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Deletions involving the long arm of chromosome 22 (22q11) are the most common microdeletions identified to date, present in ~1/3000 newborns. VCF syndrome, the most commonly associated syndrome, consists of learning disabilities or mild mental retardation, palatal defects, a hypoplastic aloe nasi and long nose, and congenital heart defects (conotruncal defect). Some individuals with 22q11 deletion are more severely affected and present with DiGeorge syndrome, which involves abnormalities in the development of the third and fourth branchial arches leading to thymic hypoplasia, parathyroid hypoplasia, and conotruncal heart defects. In ~30% of these cases, a deletion at 22q11 can be. | Chapter 063. Chromosome Disorders Part 10 Deletions involving the long arm of chromosome 22 22q11 are the most common microdeletions identified to date present in 1 3000 newborns. VCF syndrome the most commonly associated syndrome consists of learning disabilities or mild mental retardation palatal defects a hypoplastic aloe nasi and long nose and congenital heart defects conotruncal defect . Some individuals with 22q11 deletion are more severely affected and present with DiGeorge syndrome which involves abnormalities in the development of the third and fourth branchial arches leading to thymic hypoplasia parathyroid hypoplasia and conotruncal heart defects. In 30 of these cases a deletion at 22q11 can be detected with high-resolution banding by combing conventional cytogenetics FISH and molecular detection techniques i.e. Southern blotting or polymerase chain reaction analyses these rates improve to 90 . Additional studies have demonstrated a surprisingly high frequency of 22q11 deletions in individuals with nonsyndromic conotruncal defects. Approximately 10 of individuals with a 22q11 deletion inherited it from a parent with a similar deletion. Smith-Magenis syndrome involves a microdeletion localized to the proximal region of the short arm of chromosome 17 17p11.2 . Affected individuals have mental retardation dysmorphic facial features delayed speech peripheral neuropathy and behavior abnormalities. Most of these deletions can be detected with cytogenetic analysis although FISH is available to confirm these findings. In contrast William syndrome a chromosome 7 7q11.23 microdeletion cannot be diagnosed with standard or high-resolution analysis it is only detectable utilizing FISH or other molecular methods. William syndrome involves a deletion of the elastin gene and is characterized by mental retardation dysmorphic features a gregarious personality premature aging and congenital heart disease usually supravalvular aortic stenosis . In addition to microdeletion
