Inborn errors of metabolism: combining clinical and radiologic clues to solve the mystery

Epileptic Channelopathies and Neuromuscular Disorders in Newborns: A Narrative Review

Neonates can have ion channel abnormalities known as channelopathies, which can impact any organ system. These abnormalities cause seizures, which can result in developmental delays and lead to early death. For a child's long-term neurodevelopment, early identification as a channelopathy is essential to avoid any brain damage. Therefore, this review aims to focus on early diagnostic criteria. Since it might be difficult for doctors to interpret the presenting symptoms of channelopathies, a thorough diagnostic examination that follows a methodical step-by-step procedure is essential. Skeletal muscle fiber and neuron excitability depend on voltage-gated sodium channels. It is now known that mutations in voltage-gated sodium channel genes can cause a growing variety of fatal or debilitating pediatric neurological diseases. Episodic paralysis, myotonia, newborn hypotonia, respiratory impairment, laryngospasm/stridor, congenital myasthenia, and myopathy are examples of muscle phenotypes. There may be a connection between sodium channel malfunction and abrupt infant death, according to recent findings. Numerous epilepsy syndromes and complex encephalopathies are among the manifestations of different channelopathies that are becoming more widely recognized.

MR Neuroimaging in Pediatric Inborn Errors of Metabolism

Inborn errors of metabolism (IEM) are a group of disorders due to functional defects in one or more metabolic pathways that can cause considerable morbidity and death if not diagnosed early. While individually rare, the estimated global prevalence of IEMs comprises a substantial number of neonatal and infantile disorders affecting the central nervous system. Clinical manifestations of IEMs may be nonspecific. Newborn metabolic screens do not capture all IEMs, and likewise, genetic testing may not always detect pathogenic variants. Neuroimaging is a critical component of the work-up, given that imaging sometimes occurs before prenatal screen results are available, which may allow for recognition of imaging patterns that lead to early diagnosis and treatment of IEMs. This review will demonstrate the role of magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (¹H MRS) in the evaluation of IEMs. The focus will be on scenarios where MRI and ¹H MRS are suggestive of or diagnostic for IEMs, or alternatively, refute the diagnosis.

Approach to Neurological Channelopathies and Neurometabolic Disorders in Newborns

Ion channel disorders (channelopathies) can affect any organ system in newborns before 2 months of life, including the skeletal muscle and central nervous system. Channelopathies in newborns can manifest as seizure disorders, which is a critical issue as early onset seizures can mimic the presentation of neurometabolic disorders. Seizures in channelopathies can either be focal or generalized, and range in severity from benign to epileptic encephalopathies that may lead to developmental regression and eventually premature death. The presenting symptoms of channelopathies are challenging for clinicians to decipher, such that an extensive diagnostic survey through a precise step-by-step process is vital. Early diagnosis of a newborn's disease, either as a channelopathy or neurometabolic disorder, is important for the long-term neurodevelopment of the child.

Neonatal Encephalopathy: Beyond Hypoxic-Ischemic Encephalopathy

Neonatal encephalopathy is a clinical syndrome of neurologic dysfunction that encompasses a broad spectrum of symptoms and severity, from mild irritability and feeding difficulties to coma and seizures. It is vital for providers to understand that the term "neonatal encephalopathy" is simply a description of the neonate's neurologic status that is agnostic to the underlying etiology. Unfortunately, hypoxic-ischemic encephalopathy (HIE) has become common vernacular to describe any neonate with encephalopathy, but this can be misleading. The term should not be used unless there is evidence of perinatal asphyxia as the primary cause of encephalopathy. HIE is a common cause of neonatal encephalopathy; the differential diagnosis also includes conditions with infectious, vascular, epileptic, genetic/congenital, metabolic, and toxic causes. Because neonatal encephalopathy is estimated to affect 2 to 6 per 1,000 term births, of which HIE accounts for approximately 1.5 per 1,000 term births, (1)(2)(3)(4)(5)(6) neonatologists and child neurologists should familiarize themselves with the evaluation, diagnosis, and treatment of the diverse causes of neonatal encephalopathy. This review begins by discussing HIE, but also helps practitioners extend the differential to consider the broad array of other causes of neonatal encephalopathy, emphasizing the epidemiology, neurologic presentations, diagnostics, imaging findings, and therapeutic strategies for each potential category.

Reliability of MRI in detection and differentiation of acute neonatal/pediatric encephalopathy causes among neonatal/pediatric intensive care unit patients

Background

Causes of encephalopathy in neonates/pediatrics include hypoxic-ischemic injury (which is the most frequent cause and is defined as any impairment to the brain caused by insufficient blood flow and oxygenation), trauma, metabolic disorders, and congenital and infectious diseases. The aim of this study is to evaluate the value of MRI in detection and possible differentiation of different non-traumatic, non-infectious causes of acute neonatal/pediatric encephalopathy among NICU/PICU patients.

Results

This retrospective study included 60 selected patients according to the study inclusion and exclusion criteria; all presented with positive MRI findings for non-traumatic, non-infectious acute brain injury. Females (32, 53.3%) were affected more than males (28, 46.7%) with a mean age of 1.1 ± 1.02 years; all presented with variable neurological symptoms and signs that necessitate neonatal intensive care unit/pediatric intensive care unit (NICU/PICU) admission. The final diagnosis of the study group patients were hypoxic ischemia injury (HII) in 39 patients (65%), metachromatic leukodystrophy in 6 patients (10%), biotin-thiamine-responsive basal ganglia disease (BTBGD) and Leigh disease each in 4 patients (6.7%), periventricular leukomalacia (PVL) in 3 patients (5%), and mitochondrial encephalopathy with lactic acidosis and stroke-like episodes syndrome (MELAS) and non-ketotic hyperglycinemia (NKH) each in 2 patients (3.3%).

Conclusion

Much attention should be paid to pediatric non-traumatic brain injuries. MRI is a safe modality and should be the first radiological investigation if neurological causes are suggested but should be aided by meticulous clinical evaluation and dedicated laboratory investigations for better characterization and differentiation of various causes of non-traumatic, non-infective brain encephalopathy among NICU/PICU patients. When interpreting MRI, it is essential to have thorough relevant clinical data, gestational age at birth which is prognostic of the pattern of hypoxic-ischemic injury, and the time lag between the onset of HII and the time of performing the MR study.

Imaging diagnosis of ventriculomegaly: fetal, neonatal, and pediatric

Ventriculomegaly is the term used to describe abnormal enlargement of ventricles in the brain. Neuroimaging, whether it is by ultrasound, computed tomography, or magnetic resonance imaging, is the key to its identification and can help to diagnose its cause and guide management in many cases. The implementation of the imaging modalities and potential differential considerations varies from the fetus, infant, and pediatric patient. Here we discuss how the imaging modalities can be used in these patient populations and review some of the differential considerations.

Inborn Errors of Metabolism in the Era of Untargeted Metabolomics and Lipidomics

Inborn errors of metabolism (IEMs) are a group of inherited diseases with variable incidences. IEMs are caused by disrupting enzyme activities in specific metabolic pathways by genetic mutations, either directly or indirectly by cofactor deficiencies, causing altered levels of compounds associated with these pathways. While IEMs may present with multiple overlapping symptoms and metabolites, early and accurate diagnosis of IEMs is critical for the long-term health of affected subjects. The prevalence of IEMs differs between countries, likely because different IEM classifications and IEM screening methods are used. Currently, newborn screening programs exclusively use targeted metabolic assays that focus on limited panels of compounds for selected IEM diseases. Such targeted approaches face the problem of false negative and false positive diagnoses that could be overcome if metabolic screening adopted analyses of a broader range of analytes. Hence, we here review the prospects of using untargeted metabolomics for IEM screening. Untargeted metabolomics and lipidomics do not rely on predefined target lists and can detect as many metabolites as possible in a sample, allowing to screen for many metabolic pathways simultaneously. Examples are given for nontargeted analyses of IEMs, and prospects and limitations of different metabolomics methods are discussed. We conclude that dedicated studies are needed to compare accuracy and robustness of targeted and untargeted methods with respect to widening the scope of IEM diagnostics.

Contemporary scope of inborn errors of metabolism involving epilepsy or seizures

Many inborn errors of metabolism may present with epilepsy or seizures, however, current scope of these diseases is unknown. Due to available precision medicine approaches in many inborn errors of metabolism and sophisticated traditional diagnostics, this group of disorders is of special relevance to clinicians. Besides, as current treatment is challenging and unsuccessful in more than 30% of all epilepsy patients, these diseases may provide valuable models for ictogenesis and epileptogenesis studies and potentially pave the ways to identification of novel treatments. The aim of this study was to elucidate genetic architecture of inborn errors of metabolism involving epilepsy or seizures and to evaluate their diagnostic approaches. After extensive search, 880 human genes were identified with a considerable part, 373 genes (42%), associated with inborn errors of metabolism. The most numerous group comprised disorders of energy metabolism (115, 31% of all inborn errors of metabolism). A substantial number of these diseases (26%, 97/373) have established specific treatments, therefore timely diagnosis comes as an obligation. Highly heterogenous, overlapping and non-specific phenotypes in most of inborn errors of metabolism presenting with epilepsy or seizures usually preclude phenotype-driven diagnostics. Besides, as traditional diagnostics involves a range of specialized metabolic tests with low diagnostic yields and is generally inefficient and lengthy, next-generation sequencing-based methods were proposed as a cost-efficient one-step way to shorten "diagnostic odyssey". Extensive list of 373 epilepsy- or seizures-associated inborn errors of metabolism genes may be of value in development of gene panels and as a tool for variants' filtration.

Overview of neuroradiology

Neuroradiology with computed tomography (CT) and magnetic resonance imaging (MRI) is essential for the initial evaluation of patients with a clinical suspicion of brain and spine disorders. Morphologic imaging is required to obtain a probable diagnosis to support the treatment decisions in pre- and perinatal disorders, vascular diseases, traumatic injuries, metabolic disorders, epilepsy, infection/inflammation, neurodegenerative disorders, degenerative spinal disease, and tumors of the central nervous system. Different postprocessing tools are increasingly used for three-dimensional visualization and quantification of lesions. Additional information is provided by angiographic methods and physiologic CT and MRI techniques, such as diffusion MRI, perfusion CT/MRI, MR spectroscopy, functional MRI, tractography, and nuclear medicine imaging methods. Positron emission tomography (PET) is now integrated with CT (PET/CT), and PET/MR scanners have recently also been introduced. These hybrid techniques facilitate the co-registration of lesions with different modalities, and give new possibilites for functional imaging. Repeated imaging is increasingly performed for treatment monitoring. The improved imaging techniques together with the neuropathologic diagnosis after biopsy or surgery allow more personalized treatment of the patient. Neuroradiology also includes endovascular treatment of aneurysms and arteriovenous malformations as well as thrombectomy in acute stroke. This catheter-based treatment has replaced invasive neurosurgery in many cases.

Cognitive and academic outcomes in long-term survivors of infantile-onset Pompe disease: A longitudinal follow-up

This study examines the long-term cognitive and academic outcomes of 11 individuals with infantile onset Pompe disease (IOPD) (median age=11years, 1month, range=5years, 6months through 17years of age) treated with enzyme replacement therapy from an early age. All participants (7 males, 4 females) were administered individual intelligence tests (Wechsler or Leiter scales or both), a measure of their academic skill levels (Woodcock-Johnson Tests of Achievement), and a screening measure of visual-motor integration ability (Beery-Buktenica). Consistent with our earlier findings, median IQ scores for the entire group on the Wechsler (median=84) and Leiter (median=92) scales continue to fall at the lower end of the average range compared to same-aged peers. The median scores for the group on a measure of visual-motor integration (median=76), visual perception (median=74) and motor coordination (median=60) were below average. Two distinct subgroups emerged based on participants' average or below average performance on the majority of academic subtests. Those participants with below average academic skills (n=6) demonstrated average nonverbal cognitive abilities on the Leiter, but had weaknesses in speech and language skills and greater medical involvement. Their profiles were more consistent with a learning disability diagnosis than an intellectual disability. Two of these participants showed a significant decline (15 and 23 points, respectively) on repeated Wechsler scales, but one continued to earn average scores on the Leiter scales where the verbal and motor demands are minimal. Participants with average academic skills (n=5) demonstrated average cognitive abilities (verbal and nonverbal) on the Wechsler scales and less medical involvement. Their speech and language skills appeared to be more intact. However, both groups earned below average median scores on the Beery-Buktenica motor coordination task. This study highlights the importance of using appropriate tests to capture both verbal and nonverbal abilities, considering each individual's motor skills, speech and language abilities, hearing status and native language. This will allow for a more accurate assessment of whether there is a learning disability or an intellectual disability. Long-term outcomes may be related to the stability of an individual's expressive and/or receptive language abilities over time. Changes in the speech and language domain may account for the decline in IQ observed in some IOPD long-term survivors, reflecting a learning disability rather than a decline in overall cognition or an intellectual disability. These observations, in conjunction with neuroimaging, will further our understanding of the neurocognitive profile of long-term IOPD survivors.

In Vivo NMR Studies of the Brain with Hereditary or Acquired Metabolic Disorders

Metabolic disorders, whether hereditary or acquired, affect the brain, and abnormalities of the brain are related to cellular integrity; particularly in regard to neurons and astrocytes as well as interactions between them. Metabolic disturbances lead to alterations in cellular function as well as microscopic and macroscopic structural changes in the brain with diabetes, the most typical example of metabolic disorders, and a number of hereditary metabolic disorders. Alternatively, cellular dysfunction and degeneration of the brain lead to metabolic disturbances in hereditary neurological disorders with neurodegeneration. Nuclear magnetic resonance (NMR) techniques allow us to assess a range of pathophysiological changes of the brain in vivo. For example, magnetic resonance spectroscopy detects alterations in brain metabolism and energetics. Physiological magnetic resonance imaging (MRI) detects accompanying changes in cerebral blood flow related to neurovascular coupling. Diffusion and T1/T2-weighted MRI detect microscopic and macroscopic changes of the brain structure. This review summarizes current NMR findings of functional, physiological and biochemical alterations within a number of hereditary and acquired metabolic disorders in both animal models and humans. The global view of the impact of these metabolic disorders on the brain may be useful in identifying the unique and/or general patterns of abnormalities in the living brain related to the pathophysiology of the diseases, and identifying future fields of inquiry.