Genetic Landscape of Nephropathic Cystinosis in Russian Children

Abstract

Nephropathic cystinosis is a rare autosomal recessive disorder characterized by amino acid cystine accumulation and caused by biallelic mutations in the CTNS gene. The analysis methods are as follows: tandem mass spectrometry to determine the cystine concentration in polymorphonuclear blood leukocytes, Sanger sequencing for the entire coding sequence and flanking intron regions of the CTNS gene, multiplex PCR to detect a common mutation-a 57 kb deletion, and multiplex ligation-dependent probe amplification to analyze the number of exon copies in the CTNS gene. Haplotype analysis of chromosomes with major mutations was carried out using microsatellite markers D17S831, D17S1798, D17S829, D17S1828, and D17S1876. In this study, we provide clinical, biochemical, and molecular genetic characteristics of 40 Russian patients with mutations in the CTNS gene, among whom 30 patients were selected from a high-risk group of 85 people as a result of selective screening, which was carried out through cystine concentration measurement in polymorphonuclear blood leukocytes. The most common pathogenic variant, as in most described studies to date, was the 57 kb deletion, which represented 25% of all affected alleles. Previously non-described variants represented 22.5% of alleles. The founder effect in the Karachay and Chechen ethnic groups was shown for the following major variants: c.1015G > A and c.518A > G.

Keywords: children; cystine; cystinosis; lysosomal storage diseases; novel mutations in the CTNS gene; selective screening; therapy monitoring.

FIGURE 1

Calibration characteristics of the analytics system. The square of the calibration characteristic correlation quotient was 0.997. The lower threshold of quantitative cystine detection was 0.11 μmol/L. The cystine detection threshold was 0.01 μmol/L (Figure 2). The time of analysis for one probe was 15 min. The obtained data were processed using a built-in Bruker Data Analysis 4.1 program package.

FIGURE 2

Chromatogram of the standard cystine solution with a concentration of 0.11 μmol/L corresponding to the lower threshold of the quantitative detection method.

FIGURE 3

Phylogenetic analysis of ethnic Chechen children with the c.518A>G pathogenic variant; and control samples without it.