Brain cholesterol and Alzheimer's disease: challenges and opportunities in probe and drug development.

Cholesterol homeostasis is impaired in Alzheimer's disease; however, attempts to modulate brain cholesterol biology have not translated into tangible clinical benefits for patients to date. Several recent milestone developments have substantially improved our understanding of how excess neuronal cholesterol contributes to the pathophysiology of Alzheimer's disease. Indeed, neuronal cholesterol was linked to the formation of amyloid-ß and neurofibrillary tangles through molecular pathways that were recently delineated in mechanistic studies. Furthermore, remarkable advances in translational molecular imaging have now made it possible to probe cholesterol metabolism in the living human brain with PET, which is an important prerequisite for future clinical trials that target the brain cholesterol machinery in Alzheimer's disease patients-with the ultimate aim being to develop disease-modifying treatments. This work summarizes current concepts of how the biosynthesis, transport and clearance of brain cholesterol are affected in Alzheimer's disease. Further, current strategies to reverse these alterations by pharmacotherapy are critically discussed in the wake of emerging translational research tools that support the assessment of brain cholesterol biology not only in animal models but also in patients with Alzheimer's disease.

CYP46A1-mediated cholesterol turnover induces sex-specific changes in cognition and counteracts memory loss in ovariectomized mice.

The brain-specific enzyme CYP46A1 controls cholesterol turnover by converting cholesterol into 24S-hydroxycholesterol (24OH). Dysregulation of brain cholesterol turnover and reduced CYP46A1 levels are observed in Alzheimer's disease (AD). In this study, we report that CYP46A1 overexpression in aged female mice leads to enhanced estrogen signaling in the hippocampus and improved cognitive functions. In contrast, age-matched CYP46A1 overexpressing males show anxiety-like behavior, worsened memory, and elevated levels of 5α-dihydrotestosterone in the hippocampus. We report that, in neurons, 24OH contributes to these divergent effects by activating sex hormone signaling, including estrogen receptors. CYP46A1 overexpression in female mice protects from memory impairments induced by ovariectomy while having no effects in gonadectomized males. Last, we measured cerebrospinal fluid levels of 24OH in a clinical cohort of patients with AD and found that 24OH negatively correlates with neurodegeneration markers only in women. We suggest that CYP46A1 activation is a valuable pharmacological target for enhancing estrogen signaling in women at risk of developing neurodegenerative diseases.

Alpha-1 Antitrypsin Augmentation and the Liver Phenotype of Adults With Alpha-1 Antitrypsin Deficiency (Genotype Pi∗ZZ).

BACKGROUND & AIMS: α1-Antitrypsin (AAT) is a major protease inhibitor produced by hepatocytes. The most relevant AAT mutation giving rise to AAT deficiency (AATD), the 'Pi∗Z' variant, causes harmful AAT protein accumulation in the liver, shortage of AAT in the systemic circulation, and thereby predisposes to liver and lung injury. Although intravenous AAT augmentation constitutes an established treatment of AATD-associated lung disease, its impact on the liver is unknown. METHODS: Liver-related parameters were assessed in a multinational cohort of 760 adults with severe AATD (Pi∗ZZ genotype) and available liver phenotyping, of whom 344 received augmentation therapy and 416 did not. Liver fibrosis was evaluated noninvasively via the serum test AST-to-platelet ratio index and via transient elastography-based liver stiffness measurement. Histologic parameters were compared in 15 Pi∗ZZ adults with and 35 without augmentation. RESULTS: Compared with nonaugmented subjects, augmented Pi∗ZZ individuals displayed lower serum liver enzyme levels (AST 71% vs 75% upper limit of normal, P < .001; bilirubin 49% vs 58% upper limit of normal, P = .019) and lower surrogate markers of fibrosis (AST-to-platelet ratio index 0.34 vs 0.38, P < .001; liver stiffness measurement 6.5 vs 7.2 kPa, P = .005). Among biopsied participants, augmented individuals had less pronounced liver fibrosis and less inflammatory foci but no differences in AAT accumulation were noted. CONCLUSIONS: The first evaluation of AAT augmentation on the Pi∗ZZ-related liver disease indicates liver safety of a widely used treatment for AATD-associated lung disease. Prospective studies are needed to confirm the beneficial effects and to demonstrate the potential efficacy of exogenous AAT in patients with Pi∗ZZ-associated liver disease.

LIPID MAPS: update to databases and tools for the lipidomics community.

LIPID MAPS (LIPID Metabolites and Pathways Strategy), www.lipidmaps.org, provides a systematic and standardized approach to organizing lipid structural and biochemical data. Founded 20 years ago, the LIPID MAPS nomenclature and classification has become the accepted community standard. LIPID MAPS provides databases for cataloging and identifying lipids at varying levels of characterization in addition to numerous software tools and educational resources, and became an ELIXIR-UK data resource in 2020. This paper describes the expansion of existing databases in LIPID MAPS, including richer metadata with literature provenance, taxonomic data and improved interoperability to facilitate FAIR compliance. A joint project funded by ELIXIR-UK, in collaboration with WikiPathways, curates and hosts pathway data, and annotates lipids in the context of their biochemical pathways. Updated features of the search infrastructure are described along with implementation of programmatic access via API and SPARQL. New lipid-specific databases have been developed and provision of lipidomics tools to the community has been updated. Training and engagement have been expanded with webinars, podcasts and an online training school.

Sex, Genotype, and Liver Volume Progression as Risk of Hospitalization Determinants in Autosomal Dominant Polycystic Liver Disease.

BACKGROUND & AIMS: Autosomal dominant polycystic liver disease is a rare condition with a female preponderance, based mainly on pathogenic variants in 2 genes, PRKCSH and SEC63. Clinically, autosomal dominant polycystic liver disease is characterized by vast heterogeneity, ranging from asymptomatic to highly symptomatic hepatomegaly. To date, little is known about the prediction of disease progression at early stages, hindering clinical management, genetic counseling, and the design of randomized controlled trials. To improve disease prognostication, we built a consortium of European and US centers to recruit the largest cohort of patients with PRKCSH and SEC63 liver disease. METHODS: We analyzed an international multicenter cohort of 265 patients with autosomal dominant polycystic liver disease harboring pathogenic variants in PRKCSH or SEC63 for genotype-phenotype correlations, including normalized age-adjusted total liver volumes and polycystic liver disease-related hospitalization (liver event) as primary clinical end points. RESULTS: Classifying individual total liver volumes into predefined progression groups yielded predictive risk discrimination for future liver events independent of sex and underlying genetic defects. In addition, disease severity, defined by age at first liver event, was considerably more pronounced in female patients and patients with PRKCSH variants than in those with SEC63 variants. A newly developed sex-gene score was effective in distinguishing mild, moderate, and severe disease, in addition to imaging-based prognostication. CONCLUSIONS: Both imaging and clinical genetic scoring have the potential to inform patients about the risk of developing symptomatic disease throughout their lives. The combination of female sex, germline PRKCSH alteration, and rapid total liver volume progression is associated with the greatest odds of polycystic liver disease-related hospitalization.

Inhibition of 7α,26-dihydroxycholesterol biosynthesis promotes midbrain dopaminergic neuron development.

Dysregulated cholesterol metabolism has been linked to neurodegeneration. We previously found that free, non-esterified, 7α,(25R)26-dihydroxycholesterol (7α,26-diHC), was significantly elevated in the cerebrospinal fluid of patients with Parkinson's disease (PD). In this study we investigated the role of 7α,26-diHC in midbrain dopamine (mDA) neuron development and survival. We report that 7α,26-diHC induces apoptosis and reduces the number of mDA neurons in hESC-derived cultures and in mouse progenitor cultures. Voriconazole, an oxysterol 7α-hydroxylase (CYP7B1) inhibitor, increases the number of mDA neurons and prevents the loss of mDA neurons induced by 7α,26-diHC. These effects are specific since neither 7α,26-diHC nor voriconazole alter the number of Islet1+ oculomotor neurons. Furthermore, our results suggest that elevated 24(S),25-epoxycholesterol, which has been shown to promote mDA neurogenesis, may be partially responsible for the effect of voriconazole on mDA neurons. These findings suggest that voriconazole, and/or other azole CYP7B1 inhibitors may have implications in PD therapy development.

Alzheimer's disease biomarker profiling in a memory clinic cohort without common comorbidities.

Alzheimer's disease is a multifactorial disorder with large heterogeneity. Comorbidities such as hypertension, hypercholesterolaemia and diabetes are known contributors to disease progression. However, less is known about their mechanistic contribution to Alzheimer's pathology and neurodegeneration. The aim of this study was to investigate the relationship of several biomarkers related to risk mechanisms in Alzheimer's disease with the well-established Alzheimer's disease markers in a memory clinic population without common comorbidities. We investigated 13 molecular markers representing key mechanisms underlying Alzheimer's disease pathogenesis in CSF from memory clinic patients without diagnosed hypertension, hypercholesterolaemia or diabetes nor other neurodegenerative disorders. An analysis of covariance was used to compare biomarker levels between clinical groups. Associations were analysed by linear regression. Two-step cluster analysis was used to determine patient clusters. Two key markers were analysed by immunofluorescence staining in the hippocampus of non-demented control and Alzheimer's disease individuals. CSF samples from a total of 90 participants were included in this study: 30 from patients with subjective cognitive decline (age 62.4 ± 4.38, female 60%), 30 with mild cognitive impairment (age 65.6 ± 7.48, female 50%) and 30 with Alzheimer's disease (age 68.2 ± 7.86, female 50%). Angiotensinogen, thioredoxin-1 and interleukin-15 had the most prominent associations with Alzheimer's disease pathology, synaptic and axonal damage markers. Synaptosomal-associated protein 25 kDa and neurofilament light chain were increased in mild cognitive impairment and Alzheimer's disease patients. Grouping biomarkers by biological function showed that inflammatory and survival components were associated with Alzheimer's disease pathology, synaptic dysfunction and axonal damage. Moreover, a vascular/metabolic component was associated with synaptic dysfunction. In the data-driven analysis, two patient clusters were identified: Cluster 1 had increased CSF markers of oxidative stress, vascular pathology and neuroinflammation and was characterized by elevated synaptic and axonal damage, compared with Cluster 2. Clinical groups were evenly distributed between the clusters. An analysis of post-mortem hippocampal tissue showed that compared with non-demented controls, angiotensinogen staining was higher in Alzheimer's disease and co-localized with phosphorylated-tau. The identification of biomarker-driven endophenotypes in cognitive disorder patients further highlights the biological heterogeneity of Alzheimer's disease and the importance of tailored prevention and treatment strategies.

HSD3B1 is an oxysterol 3ß-hydroxysteroid dehydrogenase in human placenta.

Most biologically active oxysterols have a 3ß-hydroxy-5-ene function in the ring system with an additional site of oxidation at C-7 or on the side-chain. In blood plasma oxysterols with a 7α-hydroxy group are also observed with the alternative 3-oxo-4-ene function in the ring system formed by ubiquitously expressed 3ß-hydroxy-Δ5-C27-steroid oxidoreductase Δ5-isomerase, HSD3B7. However, oxysterols without a 7α-hydroxy group are not substrates for HSD3B7 and are not usually observed with the 3-oxo-4-ene function. Here we report the unexpected identification of oxysterols in plasma derived from umbilical cord blood and blood from pregnant women taken before delivery at 37+ weeks of gestation, of side-chain oxysterols with a 3-oxo-4-ene function but no 7α-hydroxy group. These 3-oxo-4-ene oxysterols were also identified in placenta, leading to the hypothesis that they may be formed by a previously unrecognized 3ß-hydroxy-Δ5-C27-steroid oxidoreductase Δ5-isomerase activity of HSD3B1, an enzyme which is highly expressed in placenta. Proof-of-principle experiments confirmed that HSD3B1 has this activity. We speculate that HSD3B1 in placenta is the source of the unexpected 3-oxo-4-ene oxysterols in cord and pregnant women's plasma and may have a role in controlling the abundance of biologically active oxysterols delivered to the fetus.

Magnetic Resonance Liver Iron Concentration Can Guide Venesection Decision-Making in Hyperferritinemia.

BACKGROUND: The clinical benefit of venesection in suspected iron overload can be unclear and serum ferritin may overestimate the degree of iron overload. AIMS: To help inform practice, we examined magnetic resonance liver iron concentration (MRLIC) in a cohort investigated for haemochromatosis. METHODS: One hundred and six subjects with suspected haemochromatosis underwent HFE genotyping and MRLIC with time-matched serum ferritin and transferrin saturation values. For those treated with venesection, volume of blood removed was calculated as a measure of iron overload. RESULTS: Forty-seven C282Y homozygotes had median ferritin 937 µg/l and MRLIC 4.83 mg/g; MRLIC was significantly higher vs non-homozygotes for any given ferritin concentration. No significant difference in MRLIC was observed between homozygotes with and without additional risk factors for hyperferritinemia. Thirty-three compound heterozygotes (C282Y/H63D) had median ferritin 767 µg/l and MRLIC 2.58 mg/g; ferritin < 750 µg/l showed 100% specificity for lack of significant iron overload (< 3.2 mg/g). 79% of C282Y/H63D had additional risk factors-mean MRLIC was significantly lower in this sub-group (2.4 mg/g vs 3.23 mg/g). 26 C282Y heterozygous or wild-type had median ferritin 1226 µg/l and MRLIC 2.13 mg/g; 69% with additional risk factors had significantly higher ferritin concentrations (with comparable MRLIC) and ferritin < 1000 µg/l showed 100% specificity for lack of significant iron overload. In 31 patients (26 homozygotes, 5 C282Y/H63D) venesected to ferritin < 100 µg/l, MRLIC and total venesection volume correlated strongly (r = 0.749), unlike MRLIC and serum ferritin. CONCLUSION: MRLIC is an accurate marker of iron overload in haemochromatosis. We propose serum ferritin thresholds in non-homozygotes which, if validated, could tailor cost-effective use of MRLIC in venesection decision-making.

Tandem mass tag-based quantitative proteomic profiling identifies candidate serum biomarkers of drug-induced liver injury in humans.

Diagnosis of drug-induced liver injury (DILI) and its distinction from other liver diseases are significant challenges in drug development and clinical practice. Here, we identify, confirm, and replicate the biomarker performance characteristics of candidate proteins in patients with DILI at onset (DO; n = 133) and follow-up (n = 120), acute non-DILI at onset (NDO; n = 63) and follow-up (n = 42), and healthy volunteers (HV; n = 104). Area under the receiver operating characteristic curve (AUC) for cytoplasmic aconitate hydratase, argininosuccinate synthase, carbamoylphosphate synthase, fumarylacetoacetase, fructose-1,6-bisphosphatase 1 (FBP1) across cohorts achieved near complete separation (range: 0.94-0.99) of DO and HV. In addition, we show that FBP1, alone or in combination with glutathione S-transferase A1 and leukocyte cell-derived chemotaxin 2, could potentially assist in clinical diagnosis by distinguishing NDO from DO (AUC range: 0.65-0.78), but further technical and clinical validation of these candidate biomarkers is needed.

Identification of unusual oxysterols biosynthesised in human pregnancy by charge-tagging and liquid chromatography - mass spectrometry.

The aim of this study was to identify oxysterols and any down-stream metabolites in placenta, umbilical cord blood plasma, maternal plasma and amniotic fluid to enhance our knowledge of the involvement of these molecules in pregnancy. We confirm the identification of 20S-hydroxycholesterol in human placenta, previously reported in a single publication, and propose a pathway from 22R-hydroxycholesterol to a C27 bile acid of probable structure 3ß,20R,22R-trihydroxycholest-5-en-(25R)26-oic acid. The pathway is evident not only in placenta, but pathway intermediates are also found in umbilical cord plasma, maternal plasma and amniotic fluid but not non-pregnant women.

Assessment of cholesterol homeostasis in the living human brain.

Alterations in brain cholesterol homeostasis have been broadly implicated in neurological disorders. Notwithstanding the complexity by which cholesterol biology is governed in the mammalian brain, excess neuronal cholesterol is primarily eliminated by metabolic clearance via cytochrome P450 46A1 (CYP46A1). No methods are currently available for visualizing cholesterol metabolism in the living human brain; therefore, a noninvasive technology that quantitatively measures the extent of brain cholesterol metabolism via CYP46A1 could broadly affect disease diagnosis and treatment options using targeted therapies. Here, we describe the development and testing of a CYP46A1-targeted positron emission tomography (PET) tracer, 18F-CHL-2205 (18F-Cholestify). Our data show that PET imaging readouts correlate with CYP46A1 protein expression and with the extent to which cholesterol is metabolized in the brain, as assessed by cross-species postmortem analyses of specimens from rodents, nonhuman primates, and humans. Proof of concept of in vivo efficacy is provided in the well-established 3xTg-AD murine model of Alzheimer's disease (AD), where we show that the probe is sensitive to differences in brain cholesterol metabolism between 3xTg-AD mice and control animals. Furthermore, our clinical observations point toward a considerably higher baseline brain cholesterol clearance via CYP46A1 in women, as compared to age-matched men. These findings illustrate the vast potential of assessing brain cholesterol metabolism using PET and establish PET as a sensitive tool for noninvasive assessment of brain cholesterol homeostasis in the clinic.

Reproducibility of Densitometric and Biomechanical Assessment of the Mouse Tibia From In Vivo Micro-CT Images.

Interventions for bone diseases (e.g. osteoporosis) require testing in animal models before clinical translation and the mouse tibia is among the most common tested anatomical sites. In vivo micro-Computed Tomography (microCT) based measurements of the geometrical and densitometric properties are non-invasive and therefore constitute an important tool in preclinical studies. Moreover, validated micro-Finite Element (microFE) models can be used for predicting the bone mechanical properties non-invasively. However, considering that the image processing pipeline requires operator-dependant steps, the reproducibility of these measurements has to be assessed. The aim of this study was to evaluate the intra- and inter-operator reproducibility of several bone parameters measured from microCT images. Ten in vivo microCT images of the right tibia of five mice (at 18 and 22 weeks of age) were processed. One experienced operator (intra-operator analysis) and three different operators (inter-operator) aligned each image to a reference through a rigid registration and selected a volume of interest below the growth plate. From each image the following parameters were measured: total bone mineral content (BMC) and density (BMD), BMC in 40 subregions (ten longitudinal sections, four quadrants), microFE-based stiffness and failure load. Intra-operator reproducibility was acceptable for all parameters (precision error, PE < 3.71%), with lowest reproducibility for stiffness (3.06% at week 18, 3.71% at week 22). The inter-operator reproducibility was slightly lower (PE < 4.25%), although still acceptable for assessing the properties of most interventions. The lowest reproducibility was found for BMC in the lateral sector at the midshaft (PE = 4.25%). Densitometric parameters were more reproducible than most standard morphometric parameters calculated in the proximal trabecular bone. In conclusion, microCT and microFE models provide reproducible measurements for non-invasive assessment of the mouse tibia properties.

Fazirsiran for Liver Disease Associated with Alpha1-Antitrypsin Deficiency.

BACKGROUND: Alpha1-antitrypsin (AAT) deficiency results from carriage of a homozygous SERPINA1 "Z" mutation (proteinase inhibitor [PI] ZZ). The Z allele produces a mutant AAT protein called Z-AAT, which accumulates in hepatocytes and can lead to progressive liver disease and fibrosis. This open-label, phase 2 trial investigated the safety and efficacy of fazirsiran, an RNA interference therapeutic, in patients with liver disease associated with AAT deficiency. METHODS: We assigned adults with the PI ZZ genotype and liver fibrosis to receive fazirsiran at a dose of 200 mg (cohorts 1 [4 patients] and 2 [8 patients]) or 100 mg (cohort 1b [4 patients]) subcutaneously on day 1 and week 4 and then every 12 weeks. The primary end point was the change from baseline to week 24 (cohorts 1 and 1b) or week 48 (cohort 2) in liver Z-AAT concentrations, which were measured by means of liquid chromatography-mass spectrometry. RESULTS: All the patients had reduced accumulation of Z-AAT in the liver (median reduction, 83% at week 24 or 48). The nadir in serum was a reduction of approximately 90%, and treatment was also associated with a reduction in histologic globule burden (from a mean score of 7.4 [scores range from 0 to 9, with higher scores indicating a greater globule burden] at baseline to 2.3 at week 24 or 48). All cohorts had reductions in liver enzyme concentrations. Fibrosis regression was observed in 7 of 15 patients and fibrosis progression in 2 of 15 patients after 24 or 48 weeks. There were no adverse events leading to trial or drug discontinuation. Four serious adverse events (viral myocarditis, diverticulitis, dyspnea, and vestibular neuronitis) resolved. CONCLUSIONS: In this small trial, fazirsiran was associated with a strong reduction of Z-AAT concentrations in the serum and liver and concurrent improvements in liver enzyme concentrations. (Funded by Arrowhead Pharmaceuticals; AROAAT-2002 ClinicalTrials.gov number, NCT03946449.).

The SARS-CoV2 envelope differs from host cells, exposes procoagulant lipids, and is disrupted in vivo by oral rinses.

The lipid envelope of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an essential component of the virus; however, its molecular composition is undetermined. Addressing this knowledge gap could support the design of antiviral agents as well as further our understanding of viral-host protein interactions, infectivity, pathogenicity, and innate immune system clearance. Lipidomics revealed that the virus envelope comprised mainly phospholipids (PLs), with some cholesterol and sphingolipids, and with cholesterol/phospholipid ratio similar to lysosomes. Unlike cellular membranes, procoagulant amino-PLs were present on the external side of the viral envelope at levels exceeding those on activated platelets. Accordingly, virions directly promoted blood coagulation. To investigate whether these differences could enable selective targeting of the viral envelope in vivo, we tested whether oral rinses containing lipid-disrupting chemicals could reduce infectivity. Products containing PL-disrupting surfactants (such as cetylpyridinium chloride) met European virucidal standards in vitro; however, components that altered the critical micelle concentration reduced efficacy, and products containing essential oils, povidone-iodine, or chlorhexidine were ineffective. This result was recapitulated in vivo, where a 30-s oral rinse with cetylpyridinium chloride mouthwash eliminated live virus in the oral cavity of patients with coronavirus disease 19 for at least 1 h, whereas povidone-iodine and saline mouthwashes were ineffective. We conclude that the SARS-CoV-2 lipid envelope i) is distinct from the host plasma membrane, which may enable design of selective antiviral approaches; ii) contains exposed phosphatidylethanolamine and phosphatidylserine, which may influence thrombosis, pathogenicity, and inflammation; and iii) can be selectively targeted in vivo by specific oral rinses.

Investigation and management of Wilson's disease: a practical guide from the British Association for the Study of the Liver.

Wilson's disease is an autosomal-recessive disorder of copper metabolism with hepatic, neurological, psychiatric, ophthalmological, haematological, renal, and rheumatological manifestations. Making a diagnosis can be challenging given that no single test can confirm or exclude the disease, and diagnostic delays are common. Treatment protocols vary and adverse effects, including paradoxical neurological worsening, can occur. In this Review, we provide a practical guide to the diagnosis of Wilson's disease. We include recommendations on indications for testing, how to interpret results, and when additional investigations are required. We also cover treatment initiation, ideally under the guidance of a specialist centre for Wilson's disease, and the principles behind long-term management. This guidance was developed by a multidisciplinary group of Wilson's disease experts formed through the British Association for the Study of the Liver. The guidance has been endorsed by the British Society of Gastroenterology and approved by the Association of British Neurologists.

First report of post-transplant autoimmune hepatitis recurrence following SARS-CoV-2 mRNA vaccination.

Whilst vaccination for the SARS-CoV-2 virus has been successful in reducing the severity and burden of the COVID-19 pandemic, there have been recent reports of mRNA vaccines triggering autoimmune hepatitis in the native liver. There have been no descriptions thus far of recurrent 'autoimmune hepatitis' after liver transplantation in the context of SARS-CoV-2 vaccination. We describe a patient transplanted for autoimmune hepatitis who was stable for many years until they had immune-mediated flares coinciding with Pfizer-BioNTech mRNA vaccination. Intravenous steroid treatment was required to suppress histologically evident interface hepatitis. We firmly believe that mRNA vaccination was responsible for this 'recurrence' and that clinicians should be vigilant for this reaction in patients transplanted for autoimmune hepatitis.

Synonymous mutation in adenosine triphosphatase copper-transporting beta causes enhanced exon skipping in Wilson disease.

Wilson disease (WD) is caused by biallelic pathogenic variants in adenosine triphosphatase copper-transporting beta (ATP7B); however, genetic testing identifies only one or no pathogenic ATP7B variant in a number of patients with WD. Synonymous single-nucleotide sequence variants have been recognized as pathogenic in individual families. The aim of the present study was to evaluate the prevalence and disease mechanism of the synonymous variant c.2292C>T (p.Phe764=) in WD. A cohort of 280 patients with WD heterozygous for a single ATP7B variant was investigated for the presence of c.2292C>T (p.Phe764=). In this cohort of otherwise genetically unexplained WD, the allele frequency of c.2292C>T (p.Phe764=) was 2.5% (14 of 560) compared to 7.1 × 10-6 in the general population (2 of 280,964 in the Genome Aggregation Database; p < 10-5 ; Fisher exact test). In an independent United Kingdom (UK) cohort, 2 patients with WD homozygous for p.Phe764= were identified. RNA analysis of ATP7B transcripts from patients homozygous or heterozygous for c.2292C>T and control fibroblasts showed that this variant caused high expression of an ATP7B transcript variant lacking exon 8. Conclusion: The synonymous ATP7B variant c.2292C>T (p.Phe764=) causes abnormal messenger RNA processing of ATP7B transcripts and is associated with WD in compound heterozygotes and homozygotes.