- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:3078)
- Optic atrophy (HP:0000648): Atrophy of the optic nerve. Optic atrophy results from the death of the retinal ganglion cell axons that comprise the optic nerve and manifesting as a pale optic nerve on fundoscopy. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:3078)
- Seizure (HP:0001250): A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:3078)
- Hypertonia (HP:0001276): A condition in which there is increased muscle tone so that arms or legs, for example, are stiff and difficult to move. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:3078)
- Severe postnatal growth retardation (HP:0008850): Severely slow or limited growth after birth, being four standard deviations or more below age- and sex-related norms. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:3078)
- Profound hearing impairment (HP:0012715): A profound (essentially complete) form of hearing impairment. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:3078)
- Blindness (HP:0000618): Blindness is the condition of lacking visual perception defined as a profound reduction in visual perception. On the 6m visual acuity scale, blindness is defined as less than 3/60. On the 20ft visual acuity scale, blindness is defined as less than 20/400. On the decimal visual acuity scale, blindness is defined as less than 0.05. Blindness is typically characterized by a visual field of no greater than 10 degrees in radius around central fixation. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Spasticity (HP:0001257): A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Small for gestational age (HP:0001518): Smaller than normal size according to sex and gestational age related norms, defined as a weight below the 10th percentile for the gestational age. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Dilated fourth ventricle (HP:0002198): An abnormal dilatation of the fourth cerebral ventricle. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Recurrent upper respiratory tract infections (HP:0002788): An increased susceptibility to upper respiratory tract infections as manifested by a history of recurrent upper respiratory tract infections (running ears - otitis, sinusitis, pharyngitis, tonsillitis). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Small fontanelle (HP:0005486): A fontanelle that is small for age. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Apneic episodes in infancy (HP:0005949): Recurrent episodes of apnea occurring during infancy. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Severe intellectual disability (HP:0010864): Severe intellectual disability (ID) is defined as a type of ID characterized by severely sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 20-34. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Brain atrophy (HP:0012444): Partial or complete wasting (loss) of brain tissue that was once present. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Nasogastric tube feeding (HP:0040288): The condition of inability to eat normally treated by placement of a thin tube through the nose into the stomach that is then used to carry food. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:3078)
- Vesicoureteral reflux (HP:0000076): Abnormal (retrograde) movement of urine from the bladder into ureters or kidneys related to inadequacy of the valvular mechanism at the ureterovesicular junction or other causes. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Large fontanelles (HP:0000239): In newborns, the two frontal bones, two parietal bones, and one occipital bone are joined by fibrous sutures, which form a small posterior fontanelle, and a larger, diamond-shaped anterior fontanelle. These regions allow for the skull to pass the birth canal and for later growth. The fontanelles gradually ossify, whereby the posterior fontanelle usually closes by eight weeks and the anterior fontanelle by the 9th to 16th month of age. Large fontanelles are diagnosed if the fontanelles are larger than age-dependent norms. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Micrognathia (HP:0000347): Developmental hypoplasia of the mandible. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Abnormal pinna morphology (HP:0000377): An abnormality of the pinna, which is also referred to as the auricle or external ear. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Macrotia (HP:0000400): Median longitudinal ear length greater than two standard deviations above the mean and median ear width greater than two standard deviations above the mean (objective); or, apparent increase in length and width of the pinna (subjective). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Triphalangeal thumb (HP:0001199): A thumb with three phalanges in a single, proximo-distal axis. Thus, this term applies if the thumb has an accessory phalanx, leading to a digit like appearance of the thumb. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Dandy-Walker malformation (HP:0001305): A congenital brain malformation typically characterized by incomplete formation of the cerebellar vermis, dilation of the fourth ventricle, and enlargement of the posterior fossa. In layman's terms, Dandy Walker malformation is a cyst in the cerebellum (typically symmetrical) that is involved with the fourth ventricle. This may interfere with the ability to drain cerebrospinal fluid from the brain, resulting in hydrocephalus. Dandy Walker cysts are formed during early embryonic development, while the brain forms. The cyst in the cerebellum typically has several blood vessels running through it connecting to the brain, thereby prohibiting surgical removal. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Cerebellar hypoplasia (HP:0001321): Cerebellar hypoplasia is a descriptive term implying a cerebellum with a reduced volume, but a normal shape and is stable over time. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Myoclonus (HP:0001336): Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Congenital hip dislocation (HP:0001374). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Ventricular septal defect (HP:0001629): A hole between the two bottom chambers (ventricles) of the heart. The defect is centered around the most superior aspect of the ventricular septum. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Rocker bottom foot (HP:0001838): The presence of both a prominent heel and a convex contour of the sole. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Calcaneovalgus deformity (HP:0001848): This is a postural deformity in which the foot is positioned up against the tibia. The heel (calcaneus) is positioned downward (that is, the ankle is flexed upward), and the heel is turned outward (valgus). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Short nose (HP:0003196): Distance from nasion to subnasale more than two standard deviations below the mean, or alternatively, an apparently decreased length from the nasal root to the nasal tip. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Contractures of the large joints (HP:0005781). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Severe muscular hypotonia (HP:0006829): A severe degree of muscular hypotonia characterized by markedly reduced muscle tone. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Lateral ventricle dilatation (HP:0006956). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
- Equinovarus deformity (HP:0008110). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:3078)
These phenotypes are associated with the disease Severe X-linked intellectual disability, Gustavson type (ORPHA:3078).