[Diagnosis: not more than an agreement on disease entity]

Once a hereditary disorder has been linked to a gene mutation, it is not uncommon to observe that patients with the mutation have a wider range of clinical features than was previously anticipated. This is the case with Friedreich's syndrome, of which the characteristic signs used to be progressive cerebellar ataxia and areflexia, with onset at an early age. Now that the causative mutation has been established, it also appears to be expressed as an 'atypical' disease, with a later onset, piramidal signs at an early stage, and retained tendon jerks. Diseases are defined according to a variety of criteria: cause, (patho)morphological findings, (patho)physiological changes observed by physicians, or subjective impressions by patients. The growth of biomedical knowledge often leads to diseases being redefined. Diseases are not independent entities but human constructions.