The crucial band for phenotype of trisomy 18

Partial trisomy of chromosome 18q11.2-q12: A case report

“…Although Edwards syndrome is typically associated with duplication of the entire chromosome 18, several individuals with partial trisomy of chromosome 18 have been reported [6][7][8][9][10] . These patients display a range of severity from a relatively mild phenotype with no internal organ malformations to the classic characteristics of Edwards syndrome 11,12) .…”

“…There are several possibilities for why no critical region for Edwards syndrome has been established. Since many of the case reports have been published before high-resolution banding was commonly performed, inaccuracies of the karyotype may have led to misinterpretation of duplicated areas 7,8,10,11) . Alternatively there may be no critical chromosomal region and also the classic phenotype may be due to several noncontiguous chromosomal regions or genes that must be present in three copies to lead to the Edwards syndrome phenotype 16) .…”

“…One report concluded that the critical region encompasses a region on 18q proximal to 18q12 10) , while another report offered an opposing view that the critical region lies in distal 18q, involving band q21 9) . Turleau and de Grouchy 7) proposed that an interaction between 18q11 and 18q22-qter is implicated in the etiology of the trisomy 18 …”

Combined deletion 18q22.2 and duplication/triplication 18q22.1 causes microcephaly, mental retardation and leukencephalopathy

“…These regions may comply with a combination of 18q11 and 18q22-qter (Turleau and de Grouchy, 1977) or combination of 18q12.1-q21.2 and 18q22.3-qter (Boghosian-Sell et al, 1994). In total, approximately 10 patients with Edwards syndrome phenotype among 50 patients with a partial duplication of chromosome 18 have been identified and helped to delineate further candidate regions for this phenotype: (i) 18q21 (Matsuoka et al, 1981), (ii) CRES is proximal to 18q12.2 (Mucke et al, 1982) and (iii) 18q11-q12 (Fryns et al, 1978). The possibility of an inconstant Edwards syndrome phenotype in our index case as a consequence of incomplete penetrance and phenotype variability needs to be considered.…”

Identification and characterization of a new type of asymmetrical dicentric chromosome derived from a single maternal chromosome 18

“…Clinical features associated with the duplication of 18q11.1 ] q11.2 have not been clearly defined. Although Mücke et al (1982) suggested that a region on 18q proximal to q12 was critical for trisomy 18, other studies have proposed that the critical region(s) for that phenotype were located more distal in 18q Fig. 3.…”