Parkinson’s disease was described in 1817 by Dr James Parkinson, who published an essay reporting six cases of ‘paralysis agitans’ (the disorder that was later renamed after Parkinson). He described the characteristic resting tremor, abnormal posture and gait, paralysis and diminished muscle strength, and the way that the disease progresses over time. 
Since the advent of genetic testing several genes have been found to be associated with Parkinson’s disease (PD), resulting in various classifications. Autosomal dominant Parkinson disease type 8 (PARK8) is caused by heterozygous mutation in LRRK2, the gene encoding the dardarin protein.  The G2019S variant is one of the most common genetic causes of PD. Although the clinical motor signs of PD in carriers of the G2019S mutation are largely typical, an earlier age at onset of motor symptoms has been reported in some studies. 
The word dardarin was taken from a Basque word for tremor, as the gene was first identified in families from England and the north of Spain. Mutations in LRRK2 are the most common known cause of familial and sporadic PD, accounting for approximately 5% of individuals with a family history of the disease and 3% of sporadic cases. They account for up to 10% of autosomal dominant familial and 3.6% of sporadic PD. More than 40 different variants, almost all missense, have been found. Seven seem to be proven pathogenic mutations, and are clustered in functionally important regions which are highly conserved through evolution. 
23andMe carried out a privately-funded genome-wide association study (GWAS) to search for novel genetic variants associated with PD. The results, which were published in PLOS in 2011, replicated existing associations and discovered two novel variants.  In addition, 23andMe researched genes conferring protection on those with high-risk genes.  They found that of the approximately 1 in 10,000 people who have the G2019S variant, those who also had a mutation in SGK1 were found to have a lower risk of PD than those with just the G2019S variant, conferring protection against the increased risk of PD. 
Other causes of, or factors contributing to PD include pesticide exposure,  head trauma, medication, prolonged oxidative stress from infection or high homocysteine. Genetic factors include increased function of MAOB enzymes, high histamine from HNMT mutations, elevated L-dopa from DDC mutations or B6 deficiency. The Opus 23 software contains algorithms for Parkinson’s disease associated with some of these genetic causes, risk or contributory factors found in the 23andMe raw data. A new algorithm added to the Opus 23 Lumen app looks for both the LRRK2 G2019S and the SGK1 variants to assess for both risk of PD and protection from the risk genotype, and lists natural agents associated with gene function.
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- Do CB, Tung JY, Dorfman E, et. al. Web-based genome-wide association study identifies two novel loci and a substantial genetic component for Parkinson’s disease. PLoS Genet. 2011 Jun;7(6):e1002141. PMCID: PMC3121750
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