ALG12-CDG: An unusual patient without intellectual disability and facial dysmorphism, and with a novel variant

Congenital disorder of glycosylation (CDG) type I is a group of rare disorders caused by recessive mutations in up to 25 genes that impair the N-glycan precursor formation and its transfer to proteins resulting in hypoglycosylation of multiple proteins. Congenital disorder of glycosylation causes multisystem defects usually with psychomotor delay that is diagnosed in the infancy. We aim to supply further evidences supporting that CDG may be underestimated.

Antithrombin and factor XI were studied by chromogenic and coagulometric methods. Hypoglycosylation of plasma proteins was evaluated by western blot, HPLC, Q-TOF, and RP-LC-MRM-MS. Genetic analysis included whole exome, Sanger sequencing, and PCR-allele specific assay.

We here present an intriguing patient with an exceptional phenotype: 25-year-old women with a ventricular septal defect and severe idiopathic scoliosis but no facial dysmorphism, who dances as a professional, and has a University degree. Congenital disorder of glycosylation diagnosis started through the identification of antithrombin deficiency without SERPINC1 defect and the detection of hypoglycosylated forms. Increased levels of hypoglycosylated forms of F XI (also with significant deficiency) and transferrin were also detected. Whole exome analysis showed a novel homozygous ALG12 variant c.77T>A, p.(Val26Asp) supporting an ALG12-CDG diagnosis. It also showed three new variants in KMT2D, and a mild, known ALG6 variant.

This novel ALG12-CDG patient (the 13th reported) underlines the heterogeneity of this CDG and broadens its phenotypical spectrum, supports that these disorders are underestimated, and suggests that combination of global hypoglycosylation with specific gene defects might determine the clinical manifestations of CDG patients.