Female and male carriers of TAZ mutations need to be thoroughly investigated

Dear Editor,

We read with interest the article by Bakšienė et al. about a 22-year-old female carrier of a novel TAZ variant causing Barth syndrome and her two manifesting brothers [1]. We have the following comments and concerns.

In up to 50.0% of cases, Barth syndrome is associated with left ventricular hypertrabeculation (LVHT), also known as noncompaction [2]. Were the two manifesting brothers of the index case investigated for LVHT? This is of particular interest as one of her brothers had developed fibroelastosis [1] and because subendocardial fibroelastosis is frequently associated with LVHT [3]. Did the two manifesting brothers undergo follow-up investigations as LVHT may occasionally develop after birth in Barth syndrome [4]. Was the family history positive for complications of LVHT, such as heart failure, ischemic cerebral stroke, arrhythmias, or sudden cardiac death? Left ventricular hypertrabeculation can be diagnosed during intrauterine development by ultrasound [5].

Both brothers of the index case are reported to have developed myocarditis [1]. The golden standard for diagnosing myocarditis is endomyocardial biopsy. Was the diagnosis “myocarditis” established upon endomyocardial biopsy in both of them? Was the diagnosis established upon cardiac magnetic resonance imaging (MRI) with contrast medium or was it only a clinical suspicion? Was myocarditis assumed to be due to a viral or bacterial infection or due to an immunological response? Which therapy was applied for myocarditis?

Since Barth syndrome is X-linked, transmitted by female carriers, and since some female carriers might manifest clinically [6], depending on the amount of inactivated X-chromosomes carrying the mutated gene, it would be interesting to know if the index case presented with any phenotypic features of Barth syndrome. Female carriers may manifest with dilated cardiomyopathy, hypertrophic cardiomyopathy, LVHT, heart failure, myopathy leading to muscle weakness, and neutropenia associated with recurrent infections and sepsis [6]. Because the mutation was also found in the mother and grandmother from the mother’s side of the index case, we should be informed if they had developed clinical manifestations of the disease as well.

Patients carrying TAZ mutations may not only manifest with the canonical features of Barth syndrome but also with a number of other phenotypic manifestations [7,8]. These include dysmorphism (full cheeks, deep set eyes, prominent ears), ventricular arrhythmias, sudden cardiac death, ischemic stroke, methyl-glutaconic asciduria, impaired visuo-spatial skills, mild cognitive impairment (learning disability, attention deficit), delayed motor milestones, delayed onset of puberty, feeding abnormalities, preference for salty and spicy food, strong gag reflex, lactic acidosis, miscarriages/stillbirths, recurrent infectious oral ulcers, perianal dermatitis, hyperlpidemia, osteopenia, delayed bone age, scoliosis and growth delay [7,8]. Were any of these additional manifestions found in the clinically manifesting carriers of the TAZ mutation in the described family?

Overall, this interesting case series would be more meaningful if more clinical data would have been provided and if carriers of the mutation would have been systematically investigated for LVHT. Furthermore, female carriers of TAZ mutations need to be investigated for subclinical or mild manifestations of the disease.