| Phenotype | Frequency (%) | HPO Term | Category |
|---|---:|---|---|
| Global developmental delay | 95% | HP:0001263 | Neurological |
| Severe intellectual disability | 95% | HP:0010864 | Neurological |
| Absent/limited speech | 91% | HP:0001344 | Neurological |
| Square forehead | 100% | Not specified | Craniofacial |
| Full cheeks | 100% | Not specified | Craniofacial |
| Wide mouth with full lips | 100% | HP:0000154 (Broad mouth) | Craniofacial |
| Thickened helix | 100% | Not specified | Craniofacial |
| Short neck | 100% | HP:0000470 | Craniofacial |
| Slender fingers | 100% | HP:0001238 | Craniofacial |
| Gait ataxia | 93% | HP:0001251 | Neurological |
| Muscular hypotonia | 93% | HP:0001252 | Neurological |
| Brain MRI abnormalities | 79% | HP:0410263 | Neurological |
| Epilepsy/seizures | 11–50% | HP:0001250 | Neurological |
| Smiling appearance | 91% | Not specified | Behavioral |
| Autism spectrum disorder | 67% | HP:0000729 | Behavioral |
| Visual anomalies/myopia | 85% | HP:0000545 | Ophthalmological |
| Constipation | 66% | HP:0002019 | GI |
| Breathing abnormalities/hyperventilation | 50%+ | HP:0002883 | Neurological |
| Stereotypic hand movements | 100% | HP:0000733 | Behavioral |
| Microcephaly | Variable | HP:0000252 | Neurological |
| Source |  | Clinical frequencies largely from 47-patient Chinese pediatric cohort; breathing prevalence and core syndrome features supplemented by PTHS review/model data | (pqac-00000004, pqac-00000005, pqac-00000001, pqac-00000031, pqac-00000041, pqac-00000039) |


*Table: This table summarizes the major reported clinical features of Pitt-Hopkins syndrome, including approximate frequencies, suggested HPO mappings, and broad phenotype categories. It is useful for phenotype curation and disease knowledge base population.*