Two Cases of Monozygotic Twins with Early-onset Isolated (DYT1) Dystonia Effectively Treated with Bilateral Globus Pallidus Internus Stimulation

Abstract

Early-onset isolated (DYT1) dystonia is one of the most common forms of primary dystonia in childhood, and deep brain stimulation of the globus pallidus internus (GPi-DBS) is a highly effective treatment for it. However, the effectiveness of GPi-DBS in monozygotic twins with DYT1 dystonia has never been reported globally. Here, we report the cases of monozygotic twins with DYT1 dystonia who were treated using GPi-DBS, and we include a literature review. The younger brother showed an abnormal gait, with external rotation of the right lower leg at 6 years old. The symptoms gradually became so severe that he had difficulty walking on his own at 9 years of age. Treatment with levodopa-carbidopa partially resolved his symptoms, but most of the symptoms remained. Meanwhile, the older brother developed dystonia in both upper limbs at 8 years of age, with gradual symptom progression. At 13 years of age, they were diagnosed with DYT1 dystonia. Bilateral GPi-DBS was performed in both patients at 16 years of age. Their symptoms remarkably improved after surgery. The Burke-Fahn-Marsden dystonia rating scale (BFMDRS) movement score was reduced from 52 to 2 points for the younger brother and from 35 to 1 point for the older brother. Even if monozygotic twins have the same genes, the onset and severity of symptoms might vary in accordance with differences in epigenomic profiles. However, GPi-DBS treatment was very effective for the two cases; thus, we should consider the surgical interventions for each patient.

Keywords: DYT1 dystonia; deep brain stimulation of the globus pallidus internus; monozygotic twins.

Fig. 1

Patient 1’ s posture before and after surgery. He presented with dyskinesia symptoms, with lateral and forward flexion in the upright position (A). He showed the same torsion dyskinesia when he was raising his legs before surgery (B). After surgery, he was able to hold his posture in the upright position and no longer required a wheelchair (C, D). Postoperative computed tomography (CT) images were combined with preoperative magnetic resonance imaging (MRI) using a Stealth Station. The deep brain stimulation (DBS) electrodes were placed bilaterally in the globus pallidus internus (GPi; white arrow); the right 1st electrode (E), right 2nd electrode (F), left 1st electrode (G), and left 2nd electrode in Case 1 (H).

Fig. 2

Patient 2’ s posture before and after surgery. He showed dyskinesia symptoms during movement, and in particular, he was observed to throw his left leg forward in a twisting motion while walking (A, B). After surgery, his symptoms markedly improved (C, D). The postoperative location of the bilateral deep brain stimulation (DBS) electrode for Case 2 (white arrow). The right 1st electrode (E), right 2nd electrode (F), left 1st electrode (G), and left 2nd electrode (H).