Fractionated plasma N-glycan profiling of novel cohort of ATP6AP1-CDG subjects identifies phenotypic association.

ATP6AP1-CDG is an X-linked disorder typically characterized by hepatopathy, immunodeficiency, and an abnormal type II transferrin glycosylation pattern. Here, we present 11 new patients and clinical updates with biochemical characterization on one previously reported patient. We also document intrafamilial phenotypic variability and atypical presentations, expanding the symptomatology of ATP6AP1-CDG to include dystonia, hepatocellular carcinoma, and lysosomal abnormalities on hepatic histology. Three of our subjects received successful liver transplantation. We performed N-glycan profiling of total and fractionated plasma proteins for six patients and show associations with varying phenotypes, demonstrating potential diagnostic and prognostic value of fractionated N-glycan profiles. The aberrant N-linked glycosylation in purified transferrin and remaining plasma glycoprotein fractions normalized in one patient post hepatic transplant, while the increases of Man4GlcNAc2 and Man5GlcNAc2 in purified immunoglobulins persisted. Interestingly, in the single patient with isolated immune deficiency phenotype, elevated high-mannose glycans were detected on purified immunoglobulins without glycosylation abnormalities on transferrin or the remaining plasma glycoprotein fractions. Given the diverse and often tissue specific clinical presentations and the need of clinical management post hepatic transplant in ATP6AP1-CDG patients, these results demonstrate that fractionated plasma N-glycan profiling could be a valuable tool in diagnosis and disease monitoring.

Immune dysfunction in MGAT2-CDG: A clinical report and review of the literature.

Glycosylation is a critical post/peri-translational modification required for the appropriate development and function of the immune system. As an example, abnormalities in glycosylation can cause antibody deficiency and reduced lymphocyte signaling, although the phenotype can be complex given the diverse roles of glycosylation. Human MGAT2 encodes N-acetylglucosaminyltransferase II, which is a critical enzyme in the processing of oligomannose to complex N-glycans. Complex N-glycans are essential for immune system functionality, but only one individual with MGAT2-CDG has been described to have an abnormal immunologic evaluation. MGAT2-CDG (CDG-IIa) is a congenital disorder of glycosylation (CDG) associated with profound global developmental disability, hypotonia, early onset epilepsy, and other multisystem manifestations. Here, we report a 4-year old female with MGAT2-CDG due to a novel homozygous pathogenic variant in MGAT2, a 4-base pair deletion, c.1006_1009delGACA. In addition to clinical features previously described in MGAT2-CDG, she experienced episodic asystole, persistent hypogammaglobulinemia, and defective ex vivo mitogen and antigen proliferative responses, but intact specific vaccine antibody titers. Her infection history has been mild despite the testing abnormalities. We compare this patient to the 15 previously reported patients in the literature, thus expanding both the genotypic and phenotypic spectrum for MGAT2-CDG.

p.P1379S, a benign variant with reduced ATP7B protein level in Wilson Disease.

BACKGROUND: Wilson disease (WD) is an autosomal recessive disorder of copper transport caused by inherited defects in the ATP7B gene and results in toxic accumulation of copper in various organs. We previously reported a family with three consecutive generations affected by WD that carries the variant, p.P1379S, which was classified at the time as likely pathogenic. However, recent investigations of the p.P1379S variant indicate a possible conflict of interpretations regarding its pathogenicity. This led us to explore the quantification of ATP7B in dried blood spots (DBS) using a surrogate peptide to study the effects of the p.P1379S variant on ATP7B concentrations in two unrelated families with the common p.P1379S variant. METHODS AND RESULTS: ATP7B was quantified using the peptide immunoaffinity enrichment coupled with selected reaction monitoring mass spectrometry (immuno-SRM) method which utilizes antibody-mediated peptide capture from DBS. Two patients affected with WD had undetectable ATP7B level while four compound heterozygous children with one known pathogenic variant and the p.P1379S had significantly reduced ATP7B levels. Of note, all four children remain asymptomatic without abnormal laboratory consequences despite being untreated for WD. CONCLUSION: These two families demonstrated that p.P1379S, when compounded with two known pathogenic variants, resulted in significantly reduced protein levels but retained enough function to maintain normal copper homeostasis. This implies that p.P1379S is benign in nature. A better understanding of the nature and consequences of variants in WD will help in informing patient care and avoiding unnecessary treatments.

The co-occurrence of Wilson disease and X-linked agammaglobulinemia in one family highlights the promising diagnostic potential of proteolytic analysis.

BACKGROUND: We report the first case of a family with co-occurrence of Wilson disease (WD), an autosomal recessive disorder of copper metabolism, and X-linked agammaglobulinemia (XLA), a primary immunodeficiency disorder (PIDD) that features marked reduction in circulating B lymphocytes and serum immunoglobulins. METHODS AND RESULTS: Through utilization of a multiplexed biomarker peptide quantification method known as the immuno-SRM assay, we were able to simultaneously and independently identify which family members are affected with WD and which are affected with XLA using dried blood spots (DBS). CONCLUSION: Being able to delineate multiple diagnoses using proteolytic analysis from a single DBS provides support for implementation of this methodology for clinical diagnostic use as well as large-scale population screening, such as newborn screening (NBS). This could allow for early identification and treatment of affected individuals with WD or XLA, which have been shown to reduce morbidity and decrease mortality in these two populations.

Feeding difficulty and gastrostomy tube placement in infants with Down syndrome.

The objectives of this study were to determine if any specific clinical signs, symptoms, or comorbidities could reliably predict underlying feeding difficulty and need for further evaluation (i.e., video swallow study, VSS) in infants with Down syndrome, to establish the prevalence of gastrostomy tube placement (G-tube), and to determine if any clinical signs, symptoms, or comorbidities correlated with a higher risk for needing placement of a G-tube. An electronic medical record retrospective chart review of 73 children with Down syndrome born between January 2013 and March 2017 and seen in Nationwide Children's Hospital's multidisciplinary Down Syndrome Clinic included demographic information, medical history, and results of studies and specialist evaluations. Descriptive statistics were utilized to summarize the data. Comparisons were performed to identify factors which differed between feeding difficulty vs. no feeding difficulty and G-tube placement vs. no G-tube placement. "Feeding difficulty" was the only feeding term established by the AAP guidelines which was consistently noted in charts of children with feeding abnormalities. Infants with feeding difficulty had increased use of medical services and more abnormalities on specialist evaluations and studies. Congenital heart disease, cardiothoracic surgery, obstructive sleep apnea, and hypothyroidism did not differ significantly between the groups assessed. Our cohort had a prevalence of 13.7% for requiring G-tube placement in their first year of life.Conclusion: The currently established clinical tools for determining which patients may benefit from radiographic evaluation lack sufficient sensitivity to detect all individuals with feeding difficulty. Due to the high prevalence of abnormal VSS results and high rate of G-tube placement, universal radiographic screening for individuals with Down syndrome could be considered, even in the absence of obvious clinical signs or symptoms. However, determining how to balance this with cost, availability, and radiation exposure may be difficult.What is Known: • Feeding difficulty in children with Down syndrome can lead to significantly increased morbidity, such as poor weight gain, failure to thrive, aspiration, persistent respiratory symptoms, andrecurrent pneumonia. • The AAP has established a clinical tool regarding which objective signs and symptoms should lead to a radiographic swallowing assessment within their Health Supervision for Children with Down Syndrome Clinical Report.What is New: • A comprehensive assessment of clinical signs, symptoms, and common comorbidities in infants with Down syndrome has not previously been correlated with presence of feeding difficulty nor necessity for gastrostomy tube placement, including whether or not the terms used in the AAP guidelines encompass the sensitivity required to detect all infants with feeding difficulty. • The prevalence of gastrostomy tube placement in children with Down syndrome has not previously been established.