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Developmental and epileptic encephalopathy 6B(DEE6B)

MedGen UID:
1779648
Concept ID:
C5543353
Disease or Syndrome
Synonym: Developmental and epileptic encephalopathy 6B, non-Dravet
 
Gene (location): SCN1A (2q24.3)
 
Monarch Initiative: MONDO:0030268
OMIM®: 619317

Disease characteristics

Excerpted from the GeneReview: SCN1A Seizure Disorders
SCN1A seizure disorders encompass a spectrum that ranges from simple febrile seizures and generalized epilepsy with febrile seizures plus (GEFS+) at the mild end to Dravet syndrome and intractable childhood epilepsy with generalized tonic-clonic seizures (ICE-GTC) at the severe end. Phenotypes with intractable seizures including Dravet syndrome are often associated with cognitive decline. Less commonly observed phenotypes include myoclonic astatic epilepsy (MAE), Lennox-Gastaut syndrome, infantile spasms, epilepsy with focal seizures, and vaccine-related encephalopathy and seizures. The phenotype of SCN1A seizure disorders can vary even within the same family. [from GeneReviews]
Authors:
Ian O Miller  |  Marcio A Sotero de Menezes   view full author information

Additional description

From OMIM
Developmental and epileptic encephalopathy-6B (DEE6B) is a severe neurodevelopmental disorder characterized by early-infantile seizure onset, profoundly impaired intellectual development, and a hyperkinetic movement disorder. Brain imaging usually shows progressive atrophy and other abnormalities (summary by Sadleir et al., 2017).  http://www.omim.org/entry/619317

Clinical features

From HPO
Sudden unexpected death in epilepsy
MedGen UID:
930396
Concept ID:
C4304727
Finding
Sudden unexpected death in epilepsy (SUDEP) is a sudden, unexpected, witnessed or unwitnessed, non-traumatic and non-drowning death, occurring in benign circumstances, in an individual with epilepsy, with or without evidence for a seizure and excluding documented status epilepticus, in which postmortem examination has not revealed a cause of death.
Gastrostomy tube feeding in infancy
MedGen UID:
892362
Concept ID:
C4023342
Finding
Feeding problem necessitating gastrostomy tube feeding.
Cerebellar ataxia
MedGen UID:
849
Concept ID:
C0007758
Disease or Syndrome
Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).
Chorea
MedGen UID:
3420
Concept ID:
C0008489
Disease or Syndrome
Chorea (Greek for 'dance') refers to widespread arrhythmic involuntary movements of a forcible, jerky and restless fashion. It is a random-appearing sequence of one or more discrete involuntary movements or movement fragments. Movements appear random because of variability in timing, duration or location. Each movement may have a distinct start and end. However, movements may be strung together and thus may appear to flow randomly from one muscle group to another. Chorea can involve the trunk, neck, face, tongue, and extremities.
Dystonic disorder
MedGen UID:
3940
Concept ID:
C0013421
Sign or Symptom
An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk.
Myoclonus
MedGen UID:
10234
Concept ID:
C0027066
Finding
Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements.
Motor stereotypies
MedGen UID:
21318
Concept ID:
C0038271
Individual Behavior
Use of the same abnormal action in response to certain triggers or at random. They may be used as a way to regulate one's internal state but must otherwise have no apparent functional purpose.
Arachnoid cyst
MedGen UID:
86860
Concept ID:
C0078981
Disease or Syndrome
An extra-parenchymal and intra-arachnoidal collection of fluid with a composition similar to that of cerebrospinal fluid.
Choreoathetosis
MedGen UID:
39313
Concept ID:
C0085583
Disease or Syndrome
Involuntary movements characterized by both athetosis (inability to sustain muscles in a fixed position) and chorea (widespread jerky arrhythmic movements).
Tonic seizure
MedGen UID:
82855
Concept ID:
C0270844
Disease or Syndrome
A tonic seizure is a type of motor seizure characterized by unilateral or bilateral limb stiffening or elevation, often with neck stiffening.
Bilateral tonic-clonic seizure
MedGen UID:
141670
Concept ID:
C0494475
Sign or Symptom
A bilateral tonic-clonic seizure is a seizure defined by a tonic (bilateral increased tone, lasting seconds to minutes) and then a clonic (bilateral sustained rhythmic jerking) phase.
Global developmental delay
MedGen UID:
107838
Concept ID:
C0557874
Finding
A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.
Inability to walk
MedGen UID:
107860
Concept ID:
C0560046
Finding
Incapability to ambulate.
Focal-onset seizure
MedGen UID:
199670
Concept ID:
C0751495
Disease or Syndrome
A focal-onset seizure is a type of seizure originating within networks limited to one hemisphere. They may be discretely localized or more widely distributed, and may originate in subcortical structures.
Status epilepticus without prominent motor symptoms
MedGen UID:
199677
Concept ID:
C0751523
Disease or Syndrome
There is inconclusive evidence to precisely define the duration of the seizure; however, based on current evidence an operational threshold of 10 minutes is appropriate as beyond this a seizure is likely to be more prolonged. The individual may or may not be aware or in coma.
Epileptic spasm
MedGen UID:
315948
Concept ID:
C1527366
Disease or Syndrome
A sudden flexion, extension, or mixed extension-flexion of predominantly proximal and truncal muscles that is usually more sustained than a myoclonic movement but not as sustained as a tonic seizure. Limited forms may occur
Focal hemiclonic seizure
MedGen UID:
335477
Concept ID:
C1846620
Disease or Syndrome
A type of focal clonic seizure characterized by sustained rhythmic jerking rapidly involves one side of the body at seizure onset.
Absent speech
MedGen UID:
340737
Concept ID:
C1854882
Finding
Complete lack of development of speech and language abilities.
Brisk reflexes
MedGen UID:
382164
Concept ID:
C2673700
Finding
Tendon reflexes that are noticeably more active than usual (conventionally denoted 3+ on clinical examination). Brisk reflexes may or may not indicate a neurological lesion. They are distinguished from hyperreflexia by the fact that hyerreflexia is characterized by hyperactive repeating (clonic) reflexes, which are considered to be always abnormal.
Intellectual disability, profound
MedGen UID:
892508
Concept ID:
C3161330
Mental or Behavioral Dysfunction
Profound mental retardation is defined as an intelligence quotient (IQ) below 20.
Hyperkinetic movements
MedGen UID:
854367
Concept ID:
C3887506
Disease or Syndrome
Motor hyperactivity with excessive movement of muscles of the body as a whole.
Multifocal epileptiform discharges
MedGen UID:
866864
Concept ID:
C4021219
Finding
An abnormality in cerebral electrical activity recorded along the scalp by electroencephalography (EEG) and being identified at multiple locations (foci).
Myoclonic absence seizure
MedGen UID:
869094
Concept ID:
C4023512
Disease or Syndrome
Myoclonic absence seizure is a type of generalized non-motor (absence) seizure characterized by an interruption of ongoing activities, a blank stare and rhythmic three-per-second myoclonic movements, causing ratcheting abduction of the upper limbs leading to progressive arm elevation, and associated with 3 Hz generalized spike-wave discharges on the electroencephalogram. Duration is typically 10-60 s. Whilst impairment of consciousness may not be obvious the ILAE classified this seizure as a generalized non-motor seizure in 2017.
EEG with spike-wave complexes (>3.5 Hz)
MedGen UID:
892339
Concept ID:
C4023684
Finding
The presence of complexes of spikes and waves (>3.5 Hz) in electroencephalography (EEG).
Generalized non-motor (absence) seizure
MedGen UID:
1385688
Concept ID:
C4316903
Disease or Syndrome
A generalized non-motor (absence) seizure is a type of a type of dialeptic seizure that is of electrographically generalized onset. It is a generalized seizure characterized by an interruption of activities, a blank stare, and usually the person will be unresponsive when spoken to. Any ictal motor phenomena are minor in comparison to these non-motor features.
Myoclonic seizure
MedGen UID:
1385980
Concept ID:
C4317123
Sign or Symptom
A myoclonic seizure is a type of motor seizure characterized by sudden, brief (<100 ms) involuntary single or multiple contraction of muscles or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus.
Hypoplastic hippocampus
MedGen UID:
1388294
Concept ID:
C4476822
Congenital Abnormality
Underdevelopment of the hippocampus.
Hypotonia
MedGen UID:
10133
Concept ID:
C0026827
Finding
Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.
Scoliosis
MedGen UID:
11348
Concept ID:
C0036439
Disease or Syndrome
The presence of an abnormal lateral curvature of the spine.
Axial hypotonia
MedGen UID:
342959
Concept ID:
C1853743
Finding
Muscular hypotonia (abnormally low muscle tone) affecting the musculature of the trunk.
Narrow mouth
MedGen UID:
44435
Concept ID:
C0026034
Congenital Abnormality
Distance between the commissures of the mouth more than 2 SD below the mean. Alternatively, an apparently decreased width of the oral aperture (subjective).
High forehead
MedGen UID:
65991
Concept ID:
C0239676
Finding
An abnormally increased height of the forehead.
Hypertelorism
MedGen UID:
9373
Concept ID:
C0020534
Finding
Although hypertelorism means an excessive distance between any paired organs (e.g., the nipples), the use of the word has come to be confined to ocular hypertelorism. Hypertelorism occurs as an isolated feature and is also a feature of many syndromes, e.g., Opitz G syndrome (see 300000), Greig cephalopolysyndactyly (175700), and Noonan syndrome (163950) (summary by Cohen et al., 1995).
Nystagmus
MedGen UID:
45166
Concept ID:
C0028738
Disease or Syndrome
Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms.
Spasmus nutans
MedGen UID:
154280
Concept ID:
C0546878
Disease or Syndrome
The combination of pendular nystagmus, head nodding, and torticollis.

Recent clinical studies

Diagnosis

Kaya Özçora GD, Söbü E, Gümüş U
Neurol Res 2023 Mar;45(3):226-233. Epub 2023 Feb 2 doi: 10.1080/01616412.2023.2170917. PMID: 36731496

Prognosis

Kaya Özçora GD, Söbü E, Gümüş U
Neurol Res 2023 Mar;45(3):226-233. Epub 2023 Feb 2 doi: 10.1080/01616412.2023.2170917. PMID: 36731496

Clinical prediction guides

Hamanaka K, Imagawa E, Koshimizu E, Miyatake S, Tohyama J, Yamagata T, Miyauchi A, Ekhilevitch N, Nakamura F, Kawashima T, Goshima Y, Mohamed AR, Ch'ng GS, Fujita A, Azuma Y, Yasuda K, Imamura S, Nakashima M, Saitsu H, Mitsuhashi S, Mizuguchi T, Takata A, Miyake N, Matsumoto N
Am J Hum Genet 2020 Apr 2;106(4):549-558. Epub 2020 Mar 12 doi: 10.1016/j.ajhg.2020.02.011. PMID: 32169168Free PMC Article

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