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Developmental delay and seizures with or without movement abnormalities(DEDSM)

MedGen UID:
Concept ID:
Disease or Syndrome
Gene (location): DHDDS (1p36.11)
Monarch Initiative: MONDO:0044326
OMIM®: 617836


DEDSM is a neurodevelopmental disorder characterized by global developmental delay, variable intellectual disability, and early-onset seizures with a myoclonic component. Most patients have delayed motor development and show abnormal movements, including ataxia, dystonia, and tremor (summary by Hamdan et al., 2017). [from OMIM]

Clinical features

From HPO
Short stature
MedGen UID:
Concept ID:
A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms).
Cerebellar ataxia
MedGen UID:
Concept ID:
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).
Dystonic disorder
MedGen UID:
Concept ID:
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.
MedGen UID:
Concept ID:
Sign or Symptom
An unintentional, oscillating to-and-fro muscle movement about a joint axis.
EEG abnormality
MedGen UID:
Concept ID:
Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp.
MedGen UID:
Concept ID:
Sign or Symptom
Bradykinesia literally means slow movement, and is used clinically to denote a slowness in the execution of movement (in contrast to hypokinesia, which is used to refer to slowness in the initiation of movement).
Delayed speech and language development
MedGen UID:
Concept ID:
A degree of language development that is significantly below the norm for a child of a specified age.
Bilateral tonic-clonic seizure
MedGen UID:
Concept ID:
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.
Epileptic encephalopathy
MedGen UID:
Concept ID:
Disease or Syndrome
A condition in which epileptiform abnormalities are believed to contribute to the progressive disturbance in cerebral function. Epileptic encephalaopathy is characterized by (1) electrographic EEG paroxysmal activity that is often aggressive, (2) seizures that are usually multiform and intractable, (3) cognitive, behavioral and neurological deficits that may be relentless, and (4) sometimes early death.
Global developmental delay
MedGen UID:
Concept ID:
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.
Chiari type I malformation
MedGen UID:
Concept ID:
Congenital Abnormality
Arnold-Chiari type I malformation refers to a relatively mild degree of herniation of the posteroinferior region of the cerebellum (the cerebellar tonsils) into the cervical canal with little or no displacement of the fourth ventricle. It is characterized by one or both pointed (not rounded) cerebellar tonsils that project 5 mm below the foramen magnum, measured by a line drawn from the basion to the opisthion (McRae Line)
Intellectual disability
MedGen UID:
Concept ID:
Mental or Behavioral Dysfunction
Intellectual disability, previously referred to as mental retardation, is characterized by subnormal intellectual functioning that occurs during the developmental period. It is defined by an IQ score below 70.
Generalized myoclonic seizure
MedGen UID:
Concept ID:
Disease or Syndrome
A generalized myoclonic seizure is a type of generalized motor seizure characterised by bilateral, 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.
Myoclonic absence seizure
MedGen UID:
Concept ID:
Disease or Syndrome
Myoclonic absence seizure is a type of generalized non-motor (absence) seizure characterised 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.
MedGen UID:
Concept ID:
Sign or Symptom
Continuous involuntary sustained muscle contraction. When an affected muscle is passively stretched, the degree of resistance remains constant regardless of the rate at which the muscle is stretched. This feature helps to distinguish rigidity from muscle spasticity.
Generalized hypotonia
MedGen UID:
Concept ID:
Generalized muscular hypotonia (abnormally low muscle tone).

Professional guidelines


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Recent clinical studies


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Clinical prediction guides

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