Niemann-Pick C disease (NP-C) is a neurovisceral atypical lysosomal lipid storage disorder with an estimated minimal incidence of 1/120 000 live births. The broad clinical spectrum ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease. The neurological involvement defines the disease severity in most patients but is typically preceded by systemic signs (cholestatic jaundice in the neonatal period or isolated spleno- or hepatosplenomegaly in infancy or childhood). The first neurological symptoms vary with age of onset: delay in developmental motor milestones (early infantile period), gait problems, falls, clumsiness, cataplexy, school problems (late infantile and juvenile period), and ataxia not unfrequently following initial psychiatric disturbances (adult form). The most characteristic sign is vertical supranuclear gaze palsy. The neurological disorder consists mainly of cerebellar ataxia, dysarthria, dysphagia, and progressive dementia. Cataplexy, seizures and dystonia are other common features. NP-C is transmitted in an autosomal recessive manner and is caused by mutations of either the NPC1 (95% of families) or the NPC2 genes. The exact functions of the NPC1 and NPC2 proteins are still unclear. NP-C is currently described as a cellular cholesterol trafficking defect but in the brain, the prominently stored lipids are gangliosides. Clinical examination should include comprehensive neurological and ophthalmological evaluations. The primary laboratory diagnosis requires living skin fibroblasts to demonstrate accumulation of unesterified cholesterol in perinuclear vesicles (lysosomes) after staining with filipin. Pronounced abnormalities are observed in about 80% of the cases, mild to moderate alterations in the remainder ("variant" biochemical phenotype). Genotyping of patients is useful to confirm the diagnosis in the latter patients and essential for future prenatal diagnosis. The differential diagnosis may include other lipidoses; idiopathic neonatal hepatitis and other causes of cholestatic icterus should be considered in neonates, and conditions with cerebellar ataxia, dystonia, cataplexy and supranuclear gaze palsy in older children and adults. Symptomatic management of patients is crucial. A first product, miglustat, has been granted marketing authorization in Europe and several other countries for specific treatment of the neurological manifestations. The prognosis largely correlates with the age at onset of the neurological manifestations.

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Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral lipid storage with a wide spectrum of clinical phenotypes. At the cellular level, the disorder is characterized by accumulation of unesterified cholesterol and glycolipids in the lysosomal/late endosomal system. Approximatively 95% of patients have mutations in the NPC1 gene (mapped at 18q11) which encodes a large membrane glycoprotein primarily located to late endosomes. The remainder have mutations in the NPC2 gene (mapped at 14q24.3) which encodes a small soluble lysosomal protein with cholesterol-binding properties. The identical biochemical patterns observed in NPC1 and NPC2 mutants suggest that the two proteins function in a coordinate fashion. Identification of mutations revealed a complex picture of molecular heterogeneity, allowing genotype - phenotype correlations for both genes and providing insights into structure - function relationships for the NPC1 protein. Although a whole body of evidence suggests that the NPC1 and NPC2 proteins are involved in the cellular postlysosomal/late endosomal transport of cholesterol, glycolipids and other cargo, their precise functions and relationship remain unclear and are currently the subject of intense investigation. These studies, conducted in various models, should ultimately lead to a better understanding of the pathophysiology of NPC and new therapeutic approaches.

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Niemann-Pick disease type C.

Intracellular cholesterol transport

Niemann-Pick type C (NP-C) disease is a fatal, autosomal recessive, childhood neurodegenerative disease. The NP-C mouse recapitulates the cholesterol and sphingolipid storage, onset of neurological deficits, histopathological lesions, Purkinje cell loss and early death typical of the most severe form of human NP-C. Neurosteroids, steroids made in the brain, affect neuronal growth and differentiation, and modulate neurotransmitter receptors. Disordered cholesterol trafficking might disrupt neurosteroidogenesis, thereby contributing to the NP-C phenotype. Here we show that NP-C mouse brain contains substantially less neurosteroid than wild-type brain and has an age-related decrease in the ability to synthesize 5alpha-dihydroprogesterone and allopregnanolone. Immunohistochemical assessment confirms a decrease in expression of 5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase, especially in cerebellum. Neonatal administration of allopregnanolone delays the onset of neurological symptoms, increases Purkinje and granule cell survival, reduces cortical GM2 and GM3 ganglioside accumulation and doubles the lifespan of NP-C mice. Earlier administration increases effectiveness of treatment. Decreased production of allopregnanolone apparently contributes to the pathology of NP-C; thus, neurosteroid treatment may be useful in ameliorating progression of the disease.

Niemann-Pick type C disease involves disrupted neurosteroidogenesis and responds to allopregnanolone.

Niemann-Pick disease type C (NPC) is a fatal neurovisceral lipid storage disease of autosomal inheritance resulting from mutations in either the NPC1 (95% of families) or NPC2 gene. The encoded proteins appear to be involved in lysosomal/late endosomal transport of cholesterol, glycolipids and other molecules but their exact function is still unknown. The clinical spectrum of the disease ranges from a neonatal rapidly fatal disorder to an adult-onset chronic neurodegenerative disease. Based upon a comprehensive study of 13 unrelated adult patients diagnosed in France over the past 20 years as well as the analysis of the 55 other cases published since 1969, we have attempted to delineate the major clinical, radiological, biochemical and genotypic characteristics of adult NPC. Overall, mean age at onset (+/-SD) of neuropsychiatric symptoms was 25 +/- 9.7 years. The diagnosis of NPC was established after a mean delay of 6.2 +/- 6.4 years and the mean age at death (calculated from 20 cases) was 38 +/- 10.2 years. Major clinical features included cerebellar ataxia (76%), vertical supranuclear ophthalmoplegia (VSO, 75%), dysarthria, (63%), cognitive troubles (61%), movement disorders (58%), splenomegaly (54%), psychiatric disorders (45%) and dysphagia (37%). Less frequent signs were epilepsy and cataplexy. During the course of the disease, clinical features could be subdivided into (i) visceral signs (hepatomegaly or splenomegaly), (ii) cortical signs (psychiatric cognitive disorders and epilepsy); and (iii) deep brain signs (VSO, ataxia, movement disorders, dysarthria, dysphagia, cataplexy) which exhibited different evolution patterns. Asymptomatic and non-evolutive visceral signs were often noticed since early childhood (38.5% of our patients), followed by mild cortical signs in childhood (learning difficulties) and early adulthood (62% of cases among which 38% were psychiatric disorders). Deep brain signs were observed in 96% of patients and were usually responsible for death. In general, there was a good correlation between clinical signs and the localization of brain atrophy on MRI. The 'variant' biochemical phenotype characterized by mild abnormalities of the cellular trafficking of endocytosed cholesterol was over-represented in the adult form of NPC and seemed associated with less frequent splenomegaly in childhood and lesser psychiatric signs. Involvement of the NPC1 gene was shown in 33 families and of the NPC2 gene in one. Improving the knowledge of the disease among psychiatrists and neurologists appears essential since emerging treatments should be more efficient at the visceral or cognitive/psychiatric stages of the disease, before the occurrence of widespread deep brain neurological lesions.

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The adult form of Niemann-Pick disease type C.

Analysis of the neurologic symptomatology in 22 patients with Niemann-Pick disease type C revealed 3 phenotypes: (1) an early-onset, rapidly progressive form associated with severe hepatic dysfunction and psychomotor delay during infancy and later with supranuclear vertical gaze paresis, ataxia, marked spasticity, and dementia; (2) a delayed-onset, slowly progressive form heralded by the appearance, usually in early childhood, of mild intellectual impairment, supranuclear vertical gaze paresis, and ataxia, and later associated with dementia and, variably, seizures and extrapyramidal deficits; (3) a late-onset slowly progressive form distinguished from the 2nd pattern by later age of onset (adolescence or adulthood) and a much slower rate of progression. The existence of the 1st and 2nd phenotypes within the same sibship suggests that they are variant expressions of the same clinicopathologic disorder. Niemann-Pick disease type C should be considered not only in infants and children who present with organomegaly and a progressive neurodegenerative course, but also in adolescents and adults who have insidiously progressive neurologic dysfunction and only slight organomegaly. Associated with the disease is a marked deficiency in the ability of cultured fibroblasts to esterify exogenously supplied cholesterol. Assay of this deficiency is particularly useful for confirming the diagnosis in patients with atypical presentation.

D. G. Cogan

Papers

Clinical spectrum of Niemann‐Pick disease type C