O
- Obesity, hyperphagia, and developmental delay
- Occipital horn syndrome
- Occult macular dystrophy
- Occult primary tumor
- Ochoa syndrome
- Ochronosis
- Ocular Albinism
- Ocular Muscular Dystrophy
- Ocular albinism type 1
- Ocular cicatricial pemphigoid
- Ocular coloboma-imperforate anus
- Ocular colobomas, ichthyosis, brain malformations and endocrine abnormalities
- Ocular convergence spasm
- Oculo cerebro acral syndrome
- Oculo cerebro osseous syndrome
- Oculo digital syndrome
- Oculo skeletal renal syndrome
- Oculo tricho anal syndrome
- Oculo tricho dysplasia
- Oculo-gastrointestinal muscular dystrophy
- Oculoauricular syndrome
- Oculoauriculofrontonasal syndrome
- Oculocerebral hypopigmentation syndrome type Preus
- Oculocerebral syndrome with hypopigmentation
- Oculocerebrocutaneous syndrome
- Oculocerebrorenal syndrome
- Oculocutaneous Albinism
- Oculocutaneous albinism type 1
- Oculocutaneous albinism type 1B
- Oculocutaneous albinism type 2
- Oculocutaneous albinism type 3
- Oculocutaneous albinism, type 4
- Oculocutaneous tyrosinemia
- Oculodentodigital dysplasia
- Oculodentodigital dysplasia dominant
- Oculodentodigital dysplasia, autosomal recessive
- Oculodentoosseous dysplasia dominant
- Oculodentoosseous dysplasia recessive
- Oculodigitoesophagoduodenal syndrome
- Oculoectodermal syndrome
- Oculofaciocardiodental syndrome
- Oculomaxillofacial dysostosis
- Oculomelic amyoplasia
- Oculootofacial dysplasia
- Oculopharyngeal muscular dystrophy
- Oculorenocerebellar syndrome
- Odonto onycho dysplasia with alopecia
- Odontogenic myxoma
- Odontomicronychial dysplasia
- Odontoonychodermal dysplasia
- Odontotrichomelic hypohidrotic dysplasia
- Odontotrichomelic syndrome
