Myoclonus epilepsy and ataxia due to KCNC1 mutation: Analysis of 20 cases and K+ channel properties.

OBJECTIVE: To comprehensively describe the new syndrome of myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK), including cellular electrophysiological characterization of observed clinical improvement with fever. METHODS: We analyzed clinical, electroclinical, and neuroimaging data for 20 patients with MEAK due to recurrent KCNC1 p.R320H mutation. In vitro electrophysiological studies were conducted using whole cell patch-clamp to explore biophysical properties of wild-type and mutant KV 3.1 channels. RESULTS: Symptoms began at between 3 and 15 years of age (median = 9.5), with progressively severe myoclonus and rare tonic-clonic seizures. Ataxia was present early, but quickly became overshadowed by myoclonus; 10 patients were wheelchair-bound by their late teenage years. Mild cognitive decline occurred in half. Early death was not observed. Electroencephalogram (EEG) showed generalized spike and polyspike wave discharges, with documented photosensitivity in most. Polygraphic EEG-electromyographic studies demonstrated a cortical origin for myoclonus and striking coactivation of agonist and antagonist muscles. Magnetic resonance imaging revealed symmetrical cerebellar atrophy, which appeared progressive, and a prominent corpus callosum. Unexpectedly, transient clinical improvement with fever was noted in 6 patients. To explore this, we performed high-temperature in vitro recordings. At elevated temperatures, there was a robust leftward shift in activation of wild-type KV 3.1, increasing channel availability. INTERPRETATION: MEAK has a relatively homogeneous presentation, resembling Unverricht-Lundborg disease, despite the genetic and biological basis being quite different. A remarkable improvement with fever may be explained by the temperature-dependent leftward shift in activation of wild-type KV 3.1 subunit-containing channels, which would counter the loss of function observed for mutant channels, highlighting KCNC1 as a potential target for precision therapeutics. Ann Neurol 2017;81:677-689.

Trisomy 22pter-q12.3 presenting with hepatic dysfunction variability of cat-eye syndrome.

We describe the clinical characteristics of two patients with cat-eye syndrome (CES, MIM #115470) resulting from a supernumerary marker chromosome that includes 22pter-q12.3. They both presented a constellation of features typical of CES, including coloboma, auricular malformations, heart and renal anomalies, as well as hepatic dysfunction, which led to severe effects. In one case Pierre Robin sequence was diagnosed which has not been described earlier in this trisomy. Although CES is a well known, but infrequently diagnosed disorder, we draw attention both to its clinical overlaps with other disorders and, in view of the clinical variability being identified within the 22q11 region, to the importance of careful molecular examination of proximal 22q in patients with suggestive clinical signs.

Clinical and molecular cytogenetic characterization of four patients with unbalanced translocation der(1)t(1;22)(p36;q13).

Deletion of chromosome 1p36 is the most commonly observed terminal deletion in humans with a frequency of 1 in 5,000 in the general population. In contrast, 22q13 duplications are rare and only a few cases have been reported. Unbalanced translocations resulting in monosomy 1p36 and a trisomy of 22q13.3 are, thus far, unreported in the literature. Here we present the clinical data and the results of array CGH and FISH analysis of four patients with unbalanced translocations t(1;22)(p36;q13) inherited from unrelated balanced translocation carrier parents. The sizes of the imbalances ranged from 0.12 Mb to nearly 10 Mb. One balanced translocation carrier parent had disruption of the period homolog 3 (PER3) gene and reported sleep disturbances. Overall, patients tended to have more features consistent with deletion of 1p36 than duplication of 22q.