Trisomy-18 syndrome caused by translocation or isochromosome formation. A case report with bibliography.

Abstract

(Fig. 1) was the 3rd child of healthy Italian parents having no common ancestors and without any family history of malformations. The mother indicated no previous abortions. The first 2 children are living and clinically well. The karyotypes of the parents were found to be normal. Birth of the proposita occurred spontaneously 2-i weeks before term following an uneventful pregnancy. The father was 31 years of age at that time, the mother 25 years. The placenta was said to be normal by the obstetrician, however amniotic fluid contained meconium.The baby became blue asphyxtic and was referred to our hospital.Birth weight was 2380 g, body length 45 cm, and head circumference 31-5 cm.The head had a prominent occiput with widely spaced sutures. There was a flat bridge of the nose.The proposita showed micrognathia, high arched palate, low set malformed ears, small eyes with a slight mongo-

DNA studies of mono‐ and pseudodicentric isochromosomes 18q

“…In two cases maternal age was 41 and 35 years, respectively, but they were ascertained by prenatal diagnosis because of advanced age [Romain et al, 1992;van den Berg et al, 1999]. Two liveborn children had young parents: mothers 23 and 25, fathers 28 and 31 years, respectively [Muller et al, 1972;Larson et al, 1978]. Our cases 1, 3, and 4 were cases of monoisodisomy and did not show advanced parental ages (Table I).…”

“…The phenotype is in the majority of cases described as very similar to trisomy 18 or Edward's syndrome. Isochromosome 18q appears in the classical form with one centromere and two q arms and have been described in about 20 cases [Van Dyke, 1988 for review of cases before 1988; Chen et al, 1998 for review of cases after 1988], as double isochromosomes together with i(18p) described in four cases [Muller et al, 1972;Larson et al, 1978;Romain et al, 1992;van den Berg et al, 1999], and as a pseudodicentric chromosome with two centromeres separated by p arm material [Laurent et al, 1978;Madan et al, 1981;Ward et al, 1981;Fioretti et al, 1982;Wulfsberg et al, 1984;Meguid and Habibian, 1992;Brandt et al, 1994;LevyMozziconacci et al, 1996;Gravholt et al, 1997] or q arm material [Floore et al, 1989;Bryke et al, 1990;Fujiwara et al, 1992;Ausems et al, 1994]. Isochromosomes are mirror duplications as they are composed of genetically identical arms.…”

“Structural anomaly of chromosome 18 with Edward Syndrome Phenotype”.

“…The small meta-centric arose from the joining of the tiny short arm piece of one chromosome 18 to the rest of the broken long arm of the other chromosome 18. 6 3. Duplication: Bogoshian-Sell et al identified two regions on 18q that may work in conjunction to produce Edwards syndrome phenotype; a proximal critical (18q12.1-18q21.2) and a distal critical region (18q22.3q).…”

Trisomy 18 syndrome with an unusual karyotype: possible double isochromosome.

“…In addition to the Muller et al (1972) report, one other instance was a case described by Sinha et al (1971) in which isochromosomes of both arms of a C group chromosome were present, but this occurred as a mosaic in 8 to 10% of the cells with a normal 46,XX cell line. Double isochromosomes of an autosome could probably result in viable birth of a non-mosaic in three chromosomes of the human complement.…”

“…Muller et al, (1972) considered two possibilities for the origin of the abnormal chromosomes. First, isochromosomes may arise as a misdivision of the centromere with both products being passed on to the same gamete of a parent.…”