BACKGROUND:Arginase 1 deficiency (ARG1-D; OMIM #207800) is a rare urea cycle disorder caused by loss of arginase activity, preventing the hydrolysis of arginine to ornithine and urea. The resulting hyperargininaemia leads to accumulation of neurotoxic metabolites including guanidino compounds and nitric oxide in the central nervous system. Nervous system structures are affected, including the corticospinal tracts, cerebral and cerebellar white matter, basal ganglia, hippocampus, and corpus callosum. Clinically, patients present with developmental and neurological impairment, including growth delay, spasticity, balance and coordination challenges, seizures, and cognitive dysfunction. Without effective treatment, symptoms worsen, leading to disability, reduced quality of life, and risk of premature death. PATHOPHYSIOLOGY:Persistent elevation of arginine and its metabolites drives pathology. Unlike other urea cycle disorders, neurological damage in ARG1-D is largely independent of hyperammonaemia. Excess arginine increases nitric oxide production and formation of peroxynitrite, promoting oxidative stress, mitochondrial dysfunction, and reduced ATP availability. These effects impair oligodendrocyte maturation and myelination, affecting corticospinal tracts. Supraphysiologic concentrations of arginine also result in accumulation of neurotoxic metabolites including guanidino compounds which in vitro inhibit Na+/K+-ATPase activity, disrupt membrane stability, and impair inhibitory neurotransmission. The resulting hyperexcitability contributes to seizures and progressive neuromotor decline. Structural imaging demonstrates cerebral and cerebellar atrophy, white matter dysmyelination, and thinning of the corpus callosum. Electrophysiological studies show slowed neural conduction. Notably, neurological manifestations often occur despite normal ammonia concentrations, supporting hyperargininaemia and its metabolites as the primary driver of progression. CONCLUSION:Chronic neurotoxicity from elevated arginine and its derivatives drives the progressive neurological decline in ARG1-D. Until recently, liver transplantation was the only intervention to halt progression of the disease, but it is not available to the majority of patients, is high risk, and resource intensive. In recently conducted clinical studies, enzyme therapy with pegzilarginase has demonstrated substantial reductions in arginine and its derivatives with improved clinical outcomes.

Arginase 1 deficiency (ARG1-D) is an autosomal recessive urea cycle disorder characterised by chronic hyperargininaemia, progressive spasticity, loss of mobility, and cognitive dysfunction. Standard of care (SOC), based on dietary protein restriction, rarely prevents progression. Pegzilarginase, a recombinant human enzyme, is the first approved disease-modifying therapy. We report outcomes from Study 102A (n = 14; up to 5 years) and the PEACE long-term extension (LTE) (n = 31; up to 3 years). Weekly pegzilarginase was administered with SOC. Outcomes included functional mobility (2-/6-minute walk tests [2MWT/6MWT], Gross Motor Function Measure [GMFM] D/E), spasticity (Modified Ashworth Scale [MAS]), plasma arginine, guanidino compounds, and safety. In PEACE, LTE arms were named according to initial 24-week double-blind treatment: placebo-pegzilarginase or pegzilarginase-pegzilarginase. Of 39 evaluable participants, 37 (95%) met composite response or achieved maximum score in ≥ 1 motor function domain. In 102A, mean 6MWT improved to 68.2 m (+19%; n = 12); GMFM-D/E increased by 2.7/3.7. In PEACE (pegzilarginase-pegzilarginase; placebo-pegzilarginase), 2MWT improved to 16.5 m (+25%; n = 6) and 13.5 m (+16%; n = 2); GMFM-D/E improved by 4.3/6.0 (n = 6) and 5.3/11.3 (n = 3). Spasticity improved in 21/25 (84%), with 12 reaching MAS 0 (no spasticity). Pegzilarginase sustained plasma arginine control: in 102A, means were 118 μmol/L at Week 192 (n = 9); in PEACE, < 115 μmol/L through Week 96 (n = 11). Guanidinoacetic acid normalised; N-acetylarginine approached normal; argininic acid and α-keto-δ-guanidinovaleric acid declined by > 50%. Most adverse events were mild/moderate; no treatment-related discontinuations or persistent antibodies occurred. Pegzilarginase produced sustained improvements in mobility, spasticity and biochemical control, supporting early intervention, long-term use and disease modification in ARG1-D.

ALDH7A1 deficiency is an epileptic encephalopathy whose seizures respond to treatment with supraphysiological doses of pyridoxine. It arises as a result of damaging variants in ALDH7A1, a gene in the lysine catabolism pathway. α-Aminoadipic semialdehyde (α-AASA) and Δ1-piperideine-6-carboxylate (P6C), which accumulate because of the block in the lysine pathway, are diagnostic biomarkers for this disorder. Recently, it has been reported that 6-oxo-pipecolic acid (6-oxo-PIP) also accumulates in the urine, CSF and plasma of ALDH7A1-deficient individuals and that, given its improved stability, it may be a more suitable biomarker for this disorder. This study measured 6-oxo-PIP in urine from a cohort of 30 patients where α-AASA was elevated and showed that it was above the normal range in all those above 6 months of age. However, 6-oxo-PIP levels were within the normal range in 33% of the patients below 6 months of age. Levels increased with age and correlated with a decrease in α-AASA levels. Longitudinal analysis of urine samples from ALDH7A1-deficient patients who were on a lysine restricted diet whilst receiving supraphysiological doses of pyridoxine showed that levels of 6-oxo-PIP remained elevated whilst α-AASA decreased. Similar to α-AASA, we found that elevated urinary excretion of 6-oxo-PIP can also occur in individuals with molybdenum cofactor deficiency. This study demonstrates that urinary 6-oxo-PIP may not be a suitable biomarker for ALDH7A1 deficiency in neonates. However, further studies are needed to understand the biochemistry leading to its accumulation and its potential long-term side effects.

Abstract Dihydropteridine reductase (DHPR) deficiency is a disorder that prevents regeneration of tetrahydrobiopterin (BH4), causing hyperphenylalaninemia (HPA) and low levels of neurotransmitters, including dopamine. Due to low levels of dopamine, patients present with hyperprolactinemia. Treatment consists of a phenylalanine (Phe)-restricted diet, hydroxytryptophan and levodopa (L-Dopa) supplementation, leading to a rapid normalization of prolactin (PRL) levels. We report a case of a patient with DHPR deficiency presenting with new symptomatic hyperprolactinemia and amenorrhea in adolescence despite appropriate management. The prolactinoma was confirmed with pituitary magnetic resonance imaging. The patient was started on cabergoline with rapid normalization of PRL levels and resolution of symptoms, in keeping with previous reports. Cabergoline has a stronger affinity for the D2R receptor and longer half-life than L-Dopa, leading to lactotroph apoptosis, tumor shrinkage, and rapid and maintained normalization of PRL levels, with a better side-effect profile. Patients with DHPR deficiency need to be actively monitored for symptomatic hyperprolactinemia, as L-Dopa monotherapy is insufficient to suppress PRL secretion, leading to lactotroph hypertrophy and proliferation over time and development of prolactinomas in later life.

ObjectivesNeuronal ceroid lipofuscinosis type 2 (CLN2-disease) is an inherited childhood-onset neurodegenerative condition, with classical early features of speech delay, epilepsy, myoclonus, ataxia, and motor regression. This study aimed to better characterize the spectrum of movement disorders in CLN2-disease in a cohort of children receiving enzyme replacement therapy (ERT).MethodsA cohort of 18 children attending a single center for treatment with cerliponase alfa ERT was systematically assessed using a standardized structured history and a double-scored, video-recorded examination using the Unified Batten Disease Rating Scale (UBDRS) and Abnormal Involuntary Movement Scale.ResultsNoncanonical movement disorders are common: while ataxia (89%) and myoclonus (83%) were near-universal, spasticity and dystonia were experienced by over half (61% each), with children having a median of 4 distinct movement disorder phenotypes. This progression was stereotyped with initial ataxia/myoclonus, then hyperkinesia/spasticity, and later hypokinesia. ERT slows progression of movement disorders, as measured by the UBDRS physical subscale, with 1.45 points-per-month progression before diagnosis and 0.44 points-per-month while on treatment (p = 0.019).DiscussionMovement disorders are a core feature of CLN2-disease and follow a typical pattern of progression which is slowed by ERT. Identifying and treating movement disorders should become standard, especially given increased patient survival.

Abstract Background The GM1 and GM2 gangliosidoses and type 2 Gaucher disease (GD2) are inherited lysosomal storage disorders with most cases having symptom onset in infancy and reduced life expectancy. The conditions are rare, and there is therefore a need for accurate and up to date information concerning the disease course and survival to assist in the design of clinical trials. RETRIEVE is a natural history study aiming to: (1) collect data on the survival of patients with early-onset (onset of first neurological manifestation before 24 months of age) GM1, GM2, or GD2; (2) collect data that could constitute a historical control group for future clinical trials; and (3) evaluate whether the conditions can be assessed together in a single interventional clinical trial. Group A included patients who were deceased or with unknown survival status at enrollment and was thus limited to retrospective data. Group B included patients who were alive at enrollment, who were followed prospectively with additional retrospective data collection. Results Group A included 185 patients (60 with GM1, 78 with GM2, and 47 with GD2), and Group B included 40 patients (18 with GM1, 16 with GM2, and 6 with GD2). Mean and median age at diagnosis and age at onset of first neurological manifestation were youngest in patients with GD2 and oldest in patients with GM2 in both groups. In Group A, median (95% CI) survival was 19.0 (18.0, 22.0), 44.0 (37.0, 51.9) and 14.0 (10.0, 16.0) months in patients with GM1, GM2 and GD2, respectively. In Group B, hypotonia was experienced by most patients with GM1 (17/18, 94.4%), and was less common in patients with GM2 (12/16, 75.0%) and GD2 (4/6, 66.7%). Strabismus and splenomegaly were reported in all six patients with GD2. Conclusions RETRIEVE is one of the largest natural history studies of GM1, GM2, and GD2. Results were generally consistent with the published literature, with differences potentially due to variation in inclusion criteria. The difference in median survival between patients with early-onset GM1, GM2, and GD2 reported in this study suggests that the three diseases should not be pooled for study in clinical trials.

Biotinidase deficiency is an autosomal recessive condition caused by pathogenic variants in the BTD gene. Resultant deficiency of free biotin leads to impaired activity of the enzyme carboxylase and related neurologic, dermatologic, and ocular symptoms. Many of these are reversible on treatment, but early recognition and commencement of biotin supplementation are critical. This practice is especially important in countries where routine neonatal screening for biotinidase deficiency is not performed. In this report comprising 14 patients from multiple centers, we demonstrate the MR imaging patterns of this disorder at various age groups. Knowledge of these patterns in the appropriate clinical context will help guide early diagnosis of this treatable metabolic disorder.

Argininosuccinate lyase (ASL) is integral to the urea cycle detoxifying neurotoxic ammonia and the nitric oxide (NO) biosynthesis cycle. Inherited ASL deficiency causes argininosuccinic aciduria (ASA), a rare disease with hyperammonemia and NO deficiency. Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis. A neurodegenerative phenotype has been proposed in ASA. To better characterise this neurodegenerative phenotype in ASA, we conducted a retrospective study in six paediatric and adult metabolic centres in the UK in 2022. We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour. We analysed neuroimaging with diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) in an individual with ASA with movement disorders. We assessed conventional and DTI MRI alongside single photon emission computer tomography (SPECT) with dopamine analogue radionuclide 123I-ioflupane, in Asl-deficient mice treated by hASL mRNA with normalised ureagenesis. Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia. Neuroimaging can show abnormal DTI features affecting both grey and white matter, preferentially basal ganglia. ASA mouse model with normalised ureagenesis did not recapitulate these DTI findings and showed normal 123I-ioflupane SPECT and cerebral dopamine metabolomics. Altogether these findings support the pathophysiology of a late-onset movement disorder with cell-autonomous functional central catecholamine dysregulation but without or limited neurodegeneration of dopaminergic neurons, making these symptoms amenable to targeted therapy.

OBJECTIVE:To characterize the longitudinal natural history of disease progression in pediatric subjects affected with mucopolysaccharidosis (MPS) IIIB. STUDY DESIGN:Sixty-five children with a confirmed diagnosis of MPS IIIB were enrolled into 1 of 2 natural history studies and followed for up to 4 years. Cognitive and adaptive behavior functions were analyzed in all subjects, and volumetric magnetic resonance imaging analysis of liver, spleen, and brain, as well as levels of heparan sulfate (HS) and heparan sulfate nonreducing ends (HS-NRE), were measured in a subset of subjects. RESULTS:The majority of subjects with MPS IIIB achieved an apex on both cognition and adaptive behavior age equivalent scales between age 3 and 6 years. Development quotients for both cognition and adaptive behavior follow a linear trajectory by which subjects reach a nadir with a score <25 for an age equivalent of 24 months by age 8 years on average and by 13.5 years at the latest. All tested subjects (n = 22) had HS and HS-NRE levels above the normal range in cerebrospinal fluid and plasma, along with signs of hepatomegaly. Subjects lost an average of 26 mL of brain volume (-2.7%) over 48 weeks, owing entirely to a loss of cortical gray matter (32 mL; -6.5%). CONCLUSIONS:MPS IIIB exists along a continuum based on cognitive decline and cortical gray matter atrophy. Although a few individuals with MPS IIIB have an attenuated phenotype, the majority follow predicted trajectories for both cognition and adaptive behavior. TRIAL REGISTRATION:ClinicalTrials.gov identifiers NCT02493998, NCT03227042, and NCT02754076.

The high-affinity copper transporter CTR1 is encoded by CTR1 (SLC31A1), a gene locus for which no detailed genotype-phenotype correlations have previously been reported. We describe identical twin male infants homozygous for a novel missense variant NM_001859.4:c.284 G > A (p.Arg95His) in CTR1 with a distinctive autosomal recessive syndrome of infantile seizures and neurodegeneration, consistent with profound central nervous system copper deficiency. We used clinical, biochemical and molecular methods to delineate the first recognized examples of human CTR1 deficiency. These included clinical phenotyping, brain imaging, assays for copper, cytochrome c oxidase (CCO), and mitochondrial respiration, western blotting, cell transfection experiments, confocal and electron microscopy, protein structure modeling and fetal brain and cerebral organoid CTR1 transcriptome analyses. Comparison with two other critical mediators of cellular copper homeostasis, ATP7A and ATP7B, genes associated with Menkes disease and Wilson disease, respectively, revealed that expression of CTR1 was highest. Transcriptome analyses identified excitatory neurons and radial glia as brain cell types particularly enriched for copper transporter transcripts. We also assessed the effects of Copper Histidinate in the patients' cultured cells and in the patients, under a formal clinical protocol. Treatment normalized CCO activity and enhanced mitochondrial respiration in vitro, and was associated with modest clinical improvements. In combination with present and prior studies, these infants' clinical, biochemical and molecular phenotypes establish the impact of this novel variant on copper metabolism and cellular homeostasis and illuminate a crucial role for CTR1 in human brain development. CTR1 deficiency represents a newly defined inherited disorder of brain copper metabolism.