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Dear readers: I am proud to say that we are continuing to publish many important papers on newborn screening in IJNS, and the papers published in this issue clearly support my statement [...].Dear readers: I am proud to say that we are continuing to publish many important papers on newborn screening in IJNS, and the papers published in this issue clearly support my statement [...].

Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems and long term risks for hepatocellular carcinoma. An effective medical treatment with 2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione (NTBC) exists but requires early identification of affected children for optimal long-term results. Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1. If identified early and treated appropriately, the majority of affected infants can remain asymptomatic. A clinical management scheme is needed for infants with HT-1 identified by NBS or clinical symptoms. To this end, a group of 11 clinical practitioners, including eight biochemical genetics physicians, two metabolic dietitian nutritionists, and a clinical psychologist, from the United States and Canada, with experience in providing care for patients with HT-1, initiated an evidence- and consensus-based process to establish uniform recommendations for identification and treatment of HT-1. Recommendations were developed from a literature review, practitioner management survey, and nominal group process involving two face-to-face meetings. There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet. Consensus recommendations for both immediate and long-term clinical follow-up of positive diagnoses via both newborn screening and clinical symptomatic presentation are provided.

This phase 3 trial of enzyme-replacement therapy in children and adults with lysosomal acid lipase deficiency, which causes cirrhosis and severe dyslipidemia, showed that enzyme replacement lessened multiple disease-related hepatic and lipid abnormalities. Lysosomal acid lipase deficiency (Online Mendelian Inheritance in Man number, 278000) 1 is an autosomal recessive storage disease that is caused by mutations in the LIPA gene. 2 In infants, progression of the disease (historically known as Wolman’s disease) is very rapid, with death typically occurring by 6 months of age. 2 In older patients, progression of the disease (historically known as cholesteryl ester storage disease) leads to cirrhosis and other complications in childhood or later in life. 3 Common features in infants, children, and adults include elevated serum aminotransferase levels, dyslipidemia, hepatomegaly, liver fibrosis, and cirrhosis. 3 – 5 Awareness of the disease is low, . . .

In this issue of the Journal , Muenzer and colleagues 1 report results from the first-in-human international phase 1–2 study of tividenofusp alfa in mucopolysaccharidosis type II (MPS II; also known as the Hunter syndrome), marking a milestone in the treatment of lysosomal disorders. For decades, delivery of enzyme-replacement therapy (ERT) across the blood–brain barrier has remained a major obstacle. Tividenofusp alfa surmounts this barrier, representing a breakthrough for neuronopathic MPS II and offering renewed optimism for affected families and clinicians. Intravenous ERT has long ameliorated the systemic manifestations of MPS II but has failed to prevent neurocognitive decline owing to limited penetration . . .

Purpose To assess the magnitude of benefit to early treatment initiation, enabled by newborn screening or prenatal diagnosis, in patients with cross-reactive immunological material (CRIM)-negative infantile Pompe disease (IPD), treated with enzyme replacement therapy (ERT) and prophylactic immune tolerance induction (ITI) with rituximab, methotrexate, and intravenous immunoglobulin (IVIG). Methods A total of 41 CRIM-negative IPD patients were evaluated. Among patients who were treated with ERT + ITI ( n  = 30), those who were invasive ventilator–free at baseline and had ≥6 months of follow-up were stratified based on age at treatment initiation: (1) early (≤4 weeks), (2) intermediate (>4 and ≤15 weeks), and (3) late (>15 weeks). A historical cohort of 11 CRIM-negative patients with IPD treated with ERT monotherapy served as an additional comparator group. Results Twenty patients were included; five, seven, and eight in early, intermediate, and late treatment groups, respectively. Genotypes were similar across the three groups. Early-treated patients showed significant improvements in left ventricular mass index, motor and pulmonary outcomes, as well as biomarkers creatine kinase and urinary glucose tetrasaccharide, compared with those treated later. Conclusion Our preliminary data suggest that early treatment with ERT + ITI can transform the long-term CRIM-negative IPD phenotype, which represents the most severe end of the Pompe disease spectrum.

Congenital disorders of glycosylation (CDG) represent 1 of the largest groups of metabolic disorders with >130 subtypes identified to date. The majority of CDG subtypes are disorders of -linked glycosylation, in which carbohydrate residues, namely, -glycans, are posttranslationally linked to asparagine molecules in peptides. To improve the diagnostic capability for CDG, we developed and validated a plasma -glycan assay using flow injection-electrospray ionization-quadrupole time-of-flight mass spectrometry. After PNGase F digestion of plasma glycoproteins, -glycans were linked to a quinolone using a transient amine group at the reducing end, isolated by a hydrophilic interaction chromatography column, and then identified by accurate mass and quantified using a stable isotope-labeled glycopeptide as the internal standard. This assay differed from other -glycan profiling methods because it was free of any contamination from circulating free glycans and was semiquantitative. The low end of the detection range tested was at 63 nmol/L for disialo-biantennary -glycan. The majority of -glycans in normal plasma had <1% abundance. Abnormal -glycan profiles from 19 patients with known diagnoses of 11 different CDG subtypes were generated, some of which had previously been reported to have normal -linked protein glycosylation by carbohydrate-deficient transferrin analysis. The clinical specificity and sensitivity of -glycan analysis was much improved with this method. Additional CDGs can be diagnosed that would be missed by carbohydrate-deficient transferrin analysis. The assay provides novel biomarkers with diagnostic and potentially therapeutic significance.

Background Lysosomal acid lipase deficiency (LALD) is an autosomal recessive inborn error of lipid metabolism characterized by impaired lysosomal hydrolysis and consequent accumulation of cholesteryl esters and triglycerides. The phenotypic spectrum is diverse, ranging from severe, neonatal onset failure to thrive, hepatomegaly, hepatic fibrosis, malabsorption and adrenal insufficiency to childhood-onset hyperlipidemia, hepatomegaly, and hepatic fibrosis. Sebelipase alfa enzyme replacement has been approved by the Food and Drug Administration for use in LALD after demonstrating dramatic improvement in transaminitis and dyslipidemia with initiation of enzyme replacement therapy. Methods A chart review was performed on 2 patients with childhood-onset, symptomatic LALD with persistent dyslipidemia despite appropriate enzyme replacement therapy to identify biological pathways and risk factors for incomplete response to therapy. Results Two patients with attenuated, symptomatic LALD had resolution of transaminitis on enzyme replacement therapy without concomitant effect on dyslipidemia despite dose escalation and no evidence of antibody response to enzyme. Conclusion Enzyme replacement therapy does not universally resolve all complications of LALD. Persistent dyslipidemia remains a clinically significant issue, likely related to the complex metabolic pathways implicated in LALD pathogenesis. We discuss the possible mechanistic basis for this unexpected finding and the implications for curative LALD therapy.

Background Krabbe disease is a rare neurodegenerative genetic disorder caused by deficiency of galactocerebrosidase. Patients with the infantile form of Krabbe disease can be treated at a presymptomatic stage with human stem cell transplantation which improves survival and clinical outcomes. However, without a family history, most cases of infantile Krabbe disease present after onset of symptoms and are ineligible for transplantation. In 2006, New York began screening newborns for Krabbe disease to identify presymptomatic cases. To ensure that those identified with infantile disease received timely treatment, New York public health and medical systems took steps to accurately diagnose and rapidly refer infants for human stem cell transplantation within the first few weeks of life. After 11 years of active screening in New York and the introduction of Krabbe disease newborn screening in other states, new information has been gained which can inform the design of newborn screening programs to improve infantile Krabbe disease outcomes. Findings Recent information relevant to Krabbe disease screening, diagnosis, and treatment were assessed by a diverse group of public health, medical, and advocacy professionals. Outcomes after newborn screening may improve if treatment for infantile disease is initiated before 30 days of life. Newer laboratory screening and diagnostic tools can improve the speed and specificity of diagnosis and help facilitate this early referral. Given the rarity of Krabbe disease, most recommendations were based on case series or expert opinion. Conclusion This report updates recommendations for Krabbe disease newborn screening to improve the timeliness of diagnosis and treatment of infantile Krabbe disease. In the United States, several states have begun or are considering Krabbe disease newborn screening. These recommendations can guide public health laboratories on methodologies for screening and inform clinicians about the need to promptly diagnose and treat infantile Krabbe disease. The timing of the initial referral after newborn screening, the speed of diagnostic confirmation of infantile disease, and the transplantation center’s experience and ability to rapidly respond to a suspected patient with newly diagnosed infantile Krabbe disease are critical for optimal outcomes.

Galactokinase (GALK1) deficiency is a rare hereditary galactose metabolism disorder. Beyond cataract, the phenotypic spectrum is questionable. Data from affected patients included in the Galactosemias Network registry were collected to better characterize the phenotype. Observational study collecting medical data of 53 not previously reported GALK1 deficient patients from 17 centers in 11 countries from December 2014 to April 2020. Neonatal or childhood cataract was reported in 15 and 4 patients respectively. The occurrence of neonatal hypoglycemia and infection were comparable with the general population, whereas bleeding diathesis (8.1% versus 2.17–5.9%) and encephalopathy (3.9% versus 0.3%) were reported more often. Elevated transaminases were seen in 25.5%. Cognitive delay was reported in 5 patients. Urinary galactitol was elevated in all patients at diagnosis; five showed unexpected Gal-1-P increase. Most patients showed enzyme activities ≤1%. Eleven different genotypes were described, including six unpublished variants. The majority was homozygous for NM_000154.1:c.82C>A (p.Pro28Thr). Thirty-five patients were diagnosed following newborn screening, which was clearly beneficial. The phenotype of GALK1 deficiency may include neonatal elevation of transaminases, bleeding diathesis, and encephalopathy in addition to cataract. Potential complications beyond the neonatal period are not systematically surveyed and a better delineation is needed.

Mucopolysaccharidosis (MPS) type II, or Hunter syndrome, is an X-linked lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase. Glycosaminoglycan (GAG) accumulation leads to progressive multisystemic involvement, with coarse facial features, hepatosplenomegaly, short stature, recurrent upper respiratory infections, hearing loss, hernias, dysostosis multiplex, joint contractures, and cardiac valve disease. Individuals with the neuronopathic form of the disease also have central nervous system (CNS) involvement with developmental delay and progressive cognitive decline. Enzyme replacement therapy (ERT), idursulfase, is the only FDA-approved treatment for MPS II. MPS II was added to the Recommended Uniform Screening Panel (RUSP) in the United States in 2022, and screening is ongoing in several other countries, including Taiwan. Here, we report seven individuals from four families identified through newborn screening sharing the same IDS variant: c.817C>T, p.Arg273Trp. Confirmatory testing demonstrated low iduronate-2-sulfatase activity level and elevated GAGs in every individual, but they had no signs or symptoms of MPS II. They were aged 8 months to 60 years old according to the most recent assessment and all remained asymptomatic. ERT was not initiated for any of them. Our findings suggest that the IDS c.817C>T variant is associated with abnormal biochemical findings but no clinical phenotype of MPS II. Newborn screening will likely identify additional cases and provide a better understanding of the clinical significance of this variant.