Rare diseases · Sign or symptom
Delayed ability to sit
HP:0025336
What it means
A failure to achieve the ability to sit at an appropriate developmental stage. Most children sit with support at 6 months of age and sit steadily without support at 9 months of age.
This milestone can be defined as the ability of an infant to sit up straight with head erect for at least 10 s without using arms or hands to balance body or support the position.
Rare diseases that can present with this11
Very common80–99%
2Common30–79%
6- Cortical dysgenesis with pontocerebellar hypoplasia due to TUBB3 mutation
- Intellectual disability-seizures-abnormal gait-facial dysmorphism syndrome
- Lissencephaly due to LIS1 mutation
- Muscle-eye-brain disease with bilateral multicystic leucodystrophy
- Pelizaeus-Merzbacher disease, classic form
- Skeletal dysplasia-T-cell immunodeficiency-developmental delay syndrome
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
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Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.