Barth syndrome is an X-linked disorder characterised by cardiomyopathy, growth abnormalities, neutropenia, and 3-methylglutaconic aciduria. It is caused by pathogenic variants in TAFAZZIN, which encodes a mitochondrial protein essential for cardiolipin remodelling. In this study, we describe the case of a patient with Barth syndrome in whom initial research genetic testing missed a 5' untranslated region deletion in TAFAZZIN that was later identified through a phenotype-guided reanalysis of exome sequencing data. A male infant presented with dilated cardiomyopathy at 7 months of age and underwent cardiac transplantation at 19 months. Initial comprehensive cardiac genetic testing was indeterminate. Subsequent clinical investigations recorded a slight increase in the levels of 3-methylglutaconic acid and intermittent neutropenia, and a history of intermittent neutropenia was noted in his mother and maternal grandmother, prompting a consideration of Barth syndrome. A reanalysis of exome sequencing data identified a hemizygous 116 base pair deletion spanning the 5' untranslated region and start codon of TAFAZZIN. An RNA analysis from the proband's cardiac tissue amplified truncated TAFAZZIN transcripts, and Western blotting confirmed the complete loss of full-length protein, consistent with the loss of the start codon and failure of translation initiation from a downstream in-frame methionine. We report a novel 116 bp TAFAZZIN deletion that prevents protein expression due to the loss of the canonical start codon. This case highlights the importance of including non-coding regions in genetic analysis and the diagnostic value of phenotype-guided reanalysis of genetic test data.

Congenital neutropenia (CN) encompasses a group of disorders characterized by impaired neutrophil differentiation, resulting in persistently low neutrophil counts in the peripheral blood. It presents with recurrent infections and an elevated risk of leukemia. Multiple genetic mutations have been implicated in the pathogenesis of neutropenia. This paper reports the case of a 3-year-2-month-old boy admitted with a 4-day history of cough and fever, accompanied by recurrent respiratory infections, neutropenia, and growth retardation. Whole-exome sequencing identified a mutation in the caseinolytic peptidase B homolog (CLPB) gene (NM_030813.6: c.1681C>T: p.R561W). Although the initial genetic sequencing did not reveal mutations consistent with the clinical presentation, the child continued to experience recurrent infections. Upon reanalysis, a pathogenic CLPB-related mutation was detected, leading to the diagnosis of CN. During hospitalization, the patient received targeted antimicrobial therapy based on the identification of the pathogen. Following the confirmed diagnosis, he also received intermittent granulocyte colony-stimulating factor therapy. Administration of granulocyte colony-stimulating factor successfully maintained neutrophil counts above 0.5 × 109/L and significantly reduced the frequency of respiratory tract infections. CLPB deficiency should be considered in pediatric patients presenting with CN and concurrent neurological symptoms, as early recognition allows for the timely initiation of appropriate treatment strategies and contributes to improved clinical outcomes. Barth syndrome is a multisystem disorder characterized in affected males by cardiomyopathy, neutropenia, skeletal myopathy, and prepubertal growth delay; however, not all features may be present in an affected male. Cardiomyopathy, which is almost always present before age five years, is typically dilated cardiomyopathy with or without endocardial fibroelastosis or left ventricular noncompaction; hypertrophic cardiomyopathy can also occur. Heart failure is a significant cause of morbidity and mortality; risk of arrhythmia and sudden death is increased. Neutropenia is most often associated with bacterial infections and aphthous ulcers, pneumonia, and sepsis. Skeletal myopathy predominantly affects the proximal muscles, and results in delays in development of early motor skills. Prepubertal growth delay is followed by a postpubertal growth spurt with remarkable "catch-up" growth. Heterozygous females who have a normal karyotype are asymptomatic and have normal biochemical studies. The diagnosis of Barth syndrome is established in a male proband with suggestive findings and either an increased monolysocardiolipin-to-cardiolipin ratio (if available) or a hemizygous pathogenic variant in TAFAZZIN (formerly TAZ) identified by molecular genetic testing. The diagnosis of Barth syndrome is usually established in a female proband with suggestive clinical findings and a heterozygous TAFAZZIN pathogenic variant identified by molecular genetic testing. Targeted therapy: Elamipretide is indicated for the improvement of muscle strength in individuals with Barth syndrome. Treatment of manifestations: Standard treatment of cardiac issues include: (1) for cardiac arrhythmia, consideration of antiarrhythmic medications or implantable cardiac defibrillator (ICD); (2) for heart failure, careful fluid and volume management and avoidance of overdiuresis and dehydration, standard heart failure medications, and cardiac transplantation when heart failure is severe and intractable. Interventions for other findings include granulocyte colony-stimulating factor for neutropenia; physical therapy for skeletal muscle weakness; standard treatment for talipes equinovarus and/or scoliosis; feeding therapy and consideration of gastrostomy tube placement for persistent feeding issues; uncooked cornstarch prior to bedtime for hypoglycemia; standard management of developmental delay / intellectual disability. Prevention of secondary complications: Aspirin therapy to prevent clot formation in those with severe cardiac dysfunction and/or marked left ventricular noncompaction; antibiotic prophylaxis to prevent recurrent infections; limit fasting or provide intravenous glucose infusion prior to planned medical procedures; regularly monitor blood potassium concentrations during administration of IV fluids that contain potassium and during episodes of diarrhea; consult with nutritionist and/or gastroenterologist to determine optimal caloric delivery. Surveillance: Monitoring existing manifestations, the individual's response to supportive care, and the emergence of new manifestations requires at least annual electrocardiography with Holter monitor and echocardiography; as-needed electrophysiologic studies to assess for potentially serious cardiac arrhythmia; at least semiannual complete blood count with differential as well as with all febrile episodes; at each visit, measurement of height and weight, clinical assessment of strength, and clinical assessment for scoliosis; every three to five years during childhood, formal assessments of developmental progress and educational needs. Agents/circumstances to avoid: Prolonged fasting, use of rectal thermometers in those with neutropenia, and use of succinylcholine. Although growth hormone is typically not indicated as most affected males will attain normal stature by adulthood, recommendations about use of human growth hormone may vary based on endocrinology testing and recommendations. The muscular involvement in Barth syndrome may increase the risk for malignant hyperthermia compared to the general population. Evaluations of relatives at risk: Molecular genetic testing (if the TAFAZZIN pathogenic variant in the family is known) or monolysocardiolipin-to-cardiolipin ratio testing (if the TAFAZZIN pathogenic variant in the family is not known) of male sibs of a proband and male relatives in the maternal lineage is appropriate to identify as early as possible those who would benefit from initiation of treatment and preventive measures. Barth syndrome is inherited in an X-linked manner. If the mother of the proband has a TAFAZZIN pathogenic variant, the chance of transmitting it in each pregnancy is 50%. Males who inherit the pathogenic variant will be affected. Females who inherit the pathogenic variant will be heterozygotes. Heterozygous females typically do not manifest the disease. Affected males transmit the TAFAZZIN pathogenic variant to all of their daughters and none of their sons. If the TAFAZZIN pathogenic variant has been identified in an affected family member, identification of female heterozygotes and prenatal/preimplantation genetic testing for Barth syndrome are possible.

Barth syndrome is an X-linked syndrome characterized by cardiomyopathy, skeletal myopathy, and neutropenia. This life-threatening disorder results from loss-of-function mutations in TAFAZZIN, which encodes a phospholipid-lysophospholipid transacylase located in the mitochondria inner membrane. Decreased cardiolipin levels and increased monolysocardiolipin levels perturb mitochondrial function. However, the mechanism(s) leading to myopathies and neutropenia are unknown, and no currently effective therapy exists. To address these knowledge gaps, we generated tafazzin-deficient zebrafish. Neutropenia developed 5 days post-fertilization, but surprisingly no cardiac or skeletal myopathies were detected into adulthood. tafazzin mutants displayed multiple metabolic disturbances like those observed in humans with Barth syndrome. These include increased monolysocardiolipin: Cardiolipin ratios, high levels of 3-methylglutaconic acid, decreased ATP production, increased levels of lactic acid, and hypoglycemia. There were also widespread effects on amino acid and unsaturated fatty acid synthesis. Despite these metabolic disturbances, zebrafish displayed a normal lifespan and fertility. Cardiolipin abnormalities were detected in both larvae and adult tissues, specifically in the heart and whole kidney marrow. Surprisingly, adult tafazzin mutants exhibited a higher number of neutrophils compared to wildtype fish. Further investigation revealed signs of inflammation as evidenced by elevated levels of il6 in the whole kidney marrows and hearts of adult fish. Our comprehensive studies demonstrated that while mitochondrial dysfunction and metabolic defects were evident in tafazzin-deficient zebrafish, these disturbances did not significantly affect their development nor survival. These findings suggest that zebrafish may possess salvage pathways which compensate for Tafazzin loss or that humans have a unique vulnerability to the loss of TAFAZZIN.

Barth syndrome is an X-linked syndrome characterized by cardiomyopathy, skeletal myopathy, and neutropenia. This life-threatening disorder results from loss-of-function mutations in TAFAZZIN, which encodes a phospholipid-lysophospholipid transacylase located in the mitochondria inner membrane. Decreased cardiolipin levels and increased monolysocardiolipin levels perturb mitochondrial function. However, the mechanism(s) leading to myopathies and neutropenia are unknown, and no currently effective therapy exists. To address these knowledge gaps, we generated tafazzin-deficient zebrafish. Neutropenia developed 5 days post-fertilization, but surprisingly no cardiac or skeletal myopathies were detected into adulthood. tafazzin mutants displayed multiple metabolic disturbances like those observed in humans with Barth syndrome. These include increased monolysocardiolipin: cardiolipin ratios, high levels of 3-methylglutaconic acid, decreased ATP production, increased levels of lactic acid, and hypoglycemia. There were also widespread effects on amino acid and unsaturated fatty acid synthesis. Despite these metabolic disturbances, zebrafish displayed a normal lifespan and fertility. Cardiolipin abnormalities were detected in both larvae and adult tissues, specifically in the heart and whole kidney marrow. Surprisingly, adult tafazzin mutants exhibited a higher number of neutrophils compared to wildtype fish. Further investigation revealed signs of inflammation as evidenced by elevated levels of il6 in the whole kidney marrows and hearts of adult fish. Our comprehensive studies demonstrated that while mitochondrial dysfunction and metabolic defects were evident in tafazzin-deficient zebrafish, these disturbances did not significantly affect their development nor survival. These findings suggest that zebrafish may possess salvage pathways which compensate for Tafazzin loss or that humans have a unique vulnerability to the loss of TAFAZZIN.

Barth syndrome (BTHS) is a rare X-linked recessive genetic disorder characterized by a broad spectrum of clinical features including cardiomyopathy, skeletal myopathy, neutropenia, growth delay, and 3-methylglutaconic aciduria. This disease is caused by loss-of-function mutations in the TAFAZZIN gene located on chromosome Xq28, resulting in cardiolipin deficiency. Most patients are diagnosed in childhood, and the mortality rate is highest in the early years. We report a case of acute, life-threatening metabolic decompensation occurring one day after birth. A novel TAFAZZIN splice site mutation was identified in the patient, marking the first reported case of such a mutation in BTHS identified in China. The report aims to expand our understanding of the spectrum of TAFAZZIN mutations in BTHS.