Clinical, biochemical and genetic characteristics of MOGS-CDG: a rare congenital disorder of glycosylation.

PURPOSE: To summarise the clinical, molecular and biochemical phenotype of mannosyl-oligosaccharide glucosidase-related congenital disorders of glycosylation (MOGS-CDG), which presents with variable clinical manifestations, and to analyse which clinical biochemical assay consistently supports diagnosis in individuals with bi-allelic variants in MOGS. METHODS: Phenotypic characterisation was performed through an international and multicentre collaboration. Genetic testing was done by exome sequencing and targeted arrays. Biochemical assays on serum and urine were performed to delineate the biochemical signature of MOGS-CDG. RESULTS: Clinical phenotyping revealed heterogeneity in MOGS-CDG, including neurological, immunological and skeletal phenotypes. Bi-allelic variants in MOGS were identified in 12 individuals from 11 families. The severity in each organ system was variable, without definite genotype correlation. Urine oligosaccharide analysis was consistently abnormal for all affected probands, whereas other biochemical analyses such as serum transferrin analysis was not consistently abnormal. CONCLUSION: The clinical phenotype of MOGS-CDG includes multisystemic involvement with variable severity. Molecular analysis, combined with biochemical testing, is important for diagnosis. In MOGS-CDG, urine oligosaccharide analysis via matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry can be used as a reliable biochemical test for screening and confirmation of disease.

The critical role of psychosine in screening, diagnosis, and monitoring of Krabbe disease.

PURPOSE: Newborn screening (NBS) for Krabbe disease (KD) is performed by measurement of galactocerebrosidase (GALC) activity as the primary test. This revealed that GALC activity has poor specificity for KD. Psychosine (PSY) was proposed as a disease marker useful to reduce the false positive rate for NBS and for disease monitoring. We report a highly sensitive PSY assay that allows identification of KD patients with minimal PSY elevations. METHODS: PSY was extracted from dried blood spots or erythrocytes with methanol containing d5-PSY as internal standard, and measured by liquid chromatography-tandem mass spectrometry. RESULTS: Analysis of PSY in samples from controls (N = 209), GALC pseudodeficiency carriers (N = 55), GALC pathogenic variant carriers (N = 27), patients with infantile KD (N = 26), and patients with late-onset KD (N = 11) allowed for the development of an effective laboratory screening and diagnostic algorithm. Additional longitudinal measurements were used to track therapeutic efficacy of hematopoietic stem cell transplantion (HSCT). CONCLUSION: This study supports PSY quantitation as a critical component of NBS for KD. It helps to differentiate infantile from later onset KD variants, as well as from GALC variant and pseudodeficiency carriers. Additionally, this study provides further data that PSY measurement can be useful to monitor KD progression before and after treatment.

Precision newborn screening for lysosomal disorders.

PURPOSE: The implementation of newborn screening for lysosomal disorders has uncovered overall poor specificity, psychosocial harm experienced by caregivers, and costly follow-up testing of false-positive cases. We report an informatics solution proven to minimize these issues. METHODS: The Kentucky Department for Public Health outsourced testing for mucopolysaccharidosis type I (MPS I) and Pompe disease, conditions recently added to the recommended uniform screening panel, plus Krabbe disease, which was added by legislative mandate. A total of 55,161 specimens were collected from infants born over 1 year starting from February 2016. Testing by tandem mass spectrometry was integrated with multivariate pattern recognition software (Collaborative Laboratory Integrated Reports), which is freely available to newborn screening programs for selection of cases for which a biochemical second-tier test is needed. RESULTS: Of five presumptive positive cases, one was affected with infantile Krabbe disease, two with Pompe disease, and one with MPS I. The remaining case was a heterozygote for the latter condition. The false-positive rate was 0.0018% and the positive predictive value was 80%. CONCLUSION: Postanalytical interpretive tools can drastically reduce false-positive outcomes, with preliminary evidence of no greater risk of false-negative events, still to be verified by long-term surveillance.

Fabry disease in infancy and early childhood: a systematic literature review.

PURPOSE: Fabry disease is a pan-ethnic, progressive, X-linked genetic disorder that commonly presents in childhood and is caused by deficient activity of the lysosomal enzyme alpha-galactosidaseA (α-gal A). Symptoms of Fabry disease in the pediatric population are well described for patients over five years of age; however, data are limited for infancy and early childhood. The purpose of this article is to delineate the age of detection for specific Fabry symptoms in early childhood. METHODS: A systematic retrospective analysis of PubMed indexed, peer-reviewed publications and case reports in the pediatric Fabry population was performed to review symptoms in patients reported before 5 years of age. RESULTS: The most frequently reported symptom in all age groups under 5 years was acroparesthesias/neuropathic pain, reported in 9 children, ranging in age from 2.0-4.0 years. Also notable is the frequency of gastrointestinal issues reported in 6 children aged 1.0-4.1 years of age. CONCLUSION: This article finds clear evidence that symptoms can occur in early childhood, before age 5 years. Given early presenting symptoms and the ability to monitor these disease hallmarks, a timely referral to a medical geneticist or other specialty clinician experienced in managing children with Fabry disease is strongly indicated.

Incorporation of Second-Tier Biomarker Testing Improves the Specificity of Newborn Screening for Mucopolysaccharidosis Type I.

Enzyme-based newborn screening for Mucopolysaccharidosis type I (MPS I) has a high false-positive rate due to the prevalence of pseudodeficiency alleles, often resulting in unnecessary and costly follow up. The glycosaminoglycans (GAGs), dermatan sulfate (DS) and heparan sulfate (HS) are both substrates for α-l-iduronidase (IDUA). These GAGs are elevated in patients with MPS I and have been shown to be promising biomarkers for both primary and second-tier testing. Since February 2016, we have measured DS and HS in 1213 specimens submitted on infants at risk for MPS I based on newborn screening. Molecular correlation was available for 157 of the tested cases. Samples from infants with MPS I confirmed by IDUA molecular analysis all had significantly elevated levels of DS and HS compared to those with confirmed pseudodeficiency and/or heterozygosity. Analysis of our testing population and correlation with molecular results identified few discrepant outcomes and uncovered no evidence of false-negative cases. We have demonstrated that blood spot GAGs analysis accurately discriminates between patients with confirmed MPS I and false-positive cases due to pseudodeficiency or heterozygosity and increases the specificity of newborn screening for MPS I.

Surgical septal myectomy for relief of dynamic obstruction in Anderson-Fabry Disease.

Patients with Anderson-Fabry Disease (AFD) and severe left ventricular hypertrophy complicated by left ventricular outflow tract (LVOT) obstruction may benefit from surgical septal myectomy (SSM). Mid- and late outcomes following surgery have not been established, and we sought to better characterize postoperative outcomes following septal myectomy. Between January 2011 and June 2017, 7 patients (6 females) with AFD underwent SSM. The median (range) age at the time of surgery was 53 (37-72) years; 4 patients had a positive family history of AFD and a preoperative diagnosis of AFD. Extracardiac features suggestive of AFD were present in 3 patients and all but 1 (female) had reduced α-galactosidase A activity. All patients had severe left ventricular hypertrophy and LVOT obstruction on transthoracic echocardiography. Preoperatively, all patients were severely symptomatic with New York Heart Association (NYHA) class III symptoms. There was no early mortality following surgery. The median in-hospital length of stay was 5 (4-7) days with 6 patients reporting NYHA class II or less symptoms at 3 month follow-up. Long-term outcomes were favorable with 4 patients reporting sustained NYHA class II or less symptoms, but 2 patients had recurrence of NYHA class III symptoms without evidence of recurrent LVOT obstruction. In conclusion, SSM appears to provide favorable short- and long-term relief of severe, symptomatic LVOT obstruction but may not alter progression of Fabry cardiomyopathy.

Cost Efficacy of α-Galactosidase A Enzyme Screening for Fabry Disease.

The prevalence of Fabry disease (FD) in adult patients with suspected hypertrophic cardiomyopathy (HCM) has been reported between 0.3% and 4%. Fabry disease-specific therapy necessitates early diagnosis; however, the optimal screening strategy and cost efficacy of routine α-galactosidase A (α-gal A) vs comprehensive galactosidase alpha gene (GLA) testing remain poorly understood. We identified 1192 patients who underwent routine α-gal A screening between January 1, 2011, and December 31, 2017, for suspected HCM. Cost efficacy was explored using prevalence and cost estimates. Ten patients had reduced α-gal A enzyme activity, and 5 (3 women) were ultimately diagnosed with FD (prevalence estimate, 0.42%). An alternative cardiac diagnosis was made in 3 patients with mildly reduced enzyme activity. Two women with reduced borderline enzyme levels did not undergo confirmatory testing, but FD was not suspected. The number needed to screen to diagnose 1 patient with FD in a similar cohort is estimated at 238 (5 new cases per 1192 at-risk individuals) at a cost of approximately US $24,000 per diagnosis. We identified a 0.42% prevalence of FD using routine α-gal A screening in adult patients referred to a dedicated HCM center in the United States. Compared with more comprehensive genetic testing strategies, we identified a similar prevalence of FD at a lower cost per diagnosis.

DNA carrier testing and newborn screening for maple syrup urine disease in Old Order Mennonite communities.

Maple syrup urine disease (MSUD) is an inherited metabolic disorder caused by mutations in the branched chain alpha-keto acid dehydrogenase complex. Worldwide incidence of MSUD is 1:225,000 live births. However, within Old Order Mennonite communities, the incidence is 1:150 live births and results from a common tyrosine to asparagine substitution (Y438N) in the E1alpha subunit of branched chain alpha-keto acid dehydrogenase. We developed a new DNA diagnostic assay utilizing TaqMan technology and compared its efficacy, sensitivity, and duration with an existing polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. Carrier testing was performed by both TaqMan technology and PCR-RFLP on DNA isolated from buccal swabs of 160 individuals as well as from buccal swabs and blood spots of nine at-risk newborns; assay time, sensitivity, and reliability were also evaluated. The TaqMan assay, like the PCR-RFLP assay, accurately determined Y438N E1alpha allele status. However, the TaqMan assay appeared (1) more sensitive than the PCR-RFLP assay, requiring 10-fold less DNA (10 ng) to reliably determine genotype status and (2) faster, reducing the assay time required for diagnosis from approximately 12 to 5 h. TaqMan technology allowed more rapid DNA diagnoses of MSUD in the neonate, thereby reducing the likelihood of neurological impairment while enhancing health and prognosis for affected infants.