Mitochondrial disorders

Gene: COQ5

Green List (high evidence)

Comment on list classification: There are now more than 3 unrelated families reported with biallelic COQ5 variants and mitochondrial disease (COQ5-related primary CoQ10 deficiency). Hence, this gene should be promoted to Green at the next GMS update.

Created: 1 Apr 2026, 2:32 p.m. | Last Modified: 1 Apr 2026, 2:32 p.m.

Panel Version: 9.48

PMID: 29044765 Malicdan et al., 2018
Report of 3 female siblings of Iraqi-Jewish descent, who had varying degrees of cerebellar ataxia, encephalopathy, generalized tonic-clonic seizures, and cognitive disability. WES/WGS identified biallelic duplications in the COQ5 gene [Chr12(GRCh37):120940098–120949687]. Sequencing of the cDNA from fibroblasts of patient III.4 shows an abnormal 3′UTR because of an abnormal splicing event, leading to LoF.
Study showed reduced levels of CoQ10 in peripheral white blood cells of all affected individuals and reduced CoQ10 levels in the only muscle tissue available from one affected proband. CoQ10 supplementation led to clinical improvement. Retinal examination not mentioned in report.

PMID: 36266294 Jurkute et al., 2022
2 families, 2 affected individuals with biallelic COQ5 variants and RP
Family 11: 56yo patient with isolated RP (onset at 49 years) - harboured COQ5 variants c.682-7 T > G and c.933delC, p.(Tyr311*).
Family 12: 38 yo patient with RP, nystagmus (onset at 14 yrs), Muscular weakness (hyposthenia) with onset at 5 yrs, as well as infantile appearance, hypertelorism, and undeveloped fertile function. Comp het for COQ5 c.367 C > T, p.(Arg123Trp) and c.682-7 T > G.
c.682-7 T > G variant was confirmed to cause mis-splicing, with exon 5 skipping (p.(Gln230*)), as well as exon 4-5 skipping in a small proportion of reads (p.(Leu193Phefs*27)). Muscle biopsy / fibroblast testing was not done.

PMID: 37599337 Dawidziuk et al., 2023
Report of a patient harbouring one novel c.681+1G>A and one recurrent p.Gly118Ser variant within COQ5. Symptoms included reduced COQ10 levels, intellectual disability, encephalopathy, cerebellar ataxia, cerebellar atrophy speech regression/dysarthria, short stature, and developmental delays, as well as rarer features of dysmorphia, microcephaly, and regressive social faculties. Low COQ10 level tests showing 0.6 mg/l (normal range >0.67 mg/l). Ophthalmologic investigation proved normal.

PMID: 41199775 Wongkittichote et al., 2025
Report of two siblings with profound developmental delay, epilepsy, hypotonia, and stroke‐like episodes - diagnosed with COQ5-related primary CoQ10 deficiency. Clinical exome sequencing revealed compound heterozygous variants in COQ5: c.177_178del (p.Ser60Glyfs13) and c.353G>A (p.Gly118Asp) - confirmed in trans. Brain MRI showed abnormal signal hyperintensity in basal ganglia and thalami, and signs of multiple strokes. Ophthalmologic examination of Patient 1 at the age of 4 years revealed ptosis, pale optic discs concerning for optic atrophy, and abnormal electroretinography consistent with retinopathy.

COQ5 is putatively linked to AR ?Coenzyme Q10 deficiency, primary, 9, OMIM:619028 (OMIM accessed 1st Apr 2026). The relationship between COQ5 and mitochondrial disease has been classified as Moderate in ClinGen by Cerebellar Ataxia GCEP in July 2024.

Created: 1 Apr 2026, 2:29 p.m. | Last Modified: 1 Apr 2026, 2:29 p.m.

Panel Version: 9.47

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
?Coenzyme Q10 deficiency, primary, 9, OMIM:619028; mitochondrial disease, MONDO:0044970

Publications

• 29044765
• 36266294
• 37599337
• 41199775

The rating of this gene has been updated from Amber to Red following NHS Genomic Medicine Service approval.

Created: 29 Jul 2022, 1:47 p.m. | Last Modified: 29 Jul 2022, 1:47 p.m.

Panel Version: 2.109

Red List (low evidence)

Three siblings reported, bi-allelic duplications in gene, said to lead to reduced CoQ10.

Created: 18 Mar 2020, 7 a.m. | Last Modified: 18 Mar 2020, 7 a.m.

Panel Version: 2.5

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Cerebellar ataxia; encephalopathy; generalized tonic-clonic seizures; intellectual disability

Publications

• 29044765

I don't know

Initial gene list and info collated by Carl Fratter (Oxford University Hospitals NHS Trust) January 2019 on behalf of the GMS Mitochondrial specialist test group.

Created: 23 Jul 2019, 10:13 a.m. | Last Modified: 23 Jul 2019, 10:13 a.m.

Panel Version: 1.412