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Hyperechogenicity of the substantia nigra (SN) has been found to be a typical sign in idiopathic Parkinson's disease (PD), prevalent in more than 90% of affected individuals. To see whether SN hyperechogenicity is also characteristic for monogenetically caused PD, we investigated PD patients with alpha-synuclein, LRRK2, parkin, PINK1 and DJ-1 mutations by transcranial sonography (TCS). In all these patients the area of SN echogenicity was significantly larger than in healthy controls, but smaller, than in idiopathic PD. As SN hyperechogenicity could be related to an increased iron content of the SN, these findings suggest that iron may play a less significant role in the pathogenesis of monogenetically caused compared to idiopathic PD.

In this review we summarize new developments in early diagnosis, establishing surrogate markers, genetics, neuroprotection and cell replacement in Parkinson's disease. Furthermore, we discuss the major problems in the translation of results from preclinical research into successful clinical trials.

For several decades there has been a controversy on the contribution of genetic factors to the pathogenesis of sporadic idiopathic Parkinson's disease (PD). The identification of families in which typical parkinsonism is inherited as an autosomal dominant or recessive trait sheds light on genes that cause phenotypes resembling sporadic PD. These genes are involved in molecular pathways leading to neurodegeneration and dysfunction of the nigrostriatal system. The present article gives insight into molecular pathways to neurodegeneration deciphered by the functional characterization of five genes identified in inherited forms of typical levodopa-responsive parkinsonism. There is increasing evidence that genes involved in monogenic forms of the disease may act as susceptibility factors also in the common sporadic form of PD. Transgenic animal models based on disease genes identified in monogenic forms of typical parkinsonism replicate important features of PD including protein aggregation and progressive motor symptoms. This implicates novel perspectives for neuroprotective therapeutic approaches that might be beneficial also to sporadic PD.

Following the identification of mutations in alpha-synuclein as the cause of some rare forms of familial Parkinson's disease (PD), genetic research has uncovered numerous gene loci of PD. Meanwhile, several neurodegenerative diseases have been shown to accumulate a-synuclein in neuronal and glial cells summarizing this group of diseases as synucleinopathies. All currently known gene defects causing PD alter the ubiquitin-proteasomal pathway of protein degradation. Identification of these disease mutations allows studying the functional consequences which lead to cellular dysfunction and cell death in cell culture and transgenic animal models, to identify therapeutic targets and to test potential protective strategies in these models.

The pathogenesis of Parkinsons disease (PD) is currently unknown. Environmental and genetic factors might contribute to the neurodegenerative process. Genetic mapping approaches in rare familial cases with autosomal recessive and autosomal dominant inheritance of PD suggest wide genetic heterogeneity of the disease. These gene loci in turn allow now a more specific clinical investigation of affected families to study the clinical heterogeneity of PD. The recent identification of mutations in three genes involved in protein degradation and aggregation in familial PD does now facilitate the deciphering of other genes involved in the pathogenesis of the disease.