The most common cause of the monogenic form of Parkinson’s disease known so far is the G2019S mutation of the leucine-rich repeat kinase 2 (LRRK2) gene. Its frequency varies greatly among ethnic groups and geographic regions ranging from less than 0.1% in Asia to 40% in North Africa. This mutation has three distinct haplotypes; haplotype 1 being the oldest and most common. Recent studies have dated haplotype 1 of the G2019S mutation to about 4000 years ago, but it remains controversial whether the mutation has a Near-Eastern or Moroccan-Berber ancestral origin. To decipher this evolutionary history, we genotyped 10 microsatellite markers spanning a region of 11.27 Mb in a total of 57 unrelated Moroccan PD patients carrying the G2019S mutation for which the Berber or Arab origin was established over 3 generations based on spoken language. We estimated the age of the most recent common ancestor for the 36 Arab-speaking and the 15 Berber-speaking G2019S carriers using the likelihood-based method with a mutation rate of 10−4. Data analysis suggests that the shortest haplotype originated in a patient of Berber ethnicity. The common founder was estimated to have lived 159 generations ago (95% CI 116–224) for Arab patients, and 200 generations ago (95% CI 123–348) for Berber patients. Then, 29 native North African males carrying the mutation were assessed for specific uniparental markers by sequencing the Y-chromosome (E-M81, E-M78, and M-267) and mitochondrial DNA (mtDNA) hypervariable regions (HV1 and HV2) to examine paternal and maternal contributions, respectively. Results showed that the autochthonous genetic component reached 76% for mtDNA (Eurasian and north African haplogroups) and 59% for the Y-chromosome (E-M81 and E-M78), suggesting that the G2019S mutation may have arisen in an autochthonous DNA pool. Therefore, we conclude that LRRK2 G2019S mutation most likely originated in a Berber founder who lived at least 5000 years ago (95% CI 3075–8700).

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Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer disease. Five to ten percent of patients have monogenic form of the disease, while most of sporadic PD cases are caused by the combination of genetic and environmental factors. Microtubule-associated protein tau (MAPT) has been appointed as one of the most important risk factors for several neurodegenerative diseases including PD. MAPT is characterized by an inversion in chromosome 17 resulting in two distinct haplotypes H1 and H2. Studies described a significant association of MAPT H1j subhaplotype with PD risk, while H2 haplotype was associated with Parkinsonism, particularly to its bradykinetic component. We report here an isolated case displaying an akinetic-rigid form of PD, with age of onset of 41 years and a good response to levodopa, who developed dementia gradually during the seven years of disease progression. The patient does not carry the LRRK2 G2019S mutation, copy number variations, nor pathogenic and rare variants in known genes associated with PD. MAPT subhaplotype genotyping revealed that the patient has the H1j/H2 diplotype, his mother H1j/H1j, his two healthy brothers H1j/H1v and his deceased father was by deduction H1v/H2. The H1j/H2 diplotype was shown in a total of 3 PD patients among 80, who also did not have known PD-causing mutation and in 1 out of 92 healthy individual controls. The three patients with this diplotype all have a similar clinical phenotype. Our results suggest that haplotypes H1j and H2 are strong risk factor alleles, and their combination could be responsible for early onset of PD with dementia.

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