Question: What is (are) C syndrome ?
Answer: 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.
Source: GARD

Question: What are the symptoms of C syndrome ?
Answer: What are the signs and symptoms of C syndrome? The Human Phenotype Ontology provides the following list of signs and symptoms for C syndrome. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Anteverted nares 90% Clinodactyly of the 5th finger 90% Cognitive impairment 90% Cryptorchidism 90% Depressed nasal bridge 90% Epicanthus 90% Female pseudohermaphroditism 90% Gingival overgrowth 90% Hypoplasia of the ear cartilage 90% Long philtrum 90% Low-set, posteriorly rotated ears 90% Microcephaly 90% Narrow forehead 90% Short neck 90% Short nose 90% Trigonocephaly 90% Upslanted palpebral fissure 90% Abnormality of immune system physiology 50% Cutis laxa 50% Joint dislocation 50% Limitation of joint mobility 50% Micromelia 50% Muscular hypotonia 50% Pectus excavatum 50% Sacral dimple 50% Seizures 50% Short stature 50% Single transverse palmar crease 50% Strabismus 50% Talipes 50% Thin vermilion border 50% Urogenital fistula 50% Abnormal localization of kidney 7.5% Aplasia/Hypoplasia of the abdominal wall musculature 7.5% Aplasia/Hypoplasia of the corpus callosum 7.5% Cleft palate 7.5% Congenital diaphragmatic hernia 7.5% Constipation 7.5% Hand polydactyly 7.5% Multicystic kidney dysplasia 7.5% Omphalocele 7.5% Polyhydramnios 7.5% Renal hypoplasia/aplasia 7.5% Toe syndactyly 7.5% Accessory oral frenulum - Autosomal recessive inheritance - Clinodactyly - Clitoromegaly - Delayed skeletal maturation - Dislocated radial head - Failure to thrive - Fused sternal ossification centers - Hepatomegaly - High palate - Hip dislocation - Low-set ears - Patent ductus arteriosus - Postaxial foot polydactyly - Postaxial hand polydactyly - Posteriorly rotated ears - Radial deviation of finger - Renal cortical cysts - Scoliosis - Short metacarpal - Thick anterior alveolar ridges - Ulnar deviation of finger - Ventricular septal defect - Wide mouth - Wide nasal bridge - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.
Source: GARD