- Global developmental delay (HP:0001263): A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:401986)
- Ventriculomegaly (HP:0002119): An increase in size of the ventricular system of the brain. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:401986)
- Aplasia/Hypoplasia of the corpus callosum (HP:0007370): Absence or underdevelopment of the corpus callosum. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:401986)
- Abnormality of the urinary system (HP:0000079): An abnormality of the urinary system. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Macrocephaly (HP:0000256): Occipitofrontal (head) circumference greater than 97th centile compared to appropriate, age matched, sex-matched normal standards. Alternatively, a apparently increased size of the cranium. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Compulsive behaviors (HP:0000722): Behavior that consists of repetitive acts, characterized by the feeling that one "has to" perform them, while being aware that these acts are not in line with one's overall goal. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Intellectual disability (HP:0001249): The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- 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: Frequent (HP:0040282). (ORPHA:401986)
- Hypotonia (HP:0001252): Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Frontal bossing (HP:0002007): Bilateral bulging of the lateral frontal bone prominences with relative sparing of the midline. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Tethered cord (HP:0002144): During normal embryological development, the spinal cord first occupies the entire length of the vertebral column but goes on to assume a position at the level of L1 due to differential growth of the conus medullaris and the vertebral column. The filum terminale is a slender, threadlike structure that remains after the normal regression of the distal embryonic spinal cord and attaches the spinal cord to the coccyx. A tethered cord results if there is a thickened rope-like filum terminale which anchors the cord at the level of L2 or below, potentially causing neurologic signs owing to abnormal tension on the spinal cord. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Attention deficit hyperactivity disorder (HP:0007018): Attention deficit hyperactivity disorder (ADHD) manifests at age 2-3 years or by first grade at the latest. The main symptoms are distractibility, impulsivity, hyperactivity, and often trouble organizing tasks and projects, difficulty going to sleep, and social problems from being aggressive, loud, or impatient. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Chiari type I malformation (HP:0007099): Arnold-Chiari type I malformation refers to a relatively mild degree of herniation of the posteroinferior region of the cerebellum (the cerebellar tonsils) into the cervical canal with little or no displacement of the fourth ventricle. It is characterized by one or both pointed (not rounded) cerebellar tonsils that project 5 mm below the foramen magnum, measured by a line drawn from the basion to the opisthion (McRae Line). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Intraventricular hemorrhage (HP:0030746): Bleeding into the ventricles of the brain. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:401986)
- Cutis marmorata (HP:0000965): A reticular discoloration of the skin with cyanotic (reddish-blue appearing) areas surrounding pale central areas due to dilation of capillary blood vessels and stagnation of blood within the vessels. Cutis marmorata generally occurs on the legs, arms and trunk and is often more severe in cold weather. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:401986)
- Craniosynostosis (HP:0001363): Craniosynostosis refers to the premature closure of the cranial sutures. Primary craniosynostosis refers to the closure of one or more sutures due to abnormalities in skull development, and secondary craniosynostosis results from failure of brain growth. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:401986)
- Ocular hypertension (HP:0007906): Intraocular pressure that is 2 standard deviations above the population mean. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:401986)
- Moyamoya phenomenon (HP:0011834): A noninflammatory, progressive occlusion of the intracranial carotid arteries owing to the formation of netlike collateral arteries arising from the circle of Willis. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:401986)
These phenotypes are associated with the disease 1p31p32 microdeletion syndrome (ORPHA:401986).