Compound heterozygous variants of the FBXO7 gene resulting in infantile-onset Parkinsonian-pyramidal syndrome in siblings of a Chinese family

Study of an FBXO7 patient mutation reveals Fbxo7 and PI31 co-regulate proteasomes and mitochondria

Mutations in FBXO7 have been discovered to be associated with an atypical parkinsonism. We report here a new homozygous missense mutation in a paediatric patient that causes an L250P substitution in the dimerisation domain of Fbxo7. This alteration selectively ablates the Fbxo7-PI31 interaction and causes a significant reduction in Fbxo7 and PI31 levels in patient cells. Consistent with their association with proteasomes, patient fibroblasts have reduced proteasome activity and proteasome subunits. We also show PI31 interacts with the MiD49/51 fission adaptor proteins, and unexpectedly, PI31 acts to facilitate SCFFbxo7 -mediated ubiquitination of MiD49. The L250P mutation reduces the SCFFbxo7 ligase-mediated ubiquitination of a subset of its known substrates. Although MiD49/51 expression was reduced in patient cells, there was no effect on the mitochondrial network. However, patient cells show reduced levels of mitochondrial function and mitophagy, higher levels of ROS and are less viable under stress. Our study demonstrates that Fbxo7 and PI31 regulate proteasomes and mitochondria and reveals a new function for PI31 in enhancing the SCFFbxo7 E3 ubiquitin ligase activity.

Loss of the parkinsonism-associated protein FBXO7 in glutamatergic forebrain neurons in mice leads to abnormal motor behavior and synaptic defects

Mutations in PARK15, which encodes for the F-box protein FBXO7 have been associated with Parkinsonian Pyramidal syndrome, a rare and complex movement disorder with Parkinsonian symptoms, pyramidal tract signs and juvenile onset. Our previous study showed that systemic loss of Fbxo7 in mice causes motor defects and premature death. We have also demonstrated that FBXO7 has a crucial role in neurons as the specific deletion in tyrosine hydroxylase-positive or glutamatergic forebrain neurons leads to late-onset or early-onset motor dysfunction, respectively. In this study, we examined NEX-Cre;Fbxo7fl/fl mice, in which Fbxo7 was specifically deleted in glutamatergic projection neurons. The effects of FBXO7 deficiency on striatal integrity were investigated with HPLC and histological analyses. NEX-Cre;Fbxo7fl/fl mice revealed an increase in striatal dopamine concentrations, changes in the glutamatergic, GABAergic and dopaminergic pathways, astrogliosis and microgliosis and little or no neuronal loss in the striatum. To determine the effects on the integrity of the synapse, we purified synaptic membranes, subjected them to quantitative mass spectrometry analysis and found alterations in the complement system, endocytosis and exocytosis pathways. These neuropathological changes coincide with alterations in spontaneous home cage behavior. Taken together, our findings suggest that FBXO7 is crucial for corticostriatal projections and the synaptic integrity of the striatum, and consequently for proper motor control.

The Genetics of Parkinson's Disease and Implications for Clinical Practice

The genetic landscape of Parkinson’s disease (PD) is characterised by rare high penetrance pathogenic variants causing familial disease, genetic risk factor variants driving PD risk in a significant minority in PD cases and high frequency, low penetrance variants, which contribute a small increase of the risk of developing sporadic PD. This knowledge has the potential to have a major impact in the clinical care of people with PD. We summarise these genetic influences and discuss the implications for therapeutics and clinical trial design.

A novel FBXO7-R345P mutation in a Chinese family with autosomal recessive parkinsonian-pyramidal syndrome

BACKGROUND

Mutations in the F-box protein 7 (FBXO7) gene is one of the genetic causes of early-onset Parkinson's disease, which usually presents as autosomal recessive early-onset parkinsonian-pyramidal syndrome (PPS). Herein, we report a Chinese PPS family with a novel FBXO7 homozygous mutation.

METHODS

Clinical data of the proband and his affected sister manifesting as early-onset parkinsonism combined with pyramidal signs were collected. DNAs of the two affected siblings, an unaffected sibling and their unaffected mother were isolated. Whole-exome sequencing (WES) was performed for the proband. After bioinformatic analysis, targeted variants were validated by Sanger sequencing in the family members available for DNAs.

RESULTS

The proband began to walk unsteadily at 30-year-old and developed mild parkinsonism and stiffness in both lower extremities 4 years later. His older sister also manifested as early-onset parkinsonism with stiffness in both lower limbs and postural instability. Both the proband and his older sister carried a novel homozygous FBXO7 mutation in exon 7 (c.1034G > C, p. R345P). The homozygous mutation co-segregated with disease in this pedigree. The mutation located at a highly conserved amino acid residue in the F-box domain, which was predicted to be damaging in silico.

CONCLUSIONS

Our study expands the mutational spectrum of autosomal recessive early-onset Parkinson's disease (PARK15) caused by FBXO7 mutations.

Mutation analysis of TCOF1 gene in Chinese Treacher Collins syndrome patients

Background

Treacher Collins syndrome (TCS) is a rare autosomal dominant or recessive disorder, that involves unique bilateral craniofacial malformations. The phenotypes of TCS are extremely diverse. Interventional surgery can improve hearing loss and facial deformity in TCS patients.

Method

We recruited seven TCS families. Variant screening in probands was performed by targeted next‐generation sequencing (NGS). The variants identified were confirmed by Sanger sequencing. The pathogenicity of all the mutations was evaluated using the guidelines of the American College of Medical Genetics and Genomics (ACMG) and InterVar software.

Results

Three frameshift variants, two nonsense variants, one missense variant, and one splicing variant of TCOF1 were identified in the seven TCS probands. Five variants including c.1393C > T, c.4111 + 5G>C, c.1142delC, c.2285_2286delCT, and c.1719delG had not been previously reported. Furthermore, we report the c.149A > G variant for the first time in a Chinese TCS patient. We provided prenatal diagnosis for family 4. Proband 7 chose interventional surgery.

Conclusion

We identified five novel variants in TCOF1 in Chinese patients with TCS, which expands the mutation spectrum of TCOF1 in TCS. Bone conduction hearing rehabilitation can improve hearing for TCS patients and prenatal diagnosis can provide fertility guidance for TCS families.

Compound heterozygous variants of the FBXO7 gene resulting in infantile-onset Parkinsonian-pyramidal syndrome in siblings of a Chinese family

Background

Mutations in the FBXO7 gene can cause a rare chromosomal recessive neurodegenerative disease, Parkinsonian‐pyramidal syndrome (PPS). Patients with this syndrome mainly show early‐onset Parkinson's syndrome. Here, we present a Chinese family with infantile‐onset PPS caused by FBXO7 mutations.

Methods

The clinical phenotypes and medical records of the proband and his family members were collected. The proband, his sibling, and his parents underwent whole‐exome sequencing (WES) by next‐generation sequencing.

Results

The proband and his sibling had a typical PPS phenotype with onset during infancy. WES identified compound heterozygous variants in the FBXO7 gene, including a nonsense mutation, p. Trp134*, and a splicing mutation, IVS5‐1G > A, which were shared by both siblings and inherited from each of the parents. These variants have not been reported in literatures or databases. According to the American College of Medical Genetics and Genomics guidelines, the p. Trp134* and IVS5‐1G > A mutations were classified as pathogenic variants.

Conclusions

We report a case of siblings in a Chinese family with infantile‐onset PPS caused by FBXO7 gene mutations determined by WES. These findings will contribute to the in‐depth study of the pathogenesis of PPS among patients with FBXO7 gene mutations.