Clinical and Molecular Features of Patients with Congenital Disorders of Glycosylation in Brazil

Abstract

Introduction: Congenital Disorders of Glycosylation are a group of genetic disorders due to abnormal glycosylation of glycoproteins and glycolipids. Based on isoelectric focusing of plasma transferrin results, CDG are classified in two groups: CDG-I and CDG-II. While the diagnosis of PMM2-CDG (formerly CDG-Ia) and PMI-CDG (formerly CDG-Ib) is made by demonstration of the enzyme deficiency or by gene sequencing, the diagnosis of the other CDG is not easily performed. Psychomotor delay/mental retardation, hypotonia, seizures, ataxia, cerebellar atrophy, strabismus, inverted nipples, lipodystrophy, and stroke-like episodes characterize PMM2-CDG, by far the most common CDG. There is almost no information available in the literature on the frequency of CDG in patients with psychomotor delay/ mental retardation. Patients and methods: We performed transferrin isoelectric focusing in 2619 patients who had psychomotor delay/mental retardation associated with other symptoms suggestive of CDG. Determination of leukocyte phosphomannomutase and phosphomannoseisomerase activities and PMM2 gene sequencing was performed in selected patients. Results: We found 32 affected patients (26 CDG-I and 6-CDG-II). CDG-I group: The most prevalent PMM2- CDG clinical symptoms were those expected. We identified two novel mutations: p.G79V and p.R21W. Non-PMM2, non-PMI-CDG showed more frequently coagulopathy, hypotonia, cerebellar atrophy, and cryptorchidism/micropenis. Early deaths were found exclusively in this group. Ataxia, strabismus, elevated blood FSH and LH levels were more frequent in PMM2-CDG patients. CDG-II group: four out of six patients presented cutis laxa, seizures, large fontanel, facial dysmorphism, and non-lissencephalic cortical dysplasia. Hip luxation was present in three patients, and hydronephrosis in one. The other two patients had heterogeneous features. Conclusions: We determined the frequency of CDG in a selected Brazilian cohort with symptoms suggestive of CDG as 1.2%(CDG-I ~ 1.0% and CDG-II ~ 0.2%), and identified two novel mutations in the PMM2 gene.