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

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.

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.

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.

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.