VUS: Variant of uncertain significance or very unclear situation?

Blood Biomarkers Reflecting Brain Pathology-From Common Grounds to Rare Frontiers

Understanding pathological changes in the brain is essential for guiding treatment decisions in brain injuries and diseases. Despite significant advances in brain imaging techniques, clinical practice still faces challenges due to infrastructure reliance and high resource demands. This review explores the current knowledge on blood-based biomarkers that indicate brain pathology, which can assist in identifying at-risk patients, diagnosing patients, predicting disease progression, and treatment response. We focus on the inherited metabolic disorders X-linked adrenoleukodystrophy (X-ALD) and metachromatic leukodystrophy (MLD) which share remarkable phenotypic variability. Disease-specific increases in the lipid metabolites lyso-PC26:0 in X-ALD and sulfatides in MLD might contribute to predicting clinical manifestation. Disease-unspecific biomarkers for axonal damage (neurofilament light chain protein, NfL) and glial degeneration (glial fibrillary acidic protein, GFAP) are able to distinguish X-ALD and MLD phenotypes at the group level. The implementation of X-ALD into newborn screening programs in various countries, including several U.S. states, has increased the demand for predictive blood-based biomarkers capable of detecting the early conversion from the pre-symptomatic to the early neuroinflammatory cerebral form of X-ALD. Among different biomarkers, NfL has proven most effective in reflecting neuroinflammation and correlating with brain lesion volume and the magnetic resonance imaging (MRI)-based severity scores. We discuss how NfL has moved from initial proof-of-principle towards proof-of-concept studies in brain disorders such as multiple sclerosis and how this knowledge could be applied for the clinical implementation of NfL in rare inherited metabolic disorders such as X-ALD.

Insights From Minnesota on Newborn Screening for Adrenoleukodystrophy: A 5-Year Update

Our objectives are to report on the outcomes of adrenal insufficiency (AI) and cerebral ALD (cALD) in children diagnosed with X-linked adrenoleukodystrophy (ALD) identified by newborn screening (NBS) in Minnesota in the first 5 years following initiation of NBS in 02/2017. A retrospective chart review was conducted for children diagnosed with ALD via Minnesota NBS from 02/06/2017 through 02/06/2022. Data reviewed included newborn screening data, diagnostic very long chain fatty acid levels, ABCD1 molecular testing results, serial measurements of ACTH and cortisol, and serial brain MRI results. Thirty-two boys and 11 girls were molecularly and/or biochemically confirmed to have ALD. Of these 32 boys, six (2-7 years; median age:18 months) developed AI. Two boys developed cALD and underwent stem cell transplantation, one of whom also has been diagnosed with AI. All the pathogenic/likely pathogenic variants detected during the first 5 years had initial C26:0 lysophosphatidylcholine (C26:0 lysoPC) values over 0.3 μmol/L at the time of newborn screening. The addition of ALD to NBS in Minnesota has allowed for early detection of asymptomatic AI in six young patients and asymptomatic cALD in two patients. Data from our study shows a positive correlation between high newborn screening LysoPC levels and variant pathogenicity.

A novel splice site variant in DEGS1 leads to aberrant splicing and loss of DEGS1 enzyme activity, a VUS resolved

Purpose

Pathogenic DEGS1 variants have been reported in individuals with autosomal recessive hypomyelinating leukodystrophy 18 (HLD18; MIM# 618404). We sought to resolve a 5' +4/+5 splice site variant of uncertain significance found in three individuals with HLD features.

Methods

We used next-generation DNA and transcriptome sequencing, cell-based splicing assays, and tandem mass spectrometry to detect and characterize the splice site variant. We then performed RNA structure probing and conventional antisense oligonucleotide screening to investigate molecular mechanisms for potential therapeutic intervention.

Results

A homozygous, DEGS1 5' splice site variant, c.825+4_825+5delAGinsTT (NM_003676.4) was identified in all three participants. Although the gene has been associated with autosomal recessive hypomyelinating leukodystrophy, the variant has not been previously reported in any available databases or literature. We show that the splice site variant: 1) was sufficient to induce exon two skipping in most detected transcripts; 2) resulted in structural changes to the 5' and 3' splice site regions using RNA structure probing; and 3) corresponds to plasma sphingolipid profiles consistent with loss of sphingolipid delta(4)-desaturase activity.

Discussion

Our RNA and lipidomic evidence proved that the DEGS1 variant c.825+4_825+5delAGinsTT is pathogenic and suggested a mechanistic model to explain how exon two skipping is induced.

Secondary failure of lentiviral vector gene therapy in a cerebral adrenoleukodystrophy patient with an ABCD1 whole-gene deletion

A 9-year-old boy with adrenoleukodystrophy due to ABCD1 whole-gene deletion was diagnosed with active cerebral adrenoleukodystrophy characterized by demyelination and gadolinium enhancement on brain MRI. He underwent hematopoietic cell transplant (HCT) with autologous CD34+ cells transduced with an ABCD1-expressing lentiviral vector (eli-cel [elivaldogene autotemcel]) as part of the ALD-104 clinical trial. Fifty days after HCT, the patient's MRI showed gadolinium resolution; the whole-blood vector copy number (VCN) was 0.666 copies/mL. Six months following HCT, an MRI showed re-emergence of gadolinium enhancement; the VCN had decreased to 0.029 copies/mL. Polyclonal antibodies to the ABCD1 gene product were detectable 9 months after transplant, showing reactivity to peroxisomes, suggesting an immune response; however, no antibody binding to human CD34+ cells could be shown. The patient underwent a successful allogeneic HCT 12 months after gene therapy with resultant gadolinium resolution, cerebral disease stabilization, and the disappearance of antibodies. The coincident VCN loss and appearance of antibody to the ABCD1 gene product is of interest, and we postulate that it is related to the patient's whole ABCD1 gene deletion. We suggest close monitoring of loss of gene therapy efficacy due to immune response in patients with full deletions who are considering gene therapy.

Practical Approach to Longitudinal Neurologic Care of Adults With X-Linked Adrenoleukodystrophy and Adrenomyeloneuropathy

Although X-linked adrenoleukodystrophy (ALD) has historically been considered a childhood disease managed by pediatric neurologists, it is one of the most common leukodystrophies diagnosed in adulthood. An increase in both male and female adults reaching diagnosis due to familial cases identified by state newborn screening panels and more widespread use of genetic testing results in a large cohort of presymptomatic or early symptomatic adults. This population is in urgent need of standardized assessments and follow-up care. Adults with ALD/adrenomyeloneuropathy (AMN) may be diagnosed in a variety of ways, including after another family member is identified via genetic testing or newborn screening, presenting for symptomatic evaluation, or following diagnosis with primary adrenal insufficiency. Significant provider, patient, and systems-based barriers prevent adult patients with ALD/AMN from receiving appropriate care, including lack of awareness of the importance of longitudinal neurologic management. Confirmation of and education about the diagnosis should be coordinated in conjunction with a genetic counselor. Routine surveillance for adrenal insufficiency and onset of cerebral ALD (CALD) in men should be performed systematically to avoid preventable morbidity and mortality. While women with ALD do not usually develop cerebral demyelination or adrenal insufficiency, they remain at risk for myeloneuropathy and are no longer considered "carriers." After diagnosis, patients should be connected to the robust support networks, foundations, and research organizations available for ALD/AMN. Core principles of neurologic symptom management parallel those for patients with other etiologies of progressive spastic paraplegia. Appropriate patient candidates for hematopoietic stem cell transplant (HSCT) and other investigational disease-modifying strategies require early identification to achieve optimal outcomes. All patients with ALD/AMN, regardless of sex, age, or symptom severity, benefit from a multidisciplinary approach to longitudinal care spearheaded by the neurologist. This review proposes key strategies for diagnostic confirmation, laboratory and imaging surveillance, approach to symptom management, and guidance for identification of appropriate candidates for HSCT and investigational treatments.

What can pediatricians learn from adult inherited metabolic diseases?

The field of inherited metabolic diseases (IMD) has initially emerged and developed over decades in pediatric departments. Still, today, about 50% of patients with IMD are adults, and adult metabolic medicine (AMM) is getting more structured at national and international levels. There are several domains in which pediatricians can learn from AMM. First, long-term evolution of IMD patients, especially those treated since childhood, is critical to determine nutritional and neuropsychiatric outcomes in adults so that these outcomes can be better monitored, and patient care adjusted as much as possible from childhood. Conversely, the observation of attenuated phenotypes in adults of IMD known to present with severe phenotypes in children calls for caution in the development of newborn screening programs and, more largely, in the interpretation of next-generation sequencing data. Third, it is important for pediatricians to be familiar with adult-onset IMD as they expand our understanding of metabolism, including in children, such as oxysterols and glycogen metabolism. Last, the identification of common molecular and cellular mechanisms in neurodevelopment and neurodegeneration opens the way to synergistic therapeutic developments that will benefit both fields of pediatric and adult medicine. Overall, these observations underline the need of strong interdisciplinarity between pediatricians and adult specialists for the diagnosis and the treatment of IMD well beyond the issues of patient transition from pediatric to adult medicine.

Longitudinal natural history studies based on real-world data in rare diseases: Opportunity and a novel approach

Growing interest in therapeutic development for rare diseases necessitate a systematic approach to the collection and curation of natural history data that can be applied consistently across this group of heterogenous rare diseases. In this study, we discuss the challenges facing natural history studies for leukodystrophies and detail a novel standardized approach to creating a longitudinal natural history study using existing medical records. Prospective studies are uniquely challenging for rare diseases. Delays in diagnosis and overall rarity limit the timely collection of natural history data. When feasible, prospective studies are often cross-sectional rather than longitudinal and are unlikely to capture pre- or early- symptomatic disease trajectories, limiting their utility in characterizing the full natural history of the disease. Therapeutic development in leukodystrophies is subject to these same obstacles. The Global Leukodystrophy Initiative Clinical Trials Network (GLIA-CTN) comprises of a network of research institutions across the United States, supported by a multi-center biorepository protocol, to map the longitudinal clinical course of disease across leukodystrophies. As part of GLIA-CTN, we developed Standard Operating Procedures (SOPs) that delineated all study processes related to staff training, source documentation, and data sharing. Additionally, the SOP detailed the standardized approach to data extraction including diagnosis, clinical presentation, and medical events, such as age at gastrostomy tube placement. The key variables for extraction were selected through face validity, and common electronic case report forms (eCRF) across leukodystrophies were created to collect analyzable data. To enhance the depth of the data, clinical notes are extracted into "original" and "imputed" encounters, with imputed encounter referring to a historic event (e.g., loss of ambulation 3 months prior). Retrospective Functional Assessments were assigned by child neurologists, using a blinded dual-rater approach and score discrepancies were adjudicated by a third rater. Upon completion of extraction, data source verification is performed. Data missingness was evaluated using statistics. The proposed methodology will enable us to leverage existing medical records to address the persistent gap in natural history data within this unique disease group, allow for assessment of clinical trajectory both pre- and post-formal diagnosis, and promote recruitment of larger cohorts.

Newborn screening for adrenoleukodystrophy: International experiences and challenges

X-linked adrenoleukodystrophy (XALD) is the most common leukodystrophy. It has an estimated incidence of around 1/17.000, and a variable phenotype. Following the passage of Aidens Law, New York became the first state to implement a newborn screening for XALD in 2013. Since then, 38 American states, Taiwan, and the Netherlands have included XALD in their NBS program, and Japan and Italy have ongoing pilot studies. Screening for XALD allows for early, potentially lifesaving treatment of adrenal insufficiency and cerebral demyelination but is also a complex subject, due to our limited understanding of the natural history and lack of prognostic biomarkers. Screening protocols and algorithms vary between countries and states, and results and experiences gained so far are important for the future implementation of XALD NBS in other countries. In this review, we have examined the algorithms, methodologies, and outcomes used, as well as how common challenges are addressed in countries/states that have experience using NBS for XALD. We identified 14 peer-reviewed reports on NBS for XALD. All studies presented methods for detecting XALD at birth by NBS using a combination of mass spectrometry and ABCD1 gene sequencing. This has allowed for early surveillance of presymptomatic XALD patients, and the possibility for early detection and timely treatment of XALD manifestations. Obstacles to NBS for XALD include how to deal with variants of unknown significance, whether to screen females, and the ethical concerns of an NBS for a disease where we have limited understanding of natural history and phenotype/genotype correlation.