Cerebrotendinous xanthomatosis

Genetics of familial hypercholesterolemia

Familial hypercholesterolemia (FH) is a genetic disorder characterized by elevated low-density lipoprotein (LDL) cholesterol and premature cardiovascular disease, with a prevalence of approximately 1 in 200-500 for heterozygotes in North America and Europe. Monogenic FH is largely attributed to mutations in the LDLR, APOB, and PCSK9 genes. Differential diagnosis is critical to distinguish FH from conditions with phenotypically similar presentations to ensure appropriate therapeutic management and genetic counseling. Accurate diagnosis requires careful phenotyping based on clinical and biochemical presentation, validated by genetic testing. Recent investigations to discover additional genetic loci associated with extreme hypercholesterolemia using known FH families and population studies have met with limited success. Here, we provide a brief overview of the genetic determinants, differential diagnosis, genetic testing, and counseling of FH genetics.

An adult male with progressive spastic paraparesis and gait instability

This is a case of an adult male with history of motor difficulties, speech, and behavioral problems since early childhood found to have progressive spastic paraparesis, impaired vibration and proprioception, and gait instability. His medical history included bilateral cataracts status post surgical removal at the age of 30, cholelithiasis status post cholecystectomy at age 45, and high cholesterol levels.

Marketed Drugs Can Inhibit Cytochrome P450 27A1, a Potential New Target for Breast Cancer Adjuvant Therapy

Cytochrome P450 CYP27A1 is the only enzyme in humans converting cholesterol to 27-hydroxycholesterol, an oxysterol of multiple functions, including tissue-specific modulation of estrogen and liver X receptors. Both receptors seem to mediate adverse effects of 27-hydroxycholesterol in breast cancer when the levels of this oxysterol are elevated. The present work assessed druggability of CYP27A1 as a potential antibreast cancer target. We selected 26 anticancer and noncancer medications, most approved by the Food and Drug Administration, and evaluated them first in vitro for inhibition of purified recombinant CYP27A1 and binding to the enzyme active site. Six strong CYP27A1 inhibitors/binders were identified. These were the two antibreast cancer pharmaceuticals anastrozole and fadrozole, antiprostate cancer drug bicalutamide, sedative dexmedetomidine, and two antifungals ravuconazole and posaconazole. Anastrozole was then tested in vivo on mice, which received subcutaneous drug injections for 1 week. Mouse plasma and hepatic 27-hydroxycholesterol levels were decreased 2.6- and 1.6-fold, respectively, whereas plasma and hepatic cholesterol content remained unchanged. Thus, pharmacologic CYP27A1 inhibition is possible in the whole body and individual organs, but does not negatively affect cholesterol elimination. Our results enhance the potential of CYP27A1 as an antibreast cancer target, could be of importance for the interpretation of Femara versus Anastrozole Clinical Evaluation Trial, and bring attention to posaconazole as a potential complementary anti-breast cancer medication. More medications on the US market may have unanticipated off-target inhibition of CYP27A1, and we propose strategies for their identification.

Mitochondrial function and regulation of macrophage sterol metabolism and inflammatory responses

The aim of this review is to explore the role of mitochondria in regulating macrophage sterol homeostasis and inflammatory responses within the aetiology of atherosclerosis. Macrophage generation of oxysterol activators of liver X receptors (LXRs), via sterol 27-hydroxylase, is regulated by the rate of flux of cholesterol to the inner mitochondrial membrane, via a complex of cholesterol trafficking proteins. Oxysterols are key signalling molecules, regulating the transcriptional activity of LXRs which coordinate macrophage sterol metabolism and cytokine production, key features influencing the impact of these cells within atherosclerotic lesions. The precise identity of the complex of proteins mediating mitochondrial cholesterol trafficking in macrophages remains a matter of debate, but may include steroidogenic acute regulatory protein and translocator protein. There is clear evidence that targeting either of these proteins enhances removal of cholesterol via LXRα-dependent induction of ATP binding cassette transporters (ABCA1, ABCG1) and limits the production of inflammatory cytokines; interventions which influence mitochondrial structure and bioenergetics also impact on removal of cholesterol from macrophages. Thus, molecules which can sustain or improve mitochondrial structure, the function of the electron transport chain, or increase the activity of components of the protein complex involved in cholesterol transfer, may therefore have utility in limiting or regressing atheroma development, reducing the incidence of coronary heart disease and myocardial infarction.

Bile acids and sphingosine-1-phosphate receptor 2 in hepatic lipid metabolism

The liver is the central organ involved in lipid metabolism. Dyslipidemia and its related disorders, including non-alcoholic fatty liver disease (NAFLD), obesity and other metabolic diseases, are of increasing public health concern due to their increasing prevalence in the population. Besides their well-characterized functions in cholesterol homoeostasis and nutrient absorption, bile acids are also important metabolic regulators and function as signaling hormones by activating specific nuclear receptors, G-protein coupled receptors, and multiple signaling pathways. Recent studies identified a new signaling pathway by which conjugated bile acids (CBA) activate the extracellular regulated protein kinases (ERK1/2) and protein kinase B (AKT) signaling pathway via sphingosine-1-phosphate receptor 2 (S1PR2). CBA-induced activation of S1PR2 is a key regulator of sphingosine kinase 2 (SphK2) and hepatic gene expression. This review focuses on recent findings related to the role of bile acids/S1PR2-mediated signaling pathways in regulating hepatic lipid metabolism.

Guo G. Farnesoid X receptor, the bile acid sensing nuclear receptor, in liver regeneration

The liver is unique in regenerative potential, which could recover the lost mass and function after injury from ischemia and resection. The underlying molecular mechanisms of liver regeneration have been extensively studied in the past using the partial hepatectomy (PH) model in rodents, where 2/3 PH is carried out by removing two lobes. The whole process of liver regeneration is complicated, orchestrated event involving a network of connected interactions, which still remain fully elusive. Bile acids (BAs) are ligands of farnesoid X receptor (FXR), a nuclear receptor of ligand-activated transcription factor. FXR has been shown to be highly involved in liver regeneration. BAs and FXR not only interact with each other but also regulate various downstream targets independently during liver regeneration. Moreover, recent findings suggest that tissue-specific FXR also contributes to liver regeneration significantly. These novel findings suggest that FXR has much broader role than regulating BA, cholesterol, lipid and glucose metabolism. Therefore, these researches highlight FXR as an important pharmaceutical target for potential use of FXR ligands to regulate liver regeneration in clinic. This review focuses on the roles of BAs and FXR in liver regeneration and the current underlying molecular mechanisms which contribute to liver regeneration.

Effects of 5α-cholestan-3-one on the synaptic vesicle cycle at the mouse neuromuscular junction

We have investigated the effects of 5α-cholesten-3-one (5Ch3, 200 nM) on synaptic transmission in mouse diaphragm. 5Ch3 had no impact on the amplitude or frequency of miniature endplate currents (MEPCs, spontaneous secretion), but decreased the amplitude of EPCs (evoked secretion) triggered by single action potentials. Treatment with 5Ch3 increased the depression of EPC amplitude and slowed the unloading of the dye FM1-43 from synaptic vesicles (exocytosis rate) during high-frequency stimulation. The estimated recycling time of vesicles did not change, suggesting that the decline of synaptic efficiency was due to the reduction in the size of the population of vesicles involved in release. The effects of 5Ch3 on synaptic transmission may be related to changes in the phase properties of the membrane. We have found that 5Ch3 reduces the staining of synaptic regions with the B-subunit of cholera toxin (a marker of lipid rafts) and increases the fluorescence of 22-NBD-cholesterol, indicating a phase change within the membrane. Manipulations of membrane cholesterol (saturation or depletion) strongly reduced the influence of 5Ch3 on both FM1-43 dye unloading and staining with the B-subunit of cholera toxin. Thus, 5Ch3 reduces the number of vesicles which are actively recruited during synaptic transmission and alters membrane properties. These effects of 5Ch3 depend on membrane cholesterol.

The Associations of Novel Vitamin D3 Metabolic Gene CYP27A1 Polymorphism, Adiponectin/Leptin Ratio, and Metabolic Syndrome in Middle-Aged Taiwanese Males

Metabolic syndrome (MetS) confers increased risks of cardiovascular disease (CVD). Both vitamin D3 and adipocytokines (especially adiponectin and leptin) have a great impact on CVD and MetS. In vitamin D3 metabolism, the vitamin D3 25-hydroxylase (CYP27A1) and 25-hydroxyvitamin D3 1-alpha-hydroxylase (CYP27B1) are two key enzymes. This study aimed to examine the influence of vitamin D3 CYP27 single nucleotide polymorphisms (SNPs) on adipocytokines and MetS. Cross-sectional data and DNA samples were collected from male volunteers (n = 649, age: 55.7 ± 4.7 years). Two tagging SNPs, CYP27A1 rs4674344 and CYP27B1 rs10877012, were selected from the HapMap project. MetS was significantly associated with the CYP27A1 rs4674344 SNP (P = 0.04) and the ratio of adiponectin/leptin (A/L ratio) was most correlated to the CYP27A1 rs4674344 SNP, appearing to be significantly lower in T-carriers than in AA subjects (3.7 ± 4.0 versus 5.1 ± 6.0, P = 0.001) and significantly negatively associated after adjustment. For each MetS component associated with the CYP27A1 rs4674344 SNP, the A/L ratios were significantly negative in preclinical stage (condition not meeting the individual criteria), except the blood pressure. In conclusion, CYP27A1 rs4674344 SNP, A/L ratio, and MetS are significantly associated and T-carriers might have a higher risk of developing MetS due to low A/L ratios in the preclinical stage.

Cerebrotendinous xanthomatosis: a comprehensive review of pathogenesis, clinical manifestations, diagnosis, and management

Cerebrotendinous xanthomatosis (CTX) OMIM#213700 is a rare autosomal-recessive lipid storage disease caused by mutations in the CYP27A1 gene; this gene codes for the mitochondrial enzyme sterol 27-hydroxylase, which is involved in bile acid synthesis. The CYP27A1 gene is located on chromosome 2q33-qter and contains nine exons. A CYP27A1 mutation leads to decreased synthesis of bile acid, excess production of cholestanol, and consequent accumulation of cholestanol in tissues. Currently there is no consensus on the prevalence of CTX, one estimate being <5/100,000 worldwide. The prevalence of CTX due to the CYP27A1 mutation R362C alone is approximately 1/50,000 in Caucasians. Patients with CTX have an average age of 35 years at the time of diagnosis and a diagnostic delay of 16 years. Clinical signs and symptoms include adult-onset progressive neurological dysfunction (i.e., ataxia, dystonia, dementia, epilepsy, psychiatric disorders,peripheral neuropathy, and myopathy) and premature non-neurologic manifestations (i.e., tendon xanthomas, childhood-onset cataracts, infantile-onset diarrhea, premature atherosclerosis, osteoporosis, and respiratory insufficiency). Juvenile cataracts, progressive neurologic dysfunction, and mild pulmonary insufficiency are unique symptoms that distinguish CTX from other lipid storage disorders including familial dysbetalipoproteinemia, homozygous familial hypercholesterolemia, and sitosterolemia, all of which might also present with xanthomas and cardiovascular diseases. Brain magnetic resonance imaging (MRI) shows bilateral lesions in the dentate nucleus of the cerebellum and mild white matter lesions. The classical symptoms and signs, namely elevated levels of cholestanol and bile alcohols in serum and urine, brain MRI, and the mutation in the CYP27A1 gene confirm the diagnosis of CTX. Early diagnosis and long-term treatment with chenodeoxycholic acid (750 mg/d) improve neurological symptoms and contribute to a better prognosis.

Cholestenoic acids regulate motor neuron survival via liver X receptors

Cholestenoic acids are formed as intermediates in metabolism of cholesterol to bile acids, and the biosynthetic enzymes that generate cholestenoic acids are expressed in the mammalian CNS. Here, we evaluated the cholestenoic acid profile of mammalian cerebrospinal fluid (CSF) and determined that specific cholestenoic acids activate the liver X receptors (LXRs), enhance islet-1 expression in zebrafish, and increase the number of oculomotor neurons in the developing mouse in vitro and in vivo. While 3β,7α-dihydroxycholest-5-en-26-oic acid (3β,7α-diHCA) promoted motor neuron survival in an LXR-dependent manner, 3β-hydroxy-7-oxocholest-5-en-26-oic acid (3βH,7O-CA) promoted maturation of precursors into islet-1+ cells. Unlike 3β,7α-diHCA and 3βH,7O-CA, 3β-hydroxycholest-5-en-26-oic acid (3β-HCA) caused motor neuron cell loss in mice. Mutations in CYP7B1 or CYP27A1, which encode enzymes involved in cholestenoic acid metabolism, result in different neurological diseases, hereditary spastic paresis type 5 (SPG5) and cerebrotendinous xanthomatosis (CTX), respectively. SPG5 is characterized by spastic paresis, and similar symptoms may occur in CTX. Analysis of CSF and plasma from patients with SPG5 revealed an excess of the toxic LXR ligand, 3β-HCA, while patients with CTX and SPG5 exhibited low levels of the survival-promoting LXR ligand 3β,7α-diHCA. Moreover, 3β,7α-diHCA prevented the loss of motor neurons induced by 3β-HCA in the developing mouse midbrain in vivo.Our results indicate that specific cholestenoic acids selectively work on motor neurons, via LXR, to regulate the balance between survival and death.

Homozygous familial hypercholesterolaemia: new insights and guidance for clinicians to improve detection and clinical management. A position paper from the Consensus Panel on Familial Hypercholesterolaemia of the European Atherosclerosis Society

AIMS

Homozygous familial hypercholesterolaemia (HoFH) is a rare life-threatening condition characterized by markedly elevated circulating levels of low-density lipoprotein cholesterol (LDL-C) and accelerated, premature atherosclerotic cardiovascular disease (ACVD). Given recent insights into the heterogeneity of genetic defects and clinical phenotype of HoFH, and the availability of new therapeutic options, this Consensus Panel on Familial Hypercholesterolaemia of the European Atherosclerosis Society (EAS) critically reviewed available data with the aim of providing clinical guidance for the recognition and management of HoFH.

METHODS AND RESULTS

Early diagnosis of HoFH and prompt initiation of diet and lipid-lowering therapy are critical. Genetic testing may provide a definitive diagnosis, but if unavailable, markedly elevated LDL-C levels together with cutaneous or tendon xanthomas before 10 years, or untreated elevated LDL-C levels consistent with heterozygous FH in both parents, are suggestive of HoFH. We recommend that patients with suspected HoFH are promptly referred to specialist centres for a comprehensive ACVD evaluation and clinical management. Lifestyle intervention and maximal statin therapy are the mainstays of treatment, ideally started in the first year of life or at an initial diagnosis, often with ezetimibe and other lipid-modifying therapy. As patients rarely achieve LDL-C targets, adjunctive lipoprotein apheresis is recommended where available, preferably started by age 5 and no later than 8 years. The number of therapeutic approaches has increased following approval of lomitapide and mipomersen for HoFH. Given the severity of ACVD, we recommend regular follow-up, including Doppler echocardiographic evaluation of the heart and aorta annually, stress testing and, if available, computed tomography coronary angiography every 5 years, or less if deemed necessary.

CONCLUSION

This EAS Consensus Panel highlights the need for early identification of HoFH patients, prompt referral to specialized centres, and early initiation of appropriate treatment. These recommendations offer guidance for a wide spectrum of clinicians who are often the first to identify patients with suspected HoFH.

Bile acids are nutrient signaling hormones

Bile salts play crucial roles in allowing the gastrointestinal system to digest, transport and metabolize nutrients. They function as nutrient signaling hormones by activating specific nuclear receptors (FXR, PXR, Vitamin D) and G-protein coupled receptors [TGR5, sphingosine-1 phosphate receptor 2 (S1PR2), muscarinic receptors]. Bile acids and insulin appear to collaborate in regulating the metabolism of nutrients in the liver. They both activate the AKT and ERK1/2 signaling pathways. Bile acid induction of the FXR-α target gene, small heterodimer partner (SHP), is highly dependent on the activation PKCζ, a branch of the insulin signaling pathway. SHP is an important regulator of glucose and lipid metabolism in the liver. One might hypothesize that chronic low grade inflammation which is associated with insulin resistance, may inhibit bile acid signaling and disrupt lipid metabolism. The disruption of these signaling pathways may increase the risk of fatty liver and non-alcoholic fatty liver disease (NAFLD). Finally, conjugated bile acids appear to promote cholangiocarcinoma growth via the activation of S1PR2.

Inherited neuropathies: an update

In this review, progress in hereditary neuropathy research published in the Journal of Neurology over the last 18 months is summarised.