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The Human Phenotype Ontology (HPO) is downloaded weekly from The file downloaded is considered the "last stable build" available for the ontology. For more about the HPO, view their website at

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Accession:HP:0001252 term browser browse the term
Definition: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.
Comment:Hypotonia can be caused by abnormalities of the central nervous system, any element of the motor unit (including the lower motoneuron), or both. Hypotonia is not a specific diagnosis, but can be observed in hundreds of genetic and other diseases. The first distinction to make when assessing a child with hypotonia is whether decreased muscle tone is a result of an abnormality of the central nervous system (CNS), peripheral neuromuscular system, or a combined abnormality involving both. Clinical findings suggestive of an abnormality of the CNS may include hyperreflexia, cognitive developmental delay, and seizures. In contrast, physical findings pointing towards a neuromuscular origin may include weakness, lack of antigravity movements, muscle atrophy, fasciculations, and/or diminished reflexes, most often in the context of normal cognitive function. The HPO term does not distinguish between these etiologies. Additional HPO terms should be used as required to describe associated features.
Synonyms:exact_synonym: Low muscle tone;   Low or weak muscle tone;   Muscle hypotonia;   Muscular hypotonia
 narrow_synonym: Central hypotonia;   Peripheral hypotonia
 alt_id: HP:0011398
 xref: MSH:D009123;   SNOMEDCT_US:398151007;   SNOMEDCT_US:398152000;   UMLS:C0026827

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  Human phenotype 0
    Phenotypic abnormality 0
      Abnormality of the musculoskeletal system 0
        Abnormality of the musculature 0
          Abnormal muscle physiology 0
            Abnormal muscle tone 0
              Hypotonia 0
                Appendicular hypotonia 0
                Facial hypotonia 0
                Frog-leg posture 0
                Generalized hypotonia + 0
                Infantile muscular hypotonia + 0
                Muscular hypotonia of the trunk + 0
                Neonatal hypotonia + 0
                Oral motor hypotonia 0
                Severe muscular hypotonia 0
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