Identification of two novel variants in ALG11 causing congenital disorder of glycosylation

Background: Congenital disorders of glycosylation (CDG) represent a heterogeneous group of rare inherited metabolic disorders due to abnormalities in protein or lipid glycosylation pathways, affecting multiple systems, and frequently being accompanied by neurological symptoms. ALG11-CDG, also known as CDG-1p, arises from a deficiency in a specific mannosyltransferase encoded by the ALG11 gene. To date, only 17 cases have been documented, and these patients have prominent clinical phenotypes, including seizures, developmental delay, and microcephaly. Methods: We describe a novel case of a four-month-old boy from a Chinese family exhibiting developmental delay, seizures, and microcephaly. Trio whole-exome sequencing (WES) and subsequent Sanger sequencing were employed to identify the potential genetic cause, and functional study was performed to evaluate the pathogenicity of genetic variant identified. Results: Trio WES unveiled novel compound heterozygous variants: c.1307G>T (p.G436V) and c.1403G>A (p. R468H) within exon 4 of the ALG11 gene, inherited from the father and mother, respectively. Subsequent in vitro functional analysis revealed decreased stability of the mutant protein and concurrent hypoglycosylation of GP130, a hyperglycosylated protein. Conclusions: Our findings not only expand the clinical and variant spectrum of ALG11-CDG, but also emphasize the importance of WES as a first-tier genetic test in determining the molecular diagnosis.