Estimating the sensitivity of genomic newborn screening for treatable inherited metabolic disorders.

INTRODUCTION: Over 30 research groups and companies are exploring newborn screening using genomic sequencing (NBSeq), but the sensitivity of this approach is not well understood. METHODS: We identified individuals with treatable inherited metabolic disorders (IMDs) and ascertained the proportion whose DNA analysis revealed explanatory deleterious variants (EDVs). We examined variables associated with EDV detection and estimated the sensitivity of "DNA-first" NBSeq. We further predicted the annual rate of true positive and false negative NBSeq results in the United States for several conditions on the Recommended Uniform Screening Panel (RUSP). RESULTS: We identified 635 individuals with 80 unique IMDs. In univariate analyses, Black race (OR = 0.37, 95% CI: 0.16-0.89, p = 0.02) and public insurance (OR = 0.60, 95% CI: 0.39-0.91, p = 0.02) were less likely to be associated with finding EDVs. Had all individuals been screened with NBSeq, the sensitivity would have been 80.3%. We estimated that between 0 and 649.9 cases of RUSP IMDs would be missed annually by NBSeq in the United States. CONCLUSIONS: The overall sensitivity of NBSeq for treatable IMDs is estimated at 80.3%. That sensitivity will likely be lower for Black infants and those who are on public insurance.

Diagnostic options, physiopathology, risk factors and genetic causes of permanent congenital hypothyroidism: A narrative review.

Background: In Permanent congenital hypothyroidism (PCH) is a lifelong condition characterized by a deficiency in thyroid hormone, leading to various neurodevelopmental complications. Early clinical signs are often nonspecific and easily overlooked, but newborn screening programs have improved early detection. Methods: This narrative review aims to provide insights comparatively transient and permanent PCH and also the diagnosis, risk factors, underlying pathophysiology, and genetic causes associated with PCH. Relevant studies were identified through a comprehensive search using the term 'Permanent congenital hypothyroidism' (Mesh) across scientific databases of electronic databases such as PubMed, Scopus, and Web of Science. Results: Prompt initiation of thyroid hormone replacement therapy, particularly within the initial two weeks postpartum, crucially enhances neurocognitive development outcomes. Multiple predictive approaches, encompassing screening TSH levels, maternal thyroid history, and levothyroxine dosage per kilogram assessment, aid in identifying PCH. Recent studies have demonstrated a mounting prevalence of PCH, contributing significantly to the overall rise in CH incidence. Genetic factors, primarily DUOX2 and DUOXA2 mutations, alongside environmental influences such as post-term birth, low birth weight, and macrosomia, may induce PCH. Nonetheless, reliable markers for early PCH prediction upon diagnosis remain elusive, leading to delayed recognition post-ceasing levothyroxine treatment around age 3. Conclusions: Recent studies have observed an increased incidence of PCH, contributing substantially to the overall rise in cases of congenital hypothyroidism. Understanding the diagnostic options and genetic etiologies associated with PCH is crucial for the early identification and appropriate management.

Approach to Newborns with Elevated TSH: A Different Perspective from the International Guidelines for Iodine-Deficient Countries.

Lowering of thyroid-stimulating hormone (TSH) cutoffs in newborn screening programs has created a management dilemma by leading to more frequent detection of neonates with elevated TSH concentrations due to false-positive results, transient neonatal hyperthyrotropinemia (NHT), and milder forms of congenital hypothyroidism. Current consensus guidelines recommend starting treatment if the venous TSH level is >20 mU/l in the face of a normal free thyroxin (FT4) level, which is an arbitrary threshold for treatment decisions. In countries such as Türkiye, where transient NHT may be more common due to iodine deficiency and/or overload, putting this recommendation into daily practice may lead to unnecessary and over treatments, long-term follow-ups, and increased workload and costs. In this review, we addressed alternative approaches for infants with elevated TSH concentrations detected at newborn screening. Our management approach can be summarized as follows: Infants with mild NHT (TSH<20 mU/l) should be followed without treatment. In moderate NHT (TSH 20-30 mU/l), treatment or monitoring decisions can be made according to age, TSH trend and absolute FT4 level. Moderate cases of NHT should be treated if age at confirmatory testing is >21 days or if there is no downward trend in TSH and FT4 level is in the lower half of age-specific reference range in the first 21 days. In in-between cases of moderate NHT, thyroid ultrasound can guide treatment decision by determining mild cases of thyroid dysgenesis that require life-long treatment. Otherwise, monitoring is a reasonable option. Infants with compensated hypothyroidism (TSH>30 mU/l) and persistent hyperthyrotropinemia (>6-10 mU/l after neonatal period) should receive L-thyroxine treatment. But all treated cases of isolated TSH elevation should be closely monitored to avoid overtreatment, and re-evaluated by a trial off therapy. This alternative approach will largely eliminate unnecessary treatment of infants with transient NHT, mostly caused by iodine deficiency or excess, and will reduce workload and costs by preventing unwarranted investigation and long-term follow-up.

Epigenomic newborn screening for conditions with intellectual disability and autistic features in Australian newborns.

This study describes a protocol to assess a novel workflow called Epi-Genomic Newborn Screening (EpiGNs) on 100,000 infants from the state of Victoria, Australia. The workflow uses a first-tier screening approach called methylation-specific quantitative melt analysis (MS-QMA), followed by second and third tier testing including targeted methylation and copy number variation analyzes with droplet digital PCR, EpiTYPER system and low-coverage whole genome sequencing. EpiGNs utilizes only two 3.2 mm newborn blood spot punches to screen for genetic conditions, including fragile X syndrome, Prader-Willi syndrome, Angelman syndrome, Dup15q syndrome and sex chromosome aneuploidies. The program aims to: identify clinically actionable methylation screening thresholds for the first-tier screen and estimate prevalence for the conditions screened.

[Box: see text].

Outcomes of early-treated infants with spinal muscular atrophy: A multicenter, retrospective cohort study.

INTRODUCTION/AIMS: While prompt identification and treatment of infants with spinal muscular atrophy (SMA) can ameliorate outcomes, variability persists. This study assessed management and outcomes of early-treated infants with SMA. METHODS: We analyzed retrospective data at 12 centers on infants with SMA treated at age ≤6 weeks from August 2018 to December 2023. RESULTS: Sixty-six patients, 35 with two SMN2 copies and 31 with ≥3 SMN2 copies, were included. Twenty-five (38%, 22 with two SMN2 copies), had SMA findings before initial treatment which was onasemnogene abeparvovec in 47 (71%) and nusinersen in 19 (29%). Thirty-two received sequential or combination treatments, including 16 adding nusinersen or risdiplam due to SMA findings following onasemnogene abeparvovec. All sat independently. Compared to children with ≥3 SMN2 copies, those with two SMN2 copies were less likely to walk (23/34 [68%] vs. 31/31 [100%], p < .001) and less likely to walk on time (9/34 [26%] vs. 29/31 [94%], p < .001); one non-ambulatory child was <18 months old and was excluded from this analysis. No patients required permanent ventilation or exclusively enteral nutrition; six required nocturnal non-invasive ventilation and four utilized supplemental enteral nutrition, all with two SMN2 copies. DISCUSSION: Early treatment of infants with SMA can improve outcomes as indicated by our cohort, all of whom sat independently and are without permanent ventilation. However, our study demonstrates ongoing disability in most children with two SMN2 copies despite early monotherapy and emphasizes the need for additional research, including earlier monotherapy, initial combination therapy, prenatal treatment, and non-SMN modifying treatments.

Vision and Goals as the New Editor-in-Chief of Global Pediatric Health.

As the newly appointed Editor-in-Chief (EIC) of Global Pediatric Health (GPH), it is both an honor and a privilege to lead this prestigious journal, building upon the strong foundation established by my predecessor, Dr. Aishat Akere. Under her leadership and that of her predecessors, GPH has grown into a globally recognized platform for clinical studies, case studies, public health research, and health services delivery practices focused on the pediatric population. Dr. Akere's tenure was marked by significant achievements, including the expansion of the Editorial Board, which strengthened the journal's editorial team and expanded its global reach. My appointment comes at a time when the landscape of academic publishing is rapidly evolving, particularly with the rise in the number of online journals. Despite these changes, GPH continues to stand out, receiving over 230 submissions and more than 350 000 downloads in the year 2023 alone. These numbers reflect not only the journal's relevance but also the trust that researchers and clinicians worldwide place in GPH as a reliable source of high-quality pediatric health research. As I step into this role, my vision is to further elevate the journal's standing and impact by focusing on several key goals that align with the needs of our authors, the global community, and the field of pediatric health at large.

A Rare Case of TP63-Associated Lymphopenia Revealed by Newborn Screening Using TREC.

The expanded newborn screening (NBS) program in the Russian Federation was initiated in 2023, among which severe combined immunodeficiency (SCID) is screened using TREC/KREC assays. Here, we report a rare case of a TP63-associated disease identified through this NBS program. Dried blood spots from newborns were initially screened for TREC/KREC levels, and those with values below the cut-off underwent confirmatory testing and further genetic analysis, including whole-exome sequencing (WES). A male newborn was identified with significantly reduced TREC values, indicative of T cell lymphopenia. Genetic analysis revealed a heterozygous NM_003722.5:c.1027C>T variant in TP63, leading to the p.(Arg343Trp) substitution within the DNA binding domain. This mutation has been previously associated with Ectrodactyly-Ectodermal Dysplasia-Cleft lip/palate syndrome (EEC) syndrome and shown to reduce the transactivation activity of TP63 in a dominant-negative manner. This case represents one of the few instances of immune system involvement in a patient with a TP63 mutation, highlighting the need for further investigation into the immunological aspects of TP63-associated disorders. Our findings suggest that comprehensive immunological evaluation should be considered for patients with TP63 mutations to better understand and manage potential immune dysfunctions.

A systematic framework for selecting gene-condition pairs for inclusion in newborn sequencing panels: Early Check implementation.

PURPOSE: Research is underway worldwide to investigate the feasibility, acceptability, and utility of sequencing-based newborn screening. Different methods have been used to select gene-condition pairs for screening, leading to highly inconsistent gene lists across studies. METHODS: Early Check developed and utilized actionability-based frameworks for evaluating gene-condition pairs for inclusion in newborn panels (Panel 1 - high actionability, Panel 2 - possible actionability). A previously developed framework, the Age-based Semi Quantitative Metric (ASQM), was adapted. Increasing ASQM scores, with a maximum of 15, suggest greater actionability. Wilcoxon tests were performed to compare Panel 1 gene-condition pairs on the Recommended Uniform Screening Panel (RUSP) to non-RUSP pairs. RESULTS: In our first round of assessment, Early Check identified 178 gene-condition pairs for inclusion in Panel 1 and 29 for Panel 2. Median ASQM scores of RUSP conditions on Panel 1 was 12 (range 4 to 15) and non-RUSP was 13 (range 9 to 15). Median scores for Panel 2 was 10 (range 6 to 14). CONCLUSION: The Early Check frameworks provide a transparent, semiquantitative, and reproducible methodology for selecting gene-condition pairs for NBS sequencing pilot studies that may inform future integration of genomic sequencing into population-level NBS. Collaborative efforts among newborn sequencing studies to establish shared criteria is needed to enhance cross-study comparisons.

Implementation of Newborn Screening for Mucopolysaccharidosis Type IVA and Long-Term Monitoring in Taiwan.

BACKGROUND: Mucopolysaccharidosis IVA (MPS IVA) is a rare lysosomal storage disorder arising from a deficiency in N-acetylgalactosamine-6-sulfatase (GALNS). METHODS: From September 2019 to October 2023, a total of 264,843 Taiwanese newborns underwent screening for MPS IVA using dried blood spots and tandem mass spectrometry. RESULTS: Among the 95 referred infants, nine (9%) were confirmed to have MPS IVA (Group 1), 18 (19%) were highly suspected to have MPS IVA (Group 2), 61 (64%) were identified as heterozygotes of MPS IVA (Group 3), and seven (7%) were determined not to have MPS IVA (Group 4). A total of 34 different GALNS (HGNC:4122) gene variants were identified through our MPS IVA newborn screening program. The most prevalent variant was c.857C>T p.(Thr286Met), found in 33 cases (29%), followed by c.953T>G p.(Met318Arg) in 22 cases (19%). Intravenous enzyme replacement therapy (ERT) was initiated in five patients at ages ranging from 0.3 to 1.7 years. The estimated incidence of MPS IVA in this screening program was 3.4 per 100,000 live births. CONCLUSIONS: Due to the progressive nature of MPS IVA, an early diagnosis facilitated by newborn screening and prompt initiation of ERT before irreversible organ damage occurs may result in improved clinical outcomes.

Postnatal management of preterm infants with spinal muscular atrophy: experience from German newborn screening.

BACKGROUND: The introduction of newborn screening (NBS) for spinal muscular atrophy (SMA) has increased the early diagnosis of 5q-associated SMA in presymptomatic and symptomatic preterm infants. National and international recommendations for treating preterms and newborns < 38 weeks of gestational age are unavailable. Our retrospective multicentre study aimed to evaluate the postnatal clinical course of preterm infants with 5q-associated SMA diagnosed since the implementation of NBS in Germany in 2021 and to summarize the German experience regarding the decision-making process for available treatment regimens for preterm infants with ≤ 3 survival of motor neuron 2 (SMN2) copies. RESULTS: Twelve preterm infants with 5q-associated SMA and a mean gestational age of 34.0 weeks (range: 26.1-36.8) and birth weight of 2022 g (range: 645-3370) were reported from 8/20 German SMA NBS follow-up centers using a pseudonymized questionnaire. Confirmatory diagnosis, including SMN2 copy number, was completed on average on postnatal day 13. All patients had a biallelic deletion of exon 7 or exons 7 and 8 of the survival of motor neuron 1 (SMN1) gene, with SMN2 copy numbers of two in 10 patients and three in two patients. The neonatal course was complicated by respiratory distress due to prematurity (n = 2), sepsis (n = 2), and jaundice (n = 2). At birth, 11 preterm infants (91.6%) were presymptomatic. However, the neurological status of one patient deteriorated at five weeks of age (postconceptional age of 41.8 weeks) prior to the start of treatment. Disease-modifying treatments were initiated in all patients at a mean postconceptional age of 38.8 weeks, with the majority receiving onasemnogene abeparvovec (83.3%, including 2 patients with prior risdiplam bridge therapy). Notably, consensus among participating experts from German neuromuscular centers resulted in 83.3% of patients receiving disease-modifying treatment at term. CONCLUSIONS: Premature infants with SMA require interdisciplinary care in close collaboration with the neuromuscular center. SMA NBS facilitates early initiation of disease-modifying therapy, ideally during the presymptomatic phase, which significantly influences the prognosis of the newborn.

Comparison between Liquid and Tablet Formulations in the Treatment of Congenital Hypothyroidism up to 3 Years of Age: The First Italian Study.

Background/Objectives: Levothyroxine (L-T4) is available for use in congenital hypothyroidism (CH) in three formulations: tablets, drops, and oral solution. This study aims to compare the efficacy and safety of all three L-T4 formulations. Methods: We enrolled 63 children born between January 2019 and April 2023 in the Emilia-Romagna Region (Italy) and diagnosed with CH by newborn screening. They were divided according to the L-T4 formulation used: drops (Group D), oral solution (Group S), and tablets (Group T). Clinical and laboratory data were collected up to 3 years after the start of replacement therapy. Results: Serum-free thyroxine (sFT4) and thyroid stimulating hormone (sTSH) normalization occurred within the first month of treatment in most patients of all groups. No negative effects on growth and cognitive development were observed. At 7-15 days we found higher median sTSH levels (p = 0.031) and a greater percentage of patients with sTSH > 5 µU/mL (p = 0.011) in Group S than in Group T, but comparable sFT4 levels. At 12 months, a greater percentage of patients of Group D showed sFT4 values below the normal range than Group S (p = 0.011) and Group T (p = 0.038); Conclusions: Overall, our study reported an equal efficacy of the L-T4 oral solution compared to drops and tablets in CH treatment. A larger series of patients and a long-term follow-up are needed.

Diagnostic Transitions of Cystic Fibrosis and CRMS Compared After 12 Years of Newborn Screening in California.

OBJECTIVE: To compare the long-term diagnostic transitions for cystic fibrosis (CF) and cystic fibrosis transmembrane conductance regulator (CFTR)- related metabolic syndrome (CRMS) side-by-side since the onset of newborn screening in California. STUDY DESIGN: Using real-world data, we conducted a retrospective cohort study to compare long-term observations of CRMS and CF in California and the diagnostic transitions from one to the other using clinical and diagnostic metrics. The California Genetic Disease Screening Program newborn screening for CF employs an immunoreactive trypsinogen tier-1 laboratory test, followed by molecular testing. This approach captures CF and CRMS, a diagnosis of "watchful waiting" among infants at risk for CF but with signs and symptoms that may emerge outside the screening window. Waiting entails periodic diagnostic reviews that can continue for many years; the California Genetic Disease Screening Program routinely conducts 5 years of follow-up for each child identified with a disorder. We used categorial logistic regression to compare the transitions with CRMS. RESULTS: After screening 5 944 700 newborns between July 2007 and July 2019, 694 CF cases and 1257 CRMS cases were identified. Of the 1257 CRMS cases, 66 (5.2%, 95% CI 3.9%-6.4%) transitioned from CRMS to CF (CRMS2CF) at a mean age of 3.3 years (median = 2.9 years). CRMS2CF cases had longer follow-up periods and were more likely later to develop positive sweat chloride and fecal elastase test results after 6 months of life than other CRMS cases. CONCLUSIONS: These results suggest that children who have a CRMS2CF transition are more likely to develop positive biochemical markers than other patients who are diagnosed as CRMS and have few clinical indications during the first 5 years of follow-up.

Perspectives and Insights Into Phenylketonuria: Provider Narratives About the Early Years Following Newborn Screening.

The understanding of phenylketonuria (PKU), guidelines, and treatment landscape have evolved dramatically over the decades since newborn screen implementation. We capture this rich history from the stories and experiences of a multidisciplinary provider team from Boston Children's Hospital's PKU Clinic, who treated PKU from the early years of newborn screening and who worked together for over 40 years.

The modernisation of newborn screening as a pan-European challenge - An international delphi study.

Newborn screening is a public health measure to diagnose rare diseases at birth, thereby minimising negative effects of late treatment. Genomic technologies promise an unprecedented expansion of screened diseases at low cost and with transformative potential for newborn screening programmes. However, barriers to the public funding of genomic newborn screening are poorly understood, particularly in light of the heterogenous European newborn screening landscape. This study therefore aims to understand whether international newborn screening experts share a common understanding of the barriers to fund genomic newborn screening. For this purpose, we convened 21 European newborn screening experts across a range of professions and national backgrounds in a Delphi study. Stable consensus, determined via the Wilcoxon matched-pairs signed-ranks test, was found via three consecutive survey rounds for all presented barriers. Experts generally judged the scenario of genomic newborn screening being available to every newborn in seven years to be unlikely, identifying treatability and the absence of counselling and a skilled workforce as the most significant barriers to public funding. We identify value re-definition for rare disease treatments, centralisation of genomic expertise, and international research consortia as avenues for pan-European actions which build on the consensus achieved by our Delphi panel.

Phenylketonuria - newborn screening as a health protection in society.

OBJECTIVE: Aim: Phenylketonuria is the most prevalent inherited metabolic disorder. Early detection and prompt treatment can prevent serious neurological consequences. This has become possible thanks to the implementation of newborn screening programmes. The objective of this review is to provide readers with a comprehensive understanding of the phenylketonuria and the role that neonatal screening plays in the protection of public health. PATIENTS AND METHODS: Materials and Methods: A review of the literature was conducted using the PubMed database, with the search period encompassing the most recently published scientific sources. Analysis of the literature. This article presents phenylketonuria as an example of an inherited metabolic disorder, outlines the treatment options, and discusses the potential implications of hyperphenylalaninemia. Furthermore, it also delineates the various aspects of health that are influenced by newborn screening. CONCLUSION: Conclusions: Phenylketonuria represents a significant health problem in the population. The development of screening tests has transformed healthcare, including improvements in quality of life, prognosis, and reductions in the number of comorbidities in patients. It is essential to disseminate knowledge among the society about the importance of newborn screening tests in order to enhance awareness and prevent refusal to participate.

Incorporating Next-Generation Sequencing as a Second-Tier Test for Primary Carnitine Deficiency.

BACKGROUND: Newborn screening (NBS) for primary carnitine deficiency (PCD) has poor performance. This study aimed to evaluate the feasibility of incorporating next-generation sequencing (NGS) as a second-tier PCD test. METHODS: Between March and December 2020, 60,070 newborns were screened for inherited metabolic disorders. Newborns with free carnitine (C0) levels below 8.5 µmol/L were selected for second-tier genetic testing. RESULTS: In total, 130 (0.22%) newborns with low C0 levels underwent second-tier genetic testing, 87 (66.92%) had positive genetic testing results, and 30 (23.08%) carried pathogenic variants of the SLC22A5 gene. Six newborns were diagnosed with PCD. The incidence of PCD was approximately 1 in 1:10,012 newborns. The PPV reached 20% after combining with second-tier NGS. Of the eight variants identified in patients with PCD, the three most common variants were c.760C>T (p.Arg254*), c.51C>G (p.Phe17Leu), and c.1400C>G (p.Ser467Cys). The C0 levels of patients with PCD were significantly lower than those of PCD carriers (p = 0.0026) and PCD-negative individuals (p = 0.0005). CONCLUSIONS: Our results showed that the PPV reached 20% after combining with second-tier NGS. The MS/MS-based NBS and second-tier NGS combination can effectively reduce the false-positive rate and detect PCD in patients.

The "Other E" in ELSI: The Use of Economic Evaluation to Inform the Expansion of Newborn Screening.

The utilization and application of genomic information generated from precision medicine continues to increase with the goal of improving health outcomes. Increasingly researchers, health care professionals, and public health teams include an examination of the ethical, legal, and social issues (ELSI) in their consideration of the use of precision medicine for newborn and pediatric health. In addition to ELSI considerations, stakeholders could benefit from an understanding of economics, the other "E" in ELSI. The use of an economic evaluation could aid decision-making on whether to screen newborns who may be at risk for disease, to diagnose newborns and children who present with symptoms, to inform the treatment and management of diagnosed individuals. In this manuscript we review the core concepts of economic evaluation, the framework of decision-analysis, and key parameters for consideration in assessing the economics of NBS program(s). We describe the common language used in the economic evaluation and provide a practical overview of health economic evaluations including 1) their purpose, 2) different types and components, 3) evaluation of the different types and components of economic evaluations (i.e., cost-effectiveness vs. cost-benefit analysis), 4) impact of societal or healthcare perspectives on the analysis, 5) health outcomes, 6) time horizon for the analysis, 7) identification of appropriate comparators, and 8) resources for economic data. We conclude with a use case to demonstrate the application and understanding of economic considerations for in the advancement and expansion of NBS.

Perspectives and Insights Into Phenylketonuria: Patient Narratives About the Early Years Following Newborn Screening.

Newborn screening for Phenylketonuria (PKU) began in 1963, and since then knowledge and treatment recommendations have evolved. In the decades following newborn screening for PKU, individual and family experiences varied widely. We present narratives by people living with PKU during these years, including individuals actively following in PKU clinic and those who have been out of PKU clinic for many years. These stories describe different individual experiences, including diet discontinuation in childhood, changing treatment guidelines, and new treatments that have become available.

Total Cholesterol Determination Accuracy in Dried Blood Spots.

Background Detecting total cholesterol in dried blood spots could aid in identifying individuals with a high likelihood of familial hypercholesterolemia and could be used as a screening measure. This study aims to assess the diagnostic accuracy of dried blood spots on Whatman 903 paper cards using a manual enzymatic technique. Methods: A total of 394 samples were collected as serum and dried blood spots were compared. Cholesterol was determined in serum using the automated reference method, while cholesterol on paper was measured using a manual enzymatic method. Within- and between-day diagnostic variability were analyzed. The correlation between both methods was assessed using Passing-Bablok regression and Bland-Altman plot. Internal validation of our correlation formula was performed on 149 samples, along with external validation of the formula proposed by Corso et al. Results: The within- and between-day coefficient of variation was found to be lower than 10.14% and 14.09%, respectively. Passing-Bablok regression indicated a precision of 0.803 and an accuracy of 0.96. Internal validation precision was measured at 0.716. The resulting positive and negative predicted values were 0.77 and 0.92, respectively, vs. 0.46 and 0.96 from the external formula. Conclusions: Total cholesterol analysis in dried blood spots demonstrates high precision and reproducibility. This method reliably enables the incorporation of this biological marker into neonatal screening for familial hypercholesterolemia detection.

Lysosomal storage diseases.

Lysosomal storage disorders (LSDs) are a group of inherited metabolic diseases caused by dysfunction of the lysosomal system, with subsequent progressive accumulation of macromolecules, activation of inflammatory response, and cell death. Neurologic damage is almost always present, and it is usually degenerative. White matter (WM) involvement may be primary or secondary. Diseases with primary WM involvement are leukodystrophies, demyelinating (Krabbe disease and metachromatic leukodystrophy), and hypomyelinating leukodystrophies (free sialic acid storage disease, fucosidosis, and mucolipidosis type IV). LSDs with secondary WM involvement are classified as leukoencephalopathies and include gangliosidosis, mucopolysaccharidosis (MPS), ceroid neuronal lipofuscinosis, multiple sulfatase deficiency, alpha-mannosidosis, Pompe disease, and Fabry disease. Neurologic manifestations may overlap among LSDs and include developmental delays, motor, cognitive and speech impairments, seizures, visual failure, ataxia, and extrapyramidal signs. Most of LSDs are typically present in early or late infancy, but juvenile and adult forms also exist and are associated with predominantly neuropsychiatric and behavioral symptoms. The outcome of these disorders is generally poor and specific treatments (enzyme replacement therapy, hematopoietic stem cell transplantation, or gene therapy) are only available in a small number of them.