Expanding the clinical phenotype of CAPN1-associated mutations: A new case with congenital-onset pure spastic paraplegia

White matter abnormalities in 15 subjects with SPG76

BACKGROUND AND OBJECTIVES

Hereditary spastic paraplegias (HSPs) are heterogenous genetic disorders characterized by progressive pyramidal tract involvement. SPG76 is a recently identified form of HSP, caused by biallelic calpain-1 (CAPN1) variants. The most frequently described MRI abnormality in SPG76 is mild cerebellar atrophy and non-specific white matter abnormalities were reported in only one case. Following the identification of prominent white matter abnormalities in a subject with CAPN1 variants, which delayed the diagnosis, we aimed to verify the presence of MRI patterns of white matter involvement specific to this HSP.

METHODS

We performed a retrospective radiological qualitative analysis of 15 subjects with SPG76 (4 previously unreported) initially screened for white matter involvement. Moreover, we performed quantitative analyses in our proband with available longitudinal studies.

RESULTS

We observed bilateral, periventricular white matter involvement in 12 subjects (80%), associated with multifocal subcortical abnormalities in 5 of them (33.3%). Three subjects (20%) presented only multifocal subcortical involvement. Longitudinal quantitative analyses of our proband revealed increase in multifocal white matter lesion count and increased area of periventricular white matter involvement over time.

DISCUSSION

SPG76 should be added to the list of HSPs with associated white matter abnormalities. We identified periventricular white matter involvement in subjects with SPG76, variably associated with multifocal subcortical white matter abnormalities. These findings, in the presence of progressive spastic paraparesis, can mislead the diagnostic process towards an acquired white matter disorder.

Spastic paraplegia type 76 due to novel CAPN1 mutations: three case reports with literature review

Spastic paraplegia type 76 (SPG76) is a subtype of hereditary spastic paraplegia (HSP) caused by calpain-1 (CAPN1) mutations. Our study described the phenotypic and genetic characteristics of three families with spastic ataxia due to various CAPN1 mutations and further explored the pathogenesis of the two novel mutations. The three patients were 48, 39, and 48 years old, respectively. Patients 1 and 3 were from consanguineous families, while patient 2 was sporadic. Physical examination showed hypertonia, hyperreflexia, and Babinski signs in the lower limbs. Patients 2 and 3 additionally had dysarthria and depression. CAPN1 mutations were identified by whole-exome sequencing, followed by Sanger sequencing and co-segregation analysis within the family. Functional examination of the newly identified mutations was further explored. Two homozygous mutations were detected in patient 1 (c.213dupG, p.D72Gfs*95) and patient 3 (c.1729+1G>A) with HSP, respectively. Patient 2 had compound heterozygous mutations c.853C>T (p.R285X) and c.1324G>A (p.G442S). Western blotting revealed the p.D72Gfs*95 with a smaller molecular weight than WT and p.G442S. In vitro, the wild-type calpain-1 is mostly located in the cytoplasm and colocalized with tubulin by immunostaining. However, p.D72Gfs*95 and p.G442S abnormally formed intracellular aggregation, with little colocalization with tubulin. In this study, we identified three cases with SPG76, due to four various CAPN1 mutations, presenting lower limb spasticity and ataxia, with or without bulbar involvement and emotional disorder. Among these, c.213dupG and c.1324G>A are first identified in this paper. The genotype-phenotype correlation of the SPG76 cases reported worldwide was further summarized.

Novel CAPN1 missense variants in complex hereditary spastic paraplegia with early-onset psychosis

CAPN1-associated hereditary spastic paraplegia (SPG76) is a rare and clinically heterogenous syndrome due to loss of calpain-1 function. Here we illustrate a translational approach to the case of an 18-year-old patient who first presented with psychiatric symptoms followed by spastic gait, intention tremor, and neurogenic bladder dysfunction, consistent with a complex form of HSP. Exome sequencing showed compound-heterozygous missense variants in CAPN1 (NM_001198868.2: c.1712A>G (p.Asn571Ser)/c.1991C>T (p.Ser664Leu)) and a previously reported heterozygous stop-gain variant in RCL1. In silico analyses of the CAPN1 variants predicted a deleterious effect and in vitro functional studies confirmed reduced calpain-1 activity and dysregulated downstream signaling. These findings support a diagnosis of SPG76 and highlight that the psychiatric symptoms can precede the motor symptoms in HSP. Our results also suggest that multiple genes can potentially contribute to complex neuropsychiatric diseases.

Calpains for dummies: What you need to know about the calpain family

This review was written in memory of our late friend, Dr. Hiroyuki Sorimachi, who, following the steps of his mentor Koichi Suzuki, a pioneer in calpain research, has made tremendous contributions to the field. During his career, Hiro also wrote several reviews on calpain, the last of which, published in 2016, was comprehensive. In this manuscript, we decided to put together a review with the basic information a novice may need to know about calpains. We also tried to avoid similarities with previous reviews and reported the most significant new findings, at the same time highlighting Hiro's contributions to the field. The review will cover a short history of calpain discovery, the presentation of the family, the life of calpain from transcription to activity, human diseases caused by calpain mutations and therapeutic perspectives.

Increasing involvement of CAPN1 variants in spastic ataxias and phenotype-genotype correlations

Spastic ataxias are rare neurogenetic disorders involving spinocerebellar and pyramidal tracts. Many genes are involved. Among them, CAPN1, when mutated, is responsible for a complex inherited form of spastic paraplegia (SPG76). We report the largest published series of 21 novel patients with nine new CAPN1 disease-causing variants and their clinical characteristics from two European university hospitals (Paris and Stockholm). After a formal clinical examination, causative variants were identified by next-generation sequencing and confirmed by Sanger sequencing. CAPN1 variants are a rare cause (~ 1.4%) of young-adult-onset spastic ataxia; however, together with all published cases, they allowed us to better describe the clinical and genetic spectra of this form. Truncating variants are the most frequent, and missense variants lead to earlier age at onset in favor of an additional deleterious effect. Cerebellar ataxia with cerebellar atrophy, dysarthria and lower limb weakness are often associated with spasticity. We also suggest that cognitive impairment and depression should be assessed specifically in the follow-up of SPG76 cases.

RCL1 copy number variants are associated with a range of neuropsychiatric phenotypes

Mendelian and early-onset severe psychiatric phenotypes often involve genetic variants having a large effect, offering opportunities for genetic discoveries and early therapeutic interventions. Here, the index case is an 18-year-old boy, who at 14 years of age had a decline in cognitive functioning over the course of a year and subsequently presented with catatonia, auditory and visual hallucinations, paranoia, aggression, mood dysregulation, and disorganized thoughts. Exome sequencing revealed a stop-gain mutation in RCL1 (NM_005772.4:c.370 C > T, p.Gln124Ter), encoding an RNA 3'-terminal phosphate cyclase-like protein that is highly conserved across eukaryotic species. Subsequent investigations across two academic medical centers identified eleven additional cases of RCL1 copy number variations (CNVs) with varying neurodevelopmental or psychiatric phenotypes. These findings suggest that dosage variation of RCL1 contributes to a range of neurological and clinical phenotypes.

Novel CAPN1 mutations extend the phenotypic heterogeneity in combined spastic paraplegia and ataxia

OBJECTIVE

Recessive mutations in the CAPN1 gene have recently been identified in spastic paraplegia 76 (SPG76), a complex hereditary spastic paraplegia (HSP) that is combined with cerebellar ataxia, resulting in an ataxia-spasticity disease spectrum. This study aims to assess the influence of CAPN1 variants on the occurrence of SPG76 and identify factors potentially contributing to phenotypic heterogeneity.

METHODS

We screened a cohort of 240 unrelated HSP families for variants in CAPN1 using high-throughput sequencing analysis. We described in detail the clinical and genetic features of the SPG76 patients in our cohort and summarized all reported cases.

RESULTS

Six unreported CAPN1-associated families containing eight patients with or without cerebellar ataxia were found in our cohort of HSP cases. These patients carried three previously reported homozygous truncating mutations (p.V64Gfs^* 103, c.759+1G>A, and p.R285^* ), and three additional novel compound heterozygous missense mutations (p.R481Q, p.P498L, and p.R618W). Lower limbs spasticity, hyperreflexia, and Babinski signs developed in about 94% of patients, with ataxia developing in 63% of cases. In total, 33 pathogenic mutations were distributed along the three reported functional domains of calpain-1 protein, encoded by CAPN1, with no hotspot region. A comparison of gender distribution between the two groups indicated that female SPG76 patients were significantly more likely to present with complicated HSP than male patients (P = 0.015).

INTERPRETATION

Our study supports the clinically heterogeneous inter- and intra-family variability of SPG76 patients, and demonstrates that gender and calpain-1 linker structure may contribute to clinical heterogeneity in SPG76 cases.

CAPN1 and hereditary spastic paraplegia: a novel variant in an Iranian family and overview of the genotype-phenotype correlation

PURPOSE

SPG76 is one of the rare forms of hereditary spastic paraplegia (HSP) which causes by mutations in the CAPN1 gene. The mode of inheritance of SPG76 is autosomal recessive (AR) and so far, only 24 families and 25 mutations in this gene have been reported worldwide. These mutations have been associated with a spectrum of disorders from pure HSP to spastic ataxia. HSP genetically is one of the most heterogeneous neurological disorders and to date, 79 types of HSP (SPG1-SPG79) have been identified, however, it has been suggested that many HSP-genes, particularly in AR-HSPs, remained unknown. AR-HSPs clinically overlap with other neurodegenerative disorders, making an accurate diagnosis of the disease difficult. Therefore, in addition to clinical examination, a high throughout genetic method like whole exome sequencing (WES) may be necessary for the diagnosis of this type of neurodegenerative disorders.

METHODS AND RESULTS

Herein, we present the clinical features and results of WES in the first Iranian family with a novel CAPN1 variant, c.C853T:p.R285* and pure HSP.

CONCLUSION

Some of the previous studies have mentioned that the "spasticity-ataxia phenotype might be conducted to the diagnosis of SPG76" but recently the number of pure HSP patients with CAPN1 mutation is increasing. The present study also expands the mutation spectrum of pure CAPN1-related SPG76; emphasizing that CAPN1 screening is required in both pure HSP and spasticity-ataxia phenotypes. As noted in some other literature, we suggest the clinical spectrum of this disorder to be considered as "CAPN1-associated neurodegeneration".

Mutation analysis of CAPN1 in Chinese populations with spastic paraplegia and related neurodegenerative diseases

BACKGROUND

Mutations in CAPN1 have recently been reported to cause the spastic paraplegia 76 (SPG76) subtype of hereditary spastic paraplegia (HSP). To investigate the role of CAPN1 in spastic paraplegia and other neurodegenerative diseases, including spinocerebellar ataxia (SCA), early-onset Parkinson's disease (EOPD), and amyotrophic lateral sclerosis (ALS) we conducted a mutation analysis of CAPN1 in a cohort of Chinese patients with SPG, SCA, EOPD, and ALS.

METHODS

Variants of CAPN1 were detected in the three cohorts by Sanger or whole-exome sequencing, and all exons and exon-intron boundaries of CAPN1 were analysed.

RESULTS

A novel CAPN1 splicing variant (NM_001198868: c.338-1G > A) identified in a familial SPG/SCA showed a complex phenotype, including spastic paraplegia, ataxia, and extensor plantar response. This mutation was confirmed by Sanger sequencing and completely co-segregated with the phenotypes. Sequencing of the cDNA from the three affected patients detected a guanine deletion (c.340_340delG) that was predicted to result in an early stop codon after 61 amino acids (p. D114Tfs*62). No CAPN1 pathogenic mutation was found in the EOPD or ALS groups.

CONCLUSION

Our data reveal a novel CAPN1 mutation found in patients with SPG/SCA and emphasize the spastic and ataxic phenotypes of SPG76, but CAPN1 may not play a major role in EOPD and ALS.

Clinical features and genetic spectrum in Chinese patients with recessive hereditary spastic paraplegia

BACKGROUND

Although many causative genes of hereditary spastic paraplegia (HSP) have been uncovered in recent years, there are still approximately 50% of HSP patients without genetically diagnosis, especially in autosomal recessive (AR) HSP patients. Rare studies have been performed to determine the genetic spectrum and clinical profiles of recessive HSP patients in the Chinese population.

METHODS

In this study, we investigated 24 Chinese index AR/sporadic patients by targeted next-generation sequencing (NGS), Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA). Further functional studies were performed to identify pathogenicity of those uncertain significance variants.

RESULTS

We identified 11 mutations in HSP related genes including 7 novel mutations, including two (p.V1979_L1980delinsX, p.F2343 fs) in SPG11, two (p.T55 M, p.S308 T) in AP5Z1, one (p.S242 N) in ALDH18A1, one (p.D597fs) in GBA2, and one (p.Q486X) in ATP13A2 in 8 index patients and their family members. Mutations in ALDH18A1, AP5Z1, CAPN1 and ATP13A2 genes were firstly reported in the Chinese population. Furthermore, the clinical phenotypes of the patients carrying mutations were described in detail. The mutation (p.S242 N) in ALDH18A1 decreased enzyme activity of P5CS and mutations (p.T55 M, p.S308 T) in AP5Z1 induced lysosomal dysfunction.

CONCLUSION

Our results expanded the genetic spectrum and clinical profiles of AR-HSP patients and further demonstrated the efficiency and reliability of targeted NGS diagnosing suspected HSP patients.

A Novel CAPN1 Mutation Causes a Pure Hereditary Spastic Paraplegia in an Italian Family

CAPN1 encodes calpain-1, a large subunit of μ-calpain, a calcium-activated cysteine protease widely present in the central nervous system. Mutations in CAPN1 have recently been identified in a complicated form of Hereditary Spastic Paraplegia (HSP) with a combination of cerebellar ataxia and corticomotor tract disorder (SPG76). Therefore, CAPN1 is now considered one of those genes that clinically manifest with a spectrum of disorders ranging from spasticity to cerebellar ataxia and represent a link between Spinocerebellar Ataxia and HSP, two groups of diseases previously considered separate but sharing pathophysiological pathways. We here describe clinical and molecular findings of two Italian adult siblings affected with a pure form of HSP and harboring the novel homozygote c.959delA variant (p.Tyr320Leufs^*73) in the CAPN1 gene. Although the reason why mutations in CAPN1 may cause heterogeneous clinical pictures remains speculative, our findings confirm that the spectrum of the CAPN1-linked phenotypes includes pure HSP with onset during the third decade of life. Further studies are warrantied in order to clarify the mechanism underlying the differences in CAPN1 mutation clinical expression.

Two novel homozygous mutations of CAPN1 in Chinese patients with hereditary spastic paraplegia and literatures review

BACKGROUND

Hereditary spastic paraplegias (HSP) are of great clinical and genetic heterogeneity. According to the clinical features, HSP can be divided into pure or complicated subtypes which combined with other neurological symptoms including cerebellar ataxia. Up to date, 78 loci or genes have been implicated in HSP. CAPN1 was a novel gene detected recently for spastic paraplegia 76 (SPG76).

METHODS

Patients referred to our clinic with spastic or spastic-ataxic gait were collected. Genetic testing of the probands were performed by target sequencing of a panel containing over 4000 known virulence genes. And the candidate mutations were further confirmed by polymerase chain reaction (PCR) and Sanger sequencing. The clinical materials of these patients were demonstrated retrospectively.

RESULTS

Two Chinese patients, both from consanguineous families, each carried a novel homozygous mutation of CAPN1, p.R48X and p.R339X. The male proband presented pure HSP subtype while the female proband presented complicated HSP symptoms with cerebellar ataxia. We then reviewed all the literatures of HSP patients carrying CAPN1 mutations and summarized the molecular spectrum and clinical characteristics of CAPN1-related SPG76.

CONCLUSION

These two SPG76 patients carrying CAPN1 mutations were the first reported in China. By reviewing the clinical manifestations of SPG76 patients, we validated the "spastic-ataxia" phenotype and emphasized the association between spasticity and ataxia, indicating the importance of CAPN1 screening in HSP patients.