Complex II is, as in Complex I, caused by mutations in nDNA. This mutation is defined as a “direct hit"
in the genes that encode subunits of respiratory chains complexes. It affects the enzyme succinate CoQ reductase
which is responsible for the transfer of electrons by the reduction of succinate to fumarate in the electron chain
pathway (see Table C-2). Deficiency of complex II is characterized by highly variable phenotypic expression.
The clinical features include encephalomyopathy, failure to thrive, severe developmental delay, muscle hypotonia,
lethargy, respiratory failure, ataxia, and myoclonic seizures. The presence of lactic acidosis is common. The most
frequent clinical condition is Leigh syndrome. See Table C-4.
Table C-4 Summary of Mitochondrial Syndromes and Common Clinical Manifestations ||Download (.pdf)
Table C-4 Summary of Mitochondrial Syndromes and Common Clinical Manifestations
|Syndrome||Common Clinical Manifestations|
|Coenzyme Q deficiency||Familial mitochondrial encephalomyopathy, ataxia,
seizures, mental retardation, proximal muscle weakness, pyramidal signs,
exertional fatigue with lactic acidosis (ATT: administration of coenzyme
Q10 may contribute to control of seizure activities)|
|MELAS||Short stature, sensorineural deafness, stroke-like episodes that
most often are occipital and not conforming to metabolic territories, seizures,
exercise intolerance, asthenia, severe muscle weakness, diabetes mellitus,
|NARP||Neuropathy, ataxia, retinitis pigmentosa|
|MNGIE||Gastric hypomotility, PEO, muscle wasting and weakness, deafness|
|KSS||PEO with onset before 30 years of age, retinal pigmentary degeneration,
high cerebrospinal fluid protein, heart block (always present before
50 years of age), identification of white matter abnormalities on magnetic
resonance imaging, intracranial calcification, often raised intracranial pressure|
|PEO||Ptosis and progressive complex external ophthalmoplegia, limb muscle
weakness and wasting, exercise intolerance, intracerebral calcification,
white matter abnormalities|
|LS||Psychomotor retardation, reduced ability to suck and swallow in infancy
leading to failure to thrive, signs of brainstem dysfunction
(respiratory abnormalities, sudden death in infancy, eye movement
disturbance, nystagmus), peripheral neuropathy, dystonia, other movement
|LHON||Subacute visual failure (particularly in males; male-to-female ratio 9:1), dystonia|
Succinate CoQ Reductase Deficiency; Succinate Dehydrogenase.
If we consider only cases with documented mutations, complex II deficiency appears to be a rare cause of
Inheritance is usually autosomal recessive. Deficiency of complex II is characterized by highly
variable phenotypic expression. It can be caused by mutation in the nuclear-encoded SDHA gene on chromosome 5p.
Cheam EW, Critchley LA. Anesthesia for a child with complex I respiratory
chain enzyme deficiency. J Clin Anesth