Haploinsufficiency at the  -synuclein gene underlies phenotypic severity in familial Parkinson's disease

Abstract

To date, two point mutations, G209A and G88C, have been reported in the coding region of the alpha-synuclein gene in autosomal dominant familial Parkinson's disease. When translated, these lead to the missense mutations Ala53Thr and Ala30Pro, respectively. Reduced mRNA expression of the G209A allele was reported recently in a Greek-American family. Here, we show that alpha-synuclein mRNA is normally expressed in blood cells and report the results of an analysis of alpha-synuclein mRNA and protein expression in lymphoblastoid cell lines established from kindreds with the G209A and G88C mutations. mRNA expression was characterized using a TaqMan real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) assay. We assessed five affected and three unaffected members of a German family with the G88C mutation and two affected members in different, unrelated Greek families with the G209A mutation. The ratio of wild-type to mutant alpha-synuclein allele expression ranged from 2.2 to 9.2 in the affected individuals with a severe clinical phenotype. The ratios of the expression levels of the wild-type to mutant alleles were only slightly decreased in mild cases and were less than 1.0 in two asymptomatic heterozygotes. Sequence analysis of the RT-PCR products showed only the presence of G in position 88 and G in position 209 in severely affected heterozygotes of the German and Greek families, respectively. High performance liquid chromatography/mass spectrometry demonstrated that, relative to wild-type alpha-synuclein, there is a reduction of Ala30Pro alpha-synuclein in lymphoblastoid cell lines originating from severely affected, but not mildly affected G88C/+ heterozygotes. Taken together, these data indicate that there is haploinsufficiency at the alpha-synuclein gene and that the ratio of expression of the wild-type to mutant alleles correlates with the severity of the clinical phenotype. Furthermore, these findings suggest that haploinsufficiency of alpha-synuclein mutations may contribute to disease progression in these forms of familial Parkinson's disease.

Familial Parkinson?s disease: a hint to elucidate the mechanisms of nigral degeneration

“…When translated, these lead to the missense mutations Ala53Thr and Ala30Pro, respectively. Recently, reduced mRNA expression of the G209A allele was reported in a Greek-American family [23]. Very recently, we reported that the mRNA expression of the mutant G88C and G209A alleles of the α-synuclein gene is significantly reduced relative to the wild-type allele in lymphoblastoid cell lines established from affected heterozygotes, who had mutations of either G88C or G209A alleles, with a severe clinical phenotype.…”

Allelic imbalance of expression and epigenetic regulation within the alpha-synuclein wild-type and p.Ala53Thr alleles in Parkinson disease

“…Independent reports on other patients [Kobayashi et al, 2003;Markopoulou et al, 1999] have previously shown that expression of the same SNCA allele as well as of the allele for the p.Ala30Pro mutation, was either absent or significantly reduced. This raises the question how common such monoallelic SCNA expression is; studies on this issue will provide important insights, however, they are complicated, because nucleotide variations in the coding sequence of the gene are rare.…”

“…Surprisingly, the p.Ala53Thr and p.Ala30Pro alleles were found to be silenced to different degrees, compared to the expression of the normal counterpart in the same patient, in various cases [Kobayashi et al, 2003;Markopoulou et al, 1999]. This interallelic variation of expression, unexpected on the basis of the nature of these mutations, could cause a decrease in alphasynuclein protein in these patients and lead the authors to conclude that a haploinsufficiency effect exists associated with the clinical severity of the disease.…”

-Synuclein in Parkinson's Disease

“…Posttranscriptional regulation of a-synuclein can also occur through endogenous micro RNAs, which bind to the 3 0 end of the gene (Junn et al 2009;Doxakis 2010). A particularly interesting twist to the effects of familial point mutations in SNCA has been provided by a series of studies that, somewhat counterintuitively, suggest that the expression of the mutant alleles is suppressed, especially in cases with prolonged disease (Markopoulou et al 1999;Kobayashi et al 2003), through a mechanism that may involve histone modifications (Voutsinas et al 2010). Remarkably, Voutsinas et al (2010) found that the WT allele is induced in a compensatory fashion, and that the total level of SNCA messenger RNA (mRNA) exceeds that of controls, suggesting that total SNCA levels, rather than the presence of the A53T mutant, are responsible for the disease in these cases.…”