Detection of Cryptic Mosaicism in X-linked Alport Syndrome Prompts to Re-evaluate Living-donor Kidney Transplantation

Females with Fabry disease: an expert opinion on diagnosis, clinical management, current challenges and unmet needs

Females with Fabry disease (FD) often have a milder phenotype, later symptom onset, and slower disease progression than males, causing delayed diagnosis and undertreatment. A survey was conducted at nine Italian FD centers to evaluate routine management of females with FD; results were discussed at a meeting of eleven Italian specialists and recommendations developed. Of the 227 females managed by the physicians surveyed, 85% were diagnosed through family screening and 38.5% were symptomatic at presentation. Female patients usually underwent cardiac, renal, and neurologic monitoring, and measurement of plasma lyso-globotriaosylsphingosine (Gb3) levels at 6- or 12-month intervals. Treatment was initiated in 54%, mostly enzyme replacement therapy. Experts recommended screening all female relatives of index cases and evaluating all potentially affected organ systems. Diagnosis should be based on genetic analysis. Individualized monitoring of asymptomatic females must balance the need to detect organ damage while maintaining adherence. Treatment decisions should be based primarily on signs/symptoms of FD, but age, family screening results, GLA mutations, Gb3/lyso-Gb3 accumulation, and organ damage should be considered in asymptomatic females. More research on FD in females is needed and physicians should be aware of differences in the diagnosis, monitoring, and management of females vs. males with FD.

Detection of Very Low-Level Somatic Mosaic COL4A5 Splicing Variant in Asymptomatic Female Using Droplet Digital PCR

Background

Alport syndrome is a hereditary glomerulopathy featured by haematuria, proteinuria, and progressive renal failure. X-linked Alport syndrome (XLAS) due to COL4A5 disease-causing variants is the most common form. In the case of XLAS resulting from 10–18% presumed de novo COL4A5 disease-causing variants, there are only a few studies for mosaicism in the probands or parents. Very low-level (<1.0%) somatic mosaicism for COL4A5 disease-causing variants has not been published.

Materials and Methods

Chinese XLAS families with suspected parental mosaicism were enrolled in the present study to evaluate the forms of mosaicism, to offer more appropriate genetic counseling. PCR and direct sequencing were used to detect COL4A5 disease-causing variants harbored by the affected probands in parental multi-tissue DNAs (peripheral blood, urine sediments, saliva, hair), and droplet digital PCR (ddPCR) was used to quantify the mutant COL4A5 allelic fractions in parental different samples such as peripheral blood, saliva, and urine sediments.

Results

A Chinese asymptomatic female with suspected somatic and germline mosaicism was enrolled in the present study. She gave birth to two boys with XLAS caused by a hemizygous disease-causing variant c. 2245-1G>A in COL4A5 (NM_033380) intron 28, whereas this disease-causing variant was not detected in genomic DNA extracted from peripheral blood leukocytes in the woman using Sanger sequencing. She had multiple normal urine test results, and continuous linear immunofluorescence staining of α2 (IV) and α5 (IV) chains of skin tissue. Sanger sequencing demonstrated that COL4A5 disease-causing variant c. 2245-1G>A was not detected in her genomic DNAs isolated from urine sediments, saliva, and hair roots. Using ddPCR, the wild-type and mutant-type (c.2245-1G>A) COL4A5 was identified in the female's genomic DNAs isolated from peripheral blood, saliva, and urine sediments. The mutant allelic fractions in these tissues were 0.26% (peripheral blood), 0.73% (saliva), and 1.39% (urine), respectively.

Conclusions

Germline and very low-level somatic mosaicism for a COL4A5 splicing variant was detected in an asymptomatic female, which highlights that parental mosaicism should be excluded when a COL4A5 presumed de novo disease-causing variant is detected.

Detection of Mosaic Variants in Mothers of MPS II Patients by Next Generation Sequencing

Mucopolysaccharidosis type II is an X-linked lysosomal storage disorder caused by mutations in the IDS gene that encodes the iduronate-2-sulfatase enzyme. The IDS gene is located on the long arm of the X-chromosome, comprising 9 exons, spanning approximately 24 kb. The analysis of carriers, in addition to detecting mutations in patients, is essential for genetic counseling, since the risk of recurrence for male children is 50%. Mosaicism is a well-known phenomenon described in many genetic disorders caused by a variety of mechanisms that occur when a mutation arises in the early development of an embryo. Sanger sequencing is limited in detecting somatic mosaicism and sequence change levels of less than 20% may be missed. The Next Generation Sequencing (NGS) has been increasingly used in diagnosis. It is a sensitive and fast method for the detection of somatic mosaicism. Compared to Sanger sequencing, which represents a cumulative signal, NGS technology analyzes the sequence of each DNA read in a sample. NGS might therefore facilitate the detection of mosaicism in mothers of MPS II patients. The aim of this study was to reanalyze, by NGS, all MPS II mothers that showed to be non-carriers by Sanger analysis. Twelve non-carriers were selected for the reanalysis on the Ion PGM and Ion Torrent S5 platform, using a custom panel that includes the IDS gene. Results were visualized in the Integrative Genomics Viewer (IGV). We were able to detected the presence of the variant previously found in the index case in three of the mothers, with frequencies ranging between 13 and 49% of the reads. These results suggest the possibility of mosaicism in the mothers. The use of a more sensitive technology for detecting low-level mosaic mutations is essential for accurate recurrence-risk estimates. In our study, the NGS analysis showed to be an effective methodology to detect the mosaic event.

Urine-Derived Epithelial Cells as Models for Genetic Kidney Diseases

Epithelial cells exfoliated in human urine can include cells anywhere from the urinary tract and kidneys; however, podocytes and proximal tubular epithelial cells (PTECs) are by far the most relevant cell types for the study of genetic kidney diseases. When maintained in vitro, they have been proven extremely valuable for discovering disease mechanisms and for the development of new therapies. Furthermore, cultured patient cells can individually represent their human sources and their specific variants for personalized medicine studies, which are recently gaining much interest. In this review, we summarize the methodology for establishing human podocyte and PTEC cell lines from urine and highlight their importance as kidney disease cell models. We explore the well-established and recent techniques of cell isolation, quantification, immortalization and characterization, and we describe their current and future applications.