Biallelic PI4KA variants cause a novel neurodevelopmental syndrome with hypomyelinating leukodystrophy

Phosphoinositides are lipids that play a critical role in processes such as cellular signalling, ion channel activity and membrane trafficking. When mutated, several genes that encode proteins that participate in the metabolism of these lipids give rise to neurological or developmental phenotypes. PI4KA is a phosphoinositide kinase that is highly expressed in the brain and is essential for life. Here we used whole exome or genome sequencing to identify 10 unrelated patients harbouring biallelic variants in PI4KA that caused a spectrum of conditions ranging from severe global neurodevelopmental delay with hypomyelination and developmental brain abnormalities to pure spastic paraplegia. Some patients presented immunological deficits or genito-urinary abnormalities. Functional analyses by western blotting and immunofluorescence showed decreased PI4KA levels in the patients’ fibroblasts. Immunofluorescence and targeted lipidomics indicated that PI4KA activity was diminished in fibroblasts and peripheral blood mononuclear cells. In conclusion, we report a novel severe metabolic disorder caused by PI4KA malfunction, highlighting the importance of phosphoinositide signalling in human brain development and the myelin sheath.

Hemiplegic Migraine Associated With PRRT2 Mutations: A Clinical and Genetic Study

BACKGROUND AND OBJECTIVE

PRRT2 variants have been reported in a few cases of patients with hemiplegic migraine. To clarify the role of PRRT2 in familial hemiplegic migraine, we studied this gene in a large cohort of affected probands.

METHODS

PRRT2 was analyzed in 860 probands with hemiplegic migraine and PRRT2 mutations were identified in 30 probands. Genotyping of relatives identified a total of 49 persons with mutations whose clinical manifestations were detailed.

RESULTS

PRRT2 mutations were found in 12 of 163 probands previously tested negative for CACNA1A, ATP1A2 and SCN1A mutations, and in 18 of 697 consecutive probands screened simultaneously on the four genes. In this second group, pathogenic variants were found in 105 subjects, mostly in ATP1A2 (42%), followed by CACNA1A (26%), PRRT2 (17%) and SCN1A (15%). The PRRT2 mutations included seven distinct variants, five of which already described in persons with paroxysmal kinesigenic dyskinesia, and two new variants. Eight probands had a deletion of the whole PRRT2 gene.Among the 49 PRRT2 mutated patients, 26 had pure hemiplegic migraine, 16 had hemiplegic migraine associated with another manifestation: epilepsy (8), learning disabilities (5), hypersomnia (4) or abnormal movement (3). Three patients had epilepsy without migraine, two had paroxysmal kinesigenic dyskinesia without migraine, and one was asymptomatic.

CONCLUSION

PRRT2 should be regarded as the fourth autosomal dominant gene for hemiplegic migraine, and screened in any affected patient, together with the three other main genes. Further studies are needed to understand how the same loss of function PRRT2 mutations can lead to a wide range of neurologic phenotypes including paroxysmal movement disorder, epilepsy, learning disabilities, sleep disorder and hemiplegic migraine.

Paroxysmal Dyskinesias Revealing 3-Hydroxy-Isobutyryl-CoA Hydrolase (HIBCH) Deficiency

Paroxysmal dyskinesias (PD) are rare movement disorders characterized by recurrent attacks of dystonia, chorea, athetosis, or their combination, with large phenotypic and genetic heterogeneity. 3-Hydroxy-isobutyryl-CoA hydrolase (HIBCH) deficiency is a neurodegenerative disease characterized in most patients by a continuous decline in psychomotor abilities or a secondary regression triggered by febrile infections and metabolic crises.We describe two PD patients from two pedigrees, both carrying a homozygous c.913A > G, p.Thr305Ala mutation in the HIBCH gene, associated with an unusual clinical presentation. The first patient presented in the second year of life with right paroxysmal hemidystonia lasting for 30 minutes, without any loss of consciousness and without any triggering factor. The second patient has presented since the age of 3 recurrent exercise-induced PD episodes which have been described as abnormal equinovarus, contractures of the lower limbs, lasting for 1 to 4 hours, associated with choreic movements of the hands. Their neurological examination and metabolic screening were normal, while brain magnetic resonance imaging showed abnormal signal of the pallidi.We suggest that HIBCH deficiency, through the accumulation of metabolic intermediates of the valine catabolic pathway, leads to a secondary defect in respiratory chain activity and pyruvate dehydrogenase (PDH) activity and to a broad phenotypic spectrum ranging from Leigh syndrome to milder phenotypes. The two patients presented herein expand the spectrum of the disease to include unusual paroxysmal phenotypes and HIBCH deficiency should be considered in the diagnostic strategy of PD to enable adequate preventive treatment.

Gene therapy in the putamen for curing AADC deficiency and Parkinson's disease

This commentary provides an overview of the putamen as an established target site for gene therapy in treating aromatic l‐amino acid decarboxylase (AADC) deficiency and Parkinson’s disease, two debilitating neurological disorders that involve motor dysfunction caused by dopamine deficiencies. The neuroanatomy and the function of the putamen in motor control provide good rationales for targeting this brain structure. Additionally, the efficacy and safety of intraputaminal gene therapy demonstrate that restoration of dopamine synthesis in the putamen by using low doses of adeno‐associated viral vector serotype 2 to deliver the hAADC gene is well tolerated. This restoration leads to sustained improvements in motor and nonmotor symptoms of AADC deficiency and improved uptake and conversion of exogenous l‐DOPA into dopamine in Parkinson’s patients.

Adult-onset diagnosis of urea cycle disorders: Results of a French cohort of 71 patients

Urea cycle disorders (UCD) are rare diseases that usually affect neonates or young children. During decompensations, hyperammonemia is neurotoxic, leading to severe symptoms and even coma and death if not treated rapidly. The aim was to describe a cohort of patients with adult onset of UCDs in a multicentric, retrospective and descriptive study of French adult patients with a diagnosis after 16 years of age of UCDs due to a deficiency in one of the 6 enzymes (arginase, ASL, ASS, CPS1, NAGS, OTC) or the two transporters (ORNT1 or citrin). Seventy-one patients were included (68% female, 32% male). The diagnosis was made in the context of (a) a metabolic decompensation (42%), (b) family history (55%), or (c) chronic symptoms (3%). The median age at diagnosis was 33 years (range 16-86). Eighty-nine percent of patients were diagnosed with OTC deficiency, 7% CPS1 deficiency, 3% HHH syndrome and 1% argininosuccinic aciduria. For those diagnosed during decompensations (including 23 OTC cases, mostly female), 89% required an admission in intensive care units. Seven deaths were attributed to UCD-6 decompensations and 1 epilepsy secondary to inaugural decompensation. This is the largest cohort of UCDs diagnosed in adulthood, which confirms the triad of neurological, gastrointestinal and psychiatric symptoms during hyperammonemic decompensations. We stress that females with OTC deficiency can be symptomatic. With 10% of deaths in this cohort, UCDs in adults remain a life-threatening condition. Physicians working in adult care must be aware of late-onset presentations given the implications for patients and their families.

Pathogenic variants in IMPG1 cause autosomal dominant and autosomal recessive retinitis pigmentosa

BACKGROUND

Inherited retinal disorders are a clinically and genetically heterogeneous group of conditions and a major cause of visual impairment. Common disease subtypes include vitelliform macular dystrophy (VMD) and retinitis pigmentosa (RP). Despite the identification of over 90 genes associated with RP, conventional genetic testing fails to detect a molecular diagnosis in about one third of patients with RP.

METHODS

Exome sequencing was carried out for identifying the disease-causing gene in a family with autosomal dominant RP. Gene panel testing and exome sequencing were performed in 596 RP and VMD families to identified additional IMPG1 variants. In vivo analysis in the medaka fish system by knockdown assays was performed to screen IMPG1 possible pathogenic role.

RESULTS

Exome sequencing of a family with RP revealed a splice variant in IMPG1. Subsequently, the same variant was identified in individuals from two families with either RP or VMD. A retrospective study of patients with RP or VMD revealed eight additional families with different missense or nonsense variants in IMPG1. In addition, the clinical diagnosis of the IMPG1 retinopathy-associated variant, originally described as benign concentric annular macular dystrophy, was also revised to RP with early macular involvement. Using morpholino-mediated ablation of Impg1 and its paralog Impg2 in medaka fish, we confirmed a phenotype consistent with that observed in the families, including a decreased length of rod and cone photoreceptor outer segments.

CONCLUSION

This study discusses a previously unreported association between monoallelic or biallelic IMPG1 variants and RP. Notably, similar observations have been reported for IMPG2.

A ROD-CONE DYSTROPHY IS SYSTEMATICALLY ASSOCIATED TO THE RTN4IP1 RECESSIVE OPTIC ATROPHY

PURPOSE

RTN4IP1 biallelic mutations cause a recessive optic atrophy, sometimes associated to more severe neurological syndromes, but so far, no retinal phenotype has been reported in RTN4IP1 patients, justifying their reappraisal.

METHODS

Seven patients from four families carrying biallelic RTN4IP1 variants were retrospectively reviewed, with emphasis on their age of onset, visual acuity, multimodal imaging including color and autofluorescence frames, spectral-domain optical coherence tomography with RNFL and macular analyses.

RESULTS

Seven patients from four RTN4IP1 families developed in their first decade of life a bilateral recessive optic atrophy with severe central visual loss, and primary nystagmus developed in 5 of 7 patients. Six patients were legally blind. In a second stage, the seven individuals developed a rod-cone dystrophy, sparing the macular zone and the far periphery. This retinal damage was identified by 55° field fundus autofluorescence frames and also by spectral-domain optical coherence tomography scans of the temporal part of the macular zone in five of the seven patients. Full-field electroretinography measurements disclosed reduced b-wave amplitude of the rod responses in all patients but two. Family 4 with the p.R103H and c.601A > T (p.K201*) truncating mutation had further combined neurological signs with cerebellar ataxia, seizures, and intellectual disability.

CONCLUSION

RTN4IP1 recessive optic atrophy is systematically associated to a rod-cone dystrophy, which suggests that both the retinal ganglion cells and the rods are affected as a result of a deficit in the mitochondrial respiratory chain. Thus, systematic widefield autofluorescence frames and temporal macular scans are recommended for the evaluation of patients with optic neuropathies.

High rate of hypomorphic variants as the cause of inherited ataxia and related diseases: study of a cohort of 366 families

PURPOSE

Diagnosis of inherited ataxia and related diseases represents a real challenge given the tremendous heterogeneity and clinical overlap of the various causes. We evaluated the efficacy of molecular diagnosis of these diseases by sequencing a large cohort of undiagnosed families.

METHODS

We analyzed 366 unrelated consecutive patients with undiagnosed ataxia or related disorders by clinical exome-capture sequencing. In silico analysis was performed with an in-house pipeline that combines variant ranking and copy-number variant (CNV) searches. Variants were interpreted according to American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines.

RESULTS

We established the molecular diagnosis in 46% of the cases. We identified 35 mildly affected patients with causative variants in genes that are classically associated with severe presentations. These cases were explained by the occurrence of hypomorphic variants, but also rarely suspected mechanisms such as C-terminal truncations and translation reinitiation.

CONCLUSION

A significant fraction of the clinical heterogeneity and phenotypic overlap is explained by hypomorphic variants that are difficult to identify and not readily predicted. The hypomorphic C-terminal truncation and translation reinitiation mechanisms that we identified may only apply to few genes, as it relies on specific domain organization and alterations. We identified PEX10 and FASTKD2 as candidates for translation reinitiation accounting for mild disease presentation.

Optic neuropathy linked to ACAD9 pathogenic variants: A potentially riboflavin-responsive disorder?

Mitochondrial complex I (CI) deficiencies (OMIM 252010) are the commonest inherited mitochondrial disorders in children. Acyl-CoA dehydrogenase 9 (ACAD9) is a flavoenzyme involved chiefly in CI assembly and possibly in fatty acid oxidation. Biallelic pathogenic variants result in CI dysfunction, with a phenotype ranging from early onset and sometimes fatal mitochondrial encephalopathy with lactic acidosis to late-onset exercise intolerance. Cardiomyopathy is often associated. We report a patient with childhood-onset optic and peripheral neuropathy without cardiac involvement, related to CI deficiency. Genetic analysis revealed compound heterozygous pathogenic variants in ACAD9, expanding the clinical spectrum associated to ACAD9 mutations. Importantly, riboflavin treatment (15 mg/kg/day) improved long-distance visual acuity and demonstrated significant rescue of CI activity in vitro.

Disentangling molecular and clinical stratification patterns in beta-galactosidase deficiency

INTRODUCTION

This study aims to define the phenotypic and molecular spectrum of the two clinical forms of β-galactosidase (β-GAL) deficiency, GM1-gangliosidosis and mucopolysaccharidosis IVB (Morquio disease type B, MPSIVB).

METHODS

Clinical and genetic data of 52 probands, 47 patients with GM1-gangliosidosis and 5 patients with MPSIVB were analysed.

RESULTS

The clinical presentations in patients with GM1-gangliosidosis are consistent with a phenotypic continuum ranging from a severe antenatal form with hydrops fetalis to an adult form with an extrapyramidal syndrome. Molecular studies evidenced 47 variants located throughout the sequence of the GLB1 gene, in all exons except 7, 11 and 12. Eighteen novel variants (15 substitutions and 3 deletions) were identified. Several variants were linked specifically to early-onset GM1-gangliosidosis, late-onset GM1-gangliosidosis or MPSIVB phenotypes. This integrative molecular and clinical stratification suggests a variant-driven patient assignment to a given clinical and severity group.

CONCLUSION

This study reports one of the largest series of b-GAL deficiency with an integrative patient stratification combining molecular and clinical features. This work contributes to expand the community knowledge regarding the molecular and clinical landscapes of b-GAL deficiency for a better patient management.

KMT2B-related disorders: expansion of the phenotypic spectrum and long-term efficacy of deep brain stimulation

Heterozygous mutations in KMT2B are associated with an early-onset, progressive and often complex dystonia (DYT28). Key characteristics of typical disease include focal motor features at disease presentation, evolving through a caudocranial pattern into generalized dystonia, with prominent oromandibular, laryngeal and cervical involvement. Although KMT2B-related disease is emerging as one of the most common causes of early-onset genetic dystonia, much remains to be understood about the full spectrum of the disease. We describe a cohort of 53 patients with KMT2B mutations, with detailed delineation of their clinical phenotype and molecular genetic features. We report new disease presentations, including atypical patterns of dystonia evolution and a subgroup of patients with a non-dystonic neurodevelopmental phenotype. In addition to the previously reported systemic features, our study has identified co-morbidities, including the risk of status dystonicus, intrauterine growth retardation, and endocrinopathies. Analysis of this study cohort (n = 53) in tandem with published cases (n = 80) revealed that patients with chromosomal deletions and protein truncating variants had a significantly higher burden of systemic disease (with earlier onset of dystonia) than those with missense variants. Eighteen individuals had detailed longitudinal data available after insertion of deep brain stimulation for medically refractory dystonia. Median age at deep brain stimulation was 11.5 years (range: 4.5-37.0 years). Follow-up after deep brain stimulation ranged from 0.25 to 22 years. Significant improvement of motor function and disability (as assessed by the Burke Fahn Marsden's Dystonia Rating Scales, BFMDRS-M and BFMDRS-D) was evident at 6 months, 1 year and last follow-up (motor, P = 0.001, P = 0.004, and P = 0.012; disability, P = 0.009, P = 0.002 and P = 0.012). At 1 year post-deep brain stimulation, >50% of subjects showed BFMDRS-M and BFMDRS-D improvements of >30%. In the long-term deep brain stimulation cohort (deep brain stimulation inserted for >5 years, n = 8), improvement of >30% was maintained in 5/8 and 3/8 subjects for the BFMDRS-M and BFMDRS-D, respectively. The greatest BFMDRS-M improvements were observed for trunk (53.2%) and cervical (50.5%) dystonia, with less clinical impact on laryngeal dystonia. Improvements in gait dystonia decreased from 20.9% at 1 year to 16.2% at last assessment; no patient maintained a fully independent gait. Reduction of BFMDRS-D was maintained for swallowing (52.9%). Five patients developed mild parkinsonism following deep brain stimulation. KMT2B-related disease comprises an expanding continuum from infancy to adulthood, with early evidence of genotype-phenotype correlations. Except for laryngeal dysphonia, deep brain stimulation provides a significant improvement in quality of life and function with sustained clinical benefit depending on symptoms distribution.

Clinical phenotypes of infantile onset CACNA1A-related disorder

BACKGROUND

CACNA1A-related disorders present with persistent progressive and non-progressive cerebellar ataxia and paroxysmal events: epileptic seizures and non-epileptic attacks. These phenotypes overlap and co-exist in the majority of patients.

OBJECTIVE

To describe phenotypes in infantile onset CACNA1A-related disorder and to explore intra-familial variations and genotype-phenotype correlations.

MATERIAL AND METHODS

This study was a multicenter international collaboration. A retrospective chart review of CACNA1A patients was performed. Clinical, radiological, and genetic data were collected and analyzed in 47 patients with infantile-onset disorder.

RESULTS

Paroxysmal non-epileptic events (PNEE) were observed in 68% of infants, with paroxysmal tonic upward gaze (PTU) noticed in 47% of infants. Congenital cerebellar ataxia (CCA) was diagnosed in 51% of patients including four patients with developmental delay and only one neurological sign. PNEEs were found in 63% of patients at follow-up, with episodic ataxia (EA) in 40% of the sample. Cerebellar ataxia was found in 58% of the patients at follow-up. Four patients had epilepsy in infancy and nine in childhood. Seven infants had febrile convulsions, three of which developed epilepsy later; all three patients had CCA. Cognitive difficulties were demonstrated in 70% of the children. Cerebellar atrophy was found in only one infant but was depicted in 64% of MRIs after age two.

CONCLUSIONS

Nearly all of the infants had CCA, PNEE or both. Cognitive difficulties were frequent and appeared to be associated with CCA. Epilepsy was more frequent after age two. Febrile convulsions in association with CCA may indicate risk of epilepsy in later childhood. Brain MRI was normal in infancy. There were no genotype-phenotype correlations found.

West Syndrome Is an Exceptional Presentation of Pyridoxine- and Pyridoxal Phosphate-Dependent Epilepsy: Data From a French Cohort and Review of the Literature

Objective: To characterize the electro-clinical presentation of patients with pyridoxine-dependent epilepsy (PDE) and pyridoxal phosphate (PLP)-dependent epilepsy in order to determine whether some of them could be diagnosed as de novo West syndrome, i. e., West syndrome that starts after the age of 2 months without other types of seizures (focal seizures for instance) before the onset of epileptic spasms. Methods: We analyzed data from an unpublished cohort of 28 genetically confirmed cases of PDE with antiquitine (ATQ) deficiency and performed a review of the literature looking for description of West syndrome in patients with either PDE with ATQ deficiency or PLP-dependent epilepsy with Pyridox(am)ine phosphate oxidase (PNPO) deficiency. Results: Of the 28 cases from the ATQ deficiency French cohort, 5 had spasms. In four cases, spasms were associated with other types of seizures (myoclonus, focal seizures). In the last case, seizures started on the day of birth. None of these cases corresponded to de novo West syndrome. The review of the literature found only one case of PNPO deficiency presenting as de novo West syndrome and no case of ATQ deficiency. Significance: The presentation of PDE- and PLP-dependent epilepsy as de novo West syndrome is so exceptional that it probably does not justify a systematic trial of pyridoxine or PLP. We propose considering a therapeutic trial with these vitamins in West syndrome if spasms are associated with other seizure types or start before the age of 2 months.

Pregnancy in MNGIE: a clinical and metabolic honeymoon

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an inherited disease caused by a deficiency in thymidine phosphorylase and characterized by elevated systemic deoxyribonucleotides and gastrointestinal (GI) and neurological manifestations. We report the clinical and biochemical manifestations that were evaluated in a single patient before, during, and after pregnancy, over a period of 7 years. GI symptoms significantly improved, and plasma deoxyribonucleotide concentrations decreased during pregnancy. Within days after delivery, the patient's digestive symptoms recurred, coinciding with a rapid increase in plasma deoxyribonucleotide concentrations. We hypothesize that the clinico-metabolic improvements could be attributed to the enzyme replacement action of the placental thymidine phosphorylase.

Clinical disease progression and biomarkers in Niemann-Pick disease type C: a prospective cohort study

Background

Niemann–Pick disease type C (NPC) is a rare, progressive, neurodegenerative disease associated with neurovisceral manifestations resulting from lysosomal dysfunction and aberrant lipid accumulation. A multicentre, prospective observational study (Clinical Trials.gov ID: NCT02435030) of individuals with genetically confirmed NPC1 or NPC2 receiving routine clinical care was conducted, to prospectively characterize and measure NPC disease progression and to investigate potential NPC-related biomarkers versus healthy individuals. Progression was measured using the abbreviated 5-domain NPC Clinical Severity Scale (NPCCSS), 17-domain NPCCSS and NPC clinical database (NPC-cdb) score. Cholesterol esterification and heat shock protein 70 (HSP70) levels were assessed from peripheral blood mononuclear cells (PBMCs), cholestane-3β,5α-,6β-triol (cholestane-triol) from serum, and unesterified cholesterol from both PBMCs and skin biopsy samples. The inter- and intra-rater reliability of the 5-domain NPCCSS was assessed by 13 expert clinicians’ rating of four participants via video recordings, repeated after ≥ 3 weeks. Intraclass correlation coefficients (ICCs) were calculated.

Results

Of the 36 individuals with NPC (2–18 years) enrolled, 31 (86.1%) completed the 6–14-month observation period; 30/36 (83.3%) were receiving miglustat as part of routine clinical care. A mean (± SD) increase in 5-domain NPCCSS scores of 1.4 (± 2.9) was observed, corresponding to an annualized progression rate of 1.5. On the 17-domain NPCCSS, a mean (± SD) progression of 2.7 (± 4.0) was reported. Compared with healthy individuals, the NPC population had significantly lower levels of cholesterol esterification (p < 0.0001), HSP70 (p < 0.0001) and skin unesterified cholesterol (p = 0.0006). Cholestane-triol levels were significantly higher in individuals with NPC versus healthy individuals (p = 0.008) and correlated with the 5-domain NPCCSS (Spearman’s correlation coefficient = 0.265, p = 0.0411). The 5-domain NPCCSS showed high ICC agreement in inter-rater reliability (ICC = 0.995) and intra-rater reliability (ICC = 0.937).

Conclusions

Progression rates observed were consistent with other reports on disease progression in NPC. The 5-domain NPCCSS reliability study supports its use as an abbreviated alternative to the 17-domain NPCCSS that focuses on the most relevant domains of the disease. The data support the use of cholestane-triol as a disease monitoring biomarker and the novel methods of measuring unesterified cholesterol could be applicable to support NPC diagnosis. Levels of HSP70 in individuals with NPC were significantly decreased compared with healthy individuals.

Trial registration

CT-ORZY-NPC-001: ClincalTrials.gov NCT02435030, Registered 6 May 2015, https://clinicaltrials.gov/ct2/show/NCT02435030; EudraCT 2014–005,194-37, Registered 28 April 2015, https://www.clinicaltrialsregister.eu/ctr-search/trial/2014-005194-37/DE. OR-REL-NPC-01: Unregistered.

Late-onset riboflavin transporter deficiency: a treatable mimic of various motor neuropathy aetiologies

OBJECTIVE

Riboflavin transporter deficiencies (RTDs), involving SLC52A3 and SLC52A2 genes, have recently been related to Brown-Vialetto-Van Laere (BVVL) syndrome, a hereditary paediatric condition associating motor neuropathy (MN) and deafness. BVVL/RTD has rarely been reported in adult patients, but is probably underdiagnosed due to poor knowledge and lack of awareness of this form of disease among neurologists. In this study, we aimed to investigate the phenotype and prognosis of RTD patients with late-onset MN.

METHODS

We retrospectively collected clinical, biological and electrophysiological data from all French RTD patients with MN onset after 10 years of age (n=6) and extracted data from 19 other similar RTD patients from the literature.

RESULTS

Adult RTD patients with MN had heterogeneous clinical presentations, potentially mimicking amyotrophic lateral sclerosis or distal hereditary motor neuropathy (56%), multinevritis with cranial nerve involvement (16%), Guillain-Barré syndrome (8%) and mixed motor and sensory neuronopathy syndromes (20%, only in SLC52A2 patients). Deafness was often diagnosed before MN (in 44%), but in some patients, onset began only with MN (16%). The pattern of weakness varied widely, and the classic pontobulbar palsy described in BVVL was not constant. Biochemical tests were often normal. The majority of patients improved under riboflavin supplementation (86%).

INTERPRETATION

Whereas late-onset RTD may mimic different acquired or genetic causes of motor neuropathies, it is a diagnosis not to be missed since high-dose riboflavin per oral supplementation is often highly efficient.

Defining the clinical, molecular and imaging spectrum of adaptor protein complex 4-associated hereditary spastic paraplegia

Bi-allelic loss-of-function variants in genes that encode subunits of the adaptor protein complex 4 (AP-4) lead to prototypical yet poorly understood forms of childhood-onset and complex hereditary spastic paraplegia: SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). Here, we report a detailed cross-sectional analysis of clinical, imaging and molecular data of 156 patients from 101 families. Enrolled patients were of diverse ethnic backgrounds and covered a wide age range (1.0-49.3 years). While the mean age at symptom onset was 0.8 ± 0.6 years [standard deviation (SD), range 0.2-5.0], the mean age at diagnosis was 10.2 ± 8.5 years (SD, range 0.1-46.3). We define a set of core features: early-onset developmental delay with delayed motor milestones and significant speech delay (50% non-verbal); intellectual disability in the moderate to severe range; mild hypotonia in infancy followed by spastic diplegia (mean age: 8.4 ± 5.1 years, SD) and later tetraplegia (mean age: 16.1 ± 9.8 years, SD); postnatal microcephaly (83%); foot deformities (69%); and epilepsy (66%) that is intractable in a subset. At last follow-up, 36% ambulated with assistance (mean age: 8.9 ± 6.4 years, SD) and 54% were wheelchair-dependent (mean age: 13.4 ± 9.8 years, SD). Episodes of stereotypic laughing, possibly consistent with a pseudobulbar affect, were found in 56% of patients. Key features on neuroimaging include a thin corpus callosum (90%), ventriculomegaly (65%) often with colpocephaly, and periventricular white-matter signal abnormalities (68%). Iron deposition and polymicrogyria were found in a subset of patients. AP4B1-associated SPG47 and AP4M1-associated SPG50 accounted for the majority of cases. About two-thirds of patients were born to consanguineous parents, and 82% carried homozygous variants. Over 70 unique variants were present, the majority of which are frameshift or nonsense mutations. To track disease progression across the age spectrum, we defined the relationship between disease severity as measured by several rating scales and disease duration. We found that the presence of epilepsy, which manifested before the age of 3 years in the majority of patients, was associated with worse motor outcomes. Exploring genotype-phenotype correlations, we found that disease severity and major phenotypes were equally distributed among the four subtypes, establishing that SPG47, SPG50, SPG51 and SPG52 share a common phenotype, an 'AP-4 deficiency syndrome'. By delineating the core clinical, imaging, and molecular features of AP-4-associated hereditary spastic paraplegia across the age spectrum our results will facilitate early diagnosis, enable counselling and anticipatory guidance of affected families and help define endpoints for future interventional trials.

Dominant mutations in mtDNA maintenance gene SSBP1 cause optic atrophy and foveopathy

Mutations in genes encoding components of the mitochondrial DNA (mtDNA) replication machinery cause mtDNA depletion syndromes (MDSs), which associate ocular features with severe neurological syndromes. Here, we identified heterozygous missense mutations in single-strand binding protein 1 (SSBP1) in 5 unrelated families, leading to the R38Q and R107Q amino acid changes in the mitochondrial single-stranded DNA-binding protein, a crucial protein involved in mtDNA replication. All affected individuals presented optic atrophy, associated with foveopathy in half of the cases. To uncover the structural features underlying SSBP1 mutations, we determined a revised SSBP1 crystal structure. Structural analysis suggested that both mutations affect dimer interactions and presumably distort the DNA-binding region. Using patient fibroblasts, we validated that the R38Q variant destabilizes SSBP1 dimer/tetramer formation, affects mtDNA replication, and induces mtDNA depletion. Our study showing that mutations in SSBP1 cause a form of dominant optic atrophy frequently accompanied with foveopathy brings insights into mtDNA maintenance disorders.

FGF14-related episodic ataxia: delineating the phenotype of Episodic Ataxia type 9

We report four patients from two families who presented attacks of childhood-onset episodic ataxia associated with pathogenic mutations in the FGF14 gene. Attacks were triggered by fever, lasted several days, and had variable frequencies. Nystagmus and/or postural tremor and/or learning disabilities were noticed in individuals harboring FGF14 mutation with or without episodic ataxia. These cases and literature data delineate the FGF14-mutation-related episodic ataxia phenotype: wide range of age at onset (from childhood to adulthood), variable durations and frequencies, triggering factors including fever, and association to chronic symptoms. We propose to add FGF14-related episodic ataxia to the list of primary episodic ataxia as Episodic Ataxia type 9.

Movement disorders in patients with alternating hemiplegia: "Soft" and "stiff" at the same time

OBJECTIVE

To assess nonparoxysmal movement disorders in ATP1A3 mutation-positive patients with alternating hemiplegia of childhood (AHC).

METHODS

Twenty-eight patients underwent neurologic examination with particular focus on movement phenomenology by a specialist in movement disorders. Video recordings were reviewed by another movement disorders specialist and data were correlated with patients' characteristics.

RESULTS

Ten patients were diagnosed with chorea, 16 with dystonia (nonparoxysmal), 4 with myoclonus, and 2 with ataxia. Nine patients had more than one movement disorder and 8 patients had none. The degree of movement disorder was moderate to severe in 12/28 patients. At inclusion, dystonic patients (n = 16) were older (p = 0.007) than nondystonic patients. Moreover, patients (n = 18) with dystonia or chorea, or both, had earlier disease onset (p = 0.042) and more severe neurologic impairment (p = 0.012), but this did not correlate with genotype. All patients presented with hypotonia, which was characterized as moderate or severe in 16/28. Patients with dystonia or chorea (n = 18) had more pronounced hypotonia (p = 0.011). Bradykinesia (n = 16) was associated with an early age at assessment (p < 0.01). Significant dysarthria was diagnosed in 11/25 cases. A history of acute neurologic deterioration and further regression of motor function, typically after a stressful event, was reported in 7 patients.

CONCLUSIONS

Despite the relatively limited number of patients and the cross-sectional nature of the study, this detailed categorization of movement disorders in patients with AHC offers valuable insight into their precise characterization. Further longitudinal studies on this topic are needed.

Cognitive impairment in children with CACNA1A mutations

AIM

To describe the clinico-radiological phenotype of children with a CACNA1A mutation and to precisely evaluate their learning ability and cognitive status.

METHOD

Children between the ages of 3 and 18 years harboring a pathogenic CACNA1A mutation associated with episodic ataxia, hemiplegic migraine, benign paroxysmal torticollis, benign paroxysmal vertigo, or benign paroxysmal tonic upgaze, were enrolled in this cross-sectional study. Data concerning psychomotor development, academic performance, educational management, clinical examination at inclusion, and brain imaging were collected. Cognitive assessment was performed using age-standardized scales.

RESULTS

Eighteen patients (nine males, nine females; mean age at inclusion: 11y 7mo [SD 4y 5mo; range 3y-17y 11mo]) from 14 families were enrolled. Eleven patients displayed the coexistence or consecutive occurrence of more than one type of episodic event. Nine patients exhibited abnormal neurological examination at inclusion. Brain magnetic resonance imaging (MRI) showed cerebellar atrophy in five patients. Psychomotor development was delayed in nine patients and academic difficulties were reported by the parents in 15 patients; nine patients were in special education. Impairment of intellectual function was assessed in six of the 12 patients with interpretable Full-scale IQ scores and was more frequent when cerebellar atrophy was present on MRI.

INTERPRETATION

Cognitive impairment is commonly associated with CACNA1A mutations. We suggest that CACNA1A-associated phenotype should be considered a neurodevelopmental disorder.

WHAT THIS PAPER ADDS

Cognitive disabilities and academic difficulties are common in children with CACNA1A mutations associated with episodic syndromes. Cognitive function ranges from normal to moderate intellectual disorder in wheelchair-dependent children. Patients with vermian atrophy are at a higher risk of cognitive impairment.

Adaptor protein complex 4 deficiency: a paradigm of childhood-onset hereditary spastic paraplegia caused by defective protein trafficking

Deficiency of the adaptor protein complex 4 (AP-4) leads to childhood-onset hereditary spastic paraplegia (AP-4-HSP): SPG47 (AP4B1), SPG50 (AP4M1), SPG51 (AP4E1) and SPG52 (AP4S1). This study aims to evaluate the impact of loss-of-function variants in AP-4 subunits on intracellular protein trafficking using patient-derived cells. We investigated 15 patient-derived fibroblast lines and generated six lines of induced pluripotent stem cell (iPSC)-derived neurons covering a wide range of AP-4 variants. All patient-derived fibroblasts showed reduced levels of the AP4E1 subunit, a surrogate for levels of the AP-4 complex. The autophagy protein ATG9A accumulated in the trans-Golgi network and was depleted from peripheral compartments. Western blot analysis demonstrated a 3-5-fold increase in ATG9A expression in patient lines. ATG9A was redistributed upon re-expression of AP4B1 arguing that mistrafficking of ATG9A is AP-4-dependent. Examining the downstream effects of ATG9A mislocalization, we found that autophagic flux was intact in patient-derived fibroblasts both under nutrient-rich conditions and when autophagy is stimulated. Mitochondrial metabolism and intracellular iron content remained unchanged. In iPSC-derived cortical neurons from patients with AP4B1-associated SPG47, AP-4 subunit levels were reduced while ATG9A accumulated in the trans-Golgi network. Levels of the autophagy marker LC3-II were reduced, suggesting a neuron-specific alteration in autophagosome turnover. Neurite outgrowth and branching were reduced in AP-4-HSP neurons pointing to a role of AP-4-mediated protein trafficking in neuronal development. Collectively, our results establish ATG9A mislocalization as a key marker of AP-4 deficiency in patient-derived cells, including the first human neuron model of AP-4-HSP, which will aid diagnostic and therapeutic studies.