| Clinical feature | Suggested HPO term(s) | Typical onset | Notes / frequency info if available | Key supporting citations |
|---|---|---|---|---|
| Hydrops fetalis | **Hydrops fetalis** HP:0001789 | Prenatal | Hallmark of the congenital/hydropic subtype; described as a distinguishing feature of the severe congenital group and associated with stillbirth or death shortly after birth | (pqac-00000010, pqac-00000016, pqac-00000011, pqac-00000013, pqac-00000021, pqac-00000022, pqac-00000023) |
| Ascites / neonatal ascites | **Ascites** HP:0001541; **Fetal ascites** HP:0001791 | Prenatal / neonatal | Prominent in congenital type II; often reported together with hydrops fetalis; may be isolated or refractory congenital ascites in case literature summarized in the review | (pqac-00000010, pqac-00000016, pqac-00000011, pqac-00000013, pqac-00000021, pqac-00000022, pqac-00000023) |
| Generalized edema / facial edema | **Edema** HP:0000969; **Generalized edema** HP:0007430; **Facial edema** HP:0010669 | Prenatal / neonatal | Review states hydrops, ascites, and edema are distinguishing congenital features; gene-therapy review specifically notes facial edema in acute congenital cases | (pqac-00000010, pqac-00000016, pqac-00000011, pqac-00000014) |
| Hepatomegaly | **Hepatomegaly** HP:0002240 | Prenatal / neonatal / infantile | Included in congenital presentation and severe infantile type II; may be part of broader visceromegaly | (pqac-00000010, pqac-00000016, pqac-00000011, pqac-00000013) |
| Hepatosplenomegaly | **Hepatosplenomegaly** HP:0001433; **Splenomegaly** HP:0001744 | Neonatal / infantile | Common severe type II somatic feature; congenital review notes hepatosplenomegaly among frequent findings after hydrops/ascites/edema | (pqac-00000010, pqac-00000011, pqac-00000013, pqac-00000020) |
| Coarse facial features | **Coarse facial features** HP:0000280 | Neonatal / infantile | Frequent in infantile/juvenile type II; also noted among congenital cases | (pqac-00000010, pqac-00000011, pqac-00000013, pqac-00000020) |
| Dysostosis multiplex / skeletal dysplasia | **Dysostosis multiplex** HP:0000943; **Skeletal dysplasia** HP:0002652; **Abnormal vertebral morphology** HP:0000925 | Prenatal / infantile | Congenital review highlights dysostosis multiplex; severe type II also described with skeletal dysplasia and vertebral deformities | (pqac-00000010, pqac-00000011, pqac-00000013) |
| Inguinal hernia | **Inguinal hernia** HP:0000023 | Neonatal | Specifically mentioned in acute congenital form; review notes it as an infrequent congenital manifestation | (pqac-00000010, pqac-00000011) |
| Cherry-red macula / cherry-red spot | **Cherry red spot of the macula** HP:0010729 | Infantile | More typical of infantile/juvenile severe type II than hydropic congenital cases; part of the classic ophthalmic phenotype | (pqac-00000011, pqac-00000020, pqac-00000033) |
| Myoclonus | **Myoclonus** HP:0001336 | Infantile / juvenile | Common neurologic sign in severe type II beyond the congenital lethal presentation; used clinically with seizures for symptomatic management | (pqac-00000011, pqac-00000020, pqac-00000033) |
| Seizures | **Seizure** HP:0001250 | Infantile / juvenile | Mentioned in severe type II spectrum and in supportive-care discussions; often grouped with myoclonus | (pqac-00000011, pqac-00000015) |
| Hearing loss | **Hearing impairment** HP:0000365 | Infantile / juvenile | Included in severe type II phenotype in the 2024 preclinical gene-therapy introduction; less emphasized for hydropic congenital cases | (pqac-00000011, pqac-00000001) |
| Cardiomyopathy | **Cardiomyopathy** HP:0001638 | Infantile | Listed among severe type II manifestations in recent review/preclinical summary; uncommon but clinically important | (pqac-00000011) |
| Nephrotic syndrome / nephrosialidosis | **Nephrotic syndrome** HP:0000100; **Proteinuria** HP:0000093 | Infantile / childhood | Subset of type II patients develop nephrosialidosis with abrupt fulminant glomerular nephropathy; renal involvement is infrequent in congenital review but important in severe type II | (pqac-00000009, pqac-00000032, pqac-00000040) |
| Developmental delay / severe intellectual disability | **Global developmental delay** HP:0001263; **Intellectual disability, severe** HP:0010864 | Infantile | Severe type II is associated with marked neurodevelopmental impairment/“mental retardation”; often not assessable in lethal prenatal congenital cases | (pqac-00000013, pqac-00000020, pqac-00000033) |
| Stillbirth / very early death | **Stillbirth** HP:0003826; **Neonatal death** HP:0003811 | Prenatal / neonatal | Congenital hydropic form is often lethal during fetal development or shortly after birth | (pqac-00000010, pqac-00000016, pqac-00000011, pqac-00000013) |


*Table: This table maps the major prenatal, neonatal, and infantile manifestations of congenital/severe sialidosis type II to suggested Human Phenotype Ontology terms. It is designed for knowledge-base curation and highlights which findings are characteristic of the hydropic congenital form versus the broader severe type II spectrum.*