It took 160 years but, in February 2023, the Food and Drug Administration approved the first drug specifically designed to treat the rare neuromuscular disease Friedreich ataxia (FA). The disease, first described in 1863 by German physician Nikolaus Friedreich, has an estimated incidence of 1 in 50,000 worldwide. It is the most common form of hereditary ataxia, accounting for approximately 50% of all cases of ataxia and approximately 75% of cases among patients younger than 25 years in the United States.1
FA typically presents in childhood or early adolescence; in some patients, symptoms manifest in the middle of the third decade of life. Patients exhibit symptoms such as ataxia that becomes worse over time, gait ataxia, impaired sensation in the extremities that can spread centrally, loss of normal reflexes, especially in the knees, speech disorders (dysarthria), muscle spasticity, scoliosis, and dysphagia.
Severity of disease ranges from relatively mild to completely disabling. Symptoms are progressive; patients almost inevitably require ambulatory support or a wheelchair. They might develop diabetes mellitus and can lose hearing and vision as the disease progresses. Hypertrophic cardiomyopathy is the most common cause of death among FA patients. Some patients who have less severe features might live into their 60s – even beyond that age.2There is no cure for FA. Until recently, no therapy was available other than supportive care to address associated neuromuscular, cardiovascular, and metabolic complications.
Making the diagnosis
Genetic testing can provide a definitive diagnosis of FA. (The genetic etiology of the disease is described later in this article.)
In addition to genetic screening, the workup includes a thorough medical history and physical examination that focuses on problems with balance, proprioception, absence of reflexes, and neurological signs. Tests include electromyography, nerve-conduction studies, electrocardiography, a metabolic profile, and MRI of the brain and spinal cord.
MRI utility in FA. In a paper published in July 2023 in Brain Communications, investigators from the University of Minnesota, Minneapolis, reported that various MRI techniques can be combined to detect early-stage alterations and disease progression in patients with FA.3 The researchers compared images taken at baseline and at 1, 2, and 3 years in 28 FA patients and 20 age- and gender-matched controls.
They observed that, compared with controls, patients with FA had lower cerebellar white matter volume but not lower cerebellar gray matter volume; larger cerebellar peduncle, thalamus, and brain stem structures; and a higher volume of the fourth ventricle. Using diffusion-tensor imaging and fixel-based analysis of diffusion MRI metrics, they also detected microstructural differences in several brain regions – especially in the cerebellum and corticospinal tract.
“Over time, many of these macrostructural and microstructural alterations progressed, especially cerebellar gray- and white-matter volume and microstructures of the superior cerebellar peduncle, the posterior limb of the internal capsule, and the superior corona radiata,” the investigators reported. In addition, “linear regressions showed significant associations between many of those imaging metrics and clinical scales.”
Pathophysiological basis of FA
The underlying genetic pathology of FA was first described in 1996 by investigators from the University of Valencia (Spain). They reported that FA is caused by a mutation in FXN (formerly X25), a gene that encodes for the protein frataxin, which is important for producing mitochondrial adenosine triphosphate and managing iron stores.4