Explore the signs and symptoms, genetic cause, and inheritance pattern of various health conditions.

• OA, see Ocular albinism
• OA, see Osteoarthritis
• OAS, see Ophthalmo-acromelic syndrome
• OAT deficiency, see Gyrate atrophy of the choroid and retina
• OAV complex, see Craniofacial microsomia
• OAVS, see Craniofacial microsomia
• Oberklaid-Danks syndrome, see Bohring-Opitz syndrome
• Obesity due to congenital leptin deficiency, see Congenital leptin deficiency
• Obesity due to leptin receptor gene deficiency, see Leptin receptor deficiency
• Obesity, early-onset, adrenal insufficiency, and red hair, see Proopiomelanocortin deficiency
• Obesity, morbid, due to leptin deficiency, see Congenital leptin deficiency
• Obesity, morbid, due to leptin receptor deficiency, see Leptin receptor deficiency
• Obesity, morbid, nonsyndromic 1, see Congenital leptin deficiency
• Obesity, morbid, nonsyndromic 2, see Leptin receptor deficiency
• Obesity, severe, due to leptin deficiency, see Congenital leptin deficiency
• Obesity-hypotonia syndrome, see Cohen syndrome
• Obsessive-compulsive disorder
• Obsessive-compulsive neurosis, see Obsessive-compulsive disorder
• Obstetric cholestasis, see Intrahepatic cholestasis of pregnancy
• Obstructive apnea, see Obstructive sleep apnea
• Obstructive disease of the pulmonary veins, see Pulmonary veno-occlusive disease
• Obstructive sleep apnea
• Obstructive sleep apnea syndrome, see Obstructive sleep apnea
• OCA, see Oculocutaneous albinism
• Occlusive infantile arteriopathy, see Generalized arterial calcification of infancy
• Occupational cramp, see Task-specific focal dystonia
• Occupational dystonia, see Task-specific focal dystonia
• OCD, see Obsessive-compulsive disorder
• OCD, see Familial osteochondritis dissecans
• Ochoa syndrome
• Ocular albinism
• Ocular coloboma, see Coloboma
• Ocular retraction syndrome, see Isolated Duane retraction syndrome
• Ocular rosacea, see Rosacea
• Oculo-dento-digital dysplasia, see Oculodentodigital dysplasia
• Oculo-digito-esophagoduodental (ODED) syndrome, see Feingold syndrome
• Oculo-facio-cardio-dental syndrome, see Oculofaciocardiodental syndrome
• Oculo-oto-facial dysplasia, see Burn-McKeown syndrome
• Oculo-skeletal-abdominal syndrome, see 3MC syndrome
• Oculoauriculovertebral spectrum, see Craniofacial microsomia
• Oculocerebrofacial syndrome, Kaufman type, see Kaufman oculocerebrofacial syndrome
• Oculocerebrorenal syndrome, see Lowe syndrome
• Oculocerebrorenal syndrome of Lowe, see Lowe syndrome
• Oculocutaneous albinism
• Oculocutaneous albinism with leukocyte defect, see Chediak-Higashi syndrome
• Oculodentodigital dysplasia
• Oculodentodigital dysplasia, autosomal recessive, see Oculodentodigital dysplasia
• Oculodentodigital syndrome, see Oculodentodigital dysplasia
• Oculodentodigitalis dysplasia, see Oculodentodigital dysplasia
• Oculodentoosseous dysplasia, see Oculodentodigital dysplasia
• Oculofaciocardiodental syndrome
• Oculogastrointestinal muscular dystrophy, see Mitochondrial neurogastrointestinal encephalopathy disease
• Oculootofacial dysplasia, see Burn-McKeown syndrome
• Oculopalatoskeletal syndrome, see 3MC syndrome
• Oculopharyngeal dystrophy, see Oculopharyngeal muscular dystrophy
• Oculopharyngeal muscular dystrophy
• Oculosympathetic palsy, see Horner syndrome
• OD, see Familial osteochondritis dissecans
• ODD syndrome, see Oculodentodigital dysplasia
• ODDD, see Oculodentodigital dysplasia
• ODDD syndrome, see Oculodentodigital dysplasia
• ODDD, autosomal recessive, see Oculodentodigital dysplasia
• ODOD , see Oculodentodigital dysplasia
• ODOD syndrome, see Oculodentodigital dysplasia
• ODOD, autosomal recessive, see Oculodentodigital dysplasia
• Odontoleukodystrophy, see Pol III-related leukodystrophy
• Oestrogen synthetase deficiency, see Aromatase deficiency
• OFCD syndrome, see Oculofaciocardiodental syndrome
• OFDS, see Oral-facial-digital syndrome
• OGD, see Osteoglophonic dysplasia
• OGIMD, see Mitochondrial neurogastrointestinal encephalopathy disease
• Ohaha syndrome, see Infantile-onset spinocerebellar ataxia
• Ohdo syndrome, Maat-Kievit-Brunner type
• Ohdo syndrome, MKB type, see Ohdo syndrome, Maat-Kievit-Brunner type
• Ohdo syndrome, Say-Barber-Biesecker variant, see Ohdo syndrome, Say-Barber-Biesecker-Young-Simpson variant
• Ohdo syndrome, Say-Barber-Biesecker-Young-Simpson variant
• Ohdo syndrome, SBBYS variant, see Ohdo syndrome, Say-Barber-Biesecker-Young-Simpson variant
• OI, see Osteogenesis imperfecta
• Okamoto syndrome, see Au-Kline syndrome
• Okihiro syndrome, see Duane-radial ray syndrome
• OKS, see FG syndrome
• OKT deficiency, see Gyrate atrophy of the choroid and retina
• Old Silk Route disease, see Behçet disease
• Old-aged sensorineural hearing impairment, see Age-related hearing loss
• Oligophrenia microphthalmus, see Norrie disease
• Olivopontocerebellar atrophy I, see Spinocerebellar ataxia type 1
• Ollier disease
• Ollier's syndrome, see Ollier disease
• Omenn syndrome
• Omenn's syndrome, see Omenn syndrome
• Omphalocele, see Abdominal wall defect
• ONCR, see Renal coloboma syndrome
• Ondine syndrome, see Congenital central hypoventilation syndrome
• Ondine-Hirschsprung disease, see Congenital central hypoventilation syndrome
• Onychauxis, hyponychia, and onycholysis, see Nonsyndromic congenital nail disorder 10
• OOFD, see Burn-McKeown syndrome
• OPA3, see Autosomal dominant optic atrophy and cataract
• OPA3 defect, see Costeff syndrome
• OPA3, autosomal dominant, see Autosomal dominant optic atrophy and cataract
• OPCA, see Multiple system atrophy
• OPCH, see Pontocerebellar hypoplasia
• OPD syndrome, type 1, see Otopalatodigital syndrome type 1
• OPD syndrome, type 2, see Otopalatodigital syndrome type 2
• Open spine, see Spina bifida
• Ophthalmo-acromelic syndrome
• Ophthalmoacromelic syndrome, see Ophthalmo-acromelic syndrome
• Ophthalmoplegia, hypotonia, ataxia, hypacusis, and athetosis, see Infantile-onset spinocerebellar ataxia
• Ophthalmoplegia, progressive external, and scoliosis, see Horizontal gaze palsy with progressive scoliosis
• Opiate addiction, see Opioid addiction
• Opiate dependence, see Opioid addiction
• Opioid addiction
• Opioid dependence, see Opioid addiction
• Opitz BBB syndrome, see Opitz G/BBB syndrome
• Opitz BBB/G syndrome, see Opitz G/BBB syndrome
• Opitz G syndrome, see Opitz G/BBB syndrome
• Opitz G/BBB syndrome
• Opitz syndrome, see Opitz G/BBB syndrome
• Opitz trigonocephaly-like syndrome, see Bohring-Opitz syndrome
• Opitz-Frias syndrome, see Opitz G/BBB syndrome
• Opitz-Kaveggia syndrome, see FG syndrome
• OPMD, see Oculopharyngeal muscular dystrophy
• Oppenheim dystonia, see Early-onset isolated dystonia
• Oppenheim's dystonia, see Early-onset isolated dystonia
• OPPG, see Osteoporosis-pseudoglioma syndrome
• Optic atrophy and cataract, autosomal dominant, see Autosomal dominant optic atrophy and cataract
• Optic atrophy plus syndrome, see Costeff syndrome
• Optic atrophy type 1
• Optic atrophy type 3, see Autosomal dominant optic atrophy and cataract
• Optic atrophy, autosomal dominant, see Optic atrophy type 1
• Optic atrophy, cataract, and neurologic disorder, see Autosomal dominant optic atrophy and cataract
• Optic atrophy, hereditary, autosomal dominant, see Optic atrophy type 1
• Optic atrophy, juvenile, see Optic atrophy type 1
• Optic atrophy, Kjer type, see Optic atrophy type 1
• Optic coloboma, vesicoureteral reflux, and renal anomalies, see Renal coloboma syndrome
• Optic nerve coloboma renal syndrome, see Renal coloboma syndrome
• Optic-spinal MS, see Neuromyelitis optica
• Opticoacoustic nerve atrophy with dementia, see Deafness-dystonia-optic neuronopathy syndrome
• Opticospinal MS, see Neuromyelitis optica
• Oral-facial-digital syndrome
• Oral-mandibular-auricular syndrome, see Craniofacial microsomia
• ORAS, see Otulipenia
• Ormond disease, see Retroperitoneal fibrosis
• Ormond's disease, see Retroperitoneal fibrosis
• Ornithine aminotransferase deficiency, see Gyrate atrophy of the choroid and retina
• Ornithine Carbamoyltransferase Deficiency Disease, see Ornithine transcarbamylase deficiency
• Ornithine keto acid aminotransferase deficiency, see Gyrate atrophy of the choroid and retina
• Ornithine transcarbamylase deficiency
• Ornithine translocase deficiency
• Ornithine-delta-aminotransferase deficiency, see Gyrate atrophy of the choroid and retina
• Ornithinemia with gyrate atrophy, see Gyrate atrophy of the choroid and retina
• Oro-facio-digital syndrome, see Oral-facial-digital syndrome
• Orodigitofacial dysostosis, see Oral-facial-digital syndrome
• Orodigitofacial syndrome, see Oral-facial-digital syndrome
• Orofaciodigital syndrome, see Oral-facial-digital syndrome
• Orthostatic hypotension
• OSA, see Obstructive sleep apnea
• OSA syndrome, see 3MC syndrome
• OSAHS, see Obstructive sleep apnea
• OSAS, see Obstructive sleep apnea
• Osler-Vaquez disease, see Polycythemia vera
• Osler-Weber-Rendu syndrome, see Hereditary hemorrhagic telangiectasia
• OSMED, see Otospondylomegaepiphyseal dysplasia
• Osseous Paget's disease, see Paget disease of bone
• Osseous-oculo-dental dysplasia, see Oculodentodigital dysplasia
• Osteitis deformans, see Paget disease of bone
• Osteitis fibrosa disseminata, see McCune-Albright syndrome
• Osteoarthritis
• Osteoarthritis deformans, see Osteoarthritis
• Osteoarthrosis, see Osteoarthritis
• Osteochalasia desmalis familiaris, see Juvenile Paget disease
• Osteochondritis dissecans, short stature, and early-onset osteoarthritis, see Familial osteochondritis dissecans
• Osteochondrosis of the capital femoral epiphysis, see Legg-Calvé-Perthes disease
• Osteodermia, see Progressive osseous heteroplasia
• Osteodysplastic primordial dwarfism type II, see Microcephalic osteodysplastic primordial dwarfism type II
• Osteodysplasty of Melnick and Needles, see Melnick-Needles syndrome
• Osteoectasia with hyperphosphatasia, see Juvenile Paget disease
• Osteogenesis imperfecta
• Osteogenesis imperfecta with unusual skeletal lesions, see Gnathodiaphyseal dysplasia
• Osteogenesis imperfecta, Levin type, see Gnathodiaphyseal dysplasia
• Osteogenesis imperfecta, ocular form, see Osteoporosis-pseudoglioma syndrome
• Osteoglophonic dwarfism, see Osteoglophonic dysplasia
• Osteoglophonic dysplasia
• Osteoma cutis, see Progressive osseous heteroplasia
• Osteopathia condensans disseminata, see Buschke-Ollendorff syndrome
• Osteopetroses, see Osteopetrosis
• Osteopetrosis
• Osteoporosis-pseudoglioma syndrome
• Osteosis cutis, see Progressive osseous heteroplasia
• Osterreicher syndrome, see Nail-patella syndrome
• Oto-palato-digital syndrome, type I, see Otopalatodigital syndrome type 1
• Oto-palato-digital syndrome, type II, see Otopalatodigital syndrome type 2
• Oto-spondylo-megaepiphyseal dysplasia, see Otospondylomegaepiphyseal dysplasia
• Otogenic vertigo, see Ménière disease
• Otomandibular dysostosis, see Craniofacial microsomia
• Otopalatodigital syndrome type 1
• Otopalatodigital syndrome type 2
• Otospondylomegaepiphyseal dysplasia
• Otospondylomegaepiphyseal dysplasia, autosomal dominant, see Weissenbacher-Zweymüller syndrome
• OTULIN-related autoinflammatory syndrome, see Otulipenia
• Otulipenia
• Ovarian cancer
• Ovarian carcinoma, see Ovarian cancer
• Ovarian dysgenesis with sensorineural deafness, see Perrault syndrome
• Owren disease, see Factor V deficiency
• Owren's disease, see Factor V deficiency
• Oxalosis, see Primary hyperoxaluria
• Oxaluria, primary, see Primary hyperoxaluria