Two cases of endocardial fibroelastosis--possible x-linked determination

TAZ encodes tafazzin, a transacylase essential for cardiolipin formation and central to the etiology of Barth syndrome

Tafazzin, which is encoded by the TAZ gene, catalyzes transacylation to form mature cardiolipin and shows preference for the transfer of a linoleic acid (LA) group from phosphatidylcholine (PC) to monolysocardiolipin (MLCL) with influence from mitochondrial membrane curvature. The protein contains domains and motifs involved in targeting, anchoring, and an active site for transacylase activity. Tafazzin activity affects many aspects of mitochondrial structure and function, including that of the electron transport chain, fission-fusion, as well as apoptotic signaling. TAZ mutations are implicated in Barth syndrome, an underdiagnosed and devastating disease that primarily affects male pediatric patients with a broad spectrum of disease pathologies that impact the cardiovascular, neuromuscular, metabolic, and hematologic systems.

X-linked cardioskeletal myopathy and neutropenia (Barth syndrome): an update

X-linked cardioskeletal myopathy and neutropenia (Barth syndrome, MIM302060, BTHS) is a disorder with mitochondrial functional impairments and 3-methylglutaconic aciduria that maps to Xq28. The associated G4.5 or TAZ gene has been identified but the encoded proteins have not yet been characterized. Following the prediction that the gene encodes one or more acyltransferases, lipid studies have shown a deficiency of cardiolipin, especially its tetralinoleoyl form (L(4)-CL). Deficiency of L(4)-CL was subsequently demonstrated in a variety of tissues, and determination in thrombocytes or cultured skin fibroblasts is now the most specific biochemical test available. BTHS is the first identified inborn error of metabolism that directly affects cardiolipin, a component of the inner mitochondrial membrane, necessary for proper functioning of the electron transport chain. We report here the finding of deficient docosahexaenoic acid and arachidonic acid in a proportion of patients with BTHS. The initial impression of a uniformly lethal infantile disease has to be modified. Age distribution in 54 living patients ranges between 0 and 49 years and peaks around puberty. Mortality is the highest in the first 4 years. The apex of the survival curve around puberty and the emergence of adults may reflect a dynamic shift towards increased survival. This trend is exemplified in a large pedigree previously published.

X-linked cardioskeletal myopathy and neutropenia (Barth syndrome) (MIM 302060)

X-linked cardioskeletal myopathy, neutropenia and abnormal mitochondria (MIM 302060) (synonyms: Barth syndrome, 3-methylglutaconic acid-uria type II, endocardial fibroelastosis type 2) has been reported in patients and families from Europe, North America and Australia. Previous studies characterized the main components of the disease: dilated cardiomyopathy, skeletal myopathy, neutropenia, 3-methylglutaconic aciduria and diminished statural growth. Respiratory chain impairments have been found in several studies, without pinpointing a single enzyme complex. 3-Methylglutaconic aciduria is shared with several other disorders that affect the respiratory chain. Previous studies excluded a block in the major pathway of leucine catabolism. We performed leucine loading, accompanied by fasting, in patients and observed a significant rise of 3-methylglutaconic acid and 3-methylglutaric acid. Taken together with the absence of an enzymatic block in the major leucine catabolic route, the possibility remains that the increased basal excretion of 3-methylglutaconic acid and other products of branched-chain amino acids is the result of overload of this pathway or--more likely--mitochondrial leakage. Linkage studies have localized the gene to the Xq28 region. The associated tafazzin gene (TAZ), has been fully characterized recently, and mutations located in conserved regions have been reported. Carrier detection and prenatal diagnosis have now become possible through mutation analysis. Sequence homology of the TAZ gene to a highly conserved superclass of acyltransferases (Neuwald's hypothesis) predicts a glycerophospholipid as the missing end product. This points to the (lipid) structure of the inner mitochondrial membrane as a promising new area of research.

X chromosome inactivation in carriers of Barth syndrome

Barth syndrome (BTHS) is a rare X-linked recessive disorder characterized by cardiac and skeletal myopathy, neutropenia, and short stature. A gene for BTHS, G4.5, was recently cloned and encodes several novel proteins, named "tafazzins." Unique mutations have been found. No correlation between the location or type of mutation and the phenotype of BTHS has been found. Female carriers of BTHS seem to be healthy. This could be due to a selection against cells that have the mutant allele on the active X chromosome. We therefore analyzed X chromosome inactivation in 16 obligate carriers of BTHS, from six families, using PCR in the androgen-receptor locus. An extremely skewed X-inactivation pattern (>=95:5), not found in 148 female controls, was found in six carriers. The skewed pattern in two carriers from one family was confirmed in DNA from cultured fibroblasts. Five carriers from two families had a skewed pattern (80:20-<95:5), a pattern that was found in only 11 of 148 female controls. Of the 11 carriers with a skewed pattern, the parental origin of the inactive X chromosome was maternal in all seven cases for which this could be determined. In two families, carriers with an extremely skewed pattern and carriers with a random pattern were found. The skewed X inactivation in 11 of 16 carriers is probably the result of a selection against cells with the mutated gene on the active X chromosome. Since BTHS also shows great clinical variation within families, additional factors are likely to influence the expression of the phenotype. Such factors may also influence the selection mechanism in carriers.

The X-linked gene G4.5 is responsible for different infantile dilated cardiomyopathies

Barth syndrome (BTHS) is an X-linked disorder characterized clinically by the associated features of cardiac and skeletal myopathy, short stature, and neutropenia. The clinical manifestations of the disease are, in general, quite variable, but cardiac failure as a consequence of cardiac dilatation and hypertrophy is a constant finding and is the most common cause of death in the first months of life. X-linked cardiomyopathies with clinical manifestations similar to BTHS have been reported, and it has been proposed that they may be allelic. We have recently identified the gene responsible for BTHS, in one of the Xq28 genes, G4.5. In this paper we report the sequence analysis of 11 additional familial cases: 8 were diagnosed as possibly affected with BTHS, and 3 were affected with X-linked dilated cardiomyopathies. Mutations in the G4.5 gene were found in nine of the patients analyzed. The molecular studies have linked together what were formerly considered different conditions and have shown that the G4.5 gene is responsible for BTHS (OMIM 302060), X-linked endocardial fibroelastosis (OMIM 305300), and severe X-linked cardiomyopathy (OMIM 300069). Our results also suggest that very severe phenotypes may be associated with null mutations in the gene, whereas mutations in alternative portions or missense mutations may give a "less severe" phenotype.

New syndrome of hydrocephalus, endocardial fibroelastosis, and cataracts (HEC syndrome)

We report on two unrelated male infants with similar findings of communicating hydrocephalus, endocardial fibroelastosis (EFE) and congenital cataracts, who died at 4 months of age. Both mothers reported an upper respiratory infection during the first trimester of pregnancy which was further complicated by polyhydramnios in the third trimester. The infants were diagnosed with bilateral congenital nuclear cataracts at birth. Serologic tests for toxoplasmosis, rubella, cytomegalovirus, herpes simplex virus, syphilis, and galactosemia screens were negative. Chromosome analyses were normal. Both children developed communicating hydrocephalus between one and three months after birth. Patient 1 died suddenly at 4 months following an upper respiratory infection. Patient 2 developed congestive heart failure and also died at 4 months. At autopsy, both infants had enlarged hearts with endocardial fibroelastosis. No identifiable organism could be isolated. We discuss the association of birth defects in widely separated organ systems in these patients and suggest that this may represent a genetic syndrome; however, a viral etiology cannot entirely be excluded. We believe this is a distinct disorder and propose the acronym HEC for hydrocephalus, EFE and cataracts.

X-linked dilated cardiomyopathy with neutropenia, growth retardation, and 3-methylglutaconic aciduria

Seven boys with an apparently X-linked syndrome of dilated cardiomyopathy, growth retardation, neutropenia, and persistently elevated urinary levels of 3-methylglutaconate, 3-methylglutarate, and 2-ethylhydracrylate were studied. The natural history of the disorder was characterized by severe or lethal cardiac disease and recurrent infections during infancy and early childhood but relative improvement in later childhood. The initial presentation of the syndrome varied from congenital dilated cardiomyopathy to infantile congestive heart failure to isolated neutropenia without clinical evidence of heart disease. The excretion of 3-methylglutaconate and 3-methylglutarate appeared to be independent of the metabolism of leucine, the presumed precursor of these organic acids in humans. Although the cause of the organic aciduria remains obscure, the constellation of biochemical and clinical abnormalities forms a distinct syndrome that may be a relatively common cause of dilated cardiomyopathy or neutropenia in boys during infancy and childhood.

Endocardial fibroelastosis: possible X linked inheritance

We report a pedigree in which six males died of cardiac failure within the first eight months of life. These males were related through healthy females, as with X linked recessive inheritance. There was no consanguinity. None of the affected boys had an anatomical cardiac abnormality. In two affected brothers, histological evidence for endomyocardial fibroelastosis was documented, and in one of these electron microscopy demonstrated abnormalities of the mitochondria as found in mitochondrial cytopathy. A review of published reports revealed five similar X linked pedigrees, and in two of these mitochondrial abnormalities were found. We suggest that these families may show an X linked recessive cardiomyopathy with mitochondrial abnormalities.

Endocardial fibroelastosis occurring in a mother and daughter

Endocardial fibroelastosis (EFE) in a mother and daughter are reported. This entity has a primary and secondary form. In this case, the 23-year-old mother died 11 months after delivery with findings of EFE. At age 3(1/2) years, the daughter was admitted in congestive heart failure and did not respond to medical management. The autopsy findings revealed EFE. Endocardial fibroelastosis in both mother and daughter is a very rare finding.

Endocardial fibroelastosis, neurologic dysfunction and unusual facial appearance in two brothers, coincidentally associated with dominantly inherited macrocephaly

We describe two brothers with endocardial fibroelastosis, unusual facial appearance, and cryptorchidism. The surviving brother has mental retardation, seizures and possible hypothalamic dysfunction. Both brothers have a head size greater than two standard deviations above normal; this appears to be related to superimposed presence of coincidental autosomal dominant macrocephaly in this family.

Heredity in primary endocardial fibroelastosis

Twenty-six cases of endocardial fibroelastosis were collected from three hospitals in Manchester over a ten-year period. Nine cases occurred in 4 families and these are discussed in detail. X-linked recessive inheritance seems likely in one family in which two probable female carriers had subarachnoid haemorrhages. In a second family an apparently normal man produced two children with endocardial fibroelastosis by different mothers suggesting autosomal dominant inheritance with incomplete penetrance. Autosomal recessive inheritance may be involved in the remaining two families but this was not associated with consanguinity. Genetic heterogeneity is evident in endocardial fibroelastosis and the majority of cases occur sporadically. An accurate family history is therefore necessary but it is difficult to give precise recurrence risks in sporadic cases.