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Neuronal intranuclear inclusion disease
Neuronal intranuclear inclusion disease (NIID) is a very rare multisystem neurodegenerative disorder characterized by the presence of eosinophilic intranuclear inclusions in neuronal and glial cells, and neuronal loss.
Infantile, juvenile, and adult-onset cases have been described in approximately 30 patients word-wide.
As any part of the nervous system can be affected (central, peripheral, and autonomic nervous systems), the clinical manifestations depend on the sites involved, and widely vary. The most common neurological signs include ataxia, extra-pyramidal signs (tremor and oculogyral crises), lower motor neuron findings (absent deep tendon reflexes, weakness, muscle wasting, foot deformities), and less apparent behavioural or cognitive difficulties. Dementia is reported as a predominant neurological symptom in adult patients, while infantile/juvenile cases show disproportionate ataxia and other movement symptoms. Occasionally, gastrointestinal dysmotility with severe weight loss may be present, if the enteric nervous system is involved.
NIID may be diagnosed by a full thickness rectal biopsy.
The differential diagnosis should consider spinocerebellar ataxias, progressive juvenile parkinsonism and dystonia.
Most cases are sporadic. Despite reports of several familial cases (including a pair of identical twins), no causative gene has been identified. Autosomal dominant transmission has been suggested in these families.
Management and treatment
There is no cure or treatment that slows the progression of the disease. Symptomatic treatments may improve the quality of life.
NIID is slowly progressive (within 10 to 20 years) and fatal.