A PARK7 Mutation‐Induced Early‐Onset Parkinson's Disease in a Moroccan Family: Expanding the Geographic Spectrum

Abstract

Background

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and nonmotor symptoms, with a significant genetic component. Early‐onset Parkinson's disease (EOPD), manifesting before age 45, is often linked to mutations in genes such as PARK2, PINK1, and PARK7, the latter coding for the protein DJ‐1.

Objective

We present the first reported cases of EOPD carrying a previously undescribed homozygous PARK7 mutation, p.Thr110Pro.

Methods

Whole exom sequencing was performed on two inbred Moroccan siblings with early‐onset Parkinson's disease (EOPD). Detailed clinical assessments, including neurological evaluations and cognitive testing, were conducted to understand the clinical presentation of the patients. Genetic analysis was also carried out to examine their genetic background. Therapeutic responses to treatments were monitored to assess the effectiveness of management strategies.

Results

The sequencing revealed that both siblings carried the homozygous PARK7 mutation, p.Thr110Pro. Both siblings presented with typical EOPD features, including motor and non‐motor symptoms. The patients both presented with cognitive impairment, with the male sibling exhibiting more pronounced symptoms. He also developed compulsive behaviors, which underscore the varied clinical presentations and therapeutic responses associated with this genetic variant.

Conclusion

This case study expands the genetic and geographic diversity of PD presentations, highlighting cognitive and behavioral challenges and variable therapeutic outcomes. It underscores the necessity for genetic screening and individualized management strategies for patients with PD.

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by a blend of motor and nonmotor symptoms, with a prominent genetic component. ¹ Although typically affecting people over 65 years of age, PD can also manifest in younger individuals. When symptoms emerge before the age of 45, it is classified as early‐onset Parkinson's disease (EOPD), whereas the onset of motor symptoms before the age of 21 is defined as juvenile PD. ¹ Combined, the prevalence of EOPD and juvenile PD is estimated to range between 5% and 15%. ² Up to 10% of patients with EOPD carry a major genetic component, which plays a pivotal role in the onset and progression of this disease. ³ Key genes are associated with this form, including PARKIN (PARK2), PINK1, and PARK7, with PARK7 specifically coding for the protein DJ‐1. ¹ Each gene is linked to distinct phenotypes, clinical characteristics, and varying responses to treatment. ⁴ PARKIN is the most common autosomal recessive mutated gene found in EOPD, accounting for approximately 50% of familial cases and 20% of apparently isolated cases. ⁴ PINK1 follows as the second most common mutated gene, with a prevalence of 4.26% in familial cases and between 0.5% and 1.2% in sporadic PD. ⁴ , ⁵ DJ‐1 is highly expressed in cells with important energy demands and plays a crucial role in protecting cells from oxidative stress, acting as a chaperone with protease activity and supporting cellular homeostasis. ⁶ Although DJ‐1's function is critical for cell survival, mutations in PARK7 are among the least common genetic causes of EOPD, with an estimated prevalence of 0.4% to 1%, and 20 causative variants have been identified so far. ⁶ , ⁷ This paper presents 2 inbred Moroccan siblings of Moroccan origin with EOPD associated with an undescribed homozygous PARK7 mutation. This marks the first reported instance of this genetic mutation in Morocco and potentially on the African continent.

Patients and Methods

Exome Sequencing and Analyses

Whole exome sequencing (WES) was performed at the ICM IGenSeq core facility. Exons were captured using the Twist Refseq kit, followed by a massively parallel sequencing on the NovaSeq system (Paris, France, Illumina). Read alignment and variant calling were performed using an in‐house pipeline. Briefly, FastQC was used to check the quality of the reads, and low‐quality reads were removed using Trimmomatic. Sequencing data were then aligned to the human reference genome hg19 using the bwa suite, ⁸ and variant calling was performed using GATK HaplotypeCaller ⁹ or Dragen (Illumina). Variants in genes of interest were extracted using the graphical interface developed in‐house. WES data were then analyzed using VaraFT software. ¹⁰ For nuclear families, we filtered out all homozygous variants that possibly affected the cDNA or localized in the splice site region (−8 + 11 bp from exon/intron junction), with a minor allele frequency <1% in the gnomAD public database and were in heterozygous state in available parents.

Three‐Dimensional Structural Modeling of DJ‐1 and Predicted Impact of the Mutation

DJ‐1 three‐dimensional (3D) protein structure was downloaded from Uniprot using the structure predicted by AlphaFold ¹¹ (Q99497). Then, the impact of the mutation was predicted using DynaMut2 ¹² and PremPS. ¹³

3D Structural Interaction of DJ‐1 with O‐Acetaldehydyl‐Hexaethylene Glycol

The structural interaction of DJ‐1 with one of its substrates, O‐acetaldehydyl‐hexaethylene, was studied on AlphaFold using the uniport sequence Q99497 and the ligand P4C.

Results

Two siblings, Z.H. (a 32‐year‐old woman) and Z.A. (a 30‐year‐old man), from Taza, Morocco, were diagnosed with EOPD. WES analyses of the affected siblings and their parents revealed a novel variant (Chr1: g.8037717A > C; c.328A > C; p.Thr110Pro) in the PARK7 gene, which was homozygous in the affected siblings and heterozygous in both parents (Fig. 1A). This variant is extremely rare, with an allele frequency of 1.24e‐6 in the Genome Aggregation Database (GnomAD) and is not listed in ClinVar. Located in a mutational hot spot, it was predicted to be deleterious by 14 of 17 DNA variant effect prediction tools, including PolyPhen2 (score = 0.994), SIFT (score = 0.00), MutationTaster (deleterious), CADD (Phred = 27.6), and Revel (score = 0.883). The p.Thr110 residue affects a highly conserved amino acid (up to Drosophila) (Fig. 1B). The variant is predicted to destabilize protein structure according to Dynamut2 and PremPS (Fig. 1C,D) and to interfere with ligand interactions, such as FO‐acetaldehydyl‐hexaethylene glycol (Fig. 1E). The affected siblings and the family member tested negative for the LRRK2 G2019S mutation, commonly observed among Moroccan and other North African PD patients ¹⁴ as well as GBA1 mutation. In addition, no pathogenic variants were identified in any of the other genes known to be associated with PD/parkinsonism or any genes related to other motor disorders (see the list in Table S1).

FIG. 1.

Segregation and localization of the DJ‐1 p.Thr110Pro mutation. (A) Segregation of the DJ‐1 mutation in the Moroccan family. Both patients are homozygous for the p.Thr110Pro mutation, and their unaffected parents are heterozygous for this mutation. (B) DJ‐1 amino acid conservation at position Thr110 showing a high conservation across species. Protein sequences were downloaded from http://www.ensembl.org and aligned using the msa R package, https://github.com/UBod/msa. (C) Prediction of the wild‐type DJ‐1 structure and amino acid interaction, obtained using PremPS. (D) Prediction of the mutated DJ‐1 structure due to the p.Thr110Pro mutation and amino acid interactions, obtained using PremPS. Predicted interactions are greatly modified compared to the wild‐type DJ‐1 (ΔΔG^Stability = 0.77 kcal/mol). (E) Predicted interaction of DJ‐1 with O‐acetaldehydyl‐hexaethylene glycol obtained using AlphaFold (Uniprot: Q99497, ligand P4C). The Thr110 amino acid in red is involved in the binding of DJ‐1 to this ligand. We can therefore assume that the change in amino acid at this position can modify the binding of DJ‐1 to this ligand. AO, age at onset; M, mutated; +, wild type.

Z.H. exhibited symptoms at the age of 27, whereas Z.A. began experiencing motor symptoms at 23. Consanguinity was evident in the family history, with both parents identified as carriers of a heterozygous mutation in the PARK7 gene. The 2 affected siblings were homozygous for this mutation, whereas the other 4 unaffected siblings exhibited no motor or nonmotor symptoms, and their clinical examinations were unremarkable. However, their DNA samples were not available for analysis.

During clinical examination, conducted in the off period, and shown in the accompanying video (Video 1), the male sibling, then aged 30, exhibited a tremor‐dominant type, whereas the sister, then aged 32, presented with a mixed type of PD. Additionally, they both experienced dyskinesias and motor fluctuations, common complications of levodopa (l‐dopa) therapy they had been taking for 3 years for Z.H. and 6 years for Z.A. Patient examination did not show any motor neuron abnormalities, and the same video captures other clinical features of the patients in the on period. Neuroimaging studies demonstrated no abnormalities. Both patients exhibited a favorable response to l‐dopa therapy, with Z.H. receiving a daily equivalent of 800 mg and Z.A. receiving 300 mg of l‐dopa, both alongside an Artane prescription. l‐Dopa was well tolerated by Z.H. and was introduced 2 years after she began treatment with a dopamine agonist. In contrast, Z.A., her brother, started l‐dopa only after 1 year of agonist therapy due to a poor tolerance. During dopamine agonist treatment, Z.A. developed compulsive sexual behaviors, including nonparaphilic behaviors such as excessive masturbation and paraphilic behaviors like exhibitionism. Additionally, Z.H. experienced mainly anxiety issues. No prodromal signs such as hyposmia or sleep disturbances were observed in either of them. Both siblings exhibited cognitive impairment, which was more pronounced in Z.A., the male sibling. Cognitive difficulties preceded the motor symptoms and were suggested by their academic struggles, leading them to drop out of middle school after failing several years at 14 years for Z.A. and 16 for Z.H., unlike their unaffected siblings who were able to attend university and pursue professional careers. The patients underwent the Montreal Cognitive Assessment (MoCA) test after a median of 4 years from the onset of symptoms, and their significantly altered scores indicated substantial cognitive decline; in fact Z.A. scored 16/30 on the MoCA, whereas Z.H. scored 24/30 (with a normal score being ≥26/30). Their frontal assessment battery (FAB) scores were 14/18 and 15/18, respectively (normal score ≥16/18). The Hoehn and Yahr staging was 2 for Z.H. and 3 for Z.A.

Video 1.

The video demonstrates the clinical examination of siblings Z.H. and Z.A. during an off period, followed by an on period.

Discussion

PARK7 mutations are a rare cause of autosomal recessive EOPD, ⁷ accounting for approximately 0.4% to 1% of cases. ¹⁵ Although previously described in families from China, ¹⁶ , ¹⁷ Iran, ¹⁸ , ¹⁹ , ²⁰ Iraq, ²¹ Turkey, ²² , ²³ and the United Kingdom, ¹⁵ this is the first reported occurrence in Morocco, and possibly within the African continent. The PARK7 gene encodes the DJ‐1 protein, which is highly expressed in cells experiencing oxidative stress or increased energy requirements. ²⁴ Mutated DJ‐1 protein can impair its chaperone function and its ability to protect cells from oxidative stress, potentially contributing to PD. ²⁵ As well, PARK7 is often overexpressed in different human cancers, reflecting its involvement in cellular responses to oxidative stress. ²⁶ In the testis, PARK7 expression correlates with fertility, with reduced levels associated with infertility. ²⁷ In a Turkish family, 3 patients exhibited a complex of parkinsonism, amyotrophic lateral Sclerosis (ALS), and dementia, all carrying homozygous p.Q45X mutations in PARK7 exon 3. ²³ , ²⁸ Similarly, an Italian family exhibited a similar triad, with 3 patients having homozygous E163K mutations in PARK7 exon 7 and homozygous g.168_185dup mutation in PARK7 promoter. ²⁹ This suggests a multifaceted role for DJ‐1 in cellular homeostasis, implicating its involvement in multiple pathological conditions, such as cancer, motor neuron diseases, and neurodegeneration.

The cognitive impairment was evident in the male sibling and to a lesser extent in his sister. In fact, individuals carrying PARK7 mutations exhibit higher frequencies of cognitive disorders compared to those with PARK2 or PINK1 mutations. ³⁰ In the male sibling of our presented cases, the cognitive decline even preceded motor signs, indicating the existence of potential genotype‐specific variations in disease presentation. Studies on PARK7 knockout mice support this, ³¹ indicating that the loss of DJ‐1 function is implicated in early cognitive symptoms of PD and other major nonmotor symptoms. This sheds light on why cognitive impairment appeared in our patients during their school years before motor symptoms. Additionally, dopamine agonists have been implicated in the development of compulsive sexual behavior among the male sibling, necessitating careful consideration of medication management and regular psychiatric assessment in PD patients.

This paper highlights the impact of a homozygous PARK7 mutation on EOPD within a Moroccan family, a rare occurrence in the African continent, with our report being the first identified case in Morocco and Africa. The presence of cognitive impairment and the development of compulsive behaviors underscore the varied clinical presentations associated with this genetic variant. It also adds a new geographic and genetic dimension to the diversity of PD presentations and treatment responses, emphasizing the importance of genetic screening. These findings stress the need for personalized and tailored management strategies for patients suffering from PD.

Author Roles

(1) Research project: A. Conception, B. Organization, C. Execution. (2) Statistical analysis: A. Design, B. Execution, C. Review and critique. (3) Manuscript preparation: A. Writing of the first draft, B. Review and critique.

H.E.O.: 1A, 2A, 3A

C.T.: 2B, 3B

A.B.: 2B, 3B

S.L.: 1A, 2A, 3B

Disclosures

Ethical Compliance Statement: This study was conducted in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed written consent was obtained from all family members who participated in this study, and permission was obtained from the patient, and the patient's guardian to take and publish the video. The genetic studies were approved by local ethics committees. All authors confirm that they have read the journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.

Funding Sources and Conflicts of Interest: No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work.

Financial Disclosures for the Previous 12 Months: The authors declare that there are no additional disclosures to report.

Consent

Written informed consent was obtained from the patients and their parents for publication.

Supporting information

Table S1. List of known genes associated with PD (Parkinson's disease)/parkinsonism or other motor disorders examined in this study.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.