Co-occurrence of CLCN2-related leukoencephalopathy and SPG56.

Family Report: Two rare autosomal recessive neurological disorders, leukoencephalopathy with ataxia and spastic paraplegia 56 (SPG56), were found in members of the same family. Two siblings presented with spastic paraplegia, cognitive impairment, bladder and bowel dysfunction and gait ataxia; their consanguineous parents were unaffected. Ophthalmological examination revealed chorioretinopathy. Brain MRI showed T2 hyperintensities and T1 hypointensities in the internal capsules, cerebral peduncles, pyramidal tracts and middle cerebellar peduncles. Both affected siblings were homozygous for CYP2U1 c.947A > T p.(Asp316Val), a known cause for SPG56. However, they were also homozygous for the novel variant CLCN2 c.607G > T, p.(Gly203Cys), classified as a variant of unknown significance. Testing of additional family members revealed homozygosity for both variants in an additional brother, whom we initially considered unaffected. Both male CLCN2 carriers were infertile, and review of the literature revealed one reported case with azoospermia, however the brother had no overt signs of SPG56. His testicular biopsy revealed incomplete maturation arrest in spermatogenesis; clinically we found mild memory impairment and hand tremor and MRI showed similar changes as his siblings. We consider CLCN2 c.607G > T pathogenic because of the neuroradiological and clinical findings, including azoospermia. Conclusion: Considerable workup may be required to determine the pathogenicity of novel variants, and to unambiguously associate phenotype with genotype. In very rare disorders, highly specific clinical or biomarker combinations provide sufficient evidence for a variant's pathogenicity. Phenotypic variation of monogenic disorders described in the literature may be attributed to a second co-occurring monogenic disorder, especially in consanguineous families. SPG56 may have reduced penetrance.

Macular Dystrophy with Bilateral Macular Telangiectasia Related to the CYP2U1 Pathogenic Variant Assessed with Multimodal Imaging Including OCT-Angiography.

PURPOSE: We report the case of a neurologically asymptomatic young boy presenting with an unusual phenotype of CYP2U1 related macular dystrophy associating bilateral macular telangiectasia (MacTel) and fibrotic choroidal neovascularization (CNV), assessed with complete multimodal imaging including optical coherence tomography angiography (OCT-A). CASE PRESENTATION: A twelve-year-old boy from a non-consanguineous family complained of bilateral progressive visual loss and photophobia. The best-corrected visual acuity was 2/10 on the right eye and 3/10 on the left eye. Fundus examination showed central pigmented fibrotic macular scar and yellowish punctuate deposits in both eyes. En face OCT-A detected typical macular telangiectasia (MacTel) in both eyes with dilated telangiectatic capillaries in the deep capillary plexus associated with vascular anomalies in the superficial and deep capillary plexus. Typical hypo-reflective cavities were observed within the inner foveal layers on structural OCT. En face OCT-A also confirmed the presence of bilateral inactive CNV within the fibrotic scars, showing high-flow vascular network at the level of the subretinal hyperreflective lesions. Whole exome sequencing identified a known homozygous pathogenic variant in CYP2U1 gene (c.1168C > T, p.Arg390*), which is a disease-causing mutation in autosomal recessive spastic paraplegia type 56 (SPG56). The neurological examination was normal, and electromyography and brain magnetic resonance imaging were unremarkable as well. CONCLUSION: Macular dystrophy can be the first manifestation in SPG56. A particular phenotype with MacTel was observed, and neovascular complications are possible. CYP2U1 should be included in the panels of genes tested for macular dystrophies, especially in the presence of MacTel and/or neurological manifestations.

Spastic Paraplegia-56 due to a Novel CYP2U1 Truncating Mutation in an Indian Boy: A New Report and Literature Review.

Spastic paraplegia-56 is a rare autosomal recessive disorder, caused by homozygous or compound heterozygous mutations in the CYP2U1 gene, located on chromosome 4. Till date, only 28 patients with this disorder have been reported in the literature. We report a new case of CYP2U1-related spastic paraplegia-56. We also reviewed previously published patients with this condition from various databases. Next-generation sequencing in the index child detected a novel homozygous two base pair deletion in exon 2 of the CYP2U1 gene that results in a frameshift and premature truncation of the protein 19 amino-acid downstream to codon 361. Together with the presented case, 29 were available for analysis. The mean age at the diagnosis was 17.84 ± 6.86 years. Intellectual disability/cognitive dysfunction and delayed walking or gait disturbance were the most common presenting features. Around half of the patients had neuroregression in between 1 and 2 years. It is clinically imperative to suspect this disease in children with early-onset spastic paraparesis, especially in cases accompanied by baseline development delay or cognitive impairment and consanguinity.

Rare novel CYP2U1 and ZFYVE26 variants identified in two Pakistani families with spastic paraplegia.

BAKGROUND: Hereditary Spastic paraplegias (HSPs) are a clinically and genetically heterogeneous group of degenerative disorders characterized by progressive spasticity and weakness of the lower limbs. This study aimed to identify causative gene variants in two unrelated consanguineous Pakistani families presented with 2 different forms of HSP. METHODS: Whole exome sequencing (WES) was performed in the two families and variants were validated by Sanger sequencing and segregation analysis. ANALYSIS: In family A, a homozygous pathogenic variant in ZFYVE26 was identified in one family. While in family B, a frameshift variant in CYP2U1 was identified in 4 affected individuals presented with clinical features of SPG56. Our study is the first report of ZFYVE26 mutations causing HSP in the Pakistani population and the second report of CYP2U1 in a Pakistani family. CONCLUSIONS: Our findings enhance the clinical and genetic variability associated with two rare autosomal recessive HSP genes, highlighting the complexity of HSPs. These findings further emphasize the usefulness of WES as a powerful diagnostic tool.

Whole exome sequencing identifies novel variant underlying hereditary spastic paraplegia in consanguineous Pakistani families.

Hereditary Spastic paraplegias (HSPs) are heterogeneous group of degenerative disorders characterized by progressive weakness and spasticity of the lower limbs, combined with additional neurological features. This study aimed to identify causative gene variants in two nonrelated consanguineous Pakistani families segregating HSP. Whole exome sequencing (WES) was performed on a total of five individuals from two families including four affected and one phenotypically normal individual. The variants were validated by Sanger sequencing and segregation analysis. In family A, a novel homozygous variant c.604G > A (p.Glu202Lys) was identified in the CYP2U1 gene with clinical symptoms of SPG56 in 3 siblings. Whereas, a previously reported variant c.5769delT (p.Ser1923Argfs*28) in the SPG11 gene was identified in family B manifesting clinical features of SPG11 in 3 affected individuals. Our combined findings add to the clinical and genetic variability associated with CYP2U1 and SPG11 variants highlighting the complexity of HSPs. These findings further emphasize the usefulness of WES as a powerful diagnostic tool.

CYP2U1 activity is altered by missense mutations in hereditary spastic paraplegia 56.

Hereditary spastic paraplegia (HSP) is an inherited disorder of the central nervous system mainly characterized by gradual spasticity and weakness of the lower limbs. SPG56 is a rare autosomal recessive early onset complicated form of HSP caused by mutations in CYP2U1. The CYP2U1 enzyme was shown to catalyze the hydroxylation of arachidonic acid. Here, we report two further SPG56 families carrying three novel CYP2U1 missense variants and the development of an in vitro biochemical assay to determine the pathogenicity of missense variants of uncertain clinical significance. We compared spectroscopic, enzymatic, and structural (from a 3D model) characteristics of the over expressed wild-type or mutated CYP2U1 in HEK293T cells. Our findings demonstrated that most of the tested missense variants in CYP2U1 were functionally inactive because of a loss of proper heme binding or destabilization of the protein structure. We also showed that functional data do not necessarily correlate with in silico predictions of variants pathogenicity, using different bioinformatic phenotype prediction tools. Our results therefore highlight the importance to use biological tools, such as the enzymatic test set up in this study, to evaluate the effects of newly identified variants in clinical settings.

Defining the genetic basis of early onset hereditary spastic paraplegia using whole genome sequencing.

We performed whole genome sequencing (WGS) in nine families from India with early-onset hereditary spastic paraplegia (HSP). We obtained a genetic diagnosis in 4/9 (44 %) families within known HSP genes (DDHD2 and CYP2U1), as well as perixosomal biogenesis disorders (PEX16) and GM1 gangliosidosis (GLB1). In the remaining patients, no candidate structural variants, copy number variants or predicted splice variants affecting an extended candidate gene list were identified. Our findings demonstrate the efficacy of using WGS for diagnosing early-onset HSP, particularly in consanguineous families (4/6 diagnosed), highlighting that two of the diagnoses would not have been made using a targeted approach.

CYP2U1 mutations in two Iranian patients with activity induced dystonia, motor regression and spastic paraplegia.

Hereditary spastic paraplegia (HSP) is a heterogeneous condition characterized by progressive spasticity and weakness in the lower limbs. It is divided into two major groups, complicated and uncomplicated, based on the presence of additional features such as intellectual disability, ataxia, seizures, peripheral neuropathy and visual problems. SPG56 is an autosomal recessive form of HSP with complicated and uncomplicated manifestations, complicated being more common. CYP2U1 gene mutations have been identified as responsible for SPG56. Intellectual disability, dystonia, subclinical sensory motor neuropathy, pigmentary degenerative maculopathy, thin corpus callosum and periventricular white-matter hyperintensities were additional features noted in previous cases of SPG56. Here we identified two novel mutations in CYP2U1 in two unrelated patients by whole exome sequencing. Both patients had complicated HSP with activity-induced dystonia, suggesting dystonia as an additional finding in SPG56. Two out of 14 previously reported patients had dystonia, and the addition of our patients suggests dystonia in a quarter of SPG56 patients. Developmental regression has not been reported in SPG56 patients so far but both of our patients developed motor regression in infancy.

Hereditary spastic paraplegia: Novel mutations and expansion of the phenotype variability in SPG56.

We describe a novel sporadic case of SPG56, a rare complicated form of HSP, that expands the clinical and molecular spectrum of the disease, being associated to novel mutations in CYP2U1 and showing as novel feature dorsal hydromyelia at spinal cord MRI. The patient presented an early-onset, slowly progressive paraparesis associated with mild mental retardation. Neurological assessments included the Spastic Paraplegia Rating Scale (SPRS), Mental Deterioration Battery (MDB), and Wechsler Adult Intelligence Scale (WAIS), neurophysiological and neuroimaging studies. Targeted next-generation sequencing panels for the whole set of genes associated with HSP were performed in the probands and her relatives. Neuroimaging studies showed dorsal hydromyelia but no brain MRI abnormalities. Targeted next-generation identified two novel mutations: the c.5C > A/p.S2* on the maternal allele in compound heterozygosity with the paternally-inherited c.1288+5G > C in CYP2U1. Both mutations predict early protein truncation and a loss of function. So far, only few SPG56 cases have been reported. This case, expands and further characterize the clinical and molecular spectrum of SPG56. In this regard, in consideration of the putative gene function in neurodevelopment, we suggest a causal association between CYP2U1 mutations and hydromyelia in our patient.

Pigmentary degenerative maculopathy as prominent phenotype in an Italian SPG56/CYP2U1 family.

SPG56 is an autosomal recessive form of hereditary spastic paraplegia (HSP) associated with mutations in CYP2U1. There is no clear documentation of visual impairment in the few reported cases of SPG56, although this form is complex on clinical ground and visual deficit are extremely frequent in complicated HSP. We report three patients in a consanguineous family harboring the novel homozygous c.1168C>T (p.R390*) in SPG56/CYP2U1, and showing a pigmentary degenerative maculopathy associated with progressive spastic paraplegia. Furthermore, we characterized precisely the ophthalmologic phenotype through indirect ophthalmoscopy, retinal optical coherence tomography and visual evoked potentials. This is the first formal report of pigmentary degenerative maculopathy associated with a CYP2U1 homozygous mutation.