Multiplex ARMS PCR to Detect 8 Common Mutations of ATP7B Gene in Patients With Wilson Disease

Multiplex fluorescent amplification-refractory mutation system PCR method for the detection of 10 genetic defects in Holstein cattle and its comparison with the KASP genotyping assay

The common deleterious genetic defects in Holstein cattle include haplotypes 1-6 (HH1-HH6), haplotypes for cholesterol deficiency (HCD), bovine leukocyte adhesion deficiency (BLAD), complex vertebral malformation (CVM) and brachyspina syndrome (BS). Recessive inheritance patterns of these genetic defects permit the carriers to function normally, but homozygous recessive genotypes cause embryo loss or neonatal death. Therefore, rapid detection of the carriers is essential to manage these genetic defects. This study was conducted to develop a single-tube multiplex fluorescent amplification-refractory mutation system (mf-ARMS) PCR method for efficient genotyping of these 10 genetic defects and to compare its efficiency with the kompetitive allele specific PCR (KASP) genotyping assay. The mf-ARMS PCR method introduced 10 sets of tri-primers optimized with additional mismatches in the 3' end of wild and mutant-specific primers, size differentiation between wild and mutant-specific primers, fluorescent labeling of universal primers, adjustment of annealing temperatures and optimization of primer concentrations. The genotyping of 484 Holstein cows resulted in 16.12% carriers with at least one genetic defect, while no homozygous recessive genotype was detected. This study found carrier frequencies ranging from 0.0% (HH6) to 3.72% (HH3) for individual defects. The mf-ARMS PCR method demonstrated improved detection, time and cost efficiency compared with the KASP method for these defects. Therefore, the application of mf-ARMS PCR for genotyping Holstein cattle is anticipated to decrease the frequency of lethal alleles and limit the transmission of these genetic defects.

Are the new genetic tools for diagnosis of Wilson disease helpful in clinical practice?

The diagnosis of Wilson disease is not always easy. For many patients, a combination of tests reflecting disturbed copper metabolism may be needed. Testing for ATP7B variants has become part of the routine diagnostic approach. The methods of genetic testing include analysis of the 21 coding exons and intronic flanking sequences, in which exons with recurrent variants would be prioritised depending on the mutation frequency in the local population. If sequencing the entire ATP7B gene cannot identify 2 variants and the suspicion for Wilson disease is high, after reviewing the clinical data, WES (whole-exome sequencing) or WGS (whole-genome sequencing) could be applied. A workflow based on the type and number of ATP7B variants responsible for Wilson disease is proposed. Genetic testing is indicated for confirmation of diagnosis, family screening, and screening of newborns and infants and in unclear cases suspected of suffering from Wilson disease. However, genetic testing is not a routine screening test for Wilson disease. If no additional variants can be identified, it can be assumed that other hereditary disorders may mimic Wilson disease (congenital disorders of glycosylation, MEDNIK syndrome, idiopathic or primary copper toxicoses).

Wilson's disease in Lebanon and regional countries: Homozygosity and hepatic phenotype predominance

AIM

To determine the phenotypes and predominant disease-causing mutations in Lebanese patients with Wilson's disease, as compared to regional non-European data.

METHODS

The clinical profile of 36 patients diagnosed in Lebanon was studied and their mutations were determined by molecular testing. All patients underwent full physical exam, including ophthalmologic slit-lamp examination ultrasound imaging of the liver, as well as measurement of serum ceruloplasmin and 24-h urinary-Cu levels. In addition, genetic screening using PCR followed by sequencing to determine disease-causing mutations and polymorphisms in the ATP7B gene was carried on extracted DNA from patients and immediate family members. Our phenotypic-genotypic findings were then compared to reported mutations in Wilson's disease patients from regional Arab and non-European countries.

RESULTS

Patients belonged to extended consanguineous families. The majority were homozygous for the disease-causing mutation, with no predominant mutation identified. The most common mutation, detected in 4 out of 13 families, involved the ATP hinge region and was present in patients from Lebanon, Egypt, Iran and Turkey. Otherwise, mutations in Lebanese patients and those of the region were scattered over 17 exons of ATP7B. While the homozygous exon 12 mutation Trp939Cys was only detected in patients from Lebanon but none from the regional countries, the worldwide common mutation H1069Q was not present in the Lebanese and was rare in the region. Pure hepatic phenotype was predominant in patients from both Lebanon and the region (25%-65%). Furthermore, the majority of patients, including those who were asymptomatic, had evidence of some hepatic dysfunction. Pure neurologic phenotype was rare.

CONCLUSION

Findings do not support presence of a founder effect. Clinical and genetic screening is recommended for family members with index patients and unexplained hepatic dysfunction.

Genetic and Clinical Analysis in a Cohort of Patients with Wilson's Disease in Southwestern China

BACKGROUND AND AIMS

Wilson's disease (WD), characterized by a disorder of copper metabolism, is an inherited autosomal recessive disease caused by mutations in the ATP7B gene.

METHODS

To explore genotype-phenotype correlations in Chinese WD patients and to evaluate the frequency of the ATP7B mutations, we described 77 clinically and biochemically confirmed WD patients and detected mutations in ten WD families from southwestern China. Clinical features were presented and all the exons of the ATP7B gene were screened.

RESULTS

The appearance of Kayser-Fleischer (K-F) rings was closely related to onset age, particularly before 10 years old. For those patients with predominantly neurological symptoms, MRI was the most sensitive and preferred examination. Eight mutations of the ATP7B gene were detected including seven reported mutations (c.2302dup, c.2304delC, c.2333 G>T, c.2621 C>T, c.2755 C>G, c.2975 C>T and c.1366 G>C) and four novel mutations (c.3446 G>A, c.3767insCA, c.3406 G>A and c.3700delG). c.2333 G>T was detected in 6/20 alleles (30%), accounting for the largest proportion, which could be regarded as a mutation hotspot in this region.

CONCLUSIONS

Our study extends the mutation spectrum of ATP7B and analyzes the relationship between mutations in the ATP7B gene and clinical findings of WD.

The Pragmatic Treatment of Wilson's Disease

Wilson's disease (WD) is a potentially fatal disorder of chronic copper toxicity, primarily affecting the liver and the brain. Judicious treatment can restore health and longevity, even in patients with severe neurological impairment. However, the disease is associated with considerable morbidity and mortality resulting from delay in diagnosis, and difficulty in pacing the medical treatment. In this article, we briefly review the diagnosis and treatment options for WD and share our experience in managing patients with WD. We focus on decoppering (copper chelation) treatment of WD and outline pragmatic strategies for patient management designed to recognize and minimize adverse effects while ensuring treatment compliance and effectiveness.