A case with congenital disorder of glycosylation with defective fucosylation 2 and new mutation in FUK gene

Congenital disorders of glycosylation (CDG) is a group of rare, hereditary, multisystem disorders, predominantly affecting nervous system. There are N- and O- types of glycosylation. Fucosylation, a form of N-glycosylation, involves many enzymes. Until today, type 1 and type 2 fucosylation defects were identified, having pathogenic variants in genes encoding α-1,6-fucosyltransferase and fucokinase enzymes, respectively. In this article, a patient with type 2 fucosylation defect will be presented, with hypotonia, developmental delay and blindness and a pathogenic variant that was previously described in two patients.Whole exome sequencing (WES) was performed, since the patient had no time to implement diagnostic algorithm for hypotonia etiology.WES revealed a new pathogenic variant of homozygous c.993_1011del (p.Glu335Hisfs*55) frameshift variant of the FUK gene NM_145059 transcript. She had milder clinical manifestation than reported two patients.Congenital Defect of Glycosylation should be considered when the clinical findings cannot be explained by other known diseases, particularly in patients with multisystemic, predominantly neurological involvement.