RESUMO
Microcephaly-capillary malformation syndrome (MIC-CAP syndrome) is a newly recognized autosomal recessive congenital neurocutaneous central nervous system disorder characterized by severe microcephaly, early-onset seizures, profound psychomotor disability, and multiple cutaneous capillary lesions. In addition, affected patients have variable dysmorphic facial features and hypoplastic distal phalanges. It is distinctively caused by mutations in a newly characterized gene, STAMBP, encoding the deubiquitinating (DUB) isopeptidase that has a key role in cell surface receptor-mediated endocytosis and sorting. Herein, we describe an Arab family of two siblings with classic features of MIC-CAP syndrome that harbor a novel predicted splice mutation in STAMBP, which additionally display previously unreported findings of congenital hypothyroidism and alopecia areata.
Assuntos
Anormalidades Múltiplas/diagnóstico , Capilares/anormalidades , Complexos Endossomais de Distribuição Requeridos para Transporte/genética , Microcefalia/diagnóstico , Ubiquitina Tiolesterase/genética , Malformações Vasculares/diagnóstico , Anormalidades Múltiplas/genética , Árabes , Criança , Pré-Escolar , Consanguinidade , Análise Mutacional de DNA , Estudos de Associação Genética , Humanos , Masculino , Microcefalia/genética , Mutação Puntual , SíndromeRESUMO
Nuclear genetic disorders causing mitochondrial DNA (mtDNA) depletion are clinically and genetically heterogeneous, and the molecular etiology remains undiagnosed in the majority of cases. Through whole-exome sequencing, we identified recessive nonsense and splicing mutations in FBXL4 segregating in three unrelated consanguineous kindreds in which affected children present with a fatal encephalopathy, lactic acidosis, and severe mtDNA depletion in muscle. We show that FBXL4 is an F-box protein that colocalizes with mitochondria and that loss-of-function and splice mutations in this protein result in a severe respiratory chain deficiency, loss of mitochondrial membrane potential, and a disturbance of the dynamic mitochondrial network and nucleoid distribution in fibroblasts from affected individuals. Expression of the wild-type FBXL4 transcript in cell lines from two subjects fully rescued the levels of mtDNA copy number, leading to a correction of the mitochondrial biochemical deficit. Together our data demonstrate that mutations in FBXL4 are disease causing and establish FBXL4 as a mitochondrial protein with a possible role in maintaining mtDNA integrity and stability.
