Principal Clinical Manifestations
Neurologic. Central nervous system (CNS) manifestations include encephalopathy (a wide spectrum of brain involvement with different clinical and neuroradiologic features often not further specified). In some individuals encephalopathy is associated with findings on neuroimaging resembling Leigh syndrome [López et al 2006] or MELAS (with stroke-like episodes) [Salviati et al 2005]. CNS manifestations often include seizures, dystonia, spasticity, and/or intellectual disability [López et al 2006, Mollet et al 2007, Heeringa et al 2011].
The age of onset and clinical severity range from fatal neonatal encephalopathy with hypotonia [Mollet et al 2007, Jakobs et al 2013] to a late-onset, slowly progressive multiple system atrophy (MSA)-like phenotype, a neurodegenerative disorder characterized by autonomic failure associated with various combinations of parkinsonism, cerebellar ataxia, and pyramidal dysfunction. This clinical picture resembling MSA with onset in the seventh decade was reported in two multiplex families with COQ2-related CoQ10 deficiency [Mitsui et al 2013].
Individuals with COQ8A-related CoQ10 deficiency display progressive cerebellar atrophy and ataxia with intellectual disability and seizures [Lagier-Tourenne et al 2008, Mollet et al 2008]. Ataxia has also been reported in individuals with COQ4-related CoQ10 deficiency [Bosch et al 2018, Mero et al 2021, Cordts et al 2022].
Distal motor neuropathy has been reported in several individuals with COQ7-related CoQ10 deficiency [Jacquier et al 2023, Liu et al 2023]. Peripheral neuropathy has been reported in two sibs with PDSS1-related CoQ10 deficiency [Mollet et al 2007].
Given the small number of affected individuals described to date, clinical data are insufficient to make any generalizations about other neurologic manifestations (e.g., dystonia, spasticity, seizures, intellectual disability).
Renal.
Steroid-resistant nephrotic syndrome (SRNS), an unusual feature of mitochondrial disorders, is a hallmark of primary CoQ10 deficiency. If not treated with supplementation of high-dose oral CoQ10 (see Management), SRNS usually progresses to end-stage kidney disease (ESKD). SRNS has been reported in association with variants in PDSS1, PDSS2, COQ2, COQ6, and COQ8B [Acosta et al 2016]. To date, SRNS has not been reported in association with variants in COQ4, COQ8A, and COQ9 (including the mouse model).
Renal involvement usually manifests as proteinuria in infancy. Affected individuals often present initially with SRNS that leads to ESKD, followed by an encephalomyopathy with seizures and stroke-like episodes resulting in severe neurologic impairment and ultimately death [Rötig et al 2000, Salviati et al 2005, Heeringa et al 2011].
Some affected individuals manifest only SRNS with onset in the first or second decade of life and slow progression to ESKD without extrarenal manifestations [Gigante et al 2017].
One of the two individuals in a family with COQ9-related CoQ10 deficiency manifested tubulopathy within a few hours after birth.
Cardiac. Hypertrophic cardiomyopathy (HCM) has been reported in:
COQ9-related CoQ
10 deficiency manifesting as neonatal-onset lactic acidosis followed by a multisystem disease that included HCM [
Duncan et al 2009]. The cardiac disease worsened despite treatment with CoQ
10.
Ophthalmologic. Retinopathy, sometimes as an isolated manifestation in adults, has been reported in association with variants in PDSS1, COQ2, COQ4, and COQ5 [Desbats et al 2016, Jurkute et al 2022].
Optic atrophy has been reported in some individuals with PDSS1-related CoQ10 deficiency [Mollet et al 2007], PDSS2-related CoQ10 deficiency [Rötig et al 2000], and COQ2-related CoQ10 deficiency [Stallworth et al 2023].
Sensorineural hearing loss, which is common in individuals with COQ6-related CoQ10 deficiency, is also observed in some individuals with COQ2-related CoQ10 [Drovandi et al 2022b] and PDSS1-related CoQ10 deficiency [Nardecchia et al 2021].
Muscle
findings include weakness and exercise intolerance. Muscle biopsy may show nonspecific signs of lipid accumulation and mitochondrial proliferation [Trevisson et al 2011, Desbats et al 2015b]. Muscle involvement in primary CoQ10 deficiency is virtually always accompanied by extramuscular manifestations.
Prognosis. Data on the prognosis of primary CoQ10 deficiency are limited due to the small number of affected individuals reported to date. It is a progressive disorder, with variable rates of progression and tissue involvement depending on the gene involved and the severity of the CoQ10 deficiency.
Children with severe multisystem CoQ10 deficiency respond poorly to treatment and generally die within the neonatal period or in the first year of life.
Individuals with later-onset disease show better response to supplementation with high-dose oral CoQ10. In many instances treatment can change the natural history of the disease by blocking progression of the kidney disease and preventing the onset of neurologic manifestations in persons with biallelic pathogenic variants in COQ2, COQ6, COQ8B, or PDSS2 [Montini et al 2008; Heeringa et al 2011; Ashraf et al 2013; Authors, personal communication]. See Pharmacologic Treatment.
Phenotypes of COQ2-, COQ8A-, and COQ8B-Related Coenzyme Q10 Deficiencies
COQ2. The findings in affected individuals from the ten families described to date differ in severity and age of onset [Mollet et al 2007, Diomedi-Camassei et al 2007, Dinwiddie et al 2013, Jakobs et al 2013, McCarthy et al 2013, Mitsui et al 2013, Scalais et al 2013, Desbats et al 2015b, Desbats et al 2016].
The main clinical features include SRNS, which can be:
Adult-onset retinitis pigmentosa can be an isolated manifestation or can be associated with late-onset multiple system atrophy [Mitsui et al 2013, Desbats et al 2016].
COQ8A. Affected individuals experience onset of muscle weakness and reduced exercise tolerance between ages 18 months and three years, followed by cerebellar ataxia (the predominant clinical feature) with severe cerebellar atrophy on MRI. The disease course varies, including both progressive and apparently self-limited ataxia. The ataxia may be:
COQ8B. Affected individuals generally manifest SRNS in the first and second decade, and frequently evolve to end-stage kidney disease [Ashraf et al 2013, Korkmaz et al 2016]. In addition, four affected individuals were reported with mild intellectual disability, two with occasional seizures, and one with retinitis pigmentosa.