Objective: To characterize and expand the phenotype of a family from North-East England with DYT16.

Background: DYT16 is an autosomal recessive disease associated with mutations in the PRKRA gene (protein activator of interferon induced protein kinase) in region 2q31.2. This mutation was first described in 2008 in two non-consanguineous Brazilian families with dystonia. The male proband, aged 30 had classical dystonic features of risus sardonicus, perioral dyskinesia, spasmodic dysphonia, dystonic limb posturing and parkinsonism. The female proband aged 27 was less affected, with some dystonic posturing of the hands and pronounced posturing of the great toes (causing skin abrasions from footwear). Since childhood there were psychiatric issues, with documented depression and mild paranoia. Both were described as ‘clumsy’ and physically ‘slow’ as children. The female proband described falls, triggered by loud sounds; her brother described jerking provoked by loud noises.

Methods: Case report.

Results: Urine organic acids, serum amino acids and acetylcarnitine, VLCFA and MRI brain imaging were normal. The male patient had a normal DAT scan. DYT1 gene testing was normal. Homozygous pathological PRKRA gene mutations (665C>T P(Pro 222Leu) in both probands were found on further genetic testing. MEPs and SEPs were normal. Auditory startle evoked myoelectric potentials confirmed a non-habituating startle response recorded as surface EMG from trapezius, upper and lower limb muscles in both probands. The duration of EMG bursts in response to startling acoustic stimuli was consistent with propagation via a brainstem descending pathway. Identical electrophysiologic features consistent with brainstem/reticular reflex myoclonus, have previously been documented in DYT11 Myoclonus-Dystonia Syndrome (Marelli et al, 2008).

Conclusions: DYT16 is a rare genetic diagnosis. We have described siblings with acoustic/reticular startle myoclonus in addition to dystonic features, thus expanding the clinical phenotype of DYT16.

References: Camargos S et al, DYT16, a novel young-onset dystonia-parkinsonism disorder: identification of a segregating mutation in the stress-response protein PRKRA. Lancet Neurology. 2008 Mar;7(3):207-15. Marelli C et al, A Neurophysiological Study of Myoclonus in Patients with DYT11 Myoclonus-Dystonia Syndrome. Movement Disorder. Vol. 23, No. 14, 2008, pp. 2041–2048.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/siblings-with-a-prkra-dyt16-mutation-and-startle-myoclonus/