"Jerky" dystonia in children: spectrum of phenotypes and genetic testing.

Hyperkinetic dystonia is characterized by phasic, tremulous, and "jerky" movements in addition to twisting postures. We studied longitudinally 23 index patients with hyperkinetic dystonia from a quaternary pediatric movement disorder clinic in Ireland. Four clinical categories emerged: (1) Eight patients were diagnosed with myoclonus-dystonia, of whom seven carried heterozygous epsilon sarcoglycan (SGCE) mutations, including a novel deletion of exon 10. Gait disorder, unsteadiness, or frequent falls before 18 months were detected in all SGCE mutation carriers, whereas the typical neck-predominant presentation developed only years later. (2) One patient classified as benign hereditary chorea, because jerks were choreiform and continuous rather than action-induced, carried a heterozygous stop mutation of the TITF-1 gene (Y114X, exon 2). (3) Three mutation-negative patients were grouped as "myoclonic dystonia" with jerks only in the body regions affected by dystonia. (4) Eleven patients presented with a novel combination of dystonia and low amplitude poly-mini myoclonus of the upper limbs and pectoral muscles (D-PMM). In early childhood up to 3 years of age, an initial presentation with predominant gait impairment with only subtle jerks should prompt consideration of SGCE mutation analysis in addition to testing for DYT1 mutations. A causative gene for D-PMM remains to be identified.