All reported non-canonical splice site variants in GLA cause aberrant splicing

BACKGROUND

Fabry disease is an X-linked lysosomal storage disorder caused by insufficient α-galactosidase A (GLA) activity resulting from variants in the GLA gene, which leads to glycosphingolipid accumulation and life-threatening, multi-organ complications. Approximately 50 variants have been reported that cause splicing abnormalities in GLA. Most were found within canonical splice sites, which are highly conserved GT and AG splice acceptor and donor dinucleotides, whereas one-third were located outside canonical splice sites, making it difficult to interpret their pathogenicity. In this study, we aimed to investigate the genetic pathogenicity of variants located in non-canonical splice sites within the GLA gene.

METHODS

13 variants, including four deep intronic variants, were selected from the Human Gene Variant Database Professional. We performed an in vitro splicing assay to identify splicing abnormalities in the variants.

RESULTS

All candidate non-canonical splice site variants in GLA caused aberrant splicing. Additionally, all but one variant was protein-truncating. The four deep intronic variants generated abnormal transcripts, including a cryptic exon, as well as normal transcripts, with the proportion of each differing in a cell-specific manner.

CONCLUSIONS

Validation of splicing effects using an in vitro splicing assay is useful for confirming pathogenicity and determining associations with clinical phenotypes.

Aberrant splicing caused by exonic single nucleotide variants positioned 2nd or 3rd to the last nucleotide in the COL4A5 gene

BACKGROUND AND OBJECTIVES

The evident genotype-phenotype correlation shown by the X-linked Alport syndrome warrants the assessment of the impact of identified gene variants on aberrant splicing. We previously reported that single nucleotide variants (SNVs) in the last nucleotide of exons in COL4A5 cause aberrant splicing. It is known that the nucleotides located 2nd and 3rd to the last nucleotides of exons can also play an essential role in the first step of the splicing process. In this study, we aimed to investigate whether SNVs positioned 2nd or 3rd to the last nucleotide of exons in COL4A5 resulted in aberrant splicing.

METHODS

We selected eight candidate variants: six from the Human Gene Variant Database Professional and two from our cohort. We performed an in-vitro splicing assay and reverse transcription-polymerase chain reaction (RT-PCR) for messenger RNA obtained from patients, if available.

RESULTS

The candidate variants were initially classified into the following groups: three nonsense, two missense, and three synonymous variants. Splicing assays and RT-PCR for messenger RNA revealed that six of the eight variants caused aberrant splicing. Four variants, initially classified as non-truncating variants, were found to be truncating ones, which usually show relatively more severe phenotypes.

CONCLUSION

We revealed that exonic SNVs positioned 2nd or 3rd to the last nucleotide of exons in the COL4A5 were responsible for aberrant splicing. The results of our study suggest that attention should be paid when interpreting the pathogenicity of exonic SNVs near the 5' splice site.

Nephroplex: a kidney-focused NGS panel highlights the challenges of PKD1 sequencing and identifies a founder BBS4 mutation

Background

Genetic testing of patients with inherited kidney diseases has emerged as a tool of clinical utility by improving the patients’ diagnosis, prognosis, surveillance and therapy.

Methods

The present study applied a Next Generation Sequencing (NGS)-based panel, named NephroPlex, testing 115 genes causing renal diseases, to 119 individuals, including 107 probands and 12 relatives. Thirty-five (poly)cystic and 72 non (poly)cystic individuals were enrolled. The latter subgroup of patients included Bardet-Biedl syndrome (BBS) patients, as major components.

Results

Disease-causing mutations were identified in 51.5 and 40% of polycystic and non-polycystic individuals, respectively. Autosomal dominant polycystic kidney disease (ADPKD) patients with truncating PKD1 variants showed a trend towards a greater slope of the age-estimated glomerular filtration rate (eGFR) regression line than patients with (i) missense variants, (ii) any PKD2 mutations and (iii) no detected mutations, according to previous findings. The analysis of BBS individuals showed a similar frequency of BBS4,9,10 and 12 mutations. Of note, all BBS4-mutated patients harbored the novel c.332+1G>GTT variant, which was absent in public databases, however, in our internal database, an additional heterozygote carrier was found. All BBS4-mutated individuals originated from the same geographical area encompassing the coastal provinces of Naples.

Discussion

In conclusion, these findings indicate the potential for a genetic panel to provide useful information at both clinical and epidemiological levels.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s40620-021-01048-4.

Meeting report of the 2017 KidGen Renal Genetics Symposium

The 2017 KidGen Renal Genetics Symposium was held at the Royal Children’s Hospital and Murdoch Children’s Research Institute, Melbourne, from 6 to 8 December 2017. This meeting addressed clinical, diagnostic, and research aspects of inherited kidney disease. More than 100 clinicians, researchers, and patient representatives attended the conference. The overall goal was to improve the understanding and direction of genomics in renal medicine in Australia and discuss barriers to the use of genomic testing within this area. It also aimed to strengthen collaborations between local, state, and global research and diagnostic and clinical groups.

Detection of copy number variations by pair analysis using next-generation sequencing data in inherited kidney diseases

BACKGROUND

Comprehensive genetic approaches for diagnosing inherited kidney diseases using next-generation sequencing (NGS) have recently been established. However, even with these approaches, we are still failing to detect gene defects in some patients who appear to suffer from genetic diseases. One of the reasons for this is the difficulty of detecting copy number variations (CNVs) using our current approaches. For such cases, we can apply methods of array-based comparative genomic hybridization (aCGH) or multiplex ligation and probe amplification (MLPA); however, these are expensive and laborious and also often fail to identify CNVs. Here, we report seven cases with CNVs in various inherited kidney diseases screened by NGS pair analysis.

METHODS

Targeted sequencing analysis for causative genes was conducted for cases with suspected inherited kidney diseases, for some of which a definitive genetic diagnosis had not been achieved. We conducted pair analysis using NGS data for those cases. When CNVs were detected by pair analysis, they were confirmed by aCGH and/or MLPA.

RESULTS

In seven cases, CNVs in various causative genes of inherited kidney diseases were detected by pair analysis. With aCGH and/or MLPA, pathogenic CNV variants were confirmed: COL4A5 or HNF1B in two cases each, and EYA1, CLCNKB, or PAX2 in one each.

CONCLUSION

We presented seven cases with CNVs in various genes that were screened by pair analysis. The NGS-based CNV detection method is useful for comprehensive screening of CNVs, and our results revealed that, for a certain proportion of cases, CNV analysis is necessary for accurate genetic diagnosis.