The variable penetrance of 3p deletions creates challenges in genetic counseling, as the phenotype of the offspring cannot be predicted based on chromosomal and/or genome-wide array analytical findings. 2 q32.11) associated with 9p terminal deletion and 14q distal duplication. In family B, the 1.1 Mb terminal deletion encompasses only the CHL1 gene, which is insufficient to cause 3p deletion symptoms thus the clinical features observed in this family may have a different cause. In family A, the 9 Mb deletion can be considered causal for the 3p deletion syndrome in the proband, but the extremely mild phenotype in the other family members remains unexplained. Sequencing analysis of the CHL1, CNTN4, and CRBN genes did not reveal any masked recessive alleles that might explain the more severe phenotypes in the probands. The deletions were characterized by genome-wide SNP array analysis and were 9 and 1.1 Mb in size. Hence, a true incidence of the disorder may be difficult to estimate. In many cases, individuals with mild signs and symptoms may be undiagnosed in their lifetime. The presentation of symptoms may occur at or following the birth of the child. In family B, the mother was normal and her son was affected, having some symptoms that had not been described in the 3p deletion syndrome before. Chromosome 3p Deletion Syndrome is a rare congenital disorder. In family A, the mother and daughter were extremely mildly affected whereas the son had more severe clinical features. We describe two families with terminal 3p deletions and extremely variable clinical features. The phenotype of individuals with deletions varies from normal to severe. It is characterized by growth retardation, developmental delay, mental retardation, dysmorphism, microcephaly, and ptosis. Most cases occur de novo, but a few familial cases have been reported. The 3p deletion syndrome is a rare disorder caused by deletions of different sizes in the 3p25-pter region. For a healthy development, chromosomes should contain just the right amount of genetic material not too much and not too little. It is characterized by growth retardation, developmental delay, mental retardation, dysmorphism, microcephaly, and ptosis. Duplication of 3p A duplication of 3p is a rare genetic condition caused by an extra part of one of the body’s 46 chromosomes chromosome 3. The 3p deletion syndrome is a rare disorder caused by deletions of different sizes in the 3p25-pter region.
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