RESUMO
Marshall-Smith syndrome (MSS) is a very rare malformation syndrome characterized by typical craniofacial anomalies, abnormal osseous maturation, developmental delay, failure to thrive, and respiratory difficulties. Mutations in the nuclear factor 1/X gene (NFIX) were recently identified as the cause of MSS. In our study cohort of 17 patients with a clinical diagnosis of MSS, conventional sequencing of NFIX revealed frameshift and splice-site mutations in 10 individuals. Using multiplex ligation-dependent probe amplification analysis, we identified a recurrent deletion of NFIX exon 6 and 7 in five individuals. We demonstrate this recurrent deletion is the product of a recombination between AluY elements located in intron 5 and 7. Two other patients had smaller deletions affecting exon 6. These findings show that MSS is a genetically homogeneous Mendelian disorder. RT-PCR experiments with newly identified NFIX mutations including the recurrent exon 6 and 7 deletion confirmed previous findings indicating that MSS-associated mutant mRNAs are not cleared by nonsense-mediated mRNA decay. Predicted MSS-associated mutant NFIX proteins consistently have a preserved DNA binding and dimerization domain, whereas they grossly vary in their C-terminal portion. This is in line with the hypothesis that MSS-associated mutations encode dysfunctional proteins that act in a dominant negative manner.
Assuntos
Anormalidades Múltiplas/genética , Elementos Alu , Doenças do Desenvolvimento Ósseo/genética , Anormalidades Craniofaciais/genética , Éxons , Fatores de Transcrição NFI/genética , Displasia Septo-Óptica/genética , Deleção de Sequência , Anormalidades Múltiplas/diagnóstico , Adolescente , Adulto , Doenças do Desenvolvimento Ósseo/diagnóstico , Criança , Pré-Escolar , Pontos de Quebra do Cromossomo , Anormalidades Craniofaciais/diagnóstico , Análise Mutacional de DNA , Fácies , Feminino , Expressão Gênica , Loci Gênicos , Humanos , Lactente , Masculino , Mutação , Fenótipo , RNA Mensageiro/genética , Displasia Septo-Óptica/diagnóstico , Adulto JovemRESUMO
Lymphedema, lymphangiectasias, mental retardation and unusual facial characteristics define the autosomal recessive Hennekam syndrome. Homozygosity mapping identified a critical chromosomal region containing CCBE1, the human ortholog of a gene essential for lymphangiogenesis in zebrafish. Homozygous and compound heterozygous mutations in seven subjects paired with functional analysis in a zebrafish model identify CCBE1 as one of few genes causing primary generalized lymph-vessel dysplasia in humans.