Summary
Distal trisomy of the short arm of chromosome 6 is characterized by pre- and postnatal growth retardation, a pattern of specific facial features (mostly of the eyes), microcephaly, and developmental delay. To date, approximately 40 cases of trisomy 6p have been reported. Characteristic craniofacial findings include a prominent forehead, small and short palpebral fissures (blepharophimosis), upper lid ptosis, close-set eyes with a prominent nasal bridge, a short bulbous nose, a small mouth with thin lips, a small and pointed chin, and low-set ears with poorly developed lobes. A few major malformations have been reported, including congenital heart defects (atrial septal defect, ventricular septal defect and patent arterial duct; see these terms) and renal abnormalities including hydronephrosis and hypoplastic kidney. Cataracts, microcornea and strabismus may be observed. The duplicated region almost always includes 6pter, with proximal breakpoints ranging from 6p21 to 6p25. Interstitial duplications of 6p have also been reported with different phenotypes depending on their size and location. Most cases of distal trisomy 6p result from missegregation of a familial balanced translocation, or pericentric inversion, and are accompanied by another chromosomal imbalance. Intrachromosomal duplications or de novo translocations are also observed. Diagnosis is based on clinical features and confirmed by karyotyping and fluorescence in situ hybridization (FISH) with specific 6p probes. The risk of recurrence for siblings depends on the parental karyotypes. Cytogenetic prenatal diagnosis is possible. Management is multi-disciplinary and symptomatic only. Early educational and rehabilitation programs should be offered to all patients. The prognosis is variable. A number of patients have died in infancy from respiratory or severe feeding problems. *Author: Orphanet (February 2009)*.
