Congenital Disorders of Glycosylation: successful implementation of Mass Sequencing in the diagnostic algorithm.

Abstract

Congenital Glycosylation Disorders (CDG) are human genetic diseases (1: 20,000) due to the alteration in genes involved in the multiple pathways of glycoconjugates (glycoproteins, glycolipids, GPI anchors, among others). The clinical phenotype is multisystemic with a broad range of severity, even being very serious with neonatal death. The diagnosis begins with the clinical suspicion and subsequent the study of serum transferrin (a N-glycoprotein) by the isoelectrofocusing  technique (IEF-Tf) the most frequent test. There are more than 130 genes involved in these pathologies thus the algorithm for diagnose is complex and the synchronization of Mass Sequencing technology (NGS) combined with the biochemical analysis has allowed progress in the detection of new CDG patients.

The objective was to communicate the advances in the study of CDG through the use of NGS in Argentine patients.

A total of 240 individuals with clinical suspicion of CDG, derived from different medical centers during the 2015-2019 periods were studied. The inclusion criteria were at least three manifestations: axial hypotonia, mature delay, frequent infections, enteropathy, coagulopathy, cerebellar hypoplasia, congenital myasthenic syndrome or metabolic disease of unknown origin.

The study of serum Tf-IEF was carried out and subsequently in patients with altered patterns genomic DNA was obtained and massive sequencing done (NGS Illumina platform). Results: 4 altered Tf-IEF were identified, in 3 of them a nonsense variant not yet reported (c.753G> T; p.Arg251Leu) was detected in homozygosis in exon 2 of the ALG-2 gene (OMIM # 607906) (<1 / 1,000,000). Through in silico analysis, the mutation showed to be moderately pathogenic. The genetic variants found in a fourth patient do not correspond to genes associated with CDG (Tf-IEF altered by secondary causes).

Due to the large number of genes involved in the N-glycosylation pathway and the similarity in the clinical manifestations of these patients, the use of NGS combined with biochemical screening allow to improved the diagnosis of patients with CDG in our country. Together the detection of very rare CDG classes worldwide may possibly to describe new genes associated with CDG. CONICET-UCC-UNC.