No abstract

Niemann-Pick Type C (NPC) is a progressive and life limiting autosomal recessive disorder caused by mutations in either the NPC1 or NPC2 gene. Mutations in these genes are associated with abnormal endosomal-lysosomal trafficking, resulting in the accumulation of multiple tissue specific lipids in the lysosomes. The clinical spectrum of NPC disease ranges from a neonatal rapidly progressive fatal disorder to an adult-onset chronic neurodegenerative disease. The age of onset of the first (beyond 3 months of life) neurological symptom may predict the severity of the disease and determines life expectancy.NPC has an estimated incidence of ~ 1: 100,000 and the rarity of the disease translate into misdiagnosis, delayed diagnosis and barriers to good care. For these reasons, we have developed clinical guidelines that define standard of care for NPC patients, foster shared care arrangements between expert centres and family physicians, and empower patients. The information contained in these guidelines was obtained through a systematic review of the literature and the experiences of the authors in their care of patients with NPC. We adopted the Appraisal of Guidelines for Research & Evaluation (AGREE II) system as method of choice for the guideline development process. We made a series of conclusive statements and scored them according to level of evidence, strengths of recommendations and expert opinions. These guidelines can inform care providers, care funders, patients and their carers of best practice of care for patients with NPC. In addition, these guidelines have identified gaps in the knowledge that must be filled by future research. It is anticipated that the implementation of these guidelines will lead to a step change in the quality of care for patients with NPC irrespective of their geographical location.

In various mammals, enzymatically active and inactive members of family 18 glycosyl hydrolases, containing chitinases, have been identified. In man, chitotriosidase is the functional chitinolytic enzyme, whilst the homologous human cartilage 39-kDa glycoprotein (HC gp-39) does not exhibit chitinase activity and its function is unknown. This study establishes that HC gp-39 is a chitin-specific lectin. It is experimentally demonstrated that a single amino acid substitution in the catalytic centre of the 39-kDa isoform of chitotriosidase, which generates a similar sequence to that in HC gp-39, results in a loss of hydrolytic activity and creates the capacity to bind to chitin. The possible implication of the finding for chitinolytic and chitin-binding proteins that are produced in high quantities by activated macrophages are discussed.

Bilirubin, a breakdown product of heme, is normally glucuronidated and excreted by the liver into bile. Failure of this system can lead to a buildup of conjugated bilirubin in the blood, resulting in jaundice. The mechanistic basis of bilirubin excretion and hyperbilirubinemia syndromes is largely understood, but that of Rotor syndrome, an autosomal recessive disorder characterized by conjugated hyperbilirubinemia, coproporphyrinuria, and near-absent hepatic uptake of anionic diagnostics, has remained enigmatic. Here, we analyzed 8 Rotorsyndrome families and found that Rotor syndrome was linked to mutations predicted to cause complete and simultaneous deficiencies of the organic anion transporting polypeptides OATP1B1 and OATP1B3. These important detoxification-limiting proteins mediate uptake and clearance of countless drugs and drug conjugates across the sinusoidal hepatocyte membrane. OATP1B1 polymorphisms have previously been linked to drug hypersensitivities. Using mice deficient in Oatp1a/1b and in the multispecific sinusoidal export pump Abcc3, we found that Abcc3 secretes bilirubin conjugates into the blood, while Oatp1a/1b transporters mediate their hepatic reuptake. Transgenic expression of human OATP1B1 or OATP1B3 restored the function of this detoxification-enhancing liver-blood shuttle in Oatp1a/1b-deficient mice. Within liver lobules, this shuttle may allow flexible transfer of bilirubin conjugates (and probably also drug conjugates) formed in upstream hepatocytes to downstream hepatocytes, thereby preventing local saturation of further detoxification processes and hepatocyte toxic injury. Thus, disruption of hepatic reuptake of bilirubin glucuronide due to coexisting OATP1B1 and OATP1B3 deficiencies explains Rotor-type hyperbilirubinemia. Moreover, OATP1B1 and OATP1B3 null mutations may confer substantial drug toxicity risks.

Severe progressive neurological paediatric disease mucopolysaccharidosis III type C is caused by mutations in the HGSNAT gene leading to deficiency of acetyl-CoA: α-glucosaminide N-acetyltransferase involved in the lysosomal catabolism of heparan sulphate. To understand the pathophysiology of the disease we generated a mouse model of mucopolysaccharidosis III type C by germline inactivation of the Hgsnat gene. At 6-8 months mice showed hyperactivity, and reduced anxiety. Cognitive memory decline was detected at 10 months and at 12-13 months mice showed signs of unbalanced hesitant walk and urinary retention. Lysosomal accumulation of heparan sulphate was observed in hepatocytes, splenic sinus endothelium, cerebral microglia, liver Kupffer cells, fibroblasts and pericytes. Starting from 5 months, brain neurons showed enlarged, structurally abnormal mitochondria, impaired mitochondrial energy metabolism, and storage of densely packed autofluorescent material, gangliosides, lysozyme, phosphorylated tau, and amyloid-β. Taken together, our data demonstrate for the first time that deficiency of acetyl-CoA: α-glucosaminide N-acetyltransferase causes lysosomal accumulation of heparan sulphate in microglial cells followed by their activation and cytokine release. They also show mitochondrial dysfunction in the neurons and neuronal loss explaining why mucopolysaccharidosis III type C manifests primarily as a neurodegenerative disease.