Clinical features of Niemann-Pick disease type C. An example of the delayed onset, slowly progressive phenotype and an overview of recent literature

Diagnostic and treatment implications of psychosis secondary to treatable metabolic disorders in adults: a systematic review

Objective

It is important for psychiatrists to be aware of certain inborn errors of metabolism (IEMs) as these rare disorders can present as psychosis, and because definitive treatments may be available for treating the underlying metabolic cause. A systematic review was conducted to examine IEMs that often present with schizophrenia-like symptoms.

Data sources

Published literature on MEDLINE was assessed regarding diseases of homocysteine metabolism (DHM; cystathionine beta-synthase deficiency [CbS-D] and homocysteinemia due to methyltetrahydrofolate reductase deficiency [MTHFR-D]), urea cycle disorders (UCD), acute porphyria (POR), Wilson disease (WD), cerebrotendinous-xanthomatosis (CTX) and Niemann-Pick disease type C (NP-C).

Study selection

Case reports, case series or reviews with original data regarding psychiatric manifestations and cognitive impairment published between January 1967 and June 2012 were included based on a standardized four-step selection process.

Data extraction

All selected articles were evaluated for descriptions of psychiatric signs (type, severity, natural history and treatment) in addition to key disease features.

Results

A total of 611 records were identified. Information from CbS-D (n = 2), MTHFR-D (n = 3), UCD (n = 8), POR (n = 12), WD (n = 11), CTX (n = 14) and NP-C publications (n = 9) were evaluated. Six non-systematic literature review publications were also included. In general, published reports did not provide explicit descriptions of psychiatric symptoms. The literature search findings are presented with a didactic perspective, showing key features for each disease and psychiatric signs that should trigger psychiatrists to suspect that psychotic symptoms may be secondary to an IEM.

Conclusion

IEMs with a psychiatric presentation and a lack of, or sub-clinical, neurological signs are rare, but should be considered in patients with atypical psychiatric symptoms.

Sterol, protein and lipid trafficking in Chinese hamster ovary cells with Niemann-Pick type C1 defect

We studied the trafficking of sterols, lipids and proteins in Niemann-Pick type C (NPC) cells. The NPC is an inherited disorder involving the accumulation of sterol and lipids in modified late-endosome/lysosome-like storage organelles. Most sterol accumulation studies in NPC cells have been carried out using low-density lipoprotein (LDL) as the sterol source, and it has been shown that sterol efflux from late endosomes is impaired in NPC cells. In this study, we used a fluorescent sterol analog, dehydroergosterol, which can be quickly and efficiently delivered to the plasma membrane. Thus, we were able to study the trafficking kinetics of the non-LDL-derived sterol pool, and we found that dehydroergosterol accumulates in the storage organelles over the course of several hours in NPC cells. We also found that dialkylindocarbocyanine lipid-mimetic analogs that recycle efficiently from early endosomes in wild-type cells are targeted to late endosomal organelles in NPC cells, and transferrin receptors recycle slowly and inefficiently in NPC cells. These data are consistent with multiple trafficking defects in both early and late endosomes in NPC cells.

Recent advances in elucidating Niemann-Pick C disease

Lysosomal sequestration of endocytosed LDL-derived cholesterol, premature and abnormal enrichment of cholesterol in trans Golgi cisternae and accompanying anomalies in intracellular sterol trafficking are the hallmark phenotypic features of the Niemann-Pick C (NPC) lesion. A variable severity of these alterations has been observed, with only partial correlation between clinical and biochemical phenotypes. NPC also affects the metabolism of sphingolipids, and other biochemical abnormalities have been reported. Occurrence of neurofibrillary tangles in the brain of patients with a slowly progressive course is a recent intriguing observation. Genetic heterogeneity was established by cell hybridization and linkage studies. The two complementation groups could not be distinguished from each other by clinical, cellular or biochemical criteria, suggesting that the two gene products may interact or function sequentially. The major (> 90% of patients) NPC1 gene was mapped to 18q11 and recently isolated by positional cloning. The cDNA sequence predicts a 1278-amino acid protein, with 13 to 16 possible transmembrane regions and a putative cholesterol-sensing domain. Two murine models of the disease involving the same gene are known. The murine cDNA and the npc(nih) mutation have been characterized. Described homologies of the NPC1 protein are in line with its putative involvement in cellular cholesterol traffic.

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.

Cerebral palsy and neurodegenerative disease

Cerebral palsy refers to a neurologic disorder of motor skills that is static in nature and is the result of injury to the brain before its development is complete. Many neurodegenerative or metabolic disorders have a slow rate of progression and can be misdiagnosed as cerebral palsy. Diseases that have been misdiagnosed as cerebral palsy are presented here to provide the clinician with framework for the complex evaluation of these patients.