Alternating two finger tapping with contralateral activation is an objective measure of clinical severity in Parkinson's disease and correlates with PET

We explored an objective method of measuring clinical severity of Parkinson's disease. Eighty-six patients with PD and 136 healthy subjects were studied. We serially carried out four types of finger tapping (FT) using a computerized drum machine: (i) repetitive one-finger tapping with an index-finger (F1K1); (ii) one-finger tapping on two keys separated by 20cm (F1K2); (iii) alternate tapping with index and middle fingers on two adjacent keys (F2K2); and (iv) F2K2 with contralateral activation (aF2K2). Analyses on FT included: (i) age and gender effects in healthy volunteers and Parkinson's disease; (ii) comparison between Parkinson patients and controls of similar age distribution; (iii) correlation with the Purdue Pegboard and Modified Columbia Scale in Disease; and (iv) in a subset of patients in whom PET scans were performed (n=30), correlation with 18F-DOPA uptake constant (Ki). In healthy subjects, there was a negative age effect on FT scores and a gender effect, with males scoring higher than females. All FT scores were significantly lower in the Parkinson patients, correlated with Purdue Peg Board, and inversely with the duration of illness, and with the Modified Columbia Scale. The 18F-DOPA Ki correlated significantly with aF2K2 (p=0.024), less so with PPB (p=0.038), but not with the Modified Columbia Scale. We conclude that alternating two-finger tapping with contralateral hand activation is a simple, objective test for measuring the severity of Parkinson's disease.

Evidence for impaired presynaptic dopamine function in parkinsonian patients with motor fluctuations.

We used [18F]6-fluorodopa (FD) positron emission tomography (PET) to examine the severity of nigrostriatal dopaminergic dysfunction in 67 patients with Idiopathic Parkinsonism (IP), 52 with fluctuations and 15 with a stable response to levodopa. FD uptake (Ki) was reduced by 12% in the caudate (p = 0.08) and by 28% in the putamen (p = 0.0004) of patients with fluctuations compared to those with a stable response. However, there was considerable overlap of FD Ki values between the two groups. The fluctuators had a longer symptom duration (11.6 +/- 5.7 years) than the patients with a stable response to levodopa (4.3 +/- 2.4 years; p < 0.0001) and the age of onset of symptoms was earlier in the fluctuators (43.9 +/- 8.9 versus 54.1 +/- 10.4; p = 0.0004). Similar reductions in FD Ki in the fluctuators persisted following adjustment for these variables (7.5% in the caudate and 26% in the putamen; p = n.s. and 0.007, respectively). When smaller groups (n = 15 each) were matched for duration of symptoms, the reduction in caudate Ki in the fluctuators was only 1.9% (p = n.s.), but there was still a 24% reduction in putamen Ki (p = 0.05). These findings suggest that fluctuators and non-fluctuators may differ in the severity of their nigrostriatal damage and provide modest support for the hypothesis that fluctuations may in part reflect altered "buffering" capacity of dopaminergic nerve terminals. However, the considerable overlap between groups suggests that other factors such as altered postsynaptic mechanisms and/or increased turnover of dopamine may make a substantial contribution to the development of motor fluctuations.

A protein phosphatase methylesterase (PME-1) is one of several novel proteins stably associating with two inactive mutants of protein phosphatase 2A.

Carboxymethylation of proteins is a highly conserved means of regulation in eukaryotic cells. The protein phosphatase 2A (PP2A) catalytic (C) subunit is reversibly methylated at its carboxyl terminus by specific methyltransferase and methylesterase enzymes which have been purified, but not cloned. Carboxymethylation affects PP2A activity and varies during the cell cycle. Here, we report that substitution of glutamine for either of two putative active site histidines in the PP2A C subunit results in inactivation of PP2A and formation of stable complexes between PP2A and several cellular proteins. One of these cellular proteins, herein named protein phosphatase methylesterase-1 (PME-1), was purified and microsequenced, and its cDNA was cloned. PME-1 is conserved from yeast to human and contains a motif found in lipases having a catalytic triad-activated serine as their active site nucleophile. Bacterially expressed PME-1 demethylated PP2A C subunit in vitro, and okadaic acid, a known inhibitor of the PP2A methylesterase, inhibited this reaction. To our knowledge, PME-1 represents the first mammalian protein methylesterase to be cloned. Several lines of evidence indicate that, although there appears to be a role for C subunit carboxyl-terminal amino acids in PME-1 binding, amino acids other than those at the extreme carboxyl terminus of the C subunit also play an important role in PME-1 binding to a catalytically inactive mutant.

Use of denaturing gradient gel blots to screen for point mutations in the factor VIII gene.

Denaturing gradient gel electrophoresis (DGGE) is commonly used to search for point mutations in DNA fragments amplified in vitro by the polymerase chain reaction (PCR). For the complete detection of mutations in large genes with many exons, the DGGE-PCR approach, or any other PCR-based method, requires many primer sets and amplification reactions to scan the entire protein-coding sequence. We previously demonstrated that DGGE analysis using DNA blots detects mutations in Drosophila genes and sequence polymorphisms in human genes without prior PCR amplification. To determine if human point mutations could be detected using denaturing gradient gels (DGG blots), genomic DNA samples from hemophilia A families were analyzed for mutations in the factor VIII (FVIII) gene. Restriction enzyme digested DNA samples were subjected to DGGE and transferred to nylon blots. Hybridization of the DGG blots with FVIII cDNA probes revealed mutant and polymorphic DNA sequence differences. Among 26 affected families that were not carriers of intron 22 inversion mutations, 18 family-specific DNA fragment polymorphisms and one multiexon deletion were mapped. DNA sequencing of eight patient-specific polymorphic DNA fragments revealed six single base change mutations, one 4 bp deletion, and one 13 bp duplication.

Clinical observations on the rate of progression of idiopathic parkinsonism.

The time course of evolution of clinical deficits has been a traditional guide to the nature of the aetiopathogenesis of neurological disease. We studied the influence of ageing and duration of disease on the natural history of idiopathic parkinsonism (IP). Two hundred and thirty-eight patients with IP were examined while off medication. Bradykinesia scores were analysed against patients' age and duration of disease by multiple regression. There was no significant interaction between the effects of age and of duration (P = 0.923). We conclude that age and duration of symptoms influence the natural history of IP additively and independently. Furthermore, the rate of neuronal death is more rapid in the earlier stages of evolution of the pathology; subsequently, the velocity of progression slows down to approach the rate of attrition produced by normal ageing. This time course has implications for possible models of pathogenesis.

A mathematical model of pathogenesis in idiopathic parkinsonism.

We used our observations relating clinical deficits in idiopathic parkinsonism (IP) to age and to disease duration (Lee et al, Brain 1994; 117: 501-7), to develop a mathematical model of the temporal profile of neurodegeneration in IP. We also examined other sets of relevant published observations and applied three additional assumptions which permitted the formulation of this model. Our model indicates that accelerating or decelerating processes should be excluded as the driving forces behind neuronal death in IP. Mechanisms in accord with the model include: (i) an event that kills some neurons and damages others in such a way that their life expectation is reduced; or (ii) an event that starts a process which is continuously killing healthy neurons at a constant rate. The model enables us to extrapolate back to estimate when the causal event occurred. It also explains why IP proceeds more rapidly in older patients. The model has potential relevance to other neurodegenerative disorders, such as Alzheimer's disease and amyotrophic lateral sclerosis.