Leukodystrophies and genetic leukoencephalopathies are a rare group of disorders leading to progressive degeneration of cerebral white matter. They are associated with a spectrum of clinical phenotypes dominated by dementia, psychiatric changes, movement disorders and upper motor neuron signs. Mutations in at least 60 genes can lead to leukoencephalopathy with often overlapping clinical and radiological presentations. For these reasons, patients with genetic leukoencephalopathies often endure a long diagnostic odyssey before receiving a definitive diagnosis or may receive no diagnosis at all. In this study, we used focused and whole exome sequencing to evaluate a cohort of undiagnosed adult patients referred to a specialist leukoencephalopathy service. In total, 100 patients were evaluated using focused exome sequencing of 6100 genes. We detected pathogenic or likely pathogenic variants in 26 cases. The most frequently mutated genes were NOTCH3, EIF2B5, AARS2 and CSF1R. We then carried out whole exome sequencing on the remaining negative cases including four family trios, but could not identify any further potentially disease-causing mutations, confirming the equivalence of focused and whole exome sequencing in the diagnosis of genetic leukoencephalopathies. Here we provide an overview of the clinical and genetic features of these disorders in adults.

Defects in iron–sulphur [Fe-S] cluster biogenesis are increasingly recognized as causing neurological disease. Mutations in a number of genes that encode proteins involved in mitochondrial [Fe-S] protein assembly lead to complex neurological phenotypes. One class of proteins essential in the early cluster assembly are ferredoxins. FDX2 is ubiquitously expressed and is essential in the de novo formation of [2Fe-2S] clusters in humans. We describe and genetically define a novel complex neurological syndrome identified in two Brazilian families, with a novel homozygous mutation in FDX2. Patients were clinically evaluated, underwent MRI, nerve conduction studies, EMG and muscle biopsy. To define the genetic aetiology, a combination of homozygosity mapping and whole exome sequencing was performed. We identified six patients from two apparently unrelated families with autosomal recessive inheritance of a complex neurological phenotype involving optic atrophy and nystagmus developing by age 3, followed by myopathy and recurrent episodes of cramps, myalgia and muscle weakness in the first or second decade of life. Sensory-motor axonal neuropathy led to progressive distal weakness. MRI disclosed a reversible or partially reversible leukoencephalopathy. Muscle biopsy demonstrated an unusual pattern of regional succinate dehydrogenase and cytochrome c oxidase deficiency with iron accumulation. The phenotype was mapped in both families to the same homozygous missense mutation in FDX2 (c.431C > T, p.P144L). The deleterious effect of the mutation was validated by real-time reverse transcription polymerase chain reaction and western blot analysis, which demonstrated normal expression of FDX2 mRNA but severely reduced expression of FDX2 protein in muscle tissue. This study describes a novel complex neurological phenotype with unusual MRI and muscle biopsy features, conclusively mapped to a mutation in FDX2, which encodes a ubiquitously expressed mitochondrial ferredoxin essential for early [Fe-S] cluster biogenesis.

Supratentorial Lymphocytic Inflammation with Parenchymal Perivascular Enhancement Responsive to Steroids (SLIPPERS) is a rare variant of the CLIPPERS spectrum with less than ten reports published so far. There is ongoing discussion regarding whether SLIPPERS is a disease entity on its own or just an acronym encompassing many underlying diagnoses, such as sarcoidosis, vasculitis and anti-glial fibrillary acidic protein (GFAP)-associated disease. A 40-year-old woman presented with episodes of language and attention impairment. Magnetic resonance imaging (MRI) revealed T2/FLAIR hyperintense lesions in the subcortical white matter associated with a micronodular, curvilinear perivascular contrast-enhancement. Alternative diagnoses were excluded. There was a remarkable response to steroids. A relapse occurred after six years, and the biopsy showed perivascular T-cell lymphocytic infiltrate, without granulomas, vasculitis, or neoplasia. There was complete resolution of the relapse after steroids. This case represents the longest reported follow-up of a patient diagnosed with SLIPPERS, and brain biopsy after 6 years did not suggest alternative diagnoses. This report contributes to the discussion regarding the possibility that exclusive supratentorial CLIPPERS-like pathology might be an isolated disease entity, but more biopsy-proven cases with a longer follow-up are needed to support this hypothesis. Recently, GFAP astrocytopathy has been characterized and might correspond to a significant number of cases previously diagnosed as CLIPPERS or SLIPPERS.

Introduction: Argininemia or arginase deficiency is a metabolic disorder caused by pathogenic variants in ARG1 and consists of a variable association of progressive spastic paraplegia, intellectual disability, and seizures. Hereditary spastic paraplegia (HSP) is a group of inherited diseases whose main feature is a progressive gait disorder characterized by lower limb spasticity. This study presents 7 patients with arginase 1 deficiency from 6 different families, all with an initial diagnosis of complicated HSP. Methods: We evaluated the clinical data of 7 patients belonging to six independent families who were diagnosed with hyperargininemia in a neurogenetics outpatient clinic. Results: All patients had lower limb spasticity and six had global developmental delay. Five individuals had intellectual disability and two had epilepsy. Psychiatric abnormalities were seen in two patients. In two participants of this study, MRI disclosed thinning of the corpus callosum. Molecular diagnosis was made by whole exome sequencing. All variants were present in homozygosis; we identified two novel missense variants, one novel frameshift variant, and one previously published missense variant. Discussion: Clinical diagnosis of early onset complicated hereditary spastic paraplegia was made in all patients. Two patients were initially suspected of having SPG11 due to thinning of the corpus callosum. As argininemia may present with a highly penetrant phenotype of spastic paraplegia associated with additional symptoms, this disease may represent a specific entity amongst the complicated HSPs.