Loss-of-function mutations in the G4.5 gene have been shown to cause Barth syndrome (BTHS), an X-linked disorder characterized by cardiac and skeletal myopathy, short stature, and neutropenia. We recently reported a family with a severe X-linked cardiomyopathy described as isolated noncompaction of the left ventricular myocardium (INVM). Other findings associated with BTHS (skeletal myopathy, neutropenia, growth retardation, elevated urinary organic acids, and mitochondrial abnormalities) were either absent or inconsistent. A linkage study of the X chromosome localized INVM to the Xq28 region near the BTHS locus, suggesting that these disorders are allelic. We screened the G4.5 gene for mutations in this family with SSCP and direct sequencing and found a novel glycine-to-arginine substitution at position 197. This position is conserved in a homologous Caenorhabditis elegans protein. We conclude that INVM is a severe allelic variant of BTHS with a specific effect on the heart. This finding provides further structure-function information about the G4.5 gene product and has implications for unexplained cases of severe infantile hypertrophic cardiomyopathy in males.

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Advances in high-throughput genomic technologies coupled with a growing number of genomic results potentially useful in clinical care have led to ground-breaking genomic medicine implementation programs in various nations. Many of these innovative programs capitalize on unique local capabilities arising from the structure of their health care systems or their cultural or political milieu, as well as from unusual burdens of disease or risk alleles. Many such programs are being conducted in relative isolation and might benefit from sharing of approaches and lessons learned in other nations. The National Human Genome Research Institute recently brought together 25 of these groups from around the world to describe and compare projects, examine the current state of implementation and desired near-term capabilities, and identify opportunities for collaboration to promote the responsible implementation of genomic medicine. The wide variety of nascent programs in diverse settings demonstrates that implementation of genomic medicine is expanding globally in varied and highly innovative ways. Opportunities for collaboration abound in the areas of evidence generation, health information technology, education, workforce development, pharmacogenomics, and policy and regulatory issues. Several international organizations that are already facilitating effective research collaborations should engage to ensure implementation proceeds collaboratively without potentially wasteful duplication. Efforts to coalesce these groups around concrete but compelling signature projects, such as global eradication of genetically-mediated drug reactions or developing a truly global genomic variant data resource across a wide number of ethnicities, would accelerate appropriate implementation of genomics to improve clinical care world-wide.

Isolated noncompaction of the left ventricular myocardium (INVM) is characterized by the presence of numerous prominent trabeculations and deep intertrabecular recesses within the left ventricle, sometimes also affecting the right ventricle and interventricular septum. Familial occurrence of this disorder was described previously. We present a family in which 6 affected individuals demonstrated X-linked recessive inheritance of this trait. Affected relatives presented postnatally with left ventricular failure and arrhythmias, associated with the pathognomonic echocardiographic findings of INVM. The usual findings of Barth syndrome (neutropenia, growth retardation, elevated urinary organic acids, low carnitine levels, and mitochondrial abnormalities) were either absent or found inconsistently. Fetal echocardiograms obtained between 24-30 weeks of gestation in 3 of the affected males showed a dilated left ventricle in one heart, but were not otherwise diagnostic of INVM in any of the cases. Four of the affected individuals died during infancy, one is in cardiac failure at age 8 months, and one is alive following cardiac transplant at age 9 months. The hearts from infants who died or underwent transplantation appeared, on gross examination, to be enlarged, with coarse, deep ventricular trabeculations and prominent endocardial fibroelastosis. Histologically, there were loosely organized fascicles of myocytes in subepicardial and midmyocardial zones of both ventricles, and the myocytes showed thin, often angulated fibers with prominent central clearing and reduced numbers of filaments. Markedly elongated mitochondria were present in some ventricular myocytes from one specimen, but this finding was not reproducible. Genetic linkage analysis has localized INVM to the Xq28 region, where other myopathies with cardiac involvement have been located.

Isolated noncompaction of the left ventricular myocardium (INVM) is characterized by the presence of numerous prominent trabeculations and deep intertrabecular recesses within the left ventricle, sometimes also affecting the right ventricle and interventricular septum. Familial occurrence of this disorder was described previously. We present a family in which 6 affected individuals demonstrated X-linked recessive inheritance of this trait. Affected relatives presented postnatally with left ventricular failure and arrhythmias, associated with the pathognomonic echocardiographic findings of INVM. The usual findings of Barth syndrome (neutropenia, growth retardation, elevated urinary organic acids, low carnitine levels, and mitochondrial abnormalities) were either absent or found inconsistently. Fetal echocardiograms obtained between 24-30 weeks of gestation in 3 of the affected males showed a dilated left ventricle in one heart, but were not otherwise diagnostic of INVM in any of the cases. Four of the affected individuals died during infancy, one is in cardiac failure at age 8 months, and one is alive following cardiac transplant at age 9 months. The hearts from infants who died or underwent transplantation appeared, on gross examination, to be enlarged, with coarse, deep ventricular trabeculations and prominent endocardial fibroelastosis. Histologically, there were loosely organized fascicles of myocytes in subepicardial and midmyocardial zones of both ventricles, and the myocytes showed thin, often angulated fibers with prominent central clearing and reduced numbers of filaments. Markedly elongated mitochondria were present in some ventricular myocytes from one specimen, but this finding was not reproducible. Genetic linkage analysis has localized INVM to the Xq28 region, where other myopathies with cardiac involvement have been located.