A homozygous Gly470Ala variant in PEX6 causes severe Zellweger spectrum disorder.

Zellweger spectrum disorder (ZSD) is a group of autosomal recessive disorders caused by biallelic pathogenic variants in any one of the 13 PEX genes essential for peroxisomal biogenesis. We report a cohort of nine infants who presented at birth with severe neonatal features suggestive of ZSD and found to be homozygous for a variant in PEX6 (NM_000287.4:c.1409G > C[p.Gly470Ala]). All were of Mixtec ancestry and identified by the California Newborn Screening (NBS) Program to have elevated C26:0-lysophosphatidylcholine but no reportable variants in ABCD1. The clinical and biochemical features of this cohort are described within. Gly470Ala may represent a founder variant in the Mixtec population of Central California. ZSD should be considered in patients who present at birth with severe hypotonia and enlarged fontanelles, especially in the setting of an abnormal NBS, Mixtec ancestry, or family history of infant death. There is a need to further characterize the natural history of ZSD, the Gly470Ala variant, and expand upon possible genotype-phenotype correlations.

A Retrospective Study of Hearing Loss in Patients Diagnosed with Peroxisome Biogenesis Disorders in the Zellweger Spectrum.

OBJECTIVES: Peroxisome Biogenesis Disorders in the Zellweger Spectrum (PBD-ZSD) are autosomal recessive disorders characterized by defects in peroxisome function, biosynthesis, and/or assembly. Despite its frequent documentation, hearing loss associated with PBD-ZSD has not been extensively characterized. The purpose of this retrospective natural history study was to better characterize the hearing loss associated with PBD-ZSD and to provide additional insight into the evaluation and management of PBD-ZSD patients with hearing loss. DESIGN: Audiological data from medical records of 42 patients with PBD-ZSD or D-bifunctional protein deficiency were collected from an ongoing longitudinal retrospective natural history study. An initial dataset of 300 audiograms and/or audiometric test results from the 42 patients were used to characterize the degree of hearing loss, type of hearing loss, relationships between air and bone conduction thresholds, age-related changes in hearing loss, and benefit with amplification. RESULTS: The majority of PBD-ZSD patients in this study presented with moderately-severe to severe hearing loss and relatively slow rates of longitudinal changes in hearing sensitivity. Improvements in hearing thresholds were observed with use of hearing aid amplification. Though bone conduction data were limited, air-bone gaps and air conduction threshold fluctuations observed in several patients suggest there may be an increased occurrence of mixed hearing losses in PBD-ZSD populations. CONCLUSION: The results of this retrospective study provide insight into the hearing loss associated with PBD-ZSD, but also emphasize the need for more complete assessments of hearing loss type and middle ear function in these patients. The addition of more comprehensive datasets to the ongoing natural history study will enhance our understanding of the pathophysiology underlying PBD-ZSD and guide the development of targeted evaluation and management recommendations for patients with PBD-ZSD.

Diagnostic Odyssey in an Adult Patient with Ophthalmologic Abnormalities and Hearing Loss: Contribution of RNA-Seq to the Diagnosis of a PEX1 Deficiency.

Peroxisomal biogenesis disorders (PBDs) are a heterogeneous group of genetic diseases. Multiple peroxisomal pathways are impaired, and very long chain fatty acids (VLCFA) are the first line biomarkers for the diagnosis. The clinical presentation of PBDs may range from severe, lethal multisystemic disorders to milder, late-onset disease. The vast majority of PBDs belong to Zellweger Spectrum Disordes (ZSDs) and represents a continuum of overlapping clinical symptoms, with Zellweger syndrome being the most severe and Heimler syndrome the less severe disease. Mild clinical conditions frequently present normal or slight biochemical alterations, making the diagnosis of these patients challenging. In the present study we used a combined WES and RNA-seq strategy to diagnose a patient presenting with retinal dystrophy as the main clinical symptom. Results showed the patient was compound heterozygous for mutations in PEX1. VLCFA were normal, but retrospective analysis of lysosphosphatidylcholines (LPC) containing C22:0-C26:0 species was altered. This simple test could avoid the diagnostic odyssey of patients with mild phenotype, such as the individual described here, who was diagnosed very late in adult life. We provide functional data in cell line models that may explain the mild phenotype of the patient by demonstrating the hypomorphic nature of a deep intronic variant altering PEX1 mRNA processing.

[A case of mild Zellweger spectrum disorder first diagnosed as Usher syndrome].

A 5-year-old female patient, presented with"night blindness and poor hearing for 1 year"whose first diagnosis was Usher syndrome due to retinitis pigmentosa accompanied by sensorineural deafness. Compound heterozygous variants (c.5G>A, p.W2*/c.3022C>T, p.P1008S) of PEX1, the causative gene for Zellweger spectrum disorder was confirmed by targeted exome sequencing analysis. Permanent tooth enamel dysplasia, nail leukoplakia, and biochemical abnormalities of peroxisome which is consistent with mild Zellweger spectrum disorder were found when she followed up.

Diagnostic challenges and disease management in patients with a mild Zellweger spectrum disorder phenotype.

Peroxisome Biogenesis Disorders-Zellweger spectrum disorder (PBD-ZSD) is a rare, autosomal recessive peroxisome biogenesis disorder that presents with variable symptoms. In patients with PBD-ZSD, pathogenic variants in the PEX family of genes disrupt normal peroxisomal function, impairing α- and ß-oxidation of very-long-chain fatty acids and synthesis of bile acids, resulting in increased levels of toxic bile acid intermediates and multisystem organ damage. The spectrum of severity in PBD-ZSD is variable, with some patients dying in the first year of life, while others live into adulthood. Symptoms of mild PBD-ZSD include various combinations of developmental delay, craniofacial dysmorphic features, visual impairment, sensorineural hearing loss, liver disease, and adrenal insufficiency. Disease progression in mild PBD-ZSD is generally slow, and may include extended periods of stability in some cases. The presence and extent to which symptoms occur in mild PBD-ZSD represents a diagnostic challenge that can cause delays in diagnosis with potential significant implications related to disease monitoring and treatment. There is some support for the pharmacologic therapies of Lorenzo's oil, docosohexanoic acid, and batyl alcohol in altering symptoms; however, systematic long-term studies are lacking. Cholic acid (CA) therapy has demonstrated treatment efficacy in patients with PBD-ZSD, including decreased toxic bile acid intermediates, transaminase levels, and liver inflammation, with improvement in growth parameters. However, these responses are most apparent in patients diagnosed and treated at a young age. Advanced liver disease may limit the efficacy of CA, underscoring the need to diagnose and treat these patients before significant liver damage and other related complications occur. Here we discuss the signs and symptoms of PBD-ZSD in patients with mild disease, standard diagnostic tools, factors affecting disease management, and available pharmacological interventions.

Zellweger Syndrome Disorders: From Severe Neonatal Disease to Atypical Adult Presentation.

Zellweger syndrome disorders (ZSD) is the principal group of peroxisomal disorders characterized by a defect of peroxisome biogenesis due to mutations in one of the 13 PEX genes. The clinical spectrum is very large with a continuum from antenatal forms to adult presentation. Whereas biochemical profile in body fluids is classically used for their diagnosis, the revolution of high-throughput sequencing has extended the knowledge about these disorders. The aim of this review is to offer a large panorama on molecular basis, clinical presentation and treatment of ZSD, and to update the diagnosis strategy of these disorders in the era of next-generation sequencing (NGS).

First Case of Peroxisomal D-bifunctional Protein Deficiency with Novel HSD17B4 Mutations and Progressive Neuropathy in Korea.

Peroxisomal D-bifunctional protein (DBP), encoded by the HSD17B4 gene, catalyzes ß-oxidation of very long chain fatty acids (VLCFAs). The deficiency of this peroxisomal enzyme leads to the accumulation of VLCFAs, causing multisystemic manifestations including the brain, retina, adrenal gland, hearing, and skeletal system. Herein, we report the first Korean neonatal case of peroxisomal DBP deficiency and the clinical prognosis over 2 years. This patient showed craniofacial dysmorphism, club foot, and seizures with cyanosis one day after birth. Elevated VLCFAs levels were indicative of a peroxisomal disorder. Targeted exome sequencing was performed and two missense mutations p.Asp117Val and p.Phe279Ser in the HSD17B4 gene were identified. The patient had type III DBP deficiency; therefore, docosahexaenoic acid and non-soluble vitamins were administered. However, progressive nystagmus, optic nerve atrophy, and bilateral hearing defects were observed and follow-up brain imaging revealed leukodystrophy and brain atrophy. Multiple anti-epileptic drugs were required to control the seizures. Over two years, the patient achieved normal growth with home ventilation and tube feeding. Hereby, the subject's parents had support during the second pregnancy from the proven molecular information. Moreover, targeted exome sequencing is an effective diagnostic approach, considering genetic heterogeneity of Zellweger spectrum disorders.

Carrier frequency estimation of Zellweger spectrum disorder using ExAC database and bioinformatics tools.

PURPOSE: We aimed to estimate the carrier frequency of Zellweger spectrum disorder (ZSD), a rare autosomal recessive disease, and the associated disease incidence based on data from the Exome Aggregation Consortium (ExAC) of approximately 60,000 individuals. METHODS: We obtained variants from ExAC in 13 PEX genes associated with ZSD. Potentially pathogenic missense variants were identified with computational variant analysis tools according to three stringency levels. Using variants classified as potentially pathogenic, we estimated the carrier frequency and the associated incidence for the entire ExAC population and its subpopulations. We also evaluated variants based on pathogenicity criteria for sequence variant interpretation outlined by the American College of Medical Genetics and Genomics (ACMG) and calculated the carrier frequency and incidence based on those variants. RESULTS: The bioinformatically estimated incidence rate of ZSD in the ExAC population is 1 in 83,841 using our least stringent pathogenicity cutoff. Under clinical guidelines outlined by ACMG, the estimated incidence is 1 in 3,275,751 births. CONCLUSION: We outlined a process for estimating the ZSD disease carrier frequency and incidence in a large consortium using bioinformatics tools. Our results are close to current newborn screening estimates in New York of 1 in 90,000 births, estimated from 1.08 million screenings.

Inherited metabolic disorders presenting as hypoxic ischaemic encephalopathy: A case series of patients presenting at a tertiary care hospital in Pakistan.

In spite of the efforts and interventions by the Government of Pakistan and The World Health Organization, the neonatal mortality in Pakistan has declined by only 0.9% as compared to the global average decline of 2.1% between 2000 and 2010. This has resulted in failure to achieve the global Millennium Development Goal 4. Hypoxic-ischaemic encephalopathy, still birth, sepsis, pneumonia, diarrhoea and birth defects are commonly attributed as leading causes of neonatal mortality in Pakistan. Inherited metabolic disorders often present at the time of birth or the first few days of life. The clinical presentation of the inherited metabolic disorders including hypotonia, seizure and lactic acidosis overlap with clinical features of hypoxic-ischaemic encephalopathy and sepsis. Thus, these disorders are often either missed or wrongly diagnosed as hypoxicischaemic encephalopathy or sepsis unless the physicians actively investigate for the underlying inherited metabolic disorders. We present 4 neonates who had received the diagnosis of hypoxic-ischaemic encephalopathy and eventually were diagnosed to have various inherited metabolic disorders. Neonates with sepsis and hypoxic-ischaemic encephalopathy-like clinical presentation should be evaluated for inherited metabolic disorders.

Development and validation of a severity scoring system for Zellweger spectrum disorders.

The lack of a validated severity scoring system for individuals with Zellweger spectrum disorders (ZSD) hampers optimal patient care and reliable research. Here, we describe the development of such severity score and its validation in a large, well-characterized cohort of ZSD individuals. We developed a severity scoring system based on the 14 organs that typically can be affected in ZSD. A standardized and validated method was used to classify additional care needs in individuals with neurodevelopmental disabilities (Capacity Profile [CAP]). Thirty ZSD patients of varying ages were scored by the severity score and the CAP. The median score was 9 (range 6-19) with a median scoring age of 16.0 years (range 2-36 years). The ZSD severity score was significantly correlated with all 5 domains of the CAP, most significantly with the sensory domain (r = 0.8971, P = <.0001). No correlation was found between age and severity score. Multiple peroxisomal biochemical parameters were significantly correlated with the severity score. The presently reported severity score for ZSD is a suitable tool to assess phenotypic severity in a ZSD patient at any age. This severity score can be used for objective phenotype descriptions, genotype-phenotype correlation studies, the identification of prognostic features in ZSD patients and for classification and stratification of patients in clinical trials.

Coagulopathy in Zellweger spectrum disorders: a role for vitamin K.

INTRODUCTION: Zellweger spectrum disorders (ZSDs) are caused by an impairment of peroxisome biogenesis, resulting in multiple metabolic abnormalities. This leads to a range of symptoms, including hepatic dysfunction and coagulopathy. This study evaluated the incidence and severity of coagulopathy and the effect of vitamin K supplementation orally and IV in ZSD. METHODS: Data were retrospectively retrieved from the medical records of 30 ZSD patients to study coagulopathy and the effect of vitamin K orally on proteins induced by vitamin K absence (PIVKA-II) levels. Five patients from the cohort with a prolonged prothrombin time, low factor VII, and elevated PIVKA-II levels received 10 mg of vitamin K IV. Laboratory results, including thrombin generation, at baseline and 72 h after vitamin K administration were examined. RESULTS: In the retrospective cohort, four patients (13.3%) experienced intracranial bleedings and 14 (46.7%) reported minor bleeding. No thrombotic events occurred. PIVKA-II levels decreased 38% after start of vitamin K therapy orally. In the five patients with a coagulopathy, despite treatment with oral administration of vitamin K, vitamin K IV caused an additional decrease (23%) of PIVKA-II levels and increased thrombin generation. CONCLUSION: Bleeding complications frequently occur in ZSD patients due to liver disease and vitamin K deficiency. Vitamin K deficiency is partly corrected by vitamin K supplementation orally, and vitamin K administered IV additionally improves vitamin K status, as shown by further decrease of PIVKA-II and improved thrombin generation.

Evaluation of C26:0-lysophosphatidylcholine and C26:0-carnitine as diagnostic markers for Zellweger spectrum disorders.

INTRODUCTION: Zellweger spectrum disorders (ZSD) are a group of genetic metabolic disorders caused by a defect in peroxisome biogenesis. This results in multiple metabolic abnormalities, including elevated very long-chain fatty acid (VLCFA) levels. Elevated levels of C26:0-lysophosphatidylcholine (C26:0-lysoPC) have been shown in dried blood spots (DBS) from ZSD patients. However, little is known about the sensitivity and specificity of this marker and C26:0-carnitine, another VLCFA-marker, in ZSD. We investigated C26:0-lysoPC and C26:0-carnitine as diagnostic markers for ZSD in DBS and fibroblasts. METHODS: C26:0-lysoPC levels in 91 DBS from 37 different ZSD patients were determined and compared to the levels in 209 control DBS. C26:0-carnitine levels were measured in 41 DBS from 29 ZSD patients and 97 control DBS. We measured C26:0-lysoPC levels in fibroblasts from 24 ZSD patients and 61 control individuals. RESULTS: Elevated C26:0-lysoPC levels (>72 nmol/L) were found in 86/91 ZSD DBS (n=33/37 patients) corresponding to a sensitivity of 89.2%. Median level was 567 nmol/l (range 28-3133 nmol/l). Consistently elevated C26:0-carnitine levels (>0.077 µmol/L) in DBS were found in 16 out of 29 ZSD patients corresponding to a sensitivity of 55.2%. C26:0-lysoPC levels were elevated in 21/24 ZSD fibroblast lines. DISCUSSION: C26:0-lysoPC in DBS is a sensitive and useful marker for VLCFA accumulation in patients with a ZSD. C26:0-carnitine in DBS is elevated in some ZSD patients, but is less useful as a diagnostic marker. Implementation of C26:0-lysoPC measurement in the diagnostic work-up when suspecting a ZSD is advised. This marker has the potential to be used for newborn screening for ZSD.

Peroxisome biogenesis disorders in the Zellweger spectrum: An overview of current diagnosis, clinical manifestations, and treatment guidelines.

Peroxisome biogenesis disorders in the Zellweger spectrum (PBD-ZSD) are a heterogeneous group of genetic disorders caused by mutations in PEX genes responsible for normal peroxisome assembly and functions. As a result of impaired peroxisomal activities, individuals with PBD-ZSD can manifest a complex spectrum of clinical phenotypes that typically result in shortened life spans. The extreme variability in disease manifestation ranging from onset of profound neurologic symptoms in newborns to progressive degenerative disease in adults presents practical challenges in disease diagnosis and medical management. Recent advances in biochemical methods for newborn screening and genetic testing have provided unprecedented opportunities for identifying patients at the earliest possible time and defining the molecular bases for their diseases. Here, we provide an overview of current clinical approaches for the diagnosis of PBD-ZSD and provide broad guidelines for the treatment of disease in its wide variety of forms. Although we anticipate future progress in the development of more effective targeted interventions, the current guidelines are meant to provide a starting point for the management of these complex conditions in the context of personalized health care.

Diagnostic and prognostic value of in vivo proton MR spectroscopy for Zellweger syndrome spectrum patients.

Defects in the biogenesis of peroxisomes cause a clinically and genetically heterogeneous group of neurometabolic disorders, the Zellweger syndrome spectrum (ZSS). Diagnosis predominantly is based on characteristic clinical symptoms, a typical biochemical profile, as well as on identification of the molecular defect in any of the 12 known human PEX genes. The diagnostic workup can be hindered if the typical clinical symptoms are missing and predicting the clinical course of a given patient is almost unfeasible. As a safe and noninvasive method to analyze specific chemical compounds in localized brain regions, in vivo proton magnetic resonance spectroscopy (MRS) can provide an indication in this diagnostic process and may help predict the clinical course. However, to date, there are very few reports on this topic. In this study, we performed localized in vivo proton MRS without confounding contributions from T1- and T2-relaxation effects at 2 Tesla in a comparably large group of seven ZSS patients. Patients' absolute metabolite concentrations in cortical gray matter, white matter, and basal ganglia were assessed and compared with age-matched control values. Our results confirm and extend knowledge about in vivo MRS findings in ZSS patients. Besides affirmation of nonspecific reduction of N-acetylaspartate + N-acetylaspartylglutamate (tNAA) in combination with lipid accumulation as a diagnostic hint for this disease group, the amount of tNAA loss seems to reflect disease burden and may prove to be of prognostic value regarding the clinical course of an already diagnosed patient.

Clinical and Biochemical Pitfalls in the Diagnosis of Peroxisomal Disorders.

Peroxisomal disorders are a heterogeneous group of genetic metabolic disorders, caused by a defect in peroxisome biogenesis or a deficiency of a single peroxisomal enzyme. The peroxisomal disorders include the Zellweger spectrum disorders, the rhizomelic chondrodysplasia punctata spectrum disorders, X-linked adrenoleukodystrophy, and multiple single enzyme deficiencies. There are several core phenotypes caused by peroxisomal dysfunction that clinicians can recognize. The diagnosis is suggested by biochemical testing in blood and urine and confirmed by functional assays in cultured skin fibroblasts, followed by mutation analysis. This review describes the phenotype of the main peroxisomal disorders and possible pitfalls in (laboratory) diagnosis to aid clinicians in the recognition of this group of diseases.

Newborn screening for X-linked adrenoleukodystrophy in New York State: diagnostic protocol, surveillance protocol and treatment guidelines.

PURPOSE: To describe a diagnostic protocol, surveillance and treatment guidelines, genetic counseling considerations and long-term follow-up data elements developed in preparation for X-linked adrenoleukodystrophy (X-ALD) newborn screening in New York State. METHODS: A group including the director from each regional NYS inherited metabolic disorder center, personnel from the NYS Newborn Screening Program, and others prepared a follow-up plan for X-ALD NBS. Over the months preceding the start of screening, a series of conference calls took place to develop and refine a complete newborn screening system from initial positive screen results to long-term follow-up. RESULTS: A diagnostic protocol was developed to determine for each newborn with a positive screen whether the final diagnosis is X-ALD, carrier of X-ALD, Zellweger spectrum disorder, acyl CoA oxidase deficiency or D-bifunctional protein deficiency. For asymptomatic males with X-ALD, surveillance protocols were developed for use at the time of diagnosis, during childhood and during adulthood. Considerations for timing of treatment of adrenal and cerebral disease were developed. CONCLUSION: Because New York was the first newborn screening laboratory to include X-ALD on its panel, and symptoms may not develop for years, long-term follow-up is needed to evaluate the presented guidelines.

Zellweger syndrome and secondary mitochondrial myopathy.

Defects in peroxisomes such as those associated with Zellweger syndrome (ZS) can influence diverse intracellular metabolic pathways, including mitochondrial functioning. We report on an 8-month-old female infant and a 6-month-old female infant with typical clinical, radiological and laboratory features of Zellweger syndrome; light microscopic and ultrastructural evidence of mitochondrial pathology in their muscle biopsies; and homozygous pathogenic mutations of the PEX16 gene (c.460 + 5G > A) and the PEX 12 gene (c.888_889 del p.Leu297Thrfs*12), respectively. Additionally, mitochondrial respiratory chain enzymology analysis in the first girl showed a mildly low activity in complexes II-III and IV. We also review five children previously reported in the literature with a presumptive diagnosis of ZS and additional mitochondrial findings in their muscle biopsies. In conclusion, this is the first study of patients with a molecularly confirmed peroxisomal disorder with features of a concomitant mitochondrial myopathy and underscores the role of secondary mitochondrial dysfunction in Zellweger syndrome, potentially contributing to the clinical phenotype.

[Zellweger syndrome caused by PEX6 gene variation in 2 cases and literature review].

Objective: To summarize the clinical features and genetic characteristics of Zellweger spectrum disorder caused by PEX6 gene variation. Methods: This was a case series research. Clinical date and genetic results of 2 neonatal cases of Zellweger syndrome caused by PEX6 gene variation in Wuhan Children's Hospital, Tongji Medical College, Huazhong University of Science & Technology and Affiliated Hospital of Guangdong Medical University from July 2021 to July 2022 were retrospectively collected and analyzed. Literature up to August 2023 was searched from electronic databases of China National Knowledge Infrastructure (CNKI), Wanfang Data and PubMed with the combined keywords of "Zellweger syndrome" "Zellweger spectrum disorder", and "PEX6 gene" both in Chinese and English. The main clinical features and genetic characteristics of Zellweger spectrum disorder caused by PEX6 gene variation were summarized. Results: The 2 male neonates both developed clinical manifestations as dyspnea, hypotonia, feeding difficulties, enlarged fontanelle, and high palatine arch after birth. Biochemical parameters indicated elevated bile acids, and the cranial ultrasound showed the enlarged bilateral ventricles and subependymal cyst in both 2 neonates. Zellweger syndrome was confirmed by whole exome sequencing, and the results revealed PEX6 gene variation in the 2 neonates, including compound heterozygous variants c.315G>A and c.2095-3T>G, and homozygous variant c.506_507del. Case 1 was hospitalized for 5 days, and case 2 for 32 days; they both died shortly after being discharged (the specific time is unknown). Literature review found 26 patients, including 2 neonates in this study, with Zellweger spectrum disorder caused by PEX6 gene defect reported in 1 Chinese article and 11 English articles. Clinical features included hearing loss (19 cases), developmental delay (19 cases), vision impairment (19 cases), elevated very long chain fatty acids (17 cases), brain malformations (15 cases), hypotonia (12 cases), hepatic insufficiency (12 cases), distinctive facies (10 cases), and dental impairment (9 cases). Compound heterozygous variations dominated the variation types (15 cases), and the frameshift variations (16 cases) were the main pathogenic variations. Conclusions: Zellweger spectrum disorder should be considered when neonates show hypotonia, feeding difficulty, distinctive facial appearance, brain malformations and failure of hearing screening, or when older children show retinitis pigmentosa, sensorineural hearing loss, amelogenesis imperfecta and developmental delays. Detection of genetic variation in the PEX gene is crucial for definitive diagnosis.

Zellweger Syndrome: A Case Report.

Zellweger syndrome is an autosomal recessive disease within the spectrum of peroxisome biogenesis disorder manifesting in the neonatal period with profound dysfunction of the central nervous system, liver and kidney. Common clinical presentations include hypotonia, seizure, hepatomegaly, craniofacial dysmorphism and early death. Mutation in one of the PEX genes coding for a peroxisome assembly protein creates a functionally incompetent organelle causing accumulation of very long chain fatty acids in various organs. Here we report the case of a 5-month-old male presented at birth with hypotonia, poor feeding, gross congenital anomalies and later during early infancy with failure to thrive, several episodes of seizures, aspiration due to feeding difficulties and recurrent severe pneumonia. A whole genomic sequencing brought us to the final diagnosis of Zellweger syndrome. Despite an absence of treatment options, prompt diagnosis of Zellweger syndrome is important for providing appropriate symptomatic care, definitive genetic testing and prenatal counselling. Keywords: case reports; mutation; neonate; Zellweger syndrome.

Newborn Screening for X-Linked Adrenoleukodystrophy (X-ALD): Biochemical, Molecular, and Clinical Characteristics of Other Genetic Conditions.

The state of California (CA) added X-linked adrenoleukodystrophy (X-ALD) to newborn screening (NBS) in 2016 via the measurement of C26:0-lysophosphatidylcholine (C26:0-LPC) in a two-tier fashion, followed by sequencing of the ABCD1 gene. This has resulted in the identification of individuals with genetic conditions beyond X-ALD that can also result in elevated C26:0-LPC by NBS. We describe the biochemical, molecular, and clinical characteristics of nine patients from two metabolic centers in California who screened positive by NBS for elevated C26:0-LPC between 2016 and 2022 and were ultimately diagnosed with a genetic condition other than X-ALD. Seven individuals were diagnosed with Zellweger spectrum disorder (ZSD) due to biallelic variants in PEX genes. One male was diagnosed with Klinefelter syndrome and one female was found to have an X chromosome contiguous gene deletion syndrome after the identification of a heterozygous VUS and hemizygous VUS variant in ABCD1, respectively. Patients with ZSD had significantly higher first- and second-tier C26:0-LPC levels compared to the two non-ZSD cases. Identification of children with ZSD and atypical patterns of ABCD1 variants is a secondary benefit of NBS for X-ALD, leading to earlier diagnosis, prompt therapeutic initiation, and more accurate genetic counseling. As screening for X-ALD continues via the measurement of C26:0-LPC, our knowledge of additional genetic conditions associated with elevated C26:0-LPC will continue to advance, allowing for increased recognition of other genetic disorders for which early intervention is warranted.