Hereditary deficiency in MTO1 can result in a number of clinical and laboratory findings.

Chromosome: 6q13

Gene: MTO1 (mitochondrial tRNA translation optimization 1)


Clinical features:

(1) hypertrophic cardiomyopathy

(2) seizures

(3) global developmental delay

(4) hypotonia

(5) feeding difficulties

(6) failure to thrive

(7) optic atrophy

(8) ataxia

(9) other ocular findings (ophthalmoplegia, ptosis, cataracts)


ONCE Syndrome - the presence of:

(1) optic neuropathy (ON)

(2) hypertrophic cardiomyopathy (C)

(3) encephalopathy (E)


Laboratory findings:

(1) lactic acidosis

(2) metabolites reflecting defects in mitochondrial respiratory chain (MRC) activities

(3) low residual complex I, III and IV activity in a muscle biopsy

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