Clinical, Neuroimaging, and Metabolic Footprint of the Neurodevelopmental Disorder Caused by Monoallelic HK1 Variants.

Background and Objectives: Hexokinase 1 (encoded by HK1) catalyzes the first step of glycolysis, the adenosine triphosphate-dependent phosphorylation of glucose to glucose-6-phosphate. Monoallelic HK1 variants causing a neurodevelopmental disorder (NDD) have been reported in 12 individuals. Methods: We investigated clinical phenotypes, brain MRIs, and the CSF of 15 previously unpublished individuals with monoallelic HK1 variants and an NDD phenotype. Results: All individuals had recurrent variants likely causing gain-of-function, representing mutational hot spots. Eight individuals (c.1370C>T) had a developmental and epileptic encephalopathy with infantile onset and virtually no development. Of the other 7 individuals (n = 6: c.1334C>T; n = 1: c.1240G>A), 3 adults showed a biphasic course of disease with a mild static encephalopathy since early childhood and an unanticipated progressive deterioration with, e.g., movement disorder, psychiatric disease, and stroke-like episodes, epilepsy, starting in adulthood. Individuals who clinically presented in the first months of life had (near)-normal initial neuroimaging and severe cerebral atrophy during follow-up. In older children and adults, we noted progressive involvement of basal ganglia including Leigh-like MRI patterns and cerebellar atrophy, with remarkable intraindividual variability. The CSF glucose and the CSF/blood glucose ratio were below the 5th percentile of normal in almost all CSF samples, while blood glucose was unremarkable. This biomarker profile resembles glucose transporter type 1 deficiency syndrome; however, in HK1-related NDD, CSF lactate was significantly increased in all patients resulting in a substantially different biomarker profile. Discussion: Genotype-phenotype correlations appear to exist for HK1 variants and can aid in counseling. A CSF biomarker profile with low glucose, low CSF/blood glucose, and high CSF lactate may point toward monoallelic HK1 variants causing an NDD. This can help in variant interpretation and may aid in understanding the pathomechanism. We hypothesize that progressive intoxication and/or ongoing energy deficiency lead to the clinical phenotypes and progressive neuroimaging findings.

Causative mechanisms and clinical impact of immunoglobulin deficiencies in ataxia telangiectasia.

BACKGROUND: Ataxia telangiectasia (AT) is characterized by cerebellar ataxia, telangiectasia, immunodeficiency, and increased cancer susceptibility and is caused by mutations in the ataxia telangiectasia mutated (ATM) gene. The immunodeficiency comprises predominantly immunoglobulin deficiency, mainly IgA and IgG2, with a variable severity. So far, the exact mechanisms underlying the immunoglobulin deficiency, especially the variable severity, remain unelucidated. OBJECTIVE: We characterized the clinical impact of immunoglobulin deficiencies in AT and elucidated their mechanisms in AT. METHODS: We analyzed long-term immunoglobulin levels, immunophenotyping, and survival time in our cohort (n = 87, median age 16 years; maximum 64 years). Somatic hypermutation and class-switch junctions in B cells were analyzed by next-generation sequencing. Furthermore, an in vitro class-switching induction assay was performed, followed by RNA sequencing, to assess the effect of ATM inhibition. RESULTS: Only the hyper-IgM AT phenotype significantly worsened survival time, while IgA or IgG2 deficiencies did not. The immunoglobulin levels showed predominantly decreased IgG2 and IgA. Moreover, flow cytometric analysis demonstrated reduced naive B and T lymphocytes and a deficiency of class-switched IgG2 and IgA memory B cells. Somatic hypermutation frequencies were lowered in IgA- and IgG2-deficient patients, indicating hampered germinal center reaction. In addition, the microhomology of switch junctions was elongated, suggesting alternative end joining during class-switch DNA repair. The in vitro class switching and proliferation were negatively affected by ATM inhibition. RNA sequencing analysis showed that ATM inhibitor influenced expression of germinal center reaction genes. CONCLUSION: Immunoglobulin deficiency in AT is caused by disturbed development of class-switched memory B cells. ATM deficiency affects both germinal center reaction and choice of DNA-repair pathway in class switching.

Heterozygous NOTCH1 Variants Cause CNS Immune Activation and Microangiopathy.

NOTCH1 belongs to the NOTCH family of proteins that regulate cell fate and inflammatory responses. Somatic and germline NOTCH1 variants have been implicated in cancer, Adams-Oliver syndrome, and cardiovascular defects. We describe 7 unrelated patients grouped by the presence of leukoencephalopathy with calcifications and heterozygous de novo gain-of-function variants in NOTCH1. Immunologic profiling showed upregulated CSF IP-10, a cytokine secreted downstream of NOTCH1 signaling. Autopsy revealed extensive leukoencephalopathy and microangiopathy with vascular calcifications. This evidence implicates that heterozygous gain-of-function variants in NOTCH1 lead to a chronic central nervous system (CNS) inflammatory response resulting in a calcifying microangiopathy with leukoencephalopathy. ANN NEUROL 2022;92:895-901.

Orthopedic Interventions for Foot Deformities in Non-Ambulant People with Duchenne Muscular Dystrophy: A Retrospective Study on Indications, Post-Operative and Long-Term Outcomes.

BACKGROUND: Progressive equinovarus deformities are common in people with Duchenne Muscular Dystrophy (DMD); they may provoke pain, pressure spots, cause problems with wearing footwear, and may lead to an unstable sitting position. OBJECTIVE: Explore indications and compare complications and long-term outcomes after soft tissue and osseous interventions in people with DMD. METHODS: Retrospective, monocenter, longitudinal study. Data on indications, equinus and varus deformity before and after surgery, wound healing problems, 'pain', edema, and long-term outcomes were collected from medical files. Soft tissue interventions were compared with osseous interventions. RESULTS: From a series of 18 patients, data on 32 surgical interventions and 169 follow-up visits were analyzed. 'Footrest placement' was the most frequent surgical indication, followed by pain. Osseous interventions were performed in older patients with rigid deformities. Directly after surgery remaining deformities were reported after soft tissue interventions (18 %), no remaining deformities were reported after osseous interventions. Pain and edema were frequently present, especially after osseous surgery. Longitudinal follow-up showed that surgical interventions could lead to a neutral foot for a for more than 3 years on average years. Relapses of foot deformity occurred, especially the recurrence of varus deformity after osseous interventions. CONCLUSIONS: Surgical interventions can successfully lead to a neutral foot position for for more than 3 years on average. Soft tissue interventions appear to be superior to osseous corrections, considering the varus recurrence period and complications, and may be considered when feet are still (partly) correctable. Pain management and edema prevention should be anticipated before surgery. Future research on patient reported outcomes as well as evaluating the outcome of the initial indication is needed to further identify benefits.

NANS-CDG: Delineation of the Genetic, Biochemical, and Clinical Spectrum.

Background: NANS-CDG is a recently described congenital disorder of glycosylation caused by biallelic genetic variants in NANS, encoding an essential enzyme in de novo sialic acid synthesis. Sialic acid at the end of glycoconjugates plays a key role in biological processes such as brain and skeletal development. Here, we present an observational cohort study to delineate the genetic, biochemical, and clinical phenotype and assess possible correlations. Methods: Medical and laboratory records were reviewed with retrospective extraction and analysis of genetic, biochemical, and clinical data (2016-2020). Results: Nine NANS-CDG patients (nine families, six countries) referred to the Radboudumc CDG Center of Expertise were included. Phenotyping confirmed the hallmark features including intellectual developmental disorder (IDD) (n = 9/9; 100%), facial dysmorphisms (n = 9/9; 100%), neurologic impairment (n = 9/9; 100%), short stature (n = 8/9; 89%), skeletal dysplasia (n = 8/9; 89%), and short limbs (n = 8/9; 89%). Newly identified features include ophthalmological abnormalities (n = 6/9; 67%), an abnormal septum pellucidum (n = 6/9; 67%), (progressive) cerebral atrophy and ventricular dilatation (n = 5/9; 56%), gastrointestinal dysfunction (n = 5/9; 56%), thrombocytopenia (n = 5/9; 56%), and hypo-low-density lipoprotein cholesterol (n = 4/9; 44%). Biochemically, elevated urinary excretion of N-acetylmannosamine (ManNAc) is pathognomonic, the concentrations of which show a significant correlation with clinical severity. Genotypically, eight novel NANS variants were identified. Three severely affected patients harbored identical compound heterozygous pathogenic variants, one of whom was initiated on experimental prenatal and postnatal treatment with oral sialic acid. This patient showed markedly better psychomotor development than the other two genotypically identical males. Conclusions: ManNAc screening should be considered in all patients with IDD, short stature with short limbs, facial dysmorphisms, neurologic impairment, and an abnormal septum pellucidum +/- congenital and neurodegenerative lesions on brain imaging, to establish a precise diagnosis and contribute to prognostication. Personalized management includes accurate genetic counseling and access to proper supports and tailored care for gastrointestinal symptoms, thrombocytopenia, and epilepsy, as well as rehabilitation services for cognitive and physical impairments. Motivated by the short-term positive effects of experimental treatment with oral sialic, we have initiated this intervention with protocolized follow-up of neurologic, systemic, and growth outcomes in four patients. Research is ongoing to unravel pathophysiology and identify novel therapeutic targets.

The Phenotypic Spectrum of PNKP-Associated Disease and the Absence of Immunodeficiency and Cancer Predisposition in a Dutch Cohort.

BACKGROUND: We aimed to expand the number of currently known pathogenic PNKP mutations, to study the phenotypic spectrum, including radiological characteristics and genotype-phenotype correlations, and to assess whether immunodeficiency and increased cancer risk are part of the DNA repair disorder caused by mutations in the PNKP gene. METHODS: We evaluated nine patients with PNKP mutations. A neurological history and examination was obtained. All patients had undergone neuroimaging and genetic testing as part of the prior diagnostic process. Laboratory measurements included potential biomarkers, and, in the context of a DNA repair disorder, we performed a detailed immunologic evaluation, including B cell repertoire analysis. RESULTS: We identified three new mutations in the PNKP gene and confirm the phenotypic spectrum of PNKP-associated disease, ranging from microcephaly, seizures, and developmental delay to ataxia with oculomotor apraxia type 4. Irrespective of the phenotype, alpha-fetoprotein is a biochemical marker and increases with age and progression of the disease. On neuroimaging, (progressive) cerebellar atrophy was a universal feature. No clinical signs of immunodeficiency were present, and immunologic assessment was unremarkable. One patient developed cancer, but this was attributed to a concurrent von Hippel-Lindau mutation. CONCLUSIONS: Immunodeficiency and cancer predisposition do not appear to be part of PNKP-associated disease, contrasting many other DNA repair disorders. Furthermore, our study illustrates that the previously described syndromes microcephaly, seizures, and developmental delay, and ataxia with oculomotor apraxia type 4, represent the extremes of an overlapping spectrum of disease. Cerebellar atrophy and elevated serum alpha-fetoprotein levels are early diagnostic findings across the entire phenotypical spectrum.

Disturbed brain ether lipid metabolism and histology in Sjögren-Larsson syndrome.

Sjögren-Larsson syndrome (SLS) is a rare neurometabolic syndrome caused by deficient fatty aldehyde dehydrogenase. Patients exhibit intellectual disability, spastic paraplegia, and ichthyosis. The accumulation of fatty alcohols and fatty aldehydes has been demonstrated in plasma and skin but never in brain. Brain magnetic resonance imaging and spectroscopy studies, however, have shown an abundant lipid peak in the white matter of patients with SLS, suggesting lipid accumulation in the brain as well. Using histopathology, mass spectrometry imaging, and lipidomics, we studied the morphology and the lipidome of a postmortem brain of a 65-year-old female patient with genetically confirmed SLS and compared the results with a matched control brain. Histopathological analyses revealed structural white matter abnormalities with the presence of small lipid droplets, deficient myelin, and astrogliosis. Biochemically, severely disturbed lipid profiles were found in both white and gray matter of the SLS brain, with accumulation of fatty alcohols and ether lipids. Particularly, long-chain unsaturated ether lipid species accumulated, most prominently in white matter. Also, there was a striking accumulation of odd-chain fatty alcohols and odd-chain ether(phospho)lipids. Our results suggest that the central nervous system involvement in SLS is caused by the accumulation of fatty alcohols leading to a disbalance between ether lipid and glycero(phospho)lipid metabolism resulting in a profoundly disrupted brain lipidome. Our data show that SLS is not a pure leukoencephalopathy, but also a gray matter disease. Additionally, the histopathological abnormalities suggest that astrocytes and microglia might play a pivotal role in the underlying disease mechanism, possibly contributing to the impairment of myelin maintenance.

Toward understanding tissue-specific symptoms in dolichol-phosphate-mannose synthesis disorders; insight from DPM3-CDG.

The congenital disorders of glycosylation (CDG) are inborn errors of metabolism with a great genetic heterogeneity. Most CDG are caused by defects in the N-glycan biosynthesis, leading to multisystem phenotypes. However, the occurrence of tissue-restricted clinical symptoms in the various defects in dolichol-phosphate-mannose (DPM) synthesis remains unexplained. To deepen our understanding of the tissue-specific characteristics of defects in the DPM synthesis pathway, we investigated N-glycosylation and O-mannosylation in skeletal muscle of three DPM3-CDG patients presenting with muscle dystrophy and hypo-N-glycosylation of serum transferrin in only two of them. In the three patients, O-mannosylation of alpha-dystroglycan (αDG) was strongly reduced and western blot analysis of beta-dystroglycan (ßDG) N-glycosylation revealed a consistent lack of one N-glycan in skeletal muscle. Recently, defective N-glycosylation of ßDG has been reported in patients with mutations in guanosine-diphosphate-mannose pyrophosphorylase B (GMPPB). Thus, we suggest that aberrant O-glycosylation of αDG and N-glycosylation of ßDG in skeletal muscle is indicative of a defect in the DPM synthesis pathway. Further studies should address to what extent hypo-N-glycosylation of ßDG or other skeletal muscle proteins contribute to the phenotype of patients with defects in DPM synthesis. Our findings contribute to our understanding of the tissue-restricted phenotype of DPM3-CDG and other defects in the DPM synthesis pathway.

Genotype-phenotype correlations in ataxia telangiectasia patients with ATM c.3576G>A and c.8147T>C mutations.

BACKGROUND: Ataxia telangiectasia (A-T) is a neurodegenerative disorder. While patients with classic A-T generally die in their 20s, some patients with variant A-T, who have residual ataxia-telangiectasia mutated (ATM) kinase activity, have a milder phenotype. We noticed two commonly occurring ATM mutations that appeared to be associated with prolonged survival and decided to study patients carrying one of these mutations. METHODS: Data were retrospectively collected from the Dutch, Italian, German and French A-T cohorts. To supplement these data, we searched the literature for patients with identical genotypes. RESULTS: This study included 35 patients who were homozygous or compound heterozygous for the ATM c.3576G>A; p.(Ser1135_Lys1192del58) mutation and 24 patients who were compound heterozygous for the ATM c.8147T>C; p.(Val2716Ala) mutation. Compared with 51 patients with classic A-T from the Dutch cohort, patients with ATM c.3576G>A had a longer survival and were less likely to develop cancer, respiratory disease or immunodeficiency. This was also true for patients with ATM c.8147T>C, who additionally became wheelchair users later in life and had fewer telangiectasias. The oldest patient with A-T reported so far was a 78-year-old patient who was compound heterozygous for ATM c.8147T>C. ATM kinase activity was demonstrated in cells from all patients tested with the ATM c.8147T>C mutant protein and only at a low level in some patients with ATM c.3576G>A. CONCLUSION: Compared with classic A-T, the presence of ATM c.3576G>A results in a milder classic phenotype. Patients with ATM c.8147T>C have a variant phenotype with prolonged survival, which in exceptional cases may approach a near-normal lifespan.

Genotype, extrapyramidal features, and severity of variant ataxia-telangiectasia.

OBJECTIVE: Variant ataxia-telangiectasia is caused by mutations that allow some retained ataxia telangiectasia-mutated (ATM) kinase activity. Here, we describe the clinical features of the largest established cohort of individuals with variant ataxia-telangiectasia and explore genotype-phenotype correlations. METHODS: Cross-sectional data were collected retrospectively. Patients were classified as variant ataxia-telangiectasia based on retained ATM kinase activity. RESULTS: The study includes 57 individuals. Mean age at assessment was 37.5 years. Most had their first symptoms by age 10 (81%). There was a diagnostic delay of more than 10 years in 68% and more than 20 years in one third of probands. Disease severity was mild in one third of patients, and 43% were still ambulant 20 years after disease onset. Only one third had predominant ataxia, and 18% had a pure extrapyramidal presentation. Individuals with extrapyramidal presentations had milder neurological disease severity. There were no significant respiratory or immunological complications, but 25% of individuals had a history of malignancy. Missense mutations were associated with milder neurological disease severity, but with a higher risk of malignancy, compared to leaky splice site mutations. INTERPRETATION: Individuals with variant ataxia-telangiectasia require malignancy surveillance and tailored management. However, our data suggest the condition may sometimes be mis- or underdiagnosed because of atypical features, including exclusive extrapyramidal symptoms, normal eye movements, and normal alpha-fetoprotein levels in some individuals. Missense mutations are associated with milder neurological presentations, but a particularly high malignancy risk, and it is important for clinicians to be aware of these phenotypes. ANN NEUROL 2019;85:170-180.

A brother and sister with intellectual disability and characteristic neuroimaging findings.

Leukoencephalopathy with brain calcifications and cysts (LCC) is a genetic white matter disorder, which involves the brain small blood vessels. In the absence of extra-neurological symptoms, LCC has a pathognomonic radiological phenotype. Recently, biallelic mutations in the SNORD118 gene, which is a non-protein coding gene, were discovered to cause LCC. We present here two siblings with developmental delay and a typical MRI pattern, who were diagnosed with LCC. The mutations in the SNORD118 gene were initially missed with whole exome sequencing (WES), but recognition of the MRI patterns of both children raised the suspicion of LCC and led to a genetically proven diagnosis after re-evaluation of the WES data.

B3GALNT2 mutations associated with non-syndromic autosomal recessive intellectual disability reveal a lack of genotype-phenotype associations in the muscular dystrophy-dystroglycanopathies.

BACKGROUND: The phenotypic severity of congenital muscular dystrophy-dystroglycanopathy (MDDG) syndromes associated with aberrant glycosylation of α-dystroglycan ranges from the severe Walker-Warburg syndrome or muscle-eye-brain disease to mild, late-onset, isolated limb-girdle muscular dystrophy without neural involvement. However, muscular dystrophy is invariably found across the spectrum of MDDG patients. METHODS: Using linkage mapping and whole-exome sequencing in two families with an unexplained neurodevelopmental disorder, we have identified homozygous and compound heterozygous mutations in B3GALNT2. RESULTS: The first family comprises two brothers of Dutch non-consanguineous parents presenting with mild ID and behavioral problems. Immunohistochemical analysis of muscle biopsy revealed no significant aberrations, in line with the absence of a muscular phenotype in the affected siblings. The second family includes five affected individuals from an Iranian consanguineous kindred with mild-to-moderate intellectual disability (ID) and epilepsy without any notable neuroimaging, muscle, or eye abnormalities. Complementation assays of the compound heterozygous mutations identified in the two brothers had a comparable effect on the O-glycosylation of α-dystroglycan as previously reported mutations that are associated with severe muscular phenotypes. CONCLUSIONS: In conclusion, we show that mutations in B3GALNT2 can give rise to a novel MDDG syndrome presentation, characterized by ID associated variably with seizure, but without any apparent muscular involvement. Importantly, B3GALNT2 activity does not fully correlate with the severity of the phenotype as assessed by the complementation assay.

Ataxia-telangiectasia: recommendations for multidisciplinary treatment.

Ataxia-telangiectasia is a rare, neurodegenerative, and multisystem disease, characterized by cerebellar ataxia, oculocutaneous telangiectasia, immunodeficiency, progressive respiratory failure, and an increased risk of malignancies. It demands specialized care tailored to the individual patient's needs. Besides the classic ataxia-telangiectasia phenotype, a variant phenotype exists with partly overlapping but some distinctive disease characteristics. This guideline summarizes frequently encountered medical problems in the disease course of patients with classic and variant ataxia-telangiectasia, in the domains of neurology, immunology and infectious diseases, pulmonology, anaesthetic and perioperative risk, oncology, endocrinology, and nutrition. Furthermore, it provides a practical guide with evidence- and expert-based recommendations for the follow-up and treatment of all these different clinical topics.

Ataxia-telangiectasia: Immunodeficiency and survival.

Ataxia-telangiectasia (AT) is a neurodegenerative disorder characterized by ataxia, telangiectasia, and immunodeficiency. An increased risk of malignancies and respiratory diseases dramatically reduce life expectancy. To better counsel families, develop individual follow-up programs, and select patients for therapeutic trials, more knowledge is needed on factors influencing survival. This retrospective cohort study of 61 AT patients shows that classical AT patients had a shorter survival than variant patients (HR 5.9, 95%CI 2.0-17.7), especially once a malignancy was diagnosed (HR 2.5, 95%CI 1.1-5.5, compared to classical AT patients without malignancy). Patients with the hyper IgM phenotype with hypogammaglobulinemia (AT-HIGM) and patients with an IgG2 deficiency showed decreased survival compared to patients with normal IgG (HR 9.2, 95%CI 3.2-26.5) and patients with normal IgG2 levels (HR 7.8, 95%CI 1.7-36.2), respectively. If high risk treatment trials will become available for AT, those patients with factors indicating the poorest prognosis might be considered for inclusion first.

Mutations in the histone methyltransferase gene KMT2B cause complex early-onset dystonia.

Histone lysine methylation, mediated by mixed-lineage leukemia (MLL) proteins, is now known to be critical in the regulation of gene expression, genomic stability, cell cycle and nuclear architecture. Despite MLL proteins being postulated as essential for normal development, little is known about the specific functions of the different MLL lysine methyltransferases. Here we report heterozygous variants in the gene KMT2B (also known as MLL4) in 27 unrelated individuals with a complex progressive childhood-onset dystonia, often associated with a typical facial appearance and characteristic brain magnetic resonance imaging findings. Over time, the majority of affected individuals developed prominent cervical, cranial and laryngeal dystonia. Marked clinical benefit, including the restoration of independent ambulation in some cases, was observed following deep brain stimulation (DBS). These findings highlight a clinically recognizable and potentially treatable form of genetic dystonia, demonstrating the crucial role of KMT2B in the physiological control of voluntary movement.

Clinical, radiological and possible pathological overlap of cystic leukoencephalopathy without megalencephaly and Aicardi-Goutières syndrome.

BACKGROUND: Cystic leukoencephalopathy without megalencephaly is a disorder related in some cases to RNASET2 mutations and characterized by bilateral anterior temporal subcortical cysts and multifocal lobar white matter lesions with sparing of central white matter structures. This phenotype significantly overlaps with the sequelae of in utero cytomegalovirus (CMV) infection, including the presence of intracranial calcification in some cases. Aicardi-Goutières syndrome (AGS) is another inherited leukodystrophy with cerebral calcification mimicking congenital infection. Clinical, radiological and biochemical criteria for the diagnosis of AGS have been established, although the breadth of phenotype associated with mutations in the AGS-related genes is much greater than previously envisaged. PATIENTS AND METHODS: We describe the clinical, biochemical and radiological findings of five patients demonstrating a phenotype reminiscent of AGS. RESULTS: All patients were found to carry biallelic mutations of RNASET2. CONCLUSIONS: Our patients illustrate the clinical and radiological overlap that can be seen between RNASET2-related leukodystrophy and AGS in some cases. Our data highlight the need to include both disorders in the same differential diagnosis, and hint at possible shared pathomechanisms related to auto-inflammation which are worthy of further investigation.