18p-

18p-
Other names	Monosomy 18p, deletion 18p syndrome, del(18p) syndrome, partial monosomy 18p, de Grouchy syndrome 1
4-month-old girl with cebocephaly as a result of 18p-
Specialty	Medical genetics

18p-, also known as monosomy 18p, deletion 18p syndrome, del(18p) syndrome, partial monosomy 18p, or de Grouchy syndrome 1, is a genetic condition caused by a deletion of all or part of the short arm (the p arm) of chromosome 18. It occurs in about 1 of every 50,000 births.^[1]

Patients typically have petite frames, a short neck, and a distinctive stance. They may have mild microcephaly, a round, flat, expressionless face, a broad, flat nasal bridge, horizontal palpebral fissures, epicanthal folds, strabismus, and ptosis of the eyelids. The syndrome can lead to muscle hypotonia and a slowdown in activity and movements. Mental impairment is common, with an average intelligence quotient (IQ) ranging from 25 to 75. Holoprosencephaly (HPE) is the primary abnormality, characterized by aberrant development of the midface and forebrain. Severe brain anomalies are linked to facial traits, while milder variants may have minor facial abnormalities. Skeletal abnormalities, such as coxa vara, hip dislocation, scoliosis, and foot deformities, have been documented. Growth hormone (GH) insufficiency is often detected in individuals with short stature, and serum immunoglobulin A levels may be low or absent. Other conditions include alopecia areata, hypotrichosis simplex, and keratosis pilaris and ulerythema ophryogenes.

Cytogenetic study is crucial for a definitive diagnosis of 18p deletion syndrome, as phenotype alone cannot support the diagnosis. Typically, peripheral blood karyotype analysis is used, and can also come from trophoblast cells or amniocytes during the perinatal stage. Different syndromes, like Turner syndrome or trisomy 21, may be associated with 18p deletion.

Deletion 18p syndrome has no specific treatment but is often treated with speech therapy and physical therapy for hypotonia. Severe brain abnormalities lead to poor prognosis and neonatal death, while patients without severe abnormalities have a better chance of survival. Early rehabilitative and educational interventions are recommended.