RESUMO
Multinucleate cellular syncytial formation is a hallmark of skeletal muscle differentiation. Myomaker, encoded by Mymk (Tmem8c), is a well-conserved plasma membrane protein required for myoblast fusion to form multinucleated myotubes in mouse, chick, and zebrafish. Here, we report that autosomal recessive mutations in MYMK (OMIM 615345) cause Carey-Fineman-Ziter syndrome in humans (CFZS; OMIM 254940) by reducing but not eliminating MYMK function. We characterize MYMK-CFZS as a congenital myopathy with marked facial weakness and additional clinical and pathologic features that distinguish it from other congenital neuromuscular syndromes. We show that a heterologous cell fusion assay in vitro and allelic complementation experiments in mymk knockdown and mymkinsT/insT zebrafish in vivo can differentiate between MYMK wild type, hypomorphic and null alleles. Collectively, these data establish that MYMK activity is necessary for normal muscle development and maintenance in humans, and expand the spectrum of congenital myopathies to include cell-cell fusion deficits.
Assuntos
Proteínas de Membrana/genética , Síndrome de Möbius/genética , Morfogênese/genética , Proteínas Musculares/genética , Músculo Esquelético/metabolismo , Doenças Musculares/genética , Mutação , Mioblastos/metabolismo , Síndrome de Pierre Robin/genética , Proteínas de Peixe-Zebra/genética , Adulto , Sequência de Aminoácidos , Animais , Fusão Celular , Criança , Modelos Animais de Doenças , Embrião não Mamífero , Feminino , Expressão Gênica , Genes Recessivos , Teste de Complementação Genética , Humanos , Lactente , Masculino , Proteínas de Membrana/deficiência , Síndrome de Möbius/metabolismo , Síndrome de Möbius/patologia , Proteínas Musculares/deficiência , Músculo Esquelético/crescimento & desenvolvimento , Músculo Esquelético/patologia , Doenças Musculares/metabolismo , Doenças Musculares/patologia , Mioblastos/patologia , Linhagem , Síndrome de Pierre Robin/metabolismo , Síndrome de Pierre Robin/patologia , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Peixe-Zebra , Proteínas de Peixe-Zebra/deficiênciaRESUMO
We report the transient response of a patient with the ETV6-ABL fusion gene to imatinib mesylate (STI571). A 38-year-old man was referred with an erroneous diagnosis of Philadelphia-positive chronic myeloid leukemia in blastic transformation for treatment with the ABL tyrosine kinase inhibitor, STI571. Further investigation indicated that the patient in fact had acute myeloid leukemia; no evidence of the Philadelphia translocation or BCR-ABL was found using fluorescence in situ hybridization (FISH) or reverse transcription-polymerase chain reaction. Detailed FISH analysis identified a cryptic t(9;12) translocation, and molecular studies confirmed the presence of the ETV6-ABL fusion transcript. Because the patient was gravely ill at presentation, treatment was commenced immediately with STI571 monotherapy, resulting in considerable initial improvement. However within 10 days the patient's condition again deteriorated, and he required conventional chemotherapy. This case has implications for the design of future studies using STI571 in leukemias involving ABL-encoded fusion proteins other than BCR-ABL.