Niemann-Pick disease type C

Abstract

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.

Figure 1

Age of onset of neurological disease vs lifespan. Study on 97 cases for whom appropriate clinical information was available from the cohort of 181 patients originating from French hospitals. Each horizontal bar depicts one patient. The green color indicates the period during which the patient did not present neurological symptoms, irrespective of the presence or absence of preexisting systemic disease. Patients who died in their first days or months of life from systemic disease (n = 19) are not shown on this graph.

Figure 2

Niemann-Pick disease type C as a neurovisceral disease. Schematic representation of the main forms of the disease, with particular emphasis on type and age of onset of first neurological symptoms

Figure 3

Laboratory diagnosis algorithm. Footnote: This algorithm is as proposed in Wraith et al. Mol Genet Metab 2009, 98:152-165 [27] *Sphingomyelinase deficiency (including late-onset type A) may give a dubious filipin pattern, with normal kinetics of LDL-induced cholesteryl ester formation ** False positive: I-cell disease (but very different clinical features) ***Heterozygotes may show a pattern (filipin staining and kinetics of LDL-induced cholesteryl ester formation) similar to that in "variant" patients ****In many countries, NPC1 p.P1007A or different missense mutations on codon 992 constitute the most frequent "variant" mutations Genetic studies can also be undertaken if clinical symptoms are very suggestive of a diagnosis of NP-C, even with negative results from filipin testing.

Figure 4

Age at diagnosis vs life span. Study in a cohort of 141 patients originating from French hospitals. Each horizontal bar depicts one patient. The change of color shows at which age the diagnosis was established. Median: 3.1 years; 0-9 months: 30%; < 2 years: 36%; < 5 years: 60%; > 16 years: 12%