MedGen

A chromosomal abnormality consisting of the presence of one chromosome in addition to the normal diploid number. [from NCI]

A chromosomal disorder consisting of the presence of two chromosomes of the same type in addition to the normal diploid number. [from MONDO]

A rare partial trisomy of the short arm of chromosome 18 manifesting with a highly variable clinical phenotype which may include variable developmental delay and intellectual disability, epilepsy, and non-specific dysmorphic features, among others. [from ORDO]

Tetrasomy 18p is a chromosomal condition that affects many parts of the body. This condition usually causes feeding difficulties in infancy, delayed development, intellectual disability that is often mild to moderate but can be severe, changes in muscle tone, distinctive facial features, and other birth defects. However, the signs and symptoms vary among affected individuals.

Babies with tetrasomy 18p often have trouble feeding and may vomit frequently, which makes it difficult for them to gain weight. Some affected infants also have breathing problems and jaundice, which is a yellowing of the skin and the whites of the eyes.

Changes in muscle tone are commonly seen with tetrasomy 18p. Some affected children have weak muscle tone (hypotonia), while others have increased muscle tone (hypertonia) and stiffness (spasticity). These changes contribute to delayed development of motor skills, including sitting, crawling, and walking.

Tetrasomy 18p is associated with a distinctive facial appearance that can include unusually shaped and low-set ears, a small mouth, a flat area between the upper lip and the nose (philtrum), and a thin upper lip. Many affected individuals also have a high, arched roof of the mouth (palate), and a few have had a split in the roof of the mouth (cleft palate).

Additional features of tetrasomy 18p can include seizures, vision problems, recurrent ear infections, mild to moderate hearing loss, constipation and other gastrointestinal problems, abnormal curvature of the spine (scoliosis or kyphosis), a shortage of growth hormone, and birth defects affecting the heart and other organs. Males with tetrasomy 18p may be born with undescended testes (cryptorchidism) or the opening of the urethra on the underside of the penis (hypospadias). Psychiatric conditions, such as attention-deficit/hyperactivity disorder (ADHD) and anxiety, as well as social and behavioral challenges have also been reported in some people with tetrasomy 18p. [from MedlinePlus Genetics]

Hydrocephalus is an active distension of the ventricular system of the brain resulting from inadequate passage of CSF from its point of production within the cerebral ventricles to its point of absorption into the systemic circulation. [from HPO]

A rare neurological disorder characterized by a reduced head circumference at birth with no gross anomalies of brain structure. It can be an isolated finding or it can be associated with seizures, developmental delay, intellectual disability, balance disturbances, hearing loss or vision problems. [from ORDO]

A rare central nervous system malformation characterized by abnormally enlarged cerebral ventricles due to impaired cerebrospinal fluid circulation. It arises in utero and can be either acquired or inherited. The severity of the resulting brain damage depends on the duration and extent of ventriculomegaly. [from ORDO]

Developmental hypoplasia of the mandible. [from HPO]

Distance between the commissures of the mouth more than 2 SD below the mean. Alternatively, an apparently decreased width of the oral aperture (subjective). [from HPO]

Upper insertion of the ear to the scalp below an imaginary horizontal line drawn between the inner canthi of the eye and extending posteriorly to the ear. [from HPO]

Height of the palate more than 2 SD above the mean (objective) or palatal height at the level of the first permanent molar more than twice the height of the teeth (subjective). [from HPO]

The main clinical manifestations of chromosome 18p deletion syndrome are mental retardation, growth retardation, craniofacial dysmorphism including round face, dysplastic ears, wide mouth and dental anomalies, and abnormalities of the limbs, genitalia, brain, eyes, and heart. The round face characteristic in the neonatal period and childhood may change to a long face with linear growth of the height of the face (summary by Tsukahara et al., 2001). [from OMIM]

The gradual reduction in girth of the finger from proximal to distal. [from HPO]

Death of the fetus in utero after at least 22 weeks of gestation. [from HPO]

A difference in length or diameter between the left and right leg. [from HPO]

An abnormal difference between the left and right sides of the face. [from HPO]

A group of neural cortical developmental malformations of diverse genetic causes. Clinical manifestations include epilepsy and developmental delays. [from NCI]

Severe microcephaly and lissencephaly with granular surfaces with immature cortical plate, reduced in thickness, with focal polymicrogyria and immature small neurons with rare processes, intermingled with a considerable number of glial elements. [from HPO]