TBC 1 D 24 genotype – phenotype correlation Epilepsies and other neurologic features

Objective: To evaluate the phenotypic spectrum associated with mutations in TBC1D24. Methods: We acquired new clinical, EEG, and neuroimaging data of 11 previously unreported and 37 published patients. TBC1D24mutations, identified through various sequencing methods, can be found online (http://lovd.nl/TBC1D24). Results: Forty-eight patients were included (28 men, 20 women, average age 21 years) from 30 independent families. Eighteen patients (38%) had myoclonic epilepsies. The other patients carried diagnoses of focal (25%), multifocal (2%), generalized (4%), and unclassified epilepsy (6%), and early-onset epileptic encephalopathy (25%). Most patients had drug-resistant epilepsy. We detail EEG, neuroimaging, developmental, and cognitive features, treatment responsiveness, and physical examination. In silico evaluation revealed 7 different highly conserved motifs, with the most common pathogenic mutation located in the first. Neuronal outgrowth assays showed that some TBC1D24 mutations, associated with the most severe TBC1D24-associated disorders, are not necessarily the most disruptive to this gene function. Conclusions: TBC1D24-related epilepsy syndromes show marked phenotypic pleiotropy, with multisystem involvement and severity spectrum ranging from isolated deafness (not studied here), benign myoclonic epilepsy restricted to childhood with complete seizure control and normal intellect, to early-onset epileptic encephalopathy with severe developmental delay and early death. There is no distinct correlation with mutation type or location yet, but patterns are emerging. Given the phenotypic breadth observed, TBC1D24 mutation screening is indicated in a wide variety of epilepsies. A TBC1D24 consortium was formed to develop further research on this gene and its associated phenotypes. Neurology® 2016;87:77–85 GLOSSARY ARF65 ADP ribosylation factor 6;DOORS5 deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures; EIMFS 5 epilepsy of infancy with migrating focal seizures; Rab-GAP 5 Rab GTPase-activating protein; TBC 5 Tre2/Bub2/ Cdc16. The gene TBC1D24 is involved in regulation of synaptic vesicle trafficking and in brain and somatic development. It has recently been implicated in various human diseases, many of which feature epileptic seizures; mutations can also cause nonsyndromic deafness. TBC1D24 encodes a protein containing a Tre2/Bub2/Cdc16 (TBC) domain, shared by Rab GTPase-activating proteins (Rab-GAPs). TBC domain-containing proteins regulate numerous vesicular membrane-trafficking and sorting processes by modulating the activity of RabGTPases. TBC1D24 interacts with the ADP ribosylation factor 6 (ARF6), a small GTPbinding protein involved in membrane exchange between plasma membrane and endocytic compartments. The protein also contains a TLDc domain, putatively involved in oxidative stress resistance. In TBC1D24-associated disorders, including deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures (DOORS) syndrome, a wide spectrum of epilepsies have been Simona Balestrini, MD Mathieu Milh, MD, PhD Claudia Castiglioni, MD Kevin Lüthy, PhD Mattea J. Finelli, PhD Patrik Verstreken, PhD Aaron Cardon, MD, MSc Barbara Gnidovec Stra zi sar, MD, PhD J. Lloyd Holder, Jr., MD, PhD Gaetan Lesca, MD, PhD Maria M. Mancardi, MD, PhD Anne L. Poulat, MD Gabriela M. Repetto, MD Siddharth Banka, MD, PhD Leonilda Bilo, MD, PhD Laura E. Birkeland, MS, CGC Friedrich Bosch, MD Knut Brockmann, MD J. Helen Cross, MD, PhD Diane Doummar, MD Temis M. Félix, MD Fabienne Giuliano, MD Mutsuki Hori, MD Irina Hüning, MD Hulia Kayserili, MD, PhD Usha Kini, MD Melissa M. Lees, MD Girish Meenakshi, MD Leena Mewasingh, FRCPCH Alistair T. Pagnamenta, PhD Silvio Peluso, MD Antje Mey, MD Gregory M. Rice, MD Jill A. Rosenfeld, MS Jenny C. Taylor, PhD Author list continued on next page Authors’ affiliations are listed at the end of the article. Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article. The Article Processing Charge was paid by Wellcome Trust. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 American Academy of Neurology 77 a 2016 American Academy of Neurology. Unauthorized reproduction of this article is prohibited. reported. We evaluated the types of epilepsy seen with a wide mutational spectrum in TBC1D24, using new data from 11 previously unreported and 37 published patients. METHODS Standard protocol approvals, registrations, and patient consents. This study was approved by the relevant institutional ethics committees or review boards. Parental (or legal guardian) written informed consent was obtained for all affected children and adults with intellectual disability, or existing published data were collated. Authorization has been obtained for disclosure of videos (videos 1–5 on the Neurology® Web site at Neurology.org). Participants. We collected data from a cohort of new patients and contacted physicians to seek additional information about published patients by using a standardized questionnaire. Available neuroimaging and EEG recordings were evaluated. Individuals were included if they had a confirmed TBC1D24 mutation and had epileptic seizures within their phenotype. We report 2 additional patients (31, 32) where a clear association of phenotype with changes in TBC1D24 could not be established: therefore, they were not included in the final analyses. In patient 31, 2 single nucleotide polymorphisms in the maternal allele were found through a next-generation sequencing panel; in patient 32, array comparative genomic hybridization showed a 16p13.3 duplication including TBC1D24. Procedures. TBC1D24 variants were identified through various methods, detailed in supplemental data S1. Conserved motifs were detected in MEME suite through discriminative motif discovery. Bioinformatics and in vitro modeling methods are described in supplemental data S1. RESULTS Family history. The cohort includes 48 patients (28 men, 20 women) from 30 independent families. Twenty-seven individuals are from 9 families (figure e-1), comprising 5 sibling pairs with nonconsanguineous parents, 1 pair with consanguineous parents, 4 members of a large Arab-Israeli family with multiple consanguineous unions, 8 members of a large Italian family, and 3 members of a large Turkish family (all patients born to consanguineous parents). Six other sporadic patients, including one previously described, have consanguineous parents; 15 patients (31%) are isolated, from nonconsanguineous parents. Longevity. Nine individuals (19%) were deceased (average age at death 37 months, range 6–96 months). One death (6b), at age 18 months, was defined as probable sudden unexpected death in epilepsy. The other reported causes of death were infectious episode (7a, 7c, 17a, 17b), respiratory failure (6a), status epilepticus associated with a pulmonary infection (7b), and unknown (26, 28). The average age of the living patients was 21 years in January 2015. Seizures and treatment responsiveness. The types of seizures and epilepsies were diverse. Seizure types included infantile spasms and febrile convulsive, myoclonic, clonic, tonic, absence, tonic-clonic with or without apparent focal onset, and focal seizures with retained or impaired awareness. Myoclonic or clonic seizures were the most frequent seizure types (29/48, 60%), often unresponsive to medication. Myoclonic seizures were segmental (often involving eyelids, perioral region, or other facial parts) or generalized, with initially no loss of consciousness, but sometimes evolving into tonic-clonic seizures. Various other features of myoclonic seizures were described; they could be unilateral or bilateral, migrating, alternating, rhythmic, or pseudorhythmic, occurring both at rest and on maintaining posture. They often occurred in clusters, which could be very prolonged, lasting several days. In some patients, they were triggered by fatigue, drowsiness, intense and persistent stimulation (acoustic stimuli or variations in light intensity), repetitive movements, feeding, febrile episodes, constipation, or delayed medication. Eighteen patients had myoclonic epilepsy (including infantile myoclonic and progressive myoclonic epilepsies). Semiologic features of 5 patients, 4 with myoclonic epilepsy (4, 23a, 23b, 24) and 1 with familial epilepsy of infancy with migrating focal seizures (EIMFS) (6b), are shown in videos 1–5. The other patients had focal, multifocal, generalized, or unclassified epilepsy, or early-onset epileptic encephalopathy (including EIMFS). There was no marked variability of epilepsy phenotype in affected siblings. The average age at seizure onset was 7 months (range from within 1 hour after birth to 8 years; SD 15 months). Thirty-eight (79%) individuals had had status epilepticus, either convulsive or nonconvulsive, or prolonged seizures (.5 minutes). In 19 patients, seizures or status episodes were precipitated by fever or infections. In 30 patients, epilepsy was drug-resistant; 18 patients responded well to treatment. The Italian family with familial infantile myoclonic epilepsy was drug-responsive, with 5 members (1a–1e) free from tonic-clonic seizures and with rare myoclonic seizures, on valproate or phenobarbital, while the remaining affected individuals (1f–1h) were not on any antiepileptic medication, and experienced mild myoclonic seizures triggered by repetitive movements or fatigue and rare tonic-clonic seizures (every 2–3 years). One patient (25) with generalized epilepsy was seizure-free on phenytoin and clobazam. Two siblings (12a and 12b) with focal seizures had significant improvement of seizure control after introduction of zonisamide; 1 patient (11) with infant