Extracerebral biopsies in neurodegenerative diseases of childhood

Among the numerous neurodegenerative diseases in children few may allow morphological diagnosis by extracerebral biopsy. These encompass neurometabolic conditions, foremost lysosomal disorders, but also peroxisomal and mitochondrial diseases marked by disease- or group-specific organelles. Largely, these neurometabolic conditions can also be diagnosed by biochemical and increasingly by molecular genetic techniques. However, there are a few neurodegenerative diseases which do not allow either biochemical or molecular genetic diagnosis and, thus, rely on biopsy of extracerebral tissues, so-called 'essential' biopsies to achieve a diagnosis during the patient's life. Among these few disorders only Lafora disease, as other polyglucosan disorders, may be considered a neurometabolic disease, whereas in the others, neuroaxonal dystrophies, giant axonal neuropathy and neuronal intranuclear inclusion disease no metabolic abnormalities are known, but these disorders share the peripheral nervous system as a common site of their disease-specific morphological lesions. With the progress of molecular genetics and the fact that many neurodegenerative diseases are familial, it is expected that the number of neurodegenerative disorders and the number of patients afflicted with these diseases, currently subject to diagnostic extracerebral biopsies, will be continuously reduced. Thus, it is foreseeable that within the next few years or decades diagnostic electron microscopy and the related knowledge of respective ultrastructural pathology may become outmoded, and, possibly, unknown to future generations of neuropathologists and other members of the neuroscience community.