Myopathy, Mitochondrial Anomalies, and Ataxia

Clinical Characteristics
Ocular Features: 

Ocular findings are variable.  One of three individuals with compound heterozygous mutations had a pigmentary retinopathy with pallor of the optic nerve but no visual abnormalities.  Her sister had only optic nerve pallor.  The eyes are described as "small" and "close-set".

No ocular findings were reported for the family with autosomal dominant inheritance.

Systemic Features: 

Ataxia, short stature, and gait difficulties from an early age are consistent findings.  Some patients are never able to walk.  Motor development is generally delayed.  Truncal and limb ataxia is a feature.  Some degree of intellectual disability is generally present and speech is often delayed.  

The face is long with a myopathic appearance.  Both micrognathia and a prominent jaw may be seen.  The palate is highly arched.  Patients are described as hypotonic and there is generalized muscle weakness both proximal and distal.  Distal sensory impairment has been described in the family with presumed dominant inheritance and there may be psychiatric symptoms of anxiety, depression, and schizophrenia.  Dysmetria with dysdiadochokinesis is often present and a fine intention tremor has been observed.

Mitochondria in fibroblasts exhibit abnormal dynamics and occur in a fragmented network.  Muscle biopsies reveal changes consistent with myopathy.  Serum creatine kinase may be elevated.

Genetics

Compound heterozygous mutations in the MSTO1 gene (1q22) have been found in two families with 3 affected individuals suggesting autosomal recessive inheritance.  In a third family, heterozygous mutations in the same gene were found in a mother and 3 of her adult children, consistent with autosomal dominant transmission.

Treatment
Treatment Options: 

No treatment has been reported.

References
Article Title: 

References

Nasca A, Scotton C, Zaharieva I, Neri M, Selvatici R, Magnusson OT, Gal A, Weaver D, Rossi R, Armaroli A, Pane M, Phadke R, Sarkozy A, Muntoni F, Hughes I, Cecconi A, Hajnoczky G, Donati A, Mercuri E, Zeviani M, Ferlini A, Ghezzi D. Recessive mutations in MSTO1 cause mitochondrial dynamics impairment, leading to myopathy and ataxia. Hum Mutat. 2017 Aug;38(8):970-977.

PubMedID: 28544275

Gal A, Balicza P, Weaver D, Naghdi S, Joseph SK, Varnai P, Gyuris T, Horvath A, Nagy L, Seifert EL, Molnar MJ, Hajnoczky G. MSTO1 is a cytoplasmic pro-mitochondrial fusion protein, whose mutation induces myopathy and ataxia in humans. EMBO Mol Med. 2017 Jul;9(7):967-984.

PubMedID: 28554942