Isolated succinate-CoQ reductase deficiency

What it is

From: Orphanet

A rare, mitochondrial oxidative phosphorylation disorder characterized by a highly variable phenotype. The severe, multisystemic disease involves brain, heart, muscles, liver, kidneys, and eyes and results in death in infancy. Mildly affected individuals have only isolated cardiac or muscle involvement in the adulthood. Histochemical and biochemical analysis reveals a global reduction of succinate dehydrogenase activity.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal left ventricular function · Frequent (79-30%)

Inability of the left ventricle to perform its normal physiologic function. Failure is either due to an inability to contract the left ventricle or the inability to relax completely and fill with blood during diastole.

Abnormality of the cardiovascular system · Frequent (79-30%)

Any abnormality of the cardiovascular system.

Abnormality of the eye · Frequent (79-30%)

Any abnormality of the eye, including location, spacing, and intraocular abnormalities.

Babinski sign · Frequent (79-30%)

Upturning of the big toe (and sometimes fanning of the other toes) in response to stimulation of the sole of the foot. If the Babinski sign is present it can indicate damage to the corticospinal tract.

Developmental regression · Frequent (79-30%)

Loss of developmental skills, as manifested by loss of developmental milestones.

Distal amyotrophy · Frequent (79-30%)

Muscular atrophy affecting muscles in the distal portions of the extremities.

Easy fatigability · Frequent (79-30%)

Increased susceptibility to fatigue.

Generalized muscle weakness · Frequent (79-30%)

Generalized weakness or decreased strength of the muscles, affecting both distal and proximal musculature.

Generalized myoclonic seizure · Frequent (79-30%)

A generalized myoclonic seizure is a type of generalized motor seizure characterized by bilateral, sudden, brief (<100 ms) involuntary single or multiple contraction of muscles or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus.

Hyperreflexia in upper limbs · Frequent (79-30%)

Increased intensity of the a reflex in the arm.

Hypertrophic cardiomyopathy · Frequent (79-30%)

Hypertrophic cardiomyopathy (HCM) is defined by the presence of increased ventricular wall thickness or mass in the absence of loading conditions (hypertension, valve disease) sufficient to cause the observed abnormality.

Left ventricular hypertrophy · Frequent (79-30%)

Enlargement or increased size of the heart left ventricle.

Motor delay · Frequent (79-30%)

A type of Developmental delay characterized by a delay in acquiring motor skills.

Motor deterioration · Frequent (79-30%)

Loss of previously present motor (i.e., movement) abilities.

Other findings in the same source

From: Orphanet

Additional reported features include Proportionate short stature (Frequent (79-30%)); Proximal muscle weakness (Frequent (79-30%)); Severe short stature (Frequent (79-30%)); Spasticity (Frequent (79-30%)); Weight loss (Frequent (79-30%)); Hyperactive deep tendon reflexes (Frequent (79-30%)); Hyperactive patellar reflex (Frequent (79-30%)); Progressive psychomotor deterioration (Frequent (79-30%)); Reduced visual acuity (Frequent (79-30%)); Skeletal myopathy (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

When it may begin

From: Orphanet

Infancy; Neonatal

Inheritance in the source

From: Orphanet

Autosomal recessive

Frequency and the population described

From: Orphanet

Reported case(s): 37.0; Worldwide. This is a published case count, not prevalence. Point prevalence: <1 / 1 000 000; Worldwide; Class only.

Understanding the inheritance label

From: MedlinePlus Genetics

An autosomal recessive pattern usually involves disease-causing changes in both copies of a gene. Parents may each carry one altered copy without having the condition themselves. A genetic counsellor can explain carrier testing and reproductive implications using the actual laboratory findings, rather than the condition name alone.

Which doctor should you see?

The suggested department for discussing Isolated succinate-CoQ reductase deficiency is Metabolic Medicine, with a metabolic specialist / clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with metabolic specialist / clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Is a biochemical or molecular result needed to clarify the diagnosis?
• Does this condition require an individual plan for illness or reduced food intake?
• Should nutrition advice come from a specialist metabolic dietitian?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Isolated succinate-CoQ reductase deficiency. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.