OBJECTIVE: To describe a case of hereditary spastic ataxia (HSP) presenting with childhood optic nerve atrophy and report a novel homozygous variant in the SPG7 gene.
METHODS: A 57-year-old man suffering from progressive optic nerve atrophy since childhood eventually underwent genetic testing. A targeted whole exome gene sequencing panel for optic neuropathy identified a novel homozygous variant in the SPG7 gene, c.2T > G, p.(Met?), which likely abolished production of paraplegin, an inner mitochondrial membrane protein. Subsequent neurologic examination revealed subtle signs of spastic paraplegia and ataxia in keeping with the genetic diagnosis of SPG7.
CONCLUSIONS: Spastic paraplegia 7 (SPG7) is an autosomal recessive form of the neurodegenerative disorder HSP. Pure HSP is characterized by spastic paraparesis in the lower limbs, whereas complicated HSP presents additional neurological manifestations. This case report adds to the evidence that SPG7 can present with childhood optic nerve atrophy, preceding the characteristic SPG7 manifestations. SPG7 should be considered in the workup of suspected hereditary optic neuropathy.

Primary lateral sclerosis (PLS) is considered a rare variant of motor neuron disease (MND) characterized by selective upper motor neuron dysfunction leading to limb weakness, spasticity, and even bulbar symptoms. Previous studies have demonstrated that mutations in ALSIN, spastic paraplegia 7 (SPG7), TBK1, ALS2, ERLIN2, and FIG4 are responsible for PLS. Most of them occurred in childhood to young-adult onset patients. The aim of this study was to identify the genetic lesion of patients with adult-onset PLS.
We applied whole-exome sequencing (WES) and MND and ataxia-related genes filtering strategies to discover the genetic factors in a Chinese adult-onset PLS family. Sanger sequencing was used in the cosegregation analysis in the affected family members.
A mutation (c.2219A>G/p.Y740C) in exon 17 of SPG7 was identified in an adult-onset PLS patient and cosegregated with the affected members in this family. Meanwhile, the mutation was predicted to be deleterious by 3 bioinformatics programs (Polymorphism phenotyping-2, sorting intolerant from tolerant and MutationTaster). This variant may cause the structure changes of paraplegin protein.
We employed WES to detect a missense mutation of SPG7 gene in a PLS family. This finding expands the spectrum of known SPG7 mutations, and it may contribute to novel approaches to genetic diagnosis and counseling of families with PLS.

The mitochondrial matrix ATPase associated with diverse cellular activities (m-AAA) protease spastic paraplegia 7 (SPG7) has been recently implicated as either a negative or positive regulatory component of the mitochondrial permeability transition pore (mPTP) by two research groups. To address this controversy, we investigated possible mechanisms that explain the discrepancies between these two studies. We found that loss of the SPG7 gene increased resistance to Ca2+-induced mPTP opening. However, this occurs independently of cyclophilin D (cyclosporine A insensitive) rather it is through decreased mitochondrial Ca2+ concentrations and subsequent adaptations mediated by impaired formation of functional mitochondrial Ca2+ uniporter complexes. We found that SPG7 directs the m-AAA complex to favor association with the mitochondrial Ca2+ uniporter (MCU) and MCU processing regulates higher order MCU-complex formation. The results suggest that SPG7 does not constitute a core component of the mPTP but can modulate mPTP through regulation of the basal mitochondrial Ca2+ concentration.

Hereditary spastic paraplegia is a group of clinically and genetically heterogeneous neurodegenerative disorders, often characterized by weakness and spasticity in the lower limbs. In our study, we describe a spastic paraplegia type 7 patient with an expanded phenotype who was diagnosed after the discovery of pathogenic variants in SPG7.