Structures of the human Wilson disease copper transporter ATP7B.

The P-type ATPase ATP7B exports cytosolic copper and plays an essential role in the regulation of cellular copper homeostasis. Mutants of ATP7B cause Wilson disease (WD), an autosomal recessive disorder of copper metabolism. Here, we present cryoelectron microscopy (cryo-EM) structures of human ATP7B in the E1 state in the apo, the putative copper-bound, and the putative cisplatin-bound forms. In ATP7B, the N-terminal sixth metal-binding domain (MBD6) binds at the cytosolic copper entry site of the transmembrane domain (TMD), facilitating the delivery of copper from the MBD6 to the TMD. The sulfur-containing residues in the TMD of ATP7B mark the copper transport pathway. By comparing structures of the E1 state human ATP7B and E2-Pi state frog ATP7B, we propose the ATP-driving copper transport model of ATP7B. These structures not only advance our understanding of the mechanisms of ATP7B-mediated copper export but can also guide the development of therapeutics for the treatment of WD.

Pathogenicity of Intronic and Synonymous Variants of ATP7B in Wilson Disease.

Wilson disease (WD) is a hereditary disorder of copper metabolism, resulting from mutations within ATP7B. Early diagnosis is essential for affected individuals. However, there are still patients with clinically suspected WD who do not have detectable pathogenic variants, which makes diagnosis difficult and delays treatment. This study included such patients from the authors' center and screened for the full-length sequence of ATP7B by next-generation sequencing. Newly identified synonymous and intronic variants were then analyzed with in silico tools. A minigene system was constructed to determine the pathogenicity of these variants in terms of splicing and blood RNA extraction, and RT-PCR experiments were performed on several patients to verify the splicing alterations. The phenotypes of the patients were also analyzed. Fourteen suspected pathogenic variants, including nine synonymous and five intronic variants, were detected in 12 patients with clinically suspected WD. Among them, four synonymous variants (c.1050G>A, c.1122C>G, c.3243G>A, and c.4014T>A) and four intronic variants (c.1543 +40G>A, c.1707+6_1707+16del, c.1870-49A>G, and c.2731-67A>G) resulted in splicing changes in ATP7B. After the above analysis, the diagnosis of WD could be confirmed in eight clinically suspected patients with WD who showed a late age of onset.

Serum Neurofilament Light Chain in Wilson's Disease: A Promising Indicator but Unparallel to Real-Time Treatment Response.

BACKGROUND: Wilson's disease (WD) currently lacks a promising indicator that could reflect neurological impairment and monitor treatment outcome. We aimed to investigate whether serum neurofilament light chain (sNfL) functions as a candidate for disease assessment and treatment monitoring of WD. METHODS: We assessed preclinical and manifested WD patients' sNfL levels compared to controls and analyzed the differences between patients with various clinical symptoms. We then explored the correlation between clinical scales and sNfL levels. And repeated measurements were performed in 34 patients before and after treatment. RESULTS: WD patients with neurological involvement had significantly higher sNfL levels than both hepatic patients and controls. Positive correlations were found between Unified Wilson's Disease Rating Scale scores and sNfL and between semiquantitative magnetic resonance imaging scales and sNfL levels in WD patients. However, in the treatment follow-up analysis, the trend of sNfL before and after treatment disaccorded with clinical response. CONCLUSION: These findings suggest that sNfL levels can be an ideal indicator for the severity of neurological involvement but fail to evaluate change in disease condition after treatment. © 2022 International Parkinson and Movement Disorder Society.

A novel ceruloplasmin mutation identified in a Chinese patient and clinical spectrum of aceruloplasminemia patients.

Aceruloplasminemia (ACP) is a rare disorder of iron overload resulting from ceruloplasmin (CP) variants. Because of its rarity and heterogeneity, the diagnosis of ACP is often missed or misdiagnosed. Here, we aim to present a clinical spectrum of ACP and raise more attention to the early diagnosis. Whole exome sequencing (WES) was performed in a Chinese female patient suspected with ACP and her clinical data were collected in detail. The PubMed databases was searched for published ACP patients within the last decade, and we present a systematic review of their clinical features with data extracted from these researches. A novel pathogenic variant (c.2689delC) and a known pathogenic variant (c.606dupA) within ceruloplasmin gene were identified in our patient and confirmed the diagnosis of ACP. Then we reviewed 51 ACP patients including the case we reported here. A possible timeline of symptoms was discovered, anemia appears first (29.7 years old on average), followed by diabetes (37.3 years old) and finally neurological symptoms (50.7 years old). The delay in diagnosis was significantly shortened in patients without neurological symptoms. Biochemical triad including anemia, low to undetectable serum ceruloplasmin, low serum iron and/or hyperferritinemia, showed better sensitivity in diagnosis than clinical triad including diabetes, neurological symptoms, and retinal degeneration. Due to the variable symptom spectrum, patients with ACP often visit different departments, which can lead to misdiagnosis. Clinical attention needs to be paid to symptoms and tests that have a warning effect. Prompt diagnosis in the early stage of the disease can be beneficial.

Prevalent Pathogenic Variants of ATP7B in Chinese Patients with Wilson's Disease: Geographical Distribution and Founder Effect.

Wilson's disease (WD) is an autosomal recessive disorder caused by ATP7B pathogenic variants. This study aimed to show the geographical distribution and haplotype spectrum of three prevalent pathogenic variants (p.R778L, p.P992L, p.T935M) in mainland Chinese population and clarify whether the founder effect may account for their origins. We firstly summarized the frequency and geographical distribution of p.R778L, p.P992L and p.T935M in 715 WD patients. Then, to construct haplotypes associated with the three variants, Sanger sequencing and microsatellite typing at three dinucleotide-repeat markers (D13S314, D13S301, D13S316) flanking the ATP7B gene were performed in 102 WD families. An obvious regional-specific distribution feature was found in p.T935M. Linkage disequilibrium at the three markers was shown in all the three variants and we found the common haplotypes specific for p.R778L, p.P992L and p.T935M respectively, represented successively by 10-7-7, 10-9-5 and 12-4-8, which all exhibited great significance vs. the control chromosomes (p < 0.01). Meanwhile, haplotypes for the three variants differed from the studies in other regions to some extent. The common haplotypes we found indicate that three prevalent pathogenic variants emerge due to the founder effect. Furthermore, the study contributes to expand our knowledge of the genetic diversity of WD from a cross-regional perspective.

Role for Biochemical Assays and Kayser-Fleischer Rings in Diagnosis of Wilson's Disease.

BACKGROUND & AIMS: Wilson disease is an autosomal recessive disorder that impairs copper homeostasis and is caused by homozygous or compound heterozygous mutations in ATP7B, which encodes a copper-transporting P-type ATPase. Patients have variable clinical manifestations and laboratory test results, resulting in diagnostic dilemmas. We aimed to identify factors associated with symptoms and features of Wilson disease from a large cohort, over 15 years. METHODS: We collected data from 715 patients (529 with symptoms, 146 without symptoms, and 40 uncategorized) and a genetic confirmation of Wilson's disease (mean age of diagnosis, 18.84 years), recruited from 3 hospitals in China from 2004 through 2019. We analyzed clinical data along with serum levels of ceruloplasmin (available from 636 patients), 24-hr urinary copper excretion (collected from 131 patients), Kayser-Fleisher rings (copper accumulation in eyes, with neurologic data from 355 patients), and magnetic resonance imaging (MRI) abnormalities. Differences among the groups were analyzed using 1-way analysis of variance followed by Tukey multiple comparison test. RESULTS: Of the 529 patients with symptoms, 121 had hepatic features, 355 had neurologic features, 28 had osteomuscular features (premature osteoarthritis, skeletal deformities, and pathological bone fractures), and 25 had psychiatric symptoms. Age of onset was significantly younger in patients with hepatic (16.94 ± 1.03 years; P = .0105) or osteomuscular features (13 ± 1.33 years; P = .0001) than patients with neurological features (19.48 ± 0.46 years). Serum levels of ceruloplasmin differed among asymptomatic patients and patients with osteomuscular or neurologic symptoms of Wilson disease. Serum levels of ceruloplasmin ranged from 18.93 mg/L to approximately 120.00 mg/L (quantiles of 0.025 to approximately 0.975). Fifty-one of 131 patients (39%) had urinary copper excretion levels below 100 µg/24 hr; there was significant variation in levels of urinary copper excretion between patients older than 14 years vs 14 years or younger. Of the 355 patients with neurologic features, 244 patients (69%) had abnormal findings from MRI and Kayser-Fleisher rings; only 1 patient with abnormal findings from brain MRI was negative for Kayser-Fleisher rings. CONCLUSIONS: Serum level of ceruloplasmin, 24-hour urinary copper excretion, and Kayser-Fleisher rings can be used to identify patients who might have Wilson disease. Patients with serum levels of ceruloplasmin below 120 mg/L and children with urinary copper excretion above 40 µg should undergo genetic testing for Wilson's disease. Patients with movement disorders and brain MRI abnormalities without Kayser-Fleisher rings are not likely to have Wilson disease.

Clinical features and outcome of Wilson's disease with generalized epilepsy in Chinese patients.

OBJECTIVE: Generalized epilepsy is rarely reported in patients with Wilson disease (WD) and lacks experience in clinical practice. We aim to provide better experience for the diagnosis and treatment for WD patients with epilepsy in the future. METHODS: A retrospective study was performed in 13 Chinese WD patients with generalized epilepsy. Each patient was diagnosed with WD by clinical evaluation and genetic screening. Patients were given small doses of antiepileptic drugs (AEDs), followed by copper-chelation therapy when the seizures stabilized. Clinical manifestations, brain imaging changes, and treatment and outcome after a long-term follow-up were analyzed. RESULTS: Four out of 13 (30.8%) patients stopped taking copper-chelation drugs for more than 1 year before they were admitted for epilepsy. The incidence of epilepsy of WD patients in our cohort is 1.43% (13/910), lower than those (4.5%-5.9%) in other populations. After the attack of epilepsy, frontal lobes were the most common abnormalities (13/13, 100%) in patients, followed by brain stem (8/13, 61.5%) and thalamus (7/13, 53.8%). After a long-term follow-up, brain imaging and clinical manifestations of 8 (8/9, 88.9%) WD patients were significantly improved. CONCLUSIONS: We firstly described WD patients with generalized epilepsy in the Chinese population. WD patients with aggravation of neuropsychiatric symptoms are prone to occur epilepsy; thus, brain MRI should be performed regularly in those patients. Cortical abnormality in brain MRI is a warning sign of epilepsy. Irregular use of copper-chelation drugs and excessive copper deposition in the brain may be the cause of seizures. Long-term standardized treatment for WD can effectively prevent the extensive brain damage and reduce the incidence of epilepsy in WD patients.

Clinical features and genetic spectrum in Chinese patients with recessive hereditary spastic paraplegia.

BACKGROUND: Although many causative genes of hereditary spastic paraplegia (HSP) have been uncovered in recent years, there are still approximately 50% of HSP patients without genetically diagnosis, especially in autosomal recessive (AR) HSP patients. Rare studies have been performed to determine the genetic spectrum and clinical profiles of recessive HSP patients in the Chinese population. METHODS: In this study, we investigated 24 Chinese index AR/sporadic patients by targeted next-generation sequencing (NGS), Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA). Further functional studies were performed to identify pathogenicity of those uncertain significance variants. RESULTS: We identified 11 mutations in HSP related genes including 7 novel mutations, including two (p.V1979_L1980delinsX, p.F2343 fs) in SPG11, two (p.T55 M, p.S308 T) in AP5Z1, one (p.S242 N) in ALDH18A1, one (p.D597fs) in GBA2, and one (p.Q486X) in ATP13A2 in 8 index patients and their family members. Mutations in ALDH18A1, AP5Z1, CAPN1 and ATP13A2 genes were firstly reported in the Chinese population. Furthermore, the clinical phenotypes of the patients carrying mutations were described in detail. The mutation (p.S242 N) in ALDH18A1 decreased enzyme activity of P5CS and mutations (p.T55 M, p.S308 T) in AP5Z1 induced lysosomal dysfunction. CONCLUSION: Our results expanded the genetic spectrum and clinical profiles of AR-HSP patients and further demonstrated the efficiency and reliability of targeted NGS diagnosing suspected HSP patients.

Contribution of intragenic deletions to mutation spectrum in Chinese patients with Wilson's disease and possible mechanism underlying ATP7B gross deletions.

INTRODUCTION: Wilson's disease (WD) is an autosomal recessive disorder of copper metabolism due to ATP7B pathogenic mutations. Disease manifestations can be prevented if early diagnosis and effective treatment are given. Direct sequencing is routinely used to confirm WD diagnosis, but cannot identify gross rearrangements. METHODS: Sanger sequencing of ATP7B was performed in 142 newly recruited WD index patients. The clinical effects of identified variants were classified according to American College of Medical Genetics and Genomics (ACMG) standards and guidelines. Multiplex ligation-dependent probe amplification (MLPA) was performed in 168 WD cases with clinical WD unexplained by Sanger sequencing, selected from our total case series of 774 WD patients. After identifying gross rearrangements within ATP7B, the breakpoints were determined by long-range PCR and direct sequencing. RESULTS: In the 142 WD patients, we identified 71 sequence alterations in ATP7B, of which 15 were novel; 14 of these were classified as 'pathogenic' or 'likely pathogenic', including 2 intronic variants affecting splice sites. In 6 of 168 WD patients, MLPA identified four heterozygous gross ATP7B deletions. One was a whole gene deletion, and three were intragenic deletions which were mapped to breakpoint locations, revealing non-homologous end joining. CONCLUSION: Intragenic deletions are responsible for WD and non-homologous end joining could be the pathogenesis, therefore the detection of intragenic deletions should be included in comprehensive genetic testing for WD.