Genotype And Clinical Course In Two Siblings With Wilson's Disease Presenting With Isolated Premature Osteoarthritis

BackgroundCharacterized by excess copper accumulation in various organ systems,Wilson's disease?WD,OMIM 277900;hepatolenticular degeneration,HLD?,is an autosomal-recessive Mendelian inherited disorder involving abnormal copper metabolism caused by pathogenic va:riants within the ATP7B gene at chromosome 13q14.3.ATP7B gene encodes copper-transporting P-type ATPase2?ATP7B protein?,an intracellular transmembrane copper transporter residing in the Trans-Golgi Network of hepatocytes.ATP7B protein is key in incorporating copper into apoceruloplasmin?ceruloplasmin without copper?for the synthesis of functional plasma protein holoceruplasmin?ceruloplasmin containing six copper atoms per molecule?,and is also critical in removing excess copper by excretion into bile out of hepatocytes.ATP7B protein malfunction attributed to pathogenic variants in ATP7B gene give rise to massive toxic accumulation of copper in hepatocyte together with deficiency of ceruloplasmin in plasma.Increased intracellular copper load can result in hepatic damage and even hepatocytes necrosis,and then excess free copper is released from liver into circulation.The increased concentration of free copper in circulation eventually finds its way into extrahepatic tissues and damages them.With the disease onset predominantly in WD patients' second or third decade of life,the most common clinical manifestation of WD includes liver disease and cirrhosis,neurological disorder,behavioral and psychiatric disturbances,Kayser-Fleischer rings in cornea?K-F rings?,and Coombs-negative hemolytic anemia commonly due to severe liver disease.Less common presentations include renal abnormalities,arthropathy,endocrine disorders,infertility and repeated miscarriage,etc.The treatment and monitor for WD should be started as soon as the diagnosis is established as long as there is no contraindication,and should be life-long.With early treatment,prolonged survival of WD has become a norm;whereas untreated WD is usually fatal,wherein most patients die of hepatic failure.WD has a wide range of clinical phenotypic heterogeneity and genotypic heterogeneity.To date,no firm genotype-phenotype correlation has been systematically established.The onset age of WD ranges between 9 months and 80 years;and the onset form,the course of disease and major clinical manifestations also have a large individual differences.Over 800 pathogenic or likely pathogenic variants have been identified in ATP7B gene.The large heterogeneity of WD as well as the absence of clear genotype-phenotype correlation have always been a great challenge against the early diagnosis of some WD patients with atypical clinical presentation,and thus treatment should be delayed.As a kind of atypical disorders in WD,osteoarticular changes also harbor great heterogeneity.They are usually not conspicuous during the early stage of WD's disease course.Particularly,WD individuals with premature osteoarthritis?OA?as the major presentation are prone to be misdiagnosed.ObjectiveTo describe and summarize the clinical phenotype of two WD siblings with isolated premature osteoarthritis?POA?,and to perform molecular diagnosis at DNA level for these two patients.Finally,to explore the clinical implications of this WD family,using literatures review.Subjects and MethodsThe subjects were a WD family in Jining,Shandong Province,China.The pedigree was drawed,the two WD siblings' general information,medical history,physical examination results and available laboratory test results were collected and recorded.The general information and past medical history of non-WD family members were acquired and recorded.The genomic DNA from the peripheral blood lymphocytes of the subjects was extracted.All the coding sequences and exon flanking sequences of 439 inherited metabolic disease genes were sequenced by targeted gene capture?TGC?combined with Next Generation Sequencing?NGS?technology.Bioinformatic analysis of the sequencing data were performed and significant sites were revealed.Sanger sequencing or multiple ligation-dependent probe amplification?MLPA?was used to validate the selected target sites.Further screening of the target sites in the family was carried out.The pathogenicity assessment was performed according to the guidelines published by the American College of Medical Genetics and Genomics?ACMG?in 2015 for the interpretation of sequence variants.ResultsThis Han Chinese family includes two WD patients and 4 non-WD memebers.The two WD siblings share the same clinical phenotype,manifesting POA with adolescent onset as the sole symptom during their first 20 years' duration or more after its onset.The osteoarticular disorders mainly involved the knee,hip joint and other large joints.The two WD siblings have not been correctly diagnosed and treated in two decades or more after the disease onset,and the older brother has been disabled.We did not find any previous report or study describing this kind of particular isolated POA phenotype for 20 years in WD patients.Two compound heterozygous variants of pathogenicity were found in the ATP7B gene of the proband,which were c.2790₂792del and c.2621C>T.Pedigree screening confirmed that the two WD siblings share the same compound heterozygous variants of ATP7B gene,and each of their parents carries one of the two above variants respectively.ConclusionsWhen a clinicianencounters unexplainedPOA,the possibility of WD should be ruled out in order to avoid delays in treatment,even if the OAmanifestationhas remained as the patient' sunique complaint for up to 20 years or more after disease onset.NGS has a great advantage in the rapid and accurate diagnosis of atypical WD patients and facilitates the clinical genetics study of WD.