Identification of myokymia in adult-onset hereditary spastic paraplegia type 79A: Implications for the phenotypic spectrum

ObjectiveWhile the anticipated rise of disease‐modifying therapies calls for reliable trial outcome parameters, fluid biomarkers are lacking in spastic paraplegia type 4 (SPG4), the most prevalent form of hereditary spastic paraplegia. We therefore investigated serum neurofilament light chain (sNfL) as a potential therapy response, diagnostic, monitoring, and prognostic biomarker in SPG4.Methods: We assessed sNfL levels in 93 patients with SPG4 and 60 healthy controls. The longitudinal study of sNfL levels in SPG4 patients covered a baseline, 1‐year follow‐up and 2‐year follow‐up visit.ResultsLevels of sNfL were significantly increased in patients with genetically confirmed SPG4 compared to healthy controls matched in age and sex (p = 0.013, r = 0.2). Our cross‐sectional analysis revealed a greater difference in sNfL levels between patients and controls in younger ages with decreasing fold change of patient sNfL elevation at older ages. Over our observational period of 2 years, sNfL levels remained stable in SPG4 patients. Disease severity and progression did not correlate with sNfL levels.Interpretation: Our longitudinal data indicate a stable turnover of sNfL in manifest SPG4; therefore, sNfL levels are not suitable to monitor disease progression in SPG4. However, sNfL may be valuable as a therapy response biomarker, since its turnover could be modified by interventions. As the course of sNfL levels appears to be most dynamic around the onset of SPG4, the ability to detect a therapy response appears to be especially promising in younger patients, matching the need to initiate treatment in early disease stages.

Loss of Association of REEP2 with Membranes Leads to Hereditary Spastic Paraplegia

Ubiquitin C-terminal hydrolase L1 (UCHL1) has been associated with a severe, complex autosomal recessive spastic paraplegia (HSP79) [1] [2] [3][4]. More recently, UCHL1 loss of function (LoF) variants have been associated to an autosomal dominant disease characterized by late-onset spastic ataxia, neuropathy, and frequent optic atrophy [5]. Routine clinical care whole-genome (WGS) and exome (ES) sequencing. We present three families with autosomal dominant UCHL1-related disorder. The clinical phenotype mainly associated optic atrophy, mixed cerebellar and sensory ataxia, and possible hearing loss. We delineated two major phenotypes, even within the same family: (1) juvenile severe optic atrophy followed by a later-onset ataxia, or (2) late-onset ataxia with asymptomatic or mild optic atrophy. The families harboured three novel heterozygous variants in UCHL1: two loss of function (p.Lys115AsnfsTer40; c.171_174 + 7del11), and one missense (p.Asp176Asn) involving the catalytic site of the protein and potentially altering the adjacent splice site. We confirm the existence of dominantly inherited UCHL1 pathogenic variants. We describe a considerable intrafamilial phenotypic variability, with two main phenotypes. Optic atrophy was consistently present, but with varying degrees of severity. Neither delayed motor or intellectual development, nor dysmorphic features were part of the dominant phenotype in comparison with the autosomal recessive form. The molecular mechanism appears to be haploinsufficiency. UCHL1 monoallelic variants should therefore be considered in any case of early-onset optic atrophy or in late-onset complex ataxic syndrome with asymptomatic optic atrophy.

The Troyer syndrome was found by Cross & McKusick (1967) in 20 members of 12 Old Order Amish families in Holmes County, Ohio; it is a form of hereditary spastic paraplegia combined with distal muscle wasting, i.e. signs of involvement of lower motor neurons. The condition usually begins at 1 to 2 years and progresses at variable rates. Further manifestations include growth retardation, delayed speech development with dysarthria and drooling, and cerebellar signs; mental functions are usually not affected but severe emotional lability is a common finding. Brothers in a Wisconsin Old Order Amish family are reported with spastic diplegia, mental retardation, behavioral disorder and shortness of stature; the condition apparently is not progressive, and may be a "new" syndrome but could also represent a variant of the Troyer syndrome. Autosomal recessive inheritance is most likely, although consanguinity of the parents could not be proven. Another child in this family suffers from focal scleroderma (morphea) which is not related to the neurological syndrome.

Spastic paraplegia type 4 (SPG4) is the most common autosomal dominant hereditary SPG caused by mutations in the SPAST gene. We studied the four-generation pedigree of a Japanese family with autosomal dominant hereditary SPG both clinically and genetically. Twelve available family members (ten affected; two unaffected) and two spouses were enrolled in the study. The clinical features were hyperreflexia in all four limbs, spasticity of the lower extremities, impaired vibration sense, mild cognitive impairment confirmed by the Wechsler Adult Intelligence Scale-Third Edition, and peripheral neuropathy confirmed by neurophysiological examinations. All four female patients experienced miscarriages. The cerebrospinal fluid tau levels were mildly increased in two of three patients examined. Linkage analyses revealed the highest logarithm of odds score of 2.64 at 2p23-p21 where the SPAST gene is located. Mutation scanning of the entire exonic regions of the SPAST gene by direct sequencing revealed no mutations. Exonic copy number analysis by real-time quantitative polymerase chain reaction revealed heterozygous deletion of exons 1 to 4 of the SPAST gene. Breakpoint analysis showed that the centromeric breakpoint was located within intron 4 of SPAST while the telomeric breakpoint was located within intron 3 of the neighboring DPY30 gene, causing a deletion of approximately 70 kb ranging from exons 1 to 3 of DPY30 to exons 1 to 4 of SPAST. To our knowledge, this is the first report of SPG4 associated with partial deletions of both the SPAST and DPY30 genes. The partial heterozygous deletion of DPY30 could modify the phenotypic expression of SPG4 patients with this pedigree.

Spastic paraplegia type 3A (SPG3A) is the second most common form of hereditary spastic paraplegia (HSP). This autosomal-dominant-inherited motor disorder is caused by heterozygous variants in the ATL1 gene which usually presents as a pure childhood-onset spastic paraplegia. Affected individuals present muscle weakness and spasticity in the lower limbs, with symptom onset in the first decade of life. Individuals with SPG3A typically present a slow progression and remain ambulatory throughout their life. Here we report three unrelated individuals presenting with very-early-onset (before 7 months) complex, and severe HSP phenotypes (axial hypotonia, spastic quadriplegia, dystonia, seizures and intellectual disability). For 2 of the 3 patients, these phenotypes led to the initial diagnosis of cerebral palsy (CP). These individuals carried novel ATL1 pathogenic variants (a de novo ATL1 missense p.(Lys406Glu), a homozygous frameshift p.(Arg403Glufs*3) and a homozygous missense variant (p.Tyr367His)). The parents carrying the heterozygous frameshift and missense variants were asymptomatic. Through these observations, we increase the knowledge on genotype–phenotype correlations in SPG3A and offer additional proof for possible autosomal recessive forms of SPG3A, while raising awareness on these exceptional phenotypes. Their ability to mimic CP also implies that genetic testing should be considered for patients with atypical forms of CP, given the implications for genetic counseling.

Chapter 14 SPG4, the Most Frequent Hereditary Spastic Paraplegia: Clinical and Genetic Aspects

Sirs: Spastic paraplegia type 4 (SPG4) is the most frequent type of autosomal dominant inherited spastic paraplegia. The SPG4 gene encodes spastin, an ATPase belonging to the AAA protein family. Mutations have been reported along all 17 exons of the coding region. We here report on a new truncating SPG4 mutation in a large three generation German kindred with 27 family members. Molecular genetic analysis. The causative region was mapped to chromosome 2p21-p22 which is identical to the SPG4 locus. To avoid sequencing of the complete spastin gene (SPG4) the 17 exons were screened by HPLC technology (WAVE-System, Transgenomics). All exons with flanking intron sequences were amplified by PCR. Products were analysed on the dHPLC-system at at least two different temperatures depending on the melting profiles of the amplified sequences. The clinically affected individuals showed clearly distinguishable peak patterns for exon 5 in comparison with unaffected relatives. Sequencing of this exon revealed a T to G transversion in one allele leading to an early inframe stop codon. On the amino acid level this nonsense mutation causes the p.Leu239X truncation of the SPG4 protein. Clinical data. Clinically, 11 subjects showed symptoms of spastic paraplegia (mean age: 44.6 ± 14.1 years, range: 30–61). In eight of them, there was clear evidence for spasticity and increased tendon reflexes in the lower limbs. Plantar responses were extensor in two subjects. Another three individuals had only mild symptoms with brisker tendon reflexes in the lower limbs than in the upper limbs. Phenotype-genotype correlation analysis confirmed the SPG4 mutation in all of them. Interestingly four gene carriers were personally unaware of symptoms. Among the 10 at-risk individuals with normal neurological examination, another two patients, aged 27 and 36 years, were tested positive for the SPG4 mutation. Additional loss of proprioception was present in 8, impairment of exteroception in 6 patients. Sphincter disturbances were complained of by 6 family members with combined urinary/faecal incontinence in 4 of them. There was no evidence for additional cognitive impairment, peripheral neuropathy, cerebellar symptoms, visual or hearing loss. The age of onset ranged from 6 to 48 years (mean 27.8 ± 18.1 years). Clinical severity was also highly variable with younger patients being more severely affected. The variability of the clinical severity but not of the clinical symptoms appears to be a characteristic finding of SPG4 [1]. It points to unknown biological factors positively modulating the disease in some carriers of the SPG4 mutation. The detection of these additional factors might offer therapeutic strategies in the future.

ObjectiveThe aim of this study was to investigate the role of ubiquitin C‐terminal hydrolase‐L1 (UCHL1) for motor neuron circuitry and especially in spinal motor neuron (SMN) health, function, and connectivity.MethodsSince mutations in UCHL1 gene leads to motor dysfunction in patients, we investigated the role of UCHL1 on SMN survival, axon health, and connectivity with the muscle, by employing molecular and cellular marker expression analysis and electrophysiological recordings, in healthy wild‐type and Uchl1 nm3419 (UCHL1−/−) mice, which lack all UCHL1 function.ResultsThere is pure motor neuropathy with selective degeneration of the motor, but not sensory axons in the absence of UCHL1 function. Neuromuscular junctions (NMJ) are impaired in muscle groups that are innervated by slow‐twitch or fast‐twitch SMN. However, unlike corticospinal motor neurons, SMN cell bodies remain intact with no signs of elevated endoplasmic reticulum (ER) stress.InterpretationPresence of NMJ defects and progressive retrograde axonal degeneration in the absence of major SMN soma loss suggest that defining pathology as a function of neuron number is misleading and that upper and lower motor neurons utilize UCHL1 function in different cellular events. In line with findings in patients with mutations in UCHL1 gene, our results suggest a unique role of UCHL1, especially for motor neuron circuitry. SMN require UCHL1 to maintain NMJ and motor axon health, and that observed motor dysfunction in the absence of UCHL1 is not due to SMN loss, but mostly due to disintegrated circuitry.

Spastic paraplegia type 7 is an autosomal recessive neurodegenerative disorder mainly characterized by progressive bilateral lower limb spasticity and referred to as a form of hereditary spastic paraplegia. Additional disease features may also be observed as part of a more complex phenotype. Many different mutations have already been identified, but no genotype-phenotype correlations have been found so far. From a total of almost 800 patients referred for testing, we identified 60 patients with mutations in the SPG7 gene. We identified 14 previously unreported mutations and detected a high recurrence rate of several earlier reported mutations. We were able to collect detailed clinical data for 49 patients, who were ranked based on a pure versus complex phenotype, ataxia versus no ataxia and missense versus null mutations. A generally complex phenotype occurred in 69% of all patients and was associated with a younger age at onset (trend with P = 0.07). Ataxia was observed in 57% of all patients. We found that null mutations were associated with the co-occurrence of cerebellar ataxia (trend with P = 0.06). The c.1409 G > A (p.Arg470Gln) mutation, which was found homozygously in two sibs, was associated with a specific complex phenotype that included predominant visual loss due to optical nerve atrophy. Neuropathology in one of these cases showed severe degeneration of the optic system, with less severe degeneration of the ascending tracts of the spinal cord and cerebellum. Other disease features encountered in this cohort included cervical dystonia, vertical gaze palsy, ptosis and severe intellectual disability. In this large Dutch cohort, we seem to have identified the first genotype-phenotype correlation in spastic paraplegia type 7 by observing an association between the cerebellar phenotype of spastic paraplegia type 7 and SPG7 null alleles. An overlapping phenotypic presentation with its biological counterpart AFG3L2, which when mutated causes spinocerebellar ataxia type 28, is apparent and possibly suggests that abnormal levels of the SPG7 protein impact the function of the mitochondrial ATPases associated with diverse cellular activities-protease complex (formed by SPG7 and AFG3L2) in the cerebellum. In addition, a missense mutation in exon 10 resulted in predominant optical nerve atrophy, which might suggest deleterious interactions of this SPG7 variant with its substrate OPA1, the mutated gene product in optic atrophy type 1. Functional studies are required to further investigate these interactions.

ObjectiveTo establish molecular diagnosis for a family with a complicated form of autosomal recessive hereditary spastic paraplegia with intellectual disability, cognitive decline, psychosis, peripheral neuropathy, upward gaze palsy, and thin corpus callosum (TCC).MethodsPhysical examinations, laboratory tests, structural neuroimaging studies, and exome sequence analysis were carried out.ResultsThe 3 patients exhibited intellectual disability and progressive intellectual decline accompanied by psychiatric symptoms. Gait difficulty with spasticity and pyramidal weakness appeared at the ages of 20s–30s. Brain MRI revealed TCC with atrophic changes in the frontotemporal lobes, caudate nuclei, and cerebellum. Exome sequence analysis revealed a novel homozygous c.2654C>A (p. Ala885Asp) variant in the ATP13A2, a gene responsible for a complicated form of hereditary spastic paraplegia (SPG78), Kufor-Rakeb syndrome, and neuronal ceroid lipofuscinosis. The predominant clinical presentations of the patients include progressive intellectual disability and gait difficulty with spasticity and pyramidal weakness, consistent with the diagnosis of SPG78. Of note, prominent psychiatric symptoms and extrapyramidal signs including rigidity, dystonia, and involuntary movements preceded the spastic paraparesis.ConclusionsOur study further broadens the clinical spectrum associated with ATP13A2 mutations.

Silver syndrome (SS) is a complicated form of hereditary spastic paraplegia associated with distal wasting of the small muscles of the hands. We have previously described a large kindred with SS and mapped a genetic locus (SPG17) to chromosome 11q12-q14. In the current study we analyse the clinical phenotype and perform linkage analysis in three new SS families. In addition we analyse candidate genes mapping to the SS locus (SPG17). Clinical assessments were performed on 25 (15 affected) individuals from each family in which SS segregates with variable clinical expression. Neurophysiological studies, performed in the index case of two families, suggested anterior horn cell or nerve root involvement. Linkage analysis using microsatellite markers mapping to the SPG17 locus was performed and only one of the three families had a microsatellite segregation pattern compatible with linkage. Candidate genes mapping to the SS critical region were analysed in this and one other SPG17-linked family. Mutation analysis of genes encoding calpain 1 ( CAPN1), copper chaperone for superoxide dismutase ( CCS), ADP ribosylation factor-like 2 ( ARL2), LOC120664, a putative homologue of atlastin ( ATLSTL-1) and sorting nexin 15 ( SNX15) failed to identify any disease-specific mutations. SS therefore exhibits both clinical and genetic heterogeneity and the SPG17 locus may account for a significant proportion of SS mutations in the UK.

Hereditary spastic paraplegias (HSP) share as cardinal feature progressive spastic gait disorder. SPG4 accounts for about 25% of cases and is caused by mutations in the SPAST gene. Although HSP is an upper motor neuron disease, the relevance of non-motor symptoms is increasingly recognized because of the potential response to treatment. Our study sets out to evaluate non-motor symptoms and their relevance with regard to health-related quality of life. In 118 genetically confirmed SPG4 cases and age- and gender-matched controls, validated questionnaires were used to evaluate fatigue, depression, pain, and restless legs syndrome. In addition, self-reported medical information was collected concerning comorbidities and bladder, bowel, and sexual dysfunction. In a sub-study, cognition was evaluated using the CANTAB® test-battery and the Montreal Cognitive Assessment in 26 SPG4 patients. We found depression and pain to be significantly increased. The frequency of restless legs syndrome varied largely depending on defining criteria. There were no significant deficits in cognition as examined by CANTAB® despite a significant increase in self-reported memory impairment in SPG4 patients. Bladder, sexual, and defecation problems were frequent and seemed to be underrecognized in current treatment strategies. All identified non-motor symptoms correlated with health-related quality of life, which was reduced in SPG4 compared to controls. We recommend that clinicians regularly screen for depression, pain, and fatigue and ask for bladder, sexual, and defecation problems to recognize and treat non-motor symptoms accordingly to improve quality of life in patients with SPG4.

Hereditary spastic paraplegias (HSP) are a group of inherited, neurodegenerative disorders characterized by progressive gait impairment, lower extremity spasticity and increased patellar reflexes. More than 80 types of HSP have been defined to date. In complicated forms, lower limb spasticity and gait impairment is accompanied by an additional neurological finding. Autosomal recessive (AR) HSPs are usually identified in complicated forms and occur more frequently in countries where consanguineous marriage is more widespread. Next generation sequencing techniques, developed in the last decade, have led to the identification of many new types of HSP and reduced the "diagnostic odyssey." Whole exome sequencing (WES) can diagnose up to 75% of undiagnosed HSP patients. Targeted genetic analysis with good clinical phenotyping gives the best diagnostic yields for rare diseases. Clinical heterogeneity is prominent in AR complicated HSP. However, some clinical features complicating the disease or magnetic resonance imaging findings, including thin corpus callosumor white matter abnormalities, can help to distinguish some types. AR spastic paraplegia type 64 (SPG64) is a very rare HSP, caused by a mutation in the ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1) gene, first described in 2014. To date only nine patients from five families have been reported. We present two siblings with a novel pathogenic variant in ENTPD1, diagnosed by WES, as the sixth published family. We propose that early onset in childhood, cognitive impairment, dysarthria/anarthria, dystonia and areflexia may be the distinctive features of SPG64 and more clinical evidence from families with pathogenic ENTPD1 variants is warranted.

Spastic paraplegia type 4: A novel SPAST splice site donor mutation and expansion of the phenotype variability