National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

C syndrome



Other Names:
Opitz trigonocephaly syndrome; Trigonocephaly C syndrome; Trigonocephaly syndrome
Categories:

C syndrome, also known as Opitz trigonocephaly syndrome, is characterized by trigonocephaly, severe intellectual disability, hypotonia, variable cardiac defects, redundant (extra folds of) skin, joint and limb abnormalities, and unusual facial features such as upslanted palpebral fissures (upward pointing outside corners of the eyes), epicanthal folds, depressed nasal bridge, and low-set, posteriorly rotated ears. This condition is genetically heterogeneous, meaning that there is evidence of more than one type of inheritance. While many cases are sporadic, autosomal recessive, autosomal dominant, and germline mosaicism have all been suggested. At least some cases of C syndrome have been caused by dysfunction of the CD96 gene.[1][2]  
Last updated: 6/19/2014

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Anteverted nares
Nasal tip, upturned
Upturned nasal tip
Upturned nose
Upturned nostrils
[ more ]
0000463
Biparietal narrowing 0004422
Clinodactyly of the 5th finger
Permanent curving of the pinkie finger
0004209
Cryptorchidism
Undescended testes
Undescended testis
[ more ]
0000028
Depressed nasal bridge
Depressed bridge of nose
Flat bridge of nose
Flat nasal bridge
Flat, nasal bridge
Flattened nasal bridge
Low nasal bridge
Low nasal root
[ more ]
0005280
Epicanthus
Eye folds
Prominent eye folds
[ more ]
0000286
Female pseudohermaphroditism 0010458
Gingival overgrowth
Gum enlargement
0000212
High palate
Elevated palate
Increased palatal height
[ more ]
0000218
Hypoplasia of the ear cartilage
Underdeveloped ear cartilage
0100720
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ]
0001249
Long philtrum 0000343
Low-set, posteriorly rotated ears 0000368
Microcephaly
Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference
[ more ]
0000252
Micrognathia
Little lower jaw
Small jaw
Small lower jaw
[ more ]
0000347
Short neck
Decreased length of neck
0000470
Short nose
Decreased length of nose
Shortened nose
[ more ]
0003196
Smooth philtrum 0000319
Trigonocephaly
Triangular skull shape
Wedge shaped skull
[ more ]
0000243
Upslanted palpebral fissure
Upward slanting of the opening between the eyelids
0000582
30%-79% of people have these symptoms
Abnormality of cardiovascular system morphology 0030680
Abnormality of immune system physiology 0010978
Abnormality of the anus 0004378
Accessory oral frenulum 0000191
Bilateral single transverse palmar creases 0007598
Dislocated radial head 0003083
Failure to thrive in infancy
Faltering weight in infancy
Weight faltering in infancy
[ more ]
0001531
Limitation of joint mobility
Decreased joint mobility
Decreased mobility of joints
Limited joint mobility
Limited joint motion
[ more ]
0001376
Micromelia
Smaller or shorter than typical limbs
0002983
Midline facial capillary hemangioma 0007601
Muscular hypotonia
Low or weak muscle tone
0001252
Pectus excavatum
Funnel chest
0000767
Redundant skin
Loose redundant skin
Redundant skin folds
Sagging, redundant skin
[ more ]
0001582
Sacral dimple
Spinal dimple
0000960
Seizure 0001250
Short stature
Decreased body height
Small stature
[ more ]
0004322
Strabismus
Cross-eyed
Squint
Squint eyes
[ more ]
0000486
Talipes 0001883
Thin vermilion border
Decreased volume of lip
Thin lips
[ more ]
0000233
5%-29% of people have these symptoms
Abnormal hair pattern
Abnormal distribution of hair
0010720
Aplasia/Hypoplasia of the abdominal wall musculature
Absent/small abdominal wall muscles
Absent/underdeveloped abdominal wall muscles
[ more ]
0010318
Aplasia/Hypoplasia of the corpus callosum 0007370
Cleft palate
Cleft roof of mouth
0000175
Congenital diaphragmatic hernia 0000776
Constipation 0002019
Death in infancy
Infantile death
Lethal in infancy
[ more ]
0001522
Hand polydactyly
Extra finger
0001161
Horseshoe kidney
Horseshoe kidneys
0000085
Multicystic kidney dysplasia 0000003
Omphalocele 0001539
Polyhydramnios
High levels of amniotic fluid
0001561
Renal hypoplasia/aplasia
Absent/small kidney
Absent/underdeveloped kidney
[ more ]
0008678
Toe syndactyly
Fused toes
Webbed toes
[ more ]
0001770
Percent of people who have these symptoms is not available through HPO
Autosomal dominant inheritance 0000006
Autosomal recessive inheritance 0000007
Clinodactyly
Permanent curving of the finger
0030084
Clitoral hypertrophy
Enlarged clitoris
0008665
Cutis laxa
Loose and inelastic skin
0000973
Delayed skeletal maturation
Delayed bone maturation
Delayed skeletal development
[ more ]
0002750
Failure to thrive
Faltering weight
Weight faltering
[ more ]
0001508
Fused sternal ossification centers 0006643
Generalized hypotonia
Decreased muscle tone
Low muscle tone
[ more ]
0001290
Global developmental delay 0001263
Hepatomegaly
Enlarged liver
0002240
Hip dislocation
Dislocated hips
Dislocation of hip
[ more ]
0002827
Limb undergrowth
limb shortening
Short limb
Short limbs
[ more ]
0009826
Low-set ears
Low set ears
Lowset ears
[ more ]
0000369
Patent ductus arteriosus 0001643
Postaxial foot polydactyly
Extra toe attached near the little toe
0001830
Postaxial hand polydactyly
Extra little finger
Extra pinkie finger
Extra pinky finger
[ more ]
0001162
Posteriorly rotated ears
Ears rotated toward back of head
0000358
Psychomotor retardation 0025356
Radial deviation of finger 0009466
Renal cortical cysts 0000803
Scoliosis 0002650
Short metacarpal
Shortened long bone of hand
0010049
Thick anterior alveolar ridges 0009100
Ulnar deviation of finger
Finger bends toward pinky
0009465
Ventricular septal defect
Hole in heart wall separating two lower heart chambers
0001629
Wide mouth
Broad mouth
Large mouth
[ more ]
0000154
Wide nasal bridge
Broad nasal bridge
Broad nasal root
Broadened nasal bridge
Increased breadth of bridge of nose
Increased breadth of nasal bridge
Increased width of bridge of nose
Increased width of nasal bridge
Nasal bridge broad
Wide bridge of nose
Widened nasal bridge
[ more ]
0000431
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Last updated: 7/1/2020

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources


Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Clinical Research Resources

  • ClinicalTrials.gov lists trials that are related to C syndrome. Click on the link to go to ClinicalTrials.gov to read descriptions of these studies.

    Please note: Studies listed on the ClinicalTrials.gov website are listed for informational purposes only; being listed does not reflect an endorsement by GARD or the NIH. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss C syndrome. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.


  1. C Syndrome. Online Mendelian Inheritance in Man (OMIM). October 25, 2011; http://omim.org/entry/211750. Accessed 6/19/2014.
  2. Kaname T et al.. Amer J Hum Genet. October 2007; 81(4):835-41. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2227933/. Accessed 6/19/2014.