Patients have a short stature due to post-natal growth retardation and a typical facies with high and bossing forehead, hypertelorism, puffy eyelids, midfacial hypoplasia, depressed nasal bridge, anteverted wide nostrils, thick everted lower lip, micrognathia, low-set ears and premature aging appearance mainly due to redundant hyperelastic skin with unusual wrinkles. Scalp hair may be primarily present but disappears after the first months of life leading to complete or partial alopecia. Eyebrows and/or eyelashes are sparse. Primary and permanent teeth are formed but fail to erupt. Ocular manifestations may include progressive optic atrophy, glaucoma, strabismus, megalocornea, myelinated retinal nerve fiber layer, bilateral keratoconus, nystagmus and ptosis. Otorhinolaryngologic features are choanal atresia, deafness and presence of flaccid and pulsatile masses with an audible murmur in the mastoid area associated with dilated and tortuous scalp veins. Patients have a mild intellectual deficit. Some patients have also been reported with umbilical hernia, hyperextensible joints, osseous anomalies (congenital dislocation of hips or delayed bone age) and cutaneous manifestations (hemangioma or depigmented areas). Other manifestations include intracranial hypertension in infancy, hypothyroidism, mitral valve dysfunction or cardiomyopathy, hepatomegaly, renal impairment and altered gonadal functions (irregular periods or amenorrhea, oligoastenospermia).
Homozygous nonsense or splicing mutations in the ANTXR1 gene, encoding anthrax toxin receptor 1, also known as tumor endothelial marker 8 (TEM8) cause GAPO Syndrome.
