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Isaac syndrome(NMAN)

MedGen UID:
116151
Concept ID:
C0242287
Disease or Syndrome
Synonyms: Continuous muscle fiber activity syndrome; Isaac's syndrome; Isaac's-Merten's syndrome; Isaacs Syndrome; Neuromyotonia; Quantal squander syndrome
Modes of inheritance:
Autosomal recessive inheritance
MedGen UID:
141025
Concept ID:
C0441748
Intellectual Product
Sources: HPO, OMIM, Orphanet
A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in homozygotes. In the context of medical genetics, autosomal recessive disorders manifest in homozygotes (with two copies of the mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele). [HPO:curators]
Autosomal recessive inheritance (HPO, OMIM, Orphanet)
SNOMED CT: Isaacs syndrome (80138003); Autosomal recessive axonal neuropathy with neuromyotonia (711406009); Autosomal recessive neuromyotonia with axonal neuropathy (711406009); Myokymia, myotonia and muscle wasting (711406009); Gamstorp-Wohlfart syndrome (711406009); Neuromyotonia (305719002); Continuous muscle fiber activity (305719002); Isaacs-Mertens syndrome (80138003)
 
OMIM®: 137200; 160120; 601314
Orphanet: ORPHA84142

Definition

A rare neuromuscular disorder with onset usually in late childhood or early adulthood, characterized by intermittent or continuous widespread involuntary muscle contractions; FASCICULATION; hyporeflexia; MUSCLE CRAMP; MUSCLE WEAKNESS; HYPERHIDROSIS; TACHYCARDIA; and MYOKYMIA. Involvement of pharyngeal or laryngeal muscles may interfere with speech and breathing. The continuous motor activity persists during sleep and general anesthesia (distinguishing this condition from STIFF-PERSON SYNDROME). Familial and acquired (primarily autoimmune) forms have been reported. (From Ann NY Acad Sci 1998 May 13;841:482-496; Adams et al., Principles of Neurology, 6th ed, p1491) [from MeSH]

Clinical features

Fasciculations
MedGen UID:
5124
Concept ID:
C0015644
Sign or Symptom
Fasciculations are observed as small, local, involuntary muscle contractions (twitching) visible under the skin. Fasciculations result from increased irritability of an axon (which in turn is often a manifestation of disease of a motor neuron). This leads to sporadic discharges of all the muscle fibers controlled by the axon in isolation from other motor units.
Abnormality of the foot
MedGen UID:
8888
Concept ID:
C0016506
Anatomical Abnormality
Alterations or deviations from normal shape or size which result in a disfigurement of the foot.
Muscle cramps
MedGen UID:
7749
Concept ID:
C0026821
Sign or Symptom
A sustained and usually painful contraction of muscle fibers. This may occur as an isolated phenomenon or as a manifestation of an underlying disease process (e.g., UREMIA; HYPOTHYROIDISM; MOTOR NEURON DISEASE; etc.). (From Adams et al., Principles of Neurology, 6th ed, p1398)
Myotonia
MedGen UID:
10238
Concept ID:
C0027125
Finding
An involuntary and painless delay in the relaxation of skeletal muscle following contraction or electrical stimulation.
Hyperhidrosis
MedGen UID:
11680
Concept ID:
C0038990
Finding
Abnormal excessive perspiration (sweating) despite the lack of appropriate stimuli like hot and humid weather.
Muscle stiffness
MedGen UID:
113151
Concept ID:
C0221170
Sign or Symptom
A condition in which muscles cannot be moved quickly without accompanying pain or spasm.
Skeletal muscle atrophy
MedGen UID:
902598
Concept ID:
C0234958
Disease or Syndrome
The presence of skeletal muscular atrophy (which is also known as amyotrophy).
Elevated serum creatine phosphokinase
MedGen UID:
69128
Concept ID:
C0241005
Finding
An elevation of the level of the enzyme creatine kinase (also known as creatine phosphokinase, CPK; EC 2.7.3.2) in the blood. CPK levels can be elevated in a number of clinical disorders such as myocardial infarction, rhabdomyolysis, and muscular dystrophy.
Myokymia
MedGen UID:
146882
Concept ID:
C0684219
Sign or Symptom
A disorder characterized by involuntary and irregular muscle contractions not associated with muscle weakness or atrophy. It most often affects facial muscles. It may be localized or generalized.
Sensory axonal neuropathy
MedGen UID:
334116
Concept ID:
C1842587
Finding
An axonal neuropathy of peripheral sensory nerves.
Distal sensory impairment
MedGen UID:
335722
Concept ID:
C1847584
Finding
An abnormal reduction in sensation in the distal portions of the extremities.
Foot dorsiflexor weakness
MedGen UID:
356163
Concept ID:
C1866141
Finding
Weakness of the muscles responsible for dorsiflexion of the foot, that is, of the movement of the toes towards the shin. The foot dorsiflexors include the tibialis anterior, the extensor hallucis longus, the extensor digitorum longus, and the peroneus tertius muscles.

Term Hierarchy

CClinical test,  RResearch test,  OOMIM,  GGeneReviews,  VClinVar  
  • CROGVIsaac syndrome

Recent clinical studies

Diagnosis

Lukas RV, Rezania K, Malec M, Salgia R
Neurology 2013 Jan 29;80(5):e55. doi: 10.1212/WNL.0b013e31827f0fa1. PMID: 23359380
Kass JS, Button JH, Chiou-Tan FY
Am J Phys Med Rehabil 2008 Apr;87(4):339. doi: 10.1097/PHM.0b013e318168d4e3. PMID: 18356625

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