Novel Twinkle gene mutation in autosomal dominant progressive external ophthalmoplegia and multisystem failure

Longitudinal clinical follow-up of a large family with the R357P Twinkle mutation

IMPORTANCE

Autosomal dominant progressive external ophthalmoplegia due to PEO1 mutations is considered relatively benign, but no data about long-term progression of this disease have been reported. The aim of this study was to provide a 16-year clinical follow-up of autosomal dominant progressive external ophthalmoplegia due to the p.R357P gene mutation in PEO1.

OBSERVATIONS

Twenty-two members of an Irish-American family were examined in 1996, when PEO1 sequencing revealed a c.1071G>C/p.R357P mutation in 9 of them. We reexamined the family in 2012 using a standardized clinical protocol. Autosomal dominant progressive external ophthalmoplegia due to the p.R357P PEO1 mutation is a late-onset ocular myopathy beginning with ptosis and progressing slowly. Ophthalmoparesis, if present, is mild and evident only by neurological examination.

CONCLUSIONS AND RELEVANCE

Our results are important for prognosis and genetic counseling.

Twinkle mutations in two Chinese families with autosomal dominant progressive external ophthalmoplegia

Autosomal dominant progressive external ophthalmoplegia (adPEO) is a common adult onset mitochondrial disease caused by mutations in nuclear DNA (nDNA). Twinkle is one of the nuclear genes associated with adPEO. Clinical, histochemical, and molecular genetics findings of 6 patients from two Chinese families with adPEO were reported. Two point mutations (c.1423G>C, p.A475P and c.1061G>C, p.R354P) of Twinkle gene have been found. Multiple mtDNA deletions were also detected in patient's muscle and fibroblasts. This study confirms two mutations in Chinese adPEO families, which were first reported in the Chinese population.

Progressive external ophthalmoplegia (PEO) due to a mutation in the C10orf2 (PEO1) gene mimicking a myasthenic crisis

We described a case of a patient with autosomal dominant progressive external ophthalmoplegia (PEO) who presented with the acute onset dysphagia, quadriparesis, ptosis and respiratory insufficiency following a cardiac procedure and mimicking a myasthenic crisis. A pathogenic mutation in the C10orf2 (PEO1) gene was confirmed. The unusual presentation of our patient contributes to expand the clinical phenotype of PEO1 mutations and reinforces the need to consider mitochondrial myopathy as differential diagnosis of myasthenia gravis even in the case of acute onset symptoms.

Exome sequencing reveals a homozygous mutation in TWINKLE as the cause of multisystemic failure including renal tubulopathy in three siblings

Three deceased infants from a Pakistani consanguineous family presented with a similar phenotype of cholestatic liver disease, hypotonia, severe failure to thrive, recurrent vomiting, renal tubulopathy, and a progressive neurodegenerative course. Mitochondrial DNA depletion syndrome was considered in view of multisystem involvement. Exome sequencing, revealed a homozygous novel mutation c.1183T>C (p.F395L) in exon 1 of the C10orf2 TWINKLE gene. The hepatocerebral phenotype is well recognized in association with recessive mutations involving the C10orf2 TWINKLE gene. The feature of renal tubulopathy adds to the multisystemic presentation in our patients and further demonstrates an expansion of the phenotype in mitochondrial DNA depletion syndrome associated with TWINKLE gene mutations. The absence of features of an epileptic encephalopathy appears to be of added interest.

The human mitochondrial replication fork in health and disease

Mitochondria are organelles whose main function is to generate power by oxidative phosphorylation. Some of the essential genes required for this energy production are encoded by the mitochondrial genome, a small circular double stranded DNA molecule. Human mtDNA is replicated by a specialized machinery distinct from the nuclear replisome. Defects in the mitochondrial replication machinery can lead to loss of genetic information by deletion and/or depletion of the mtDNA, which subsequently may cause disturbed oxidative phosphorylation and neuromuscular symptoms in patients. We discuss here the different components of the mitochondrial replication machinery and their role in disease. We also review the mode of mammalian mtDNA replication.