Part of the causal chain leading to Alzheimer's disease. Although the brain and spinal cord are surrounded by tough membranes, enclosed in the bones of the skull and spinal vertebrae, and chemically isolated by the blood–brain barrier, they are very susceptible if compromised. Nerves tend to lie deep under the skin but can still become exposed to damage. Individual neurons, the neural circuits, and nerves into which they form are susceptible to electrochemical and structural disruption. Neuroregeneration may occur in the peripheral nervous system and thus overcome or work around injuries to some extents, but it is thought to be rare in the brain and spinal cord. The specific causes of<unk>  problems vary, but can include genetic<unk> s, congenital abnormalities or<unk> s, infections, lifestyle or environmental health problems including malnutrition, brain damage, spinal cord injury, nerve injury or gluten sensitivity (with or without intestinal damage or digestive symptoms). Metal poisoning, where metals accumulate in the human body and disrupt biological processes, has been reported to induce<unk>  problems, at least in the case of lead. The<unk>  problem may start in another body system that interacts with the nervous system. For example, cerebrovascular disease involves brain injury due to problems with the blood vessels (cardiovascular system) supplying the brain; autoimmune<unk> s involve damage caused by the body's own immune system; lysosomal storage diseases such as Niemann–Pick disease can lead to<unk>  deterioration. The National Institute for Health and Care Excellence recommends considering the evaluation of an underlying coeliac disease in people with unexplained<unk>  symptoms, particularly peripheral neuropathy or ataxia. In a substantial minority of cases of<unk>  symptoms, no neural cause can be identified using current testing procedures, and such "idiopathic" conditions can invite different theories about what is occurring. Generally speaking, a substantial number of<unk> s may have originated from a previous clinically not recognized viral infection. For example it is thought that infection with the Hepatitis E virus, which is often initially asymptomatic may provoke<unk> s, but there are many other examples as well. Numerous examples have been described of<unk> s that are associated with mutated DNA repair genes (for reviews see). Inadequate repair of DNA damages can lead directly to cell death and neuron depletion as well as disruptions in the pattern of epigenetic alterations required for normal neuronal function.
Neurological disorder
Central nervous system disease
Brain damage
Endocrine disease
Musculoskeletal abnormality
Neuromuscular disease
Hematologic disease
Disease