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In 1975, Myklebust proposed a special form of learning disabilities characterizes by impairment of spatial cognition, social interaction and conceptualization, and named it as non-verbal learning disabilities (NLD). Since the brain locus for spatial cognition was thought to be localized in the right hemisphere, NLD was regarded as a disorder of the right hemispheric function. The clinical characteristics of NLD are almost identical to those of Asperger syndrome (AS), which was introduced in English literature in 1981. Since Asperger syndrome is regarded as one of the autistic spectrum disorders, and autism was once regarded as the left hemispheric dysfunction, it has long been believed that NLD and AS are clinically different entities. However, their clinical similarities have raised a growing opinion that these two disorders are probably identical or at least closely related.

Among many metabolic disorders, porphyrias and Fabry disease are known to affect autonomic nervous system. In patients with acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria, autonomic symptoms such as abdominal pain, vomiting, hypertension and tachycardia are among the most prominent clinical manifestations. Fabry disease is clinically characterized by severe limb pain, hypohidrosis, angiokeratomas and various autonomic symptoms. In both porphyrias and Fabry disease, pathological changes in the central and peripheral autonomic nervous system have been documented. In porphyrias, a loss of myelinated fibers, axonal degeneration, and segmental demyelination in peripheral autonomic nerves as well as chromatolysis of several brain stem nuclei have been found. In Fabry disease, abnormal amount of the substrates of alpha-galactosidase, i.e. ceramide di- and trihexoside, are found to be accumulated in the central and peripheral autonomic nerves.