Faculty Bibliography

OBJECTIVE: To determine the motor phenotype of LRRK2 G2019S mutation carriers. LRRK2 mutation carriers were previously reported to manifest the tremor dominant motor phenotype, which has been associated with slower motor progression and less cognitive impairment compared with the postural instability and gait difficulty (PIGD) phenotype. DESIGN: Cross-sectional observational study. SETTING: Thirteen movement disorders centers. PARTICIPANTS: Nine hundred twenty-five early-onset Parkinson disease cases defined as age at onset younger than 51 years. MAIN OUTCOME MEASURES: LRRK2 mutation status and Parkinson disease motor phenotype: tremor dominant or PIGD. Demographic information, family history of Parkinson disease, and the Unified Parkinson's Disease Rating Scale score were collected on all participants. DNA samples were genotyped for LRRK2 mutations (G2019S, I2020T, R1441C, and Y1699C). Logistic regression was used to examine associations of G2019S mutation status with motor phenotype adjusting for disease duration, Ashkenazi Jewish ancestry, levodopa dose, and family history of Parkinson disease. RESULTS: Thirty-four cases (3.7%) (14 previously reported) were G2019S carriers. No other mutations were found. Carriers were more likely to be Ashkenazi Jewish (55.9% vs 11.9%; P < .001) but did not significantly differ in any other demographic or disease characteristics. Carriers had a lower tremor score (P = .03) and were more likely to have a PIGD phenotype (92.3% vs 58.9%; P = .003). The association of the G2019S mutation with PIGD phenotype remained after controlling for disease duration and Ashkenazi Jewish ancestry (odds ratio, 17.7; P < .001). CONCLUSION: Early-onset Parkinson disease G2019S LRRK2 carriers are more likely to manifest the PIGD phenotype, which may have implications for disease course.

Focal task-specific dystonia (FTSD) is an unusual disorder of motor control, which typically affects the hand but may also involve the face, jaw, and tongue. We report 89 musicians with dystonia of the embouchure (ED), the muscles of the lower face, jaw, and tongue used to control the flow of air into the mouthpiece of a woodwind or brass instrument. Symptoms of ED began at an average age of 36, were typically painless and only rarely were preceded by trauma. Specific musical techniques commonly triggered dystonia, often in one instrumental register. Task-specific embouchure tremor and lip-pulling ED phenotypes were common among high-register brass players (trumpet and French horn), whereas lip-locking occurred exclusively in low-register brass players (trombone and tuba). Jaw and tongue ED phenotypes occurred predominantly in woodwind players, and once present, frequently spread to speaking or eating. Six percent of all ED patients had coincident writer's cramp, suggesting a possible genetic predisposition to develop dystonia. We assessed two-point sensory discrimination in the upper lip, lower lip, and hand in ED patients, normal musicians, and nonmusician age-matched controls--there were no differences between groups. Once present, symptoms of ED did not remit and often disrupted careers and livelihoods. Better treatments are urgently needed for this unusual disorder of oral motor control.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an effective treatment for patients with medically refractory Parkinson's disease (PD). The degree to which the anatomic location of the DBS electrode tip determines the improvement of contralateral limb movement function has not been defined. This retrospective study was performed to address this issue. Forty-two DBS electrode tips in 21 bilaterally implanted patients were localized on postoperative MRI. The postoperative and preoperative planning MRIs were merged with the Stealth FrameLink 4.0 stereotactic planning workstation (Medtronic Inc., Minneapolis, MN, USA) to determine the DBS tip coordinates. Stimulation settings were postoperatively optimized for maximal clinical effect. Patients were videotaped 1 year postoperatively and assessed by a movement disorder neurologist blinded to electrode tip locations. The nine limb-related components of the Unified PD Rating Scale Part III were tabulated to obtain a limb score, and the electrode tip locations associated with the 15 least and 15 greatest limb scores were evaluated. Two-tailed t-tests revealed no significant difference in electrode tip location between the two groups in three-dimensional distance (p=0.759), lateral-medial (x) axis (p=0.983), anterior-posterior (y) axis (p=0.949) or superior-inferior (z) axis (p=0.894) from the intended anatomical target. The range of difference in tip location and limb scores was extensive. Our results suggest that anatomic targeting alone may provide the same clinical efficacy as is achieved by 'fine-tuning' DBS placement with microelectrode recording to a specific target

NARRATIVE REVIEW: Watching a concert pianist perform a Chopin etude or a violin soloist perform a Paganini caprice, one cannot help but be awed by the miracle of motor control in man. These "athletes of the small muscles" are susceptible, however, to a condition known as focal, task-specific dystonia (FTSD), a disorder of motor control in which the hands that perform these exquisite maneuvers disobey their master's command. Affected patients offer a unique window to investigate motor learning and aberrant cerebral plasticity. Effective treatments including sensory rehabilitation and botulinum toxin injection offer real hope for symptomatic relief and also afford scientists the opportunity to investigate sensorimotor networks in the normal and abnormal state.