Rare familial smaller deletions with significant variability in the phenotype within a family have been described, including one where a parent was ascertained after prenatal diagnosis of an affected fetus.
The remainder are caused by unbalanced translocations, of which 5% are de novo and the remainder are familial, inherited from a parent carrying a balanced translocation (4%) or rarely an inversion (1%). For reasons incompletely understood, 80% of de novo deletions occur on the paternally inherited chromosome 5. Most cases are the result of de novo terminal deletions (77%) or interstitial deletions (9%). The 5p deletion syndrome is caused by heterozygous partial deletions of the short arm of chromosome 5, which can be between 5 and 40 Mb. The 5p deletion syndrome is a rare genetic syndrome, affecting 0.2–0.6 : 10,000 individuals and is found in 0.3% to 1% of individuals with severe intellectual disability. Affected children often have a high-pitched monotonous cry in infancy and have variable, but sometimes severe, psychomotor delay and intellectual disability. The 5p deletion syndrome is characterized by poor prenatal and postnatal growth, hypotonia, microcephaly, and a distinct round face with hypertelorism, micrognathia, epicanthal folds, and low-set ears. Thus practitioners should be familiar with the clinical presentation and prognosis of 5p deletion syndrome, including features that can be seen by prenatal imaging and those that are not prenatally detectable, as well as with the implications for perinatal management and counseling when a 5p deletion is diagnosed prenatally. The prenatal diagnosis of this rare deletion syndrome is relatively uncommon however, recent introduction of noninvasive prenatal screening for microdeletion syndromes using (cffDNA) in maternal plasma has widened the prenatal ascertainment of 5p deletion syndrome to screening for potentially affected fetuses in low-risk pregnancies. Initially described in 1963 by Lejeune et al., this syndrome is readily detectable by karyotype or with molecular cytogenetic methods, such as chromosomal microarray analysis (CMA). Monosomy for the distal portion of the short arm of chromosome 5 causes 5p deletion syndrome, which is also known by the currently less favored term “cri du chat” syndrome, from the French description of the monotonous high-pitched “cat-like” cry of affected infants.
However, the recent introduction of noninvasive prenatal screening for microdeletion syndromes using cell-free fetal DNA (cffDNA) in maternal plasma has widened the prenatal ascertainment of 5p deletion syndrome to screening for potentially affected fetuses in low-risk pregnancies.
The prenatal diagnosis of this rare deletion syndrome is relatively uncommon.
0 kommentar(er)
