Novel mitochondrial 16S rRNA polymorphism in a girl with Rett syndrome

High-frequency involved hearing loss caused by novel mitochondrial DNA mutation in 16S ribosomal RNA gene

OBJECTIVE

To clarify the responsible gene for a family associated with hearing loss but having no well-known mitochondrial mutations.

SUBJECTS

A Japanese family showing late-onset, progressive, and ski-sloping sensorineural hearing loss.

RESULTS

Whole mitochondrial genome sequencing identified the 1673T>C mutation, a novel mitochondrial DNA mutation in the 16S ribosomal RNA gene.

CONCLUSION

Whole mitochondrial genome sequencing is a powerful tool to identify the responsible gene for plausible mitochondrially inherited families. This is additional evidence that mitochondrial gene mutations may cause late-onset, progressive, and ski-sloping sensorineural hearing loss.

MECP2 and beyond: phenotype-genotype correlations in Rett syndrome

The association of Rett syndrome with pathogenic mutations of the methyl-CpG binding protein 2 (MECP2) gene was first made in 1999. Since that time, it has been found that the clinical phenotype can, at least in part, be explained in terms of the type and location of the MECP2 mutation and epigenetic factors such as skewing of X-chromosome inactivation. In addition, MECP2 mutations may be associated with non-Rett syndrome clinical phenotypes, including nonsyndromic and syndromic X-linked mental retardation and Angelman-like phenotypes. Intense research efforts are currently focused on understanding the pathogenesis of Rett syndrome, using sophisticated techniques such as microarray analysis, and the development of mouse models, with an ultimate aim being the development of targeted therapies that could ameliorate or even prevent the devastating consequences of this enigmatic neurodevelopmental disorder.

Genetics of Rett syndrome: properties of the newly discovered gene and pathobiology of the disorder

The recent identification of mutations in the gene methyl-Cpg-binding protein-2 (MECP2) in girls with Rett syndrome (RS) has firmly established the molecular genetic basis of this unique, X-linked, dominant disorder and provides a dramatic conclusion to an intensive, decade-long search. This finding has ramifications far beyond establishing the gene for RS. Recent data indicate that the clinical phenotypes for MECP2 mutations range from mild disability in the mother of a girl with RS to rapidly progressive encephalopathy in her brother. Further, the pathobiology of MECP2 could be a prototype for other disorders of neurodevelopment. MECP2 encodes a methyl-CpG-binding protein (MeCP2), which is critical for transcriptional silencing of an as yet unknown number and type of genes responsible for the pathobiology of RS. As such, this discovery opens up completely new vistas as to fundamental neurobiologic processes, to disease mechanisms in the neurodevelopmental disabilities, and to potential new therapeutic strategies for RS and related disorders.