OBJECTIVE:Our report describes clinical, genetic, and biochemical features of participants with a molecularly confirmed congenital disorder of glycosylation (CDG) enrolled in the Frontiers in Congenital Disorders of Glycosylation (FCDGC) Natural History cohort at year 5 of the study. METHODS:We enrolled individuals with a known or suspected CDG into the FCDGC Natural History Study, a multicenter prospective and retrospective natural history study of all genetic causes of CDG. We conducted a cross-sectional analysis of baseline study visit data from participants with confirmed CDG who were consented into the FCDGC Natural History Study (5U54NS115198) from October 2019 to November 2023. RESULTS:Three hundred thirty-three subjects consented to the FCDGC Natural History Study. Of these, 280 unique individuals had genetic data available that was consistent with a diagnosis of CDG. These 280 individuals were enrolled into the study between October 8, 2019 and November 29, 2023. One hundred forty-one (50.4%) were female, and 139 (49.6%) were male. Mean and median age at enrollment was 10.1 and 6.5 years, respectively, with a range of 0.22 to 71.4 years. The cohort encompassed individuals with disorders of N-linked protein glycosylation (57%), glycosylphosphatidylinositol anchor disorder (GPI anchor) (15%), disorders of Golgi homeostasis, trafficking and transport (12%), dolichol metabolism disorders (5%), disorders of multiple pathways (6%), and other (5%). The most frequent presenting symptom(s) leading to diagnosis were developmental delay/disability (77%), followed by hypotonia (56%) and feeding difficulties (42%). Mean and median time between first related symptom and diagnosis was 2.7 and 0.8 years, respectively. One hundred percent of individuals in our cohort had developmental differences/disabilities at the time of their baseline visit, followed by 97% with neurologic involvement, 91% with gastrointestinal (GI)/liver involvement, and 88% with musculoskeletal involvement. Severity of disease in individuals was scored on the Nijmegen Progression CDG Rating Scale (NPCRS) with 27% of scores categorized as mild, 44% moderate, and 29% severe. Of the individuals with N-linked protein glycosylation defects, 83% of those with data showed a type 1 pattern on carbohydrate deficient transferrin (CDT) analysis including 82/84 individuals with PMM2-CDG, 6% a type 2 pattern, 1% both type 1 and type 2 pattern and 10% a normal or nonspecific pattern. One hundred percent of individuals with Golgi homeostasis and trafficking defects with data showed a type 2 pattern on CDT analysis, while Golgi transport defect showed a type II pattern 73% of the time, a type 1 pattern for 7%, and 20% had a normal or nonspecific pattern. Most of the variants documented were classified as pathogenic or likely pathogenic using ACMG criteria. For the majority of the variants, the predicted molecular consequence was missense followed by nonsense and splice site, and the majority of the diagnoses are inherited in an autosomal recessive pattern but with disorders of all major nuclear inheritance included. DISCUSSION:The FCDGC Natural History Study serves as an important resource to build future research studies, improve clinical care, and prepare for clinical trial readiness. Herein is the first overview of CDG participants of the FCDGC Natural History Study.

Objective Primary mitochondrial diseases (PMDs) are heterogeneous disorders caused by inherited mitochondrial dysfunction. Classically defined neuropathologically as subacute necrotizing encephalomyelopathy, Leigh syndrome spectrum (LSS) is the most frequent manifestation of PMD in children, but may also present in adults. A major challenge for accurate diagnosis of LSS in the genomic medicine era is establishing gene–disease relationships (GDRs) for this syndrome with >100 monogenic causes across both nuclear and mitochondrial genomes. Methods The Clinical Genome Resource (ClinGen) Mitochondrial Disease Gene Curation Expert Panel (GCEP), comprising 40 international PMD experts, met monthly for 4 years to review GDRs for LSS. The GCEP standardized gene curation for LSS by refining the phenotypic definition, modifying the ClinGen Gene–Disease Clinical Validity Curation Framework to improve interpretation for LSS, and establishing a scoring rubric for LSS. Results The GDR with LSS across the nuclear and mitochondrial genomes was classified as definitive for 31 of 114 GDRs curated (27%), moderate for 38 (33%), limited for 43 (38%), and disputed for 2 (2%). Ninety genes were associated with autosomal recessive inheritance, 16 were maternally inherited, 5 were autosomal dominant, and 3 were X‐linked. Interpretation GDRs for LSS were established for genes across both nuclear and mitochondrial genomes. Establishing these GDRs will allow accurate variant interpretation, expedite genetic diagnosis of LSS, and facilitate precision medicine, multisystem organ surveillance, recurrence risk counseling, reproductive choice, natural history studies, and determination of eligibility for interventional clinical trials. ANN NEUROL 2023;94:696–712

Mitochondrial dysfunction can be associated with a range of clinical manifestations. Here, we report a family with a complex phenotype including combinations of connective tissue, neurological, and metabolic symptoms that were passed on to all surviving children. Analysis of the maternally inherited mtDNA revealed a novel genotype encompassing the haplogroup J - defining mitochondrial DNA (mtDNA) ND5 m.13708G>A (A458T) variant arising on the mtDNA haplogroup H7A background, an extremely rare combination. Analysis of transmitochondrial cybrids with the 13708A-H7 mtDNA revealed a lower mitochondrial respiration, increased reactive oxygen species production (mROS), and dysregulation of connective tissue gene expression. The mitochondrial dysfunction was exacerbated by histamine, explaining why all eight surviving children inherited the dysfunctional histidine decarboxylase allele (W327X) from the father. Thus, certain combinations of common mtDNA variants can cause mitochondrial dysfunction, mitochondrial dysfunction can affect extracellular matrix gene expression, and histamine-activated mROS production can augment the severity of mitochondrial dysfunction. Most important, we have identified a previously unreported genetic cause of mitochondrial disorder arising from the incompatibility of common, nonpathogenic mtDNA variants.

Asparagine and glutamate are synthesized from aspartate and glutamine using the enzyme asparagine synthetase. A deficiency of this enzyme leads to asparagine synthetase deficiency (ASNSD). ASNSD is an autosomal recessive progressive neurological disorder classically characterized by congenital microcephaly, early onset epileptic encephalopathy, and developmental delay or regression. Seizures are typically present at birth but have been reported to start as late as 9 months of age. Asparagine levels may be low or normal in the serum but have been reported to be low or absent in the CSF. The diagnosis is made through molecular testing. Brain imaging may reveal cerebral atrophy, small pons, delayed myelination and simplified gyri. No treatment is available, and it is thought that most therapies would not be effective as deficiency of asparagine synthetase affects neuronal development during both the embryonic and postembryonic periods. Asparagine supplementation has been trialed, but with negative consequences in some patients. It is reported that seizures may respond well to valproate therapy due to a decrease in aspartate release at excitatory nerve terminals. Drugs that target NMDA or AMPA receptors may also be considered in the management of refractory seizures in ASNSD. We present a 3-year-old male diagnosed with asparagine synthetase deficiency due to biallelic variants in ASNS with associated microcephaly, developmental delay, recurrent seizure episodes in the setting of illness, and oral texture aversion. Perinatal history was unremarkable with the exception of nuchal thickening noted on antenatal ultrasound. Of note, microcephaly was not reported prenatally. His newborn screen was normal. He initially presented at the age of 9 months with gross motor delays. His first seizure episode was at the age of 11 months in the context of a febrile illness due to adenovirus. His first seizure was focal with unilateral weakness, but this was followed by subsequent generalized seizures in the setting of febrile illnesses. His seizures are now controlled on Keppra. His initial routine electroencephalogram (EEG) was normal, but a subsequent 36-hour video EEG was abnormal with diffuse slowing, intermittent rhythmic slow waves and sharp waves. EEG patterns may vary in patients with ASNSD, but disorganization and intermittent sharp waves have been reported consistently. HIs brain MRI revealed parenchymal volume loss with otherwise normal anatomy. Mild regression of motor skills was noted following seizure episodes, but these skills were regained, and he continued to have developmental progression. He was also noted to have expressive and receptive speech delays and is only able to babble at the age of 3 years. Family history was noncontributory. His weight gain and linear growth were stable. The physical exam findings of hypotonia, hyperreflexia, and microcephaly were consistent with ASNSD. At birth, his head circumference was –0.9 SD, and has now progressed to –2.8 SD on the CDC growth curves. The patient also has mild bilateral myopic astigmatism and pseudo strabismus. Attempts at audiology evaluation have been unsuccessful, and evaluation under sedation is being avoided at this time due to potential risk of neurological decline. The diagnosis was made on the basis of a paternally inherited pathogenic (c.1192dupT) variant and a maternally inherited likely pathogenic (c.614A>C) variant in ASNS (NM_133436.3) detected on an epilepsy panel at a commercial lab. Both variants have not been previously reported in other affected individuals. The pathogenic frameshift variant is predicted to result in protein truncation or nonsense mediated decay. The likely pathogenic missense variant is predicted to be deleterious in computer models. Plasma amino acids were normal with normal glutamate and asparagine levels. CSF amino acids were not obtained. We present a patient with a mild phenotype of asparagine synthetase deficiency. Our patient did not have onset of seizure-like activity until the age of 11 months which is the latest onset of seizures in this disease reported to our knowledge. His seizures have also been controlled on Keppra. Our patient was identified via an expanded seizure panel, suggesting that the addition of ASNS to seizure panels may lead to the diagnosis of more patients with a mild form of ASNSD. Most patients previously reported were diagnosed via exome sequencing, which may not be pursued for patients with mild phenotypes. These patients may be more amenable to therapy with common antiepileptics, but there continues to be a lack of therapy available for the underlying disorder. Severe phenotypes are expected to be associated with compromised protein function or protein truncation, so we hypothesize that the maternally inherited likely pathogenic variant may have some residual function leading to the milder phenotype. At this time, we are avoiding procedures requiring sedation, but if there is medical necessity for sedation in the future, we will consider obtaining an MR Spectroscopy and/or CSF amino acids at that time.

Mitochondrial dysfunction is associated with a range of clinical manifestations including neuropsychiatric and metabolic disorder. Here, we reanalyzed a family with an L-Histidine Decarboxylase (HDC) variant previously linked to Tourette syndrome but with associated connective tissue and metabolic features of unknown etiology. We identified a mitochondrial haplogroup J-defining mutation on the haplogroup H background that functionally interacts with the L-Histidine Decarboxylase variant via calcium homeostasis. Our findings establish how a common mtDNA variant on a different mtDNA background can result in mitochondrial dysfunction, demonstrate a role for histaminergic signaling in modifying mitochondrial phenotypes, and link mitochondria dysfunction to connective tissue phenotypes.

Asymptomatic aminotransferase elevation has a broad differential in the pediatric population. We report an 11-year old male with a history of urine discoloration found to have persistently elevated aminotransferases. Biochemical evaluation was notable for elevated uroporphyrin, consistent with porphyria cutanea tarda (PCT). Genetic testing revealed biallelic pathogenic variants in HFE and a pathogenic variant in UROD, consistent with a diagnosis of hereditary hemochromatosis (HHC) and PCT, respectively. Dual diagnosis likely explains the pediatric onset of these typically adult-onset conditions.

May 8, 2019April 9, 2019Free AccessAberrant Mitophagy In The Pediatric Neurodegenerative Syndrome TBCKE (P4.6-064)Jesus Tintos-Hernandez, Kierstin Keller, Douglas Wallace, and Xilma Ortiz-GonzalezAuthors Info & AffiliationsApril 9, 2019 issue92 (15_supplement)https://doi.org/10.1212/WNL.92.15_supplement.P4.6-064 Letters to the Editor

ObjectiveAutosomal‐recessive mutations in TBCK cause intellectual disability of variable severity. Although the physiological function of TBCK remains unclear, loss‐of‐function mutations are associated with inhibition of mechanistic target of rapamycin complex 1 (mTORC1) signaling. Given that mTORC1 signaling is known to regulate autophagy, we hypothesized that TBCK‐encephalopathy patients with a neurodegenerative course have defects in autophagic‐lysosomal dysfunction.MethodsChildren (n = 8) of Puerto Rican (Boricua) descent affected with homozygous TBCK p.R126X mutations underwent extensive neurological phenotyping and neurophysiological studies. We quantified autophagosome content in TBCK−/− patient‐derived fibroblasts by immunostaining and assayed autophagic markers by western assay. Free sialylated oligosaccharide profiles were assayed in patient's urine and fibroblasts.ResultsThe neurological phenotype of children with TBCK p.R126X mutations, which we call TBCK‐encephaloneuronopathy (TBCKE), include congenital hypotonia, progressive motor neuronopathy, leukoencephalopathy, and epilepsy. Systemic features include coarse facies, dyslipidemia, and osteoporosis. TBCK−/− fibroblasts in vitro exhibit increased numbers of LC3+ autophagosomes and increased autophagic flux by immunoblots. Free oligosaccharide profiles in fibroblasts and urine of TBCKE patients differ from control fibroblasts and are ameliorated by treatment with the mTORC1 activator leucine.InterpretationTBCKE is a clinically distinguishable syndrome with progressive central and peripheral nervous system dysfunction, consistently observed in patients with the p.R126X mutation. We provide evidence that inappropriate autophagy in the absence of cellular stressors may play a role in this disorder, and that mTORC1 activation may ameliorate the autophagic‐lysosomal system dysfunction. Free oligosaccharide profiles could serve as a novel biomarker for this disorder as well as a tool to evaluate potential therapeutic interventions. Ann Neurol 2018;83:153–165