaconic aciduria type II) typically presents during infancy or childhood with significant heart failure due to cardiomyopathy, which is the main cause of death (Takeda A et al. Eur J Pediatr. 2011;170:1365–1367). Dilated cardiomyopathy (DCM), isolated noncompaction of left ventricular myocardium (INVM), arrhythmias, endocardial fibroelastosis, and hypertrophic cardiomyopathy (HCM) have been reported. Additional features may include proximal myopathy, growth retardation, neutropenia, frequent infections, organic aciduria, and variable respiratory chain abnormalities (Johnston J et al. Am J Hum Genet. 1997;61:1053-1058; Steward CG et al. Prenat Diagn. 2010;30(10):970-6; Takeda A et al. Eur J Pediatr. 2011;170:1365–1367). Additionally, Barth syndrome has also been reported to cause an increased risk for fetal cardiomyopathy, hydrops, male fetal loss, stillbirth, or severe neonatal illness or death (Steward CG et al. Prenat Diagn. 2010;30(10):970-6). Female carriers of TAZ alterations are not thought to be at an increased risk for symptoms, most likely due to skewed X-inactivation (Orstavik KH et al. Am J Hum Genet. 1998;63(5):1457-63).