Medicine – Friedreich Ataxia

Friedreich ataxia is an inherited progressive neurodegenerative disorder that primarily affects the spinal cord, peripheral nerves, and cerebellar pathways. It is one of the most important hereditary causes of ataxia beginning in childhood or adolescence.

The disorder produces a characteristic combination of progressive gait and limb ataxia, sensory neuropathy, pyramidal tract abnormalities, skeletal deformities, cardiomyopathy, and an increased risk of diabetes mellitus.

1. Inheritance

Friedreich ataxia is inherited in an autosomal recessive pattern.

This means that an affected person usually inherits one abnormal allele from each parent, while the parents are typically unaffected carriers.

Therefore, affected siblings may occur in the same family even when the parents have no neurological symptoms.

2. Genetic Abnormality

Friedreich ataxia is caused by pathogenic variants in the FXN gene on chromosome 9.

The most common abnormality is a GAA trinucleotide-repeat expansion within the FXN gene.

This leads to reduced production of the protein:

Frataxin.

3. Frataxin

Frataxin is a mitochondrial protein involved particularly in iron–sulfur cluster formation and normal mitochondrial energy metabolism.

Reduced frataxin causes mitochondrial dysfunction, abnormal iron handling, oxidative injury, and progressive cellular damage.

Tissues with high metabolic requirements are particularly affected, including:

Nervous system.

Heart.

Pancreatic beta cells.

This helps explain the combination of neurological disease, cardiomyopathy, and diabetes.

4. Age at Onset

Friedreich ataxia usually begins in childhood or adolescence.

An average onset around 10–15 years is often quoted, so the original figure of approximately 12 years is reasonable as a typical teaching value.

However, age at onset is variable, and some patients present later in adulthood.

Earlier onset is often associated with more severe disease.

5. Neurological Pathology

Friedreich ataxia affects several neurological pathways simultaneously.

Important structures include:

Dorsal columns of the spinal cord.

Spinocerebellar tracts.

Corticospinal tracts.

Peripheral sensory nerves and dorsal root ganglia.

This combination explains why patients may have both ataxic features and pyramidal signs, together with peripheral sensory abnormalities.

6. Ataxia

Progressive ataxia is the central neurological feature.

Patients commonly first develop difficulty with:

Walking.

Running.

Balance.

Coordination.

The gait becomes broad-based and unsteady.

As the disorder progresses, the upper limbs may also become ataxic, interfering with writing, eating, and other fine motor tasks.

7. Cerebellar-Type Signs

Patients may demonstrate several signs commonly associated with cerebellar dysfunction.

These can include:

Gait ataxia.

Limb incoordination.

Dysmetria.

Dysarthria.

However, the ataxia in Friedreich disease is not due solely to primary cerebellar degeneration. Loss of proprioceptive information from the dorsal columns and peripheral sensory nerves contributes substantially.

Therefore, it is better regarded as a mixed sensory and spinocerebellar ataxia.

8. Loss of Proprioception

Damage to the dorsal columns and large sensory fibres leads to impaired:

Joint-position sense.

Vibration sensation.

This produces sensory ataxia in addition to the spinocerebellar component.

Patients may therefore become especially unstable when visual input is removed, and a positive Romberg sign can occur.

9. Peripheral Neuropathy

A peripheral sensory neuropathy is common.

Patients may develop:

Reduced vibration sensation.

Reduced proprioception.

Distal sensory impairment.

Absent or reduced tendon reflexes, particularly at the ankles and knees.

This peripheral neuropathy contributes significantly to the gait disturbance.

10. Pyramidal Tract Involvement

The corticospinal tracts may also be affected.

This can produce upper motor neurone features such as:

Extensor plantar responses.

Weakness.

Increased tone or spasticity in some patients.

This creates an important mixed neurological pattern because tendon reflexes may be reduced from peripheral neuropathy while Babinski responses remain extensor because of corticospinal tract disease.

11. Spastic Paraparesis

As the disease advances, weakness and corticospinal tract involvement may result in spastic paraparesis, meaning bilateral weakness of the legs with pyramidal tract involvement.

However, the neurological picture is often mixed rather than a pure spastic paraparesis because peripheral neuropathy and sensory pathway degeneration occur simultaneously.

12. Reflex Pattern

A characteristic examination combination may be:

Absent lower-limb tendon reflexes.

with

Extensor plantar responses.

At first this may seem contradictory.

It occurs because:

Peripheral nerve involvement → reduced tendon reflexes.

while

Corticospinal tract involvement → extensor plantar responses.

This mixed pattern is an important clue to Friedreich ataxia.

13. Pes Cavus

Pes cavus means an abnormally high arch of the foot.

It is common in Friedreich ataxia and develops in association with chronic neuromuscular imbalance.

Other foot deformities may also develop.

Therefore:

Young patient + progressive ataxia + pes cavus → consider Friedreich ataxia.

14. Kyphoscoliosis

Spinal deformity is common.

Patients may develop:

Scoliosis.

Kyphosis.

or

Kyphoscoliosis.

These deformities may become clinically important as the disease progresses and can contribute to impaired posture and respiratory mechanics.

15. High-Arched Palate

A high-arched palate has traditionally been described among the physical features of Friedreich ataxia.

It may form part of the skeletal phenotype but is much less diagnostically important than:

Progressive ataxia.

Pes cavus.

Scoliosis.

Neuropathy.

Cardiomyopathy.

16. Cardiomyopathy

Cardiac involvement is one of the most important non-neurological manifestations of Friedreich ataxia.

Cardiomyopathy is common and may significantly influence prognosis.

The classic cardiac abnormality is hypertrophic cardiomyopathy, although other patterns can occur.

Patients may develop:

Palpitations.

Dyspnoea.

Chest symptoms.

Arrhythmias.

Heart failure in advanced disease.

Regular cardiac assessment is therefore important.

17. Diabetes Mellitus

Friedreich ataxia is associated with abnormalities of glucose metabolism.

Some patients develop:

Impaired glucose tolerance.

or

Diabetes mellitus.

This is related partly to mitochondrial dysfunction involving pancreatic beta cells and insulin metabolism.

Therefore, metabolic monitoring forms part of long-term care.

18. Other Clinical Features

Other manifestations may include:

Dysarthria.

Nystagmus or abnormal eye movements.

Optic neuropathy in some patients.

Hearing impairment in some cases.

Muscle weakness and wasting as disease advances.

The exact phenotype and severity vary considerably between individuals.

19. Diagnosis

Diagnosis is primarily confirmed by genetic testing of the FXN gene, particularly testing for the characteristic GAA repeat expansion.

The clinical picture provides important clues, especially when a young patient has:

Progressive ataxia + sensory neuropathy + absent reflexes + extensor plantar responses + pes cavus/scoliosis + cardiomyopathy.

20. Investigations

Investigations may include:

Genetic testing → confirms FXN-related disease.

ECG and echocardiography → assess cardiac involvement.

Blood glucose or HbA1c → screen for diabetes.

Nerve-conduction studies → demonstrate sensory neuropathy.

MRI → may help exclude alternative neurological disorders and can show spinal cord changes.

21. Treatment

Management is multidisciplinary because Friedreich ataxia affects several organ systems.

Treatment may include:

Physiotherapy and rehabilitation.

Mobility and occupational support.

Management of scoliosis and foot deformities.

Cardiac surveillance and treatment.

Diabetes screening and treatment.

Speech and swallowing assessment when required.

Disease-modifying therapies have also emerged for selected patients in some jurisdictions, but supportive multidisciplinary care remains essential.

22. Friedreich Ataxia – Note Form

Type: hereditary progressive ataxia.

Inheritance: autosomal recessive.

Gene: FXN on chromosome 9.

Common genetic abnormality: GAA trinucleotide-repeat expansion.

Protein affected: frataxin.

Main mechanism: reduced frataxin → mitochondrial dysfunction and progressive neuronal/cardiac injury.

Typical onset: childhood or adolescence, often around the early teenage years.

Ataxia: progressive gait and limb incoordination.

Sensory involvement: loss of vibration and joint-position sense.

Peripheral neuropathy: commonly sensory, causing reduced or absent tendon reflexes.

Pyramidal involvement: extensor plantar responses ± spasticity and weakness.

Skeletal abnormalities: pes cavus, scoliosis/kyphoscoliosis and sometimes high-arched palate.

Cardiac involvement: cardiomyopathy, classically hypertrophic, with possible arrhythmias.

Metabolic association: impaired glucose tolerance and diabetes mellitus.

23. Characteristic Examination Pattern

A particularly useful neurological combination is:

Progressive ataxia.

Loss of proprioception and vibration sensation.

Absent lower-limb reflexes.

Extensor plantar responses.

Pes cavus.

This combination reflects simultaneous damage to:

Peripheral sensory nerves + dorsal columns + spinocerebellar tracts + corticospinal tracts.

Key Clinical Pattern

Think of Friedreich ataxia as:

Autosomal recessive FXN mutation on chromosome 9 → reduced frataxin → mitochondrial dysfunction.

The classic clinical picture is:

Young patient + progressive ataxia + peripheral sensory neuropathy + absent reflexes + extensor plantar responses + pes cavus/kyphoscoliosis + cardiomyopathy ± diabetes.

A particularly high-yield association is:

Friedreich ataxia → neurological disease + skeletal deformity + hypertrophic cardiomyopathy + diabetes mellitus.