9p trisomy: a new case due to maternal t(9;18) translocation

Patient with trisomy 9p and a hypoplastic left heart with a tricentric chromosome 9

We present a patient with a hypoplastic left heart (HLH), dislocations of the hips and knees, and minor dysmorphic features, who had an abnormal karyotype that resulted in trisomy for 9p and a portion of 9q: 46,((, dic(or tri?)(9)(9pter --> 9q34::9q21 --> 9pter).ish(WCP9++).ish(D9Z5X4 +/+++). The derivative chromosome consisted of an additional copy of the proximal q arm and p arm attached to 9qter in an inverted fashion. Fluorescence in situ hybridization (FISH) using a chromosome 9 beta-satellite probe revealed three signals on the abnormal chromosome 9, suggesting the presence of 3 pericentromeric regions on the der(9). The 9q subtelomere was present on both the normal and derivative chromosome 9, suggesting that very little material, if any, is deleted.

Maternal translocation (9;18) with two abnormal offspring each with different chromosome derivatives

We report a phenotypically normal woman with an apparently balanced reciprocal translocation between chromosomes 9 and 18 [46,XX,t(9;18)(p22;p11.2)], giving rise to unbalanced chromosome complements in two of her children, each of whom received a different derivative chromosome. The proband's karyotype is 46,XY,-18,+der(18), t(9;18)(p22;p11.2)mat, which results in a duplication of the distal portion of the short arm of chromosome 9 with a concomitant deletion of much of the short arm of chromosome 18. The karyotype of the proband's brother is 46, XY,-9,+der(9),t(9;18)(p22;p11.2)mat, which results in a deletion of the distal short arm of chromosome 9 and a duplication of most of the short arm of chromosome 18. The phenotype of each child is significantly different from that of his sib and is not consistent with any previously reported chromosome abnormality.

Genetic risks for familial reciprocal translocations with special emphasis on those leading to 9p, 10p and 12p trisomies

An analysis of genetic risks for reciprocal translocations is given. Data from translocation families, ascertained through unbalanced offspring with trisomy 9p, 10p and 12p, were taken from the literature. The translocations were specified according to (1) the type of trisomy, (2) the degree of resulting chromosomal imbalance (partial short arm trisomies, complete short arm trisomies, complete short arm trisomies including long arm segments) and (3) the type of disjunction (2:2 or 3:1) and segregation (adjacent-1, adjacent-2; tertiary trisomy, interchange trisomy). The risks for unbalanced liveborn offspring were high for translocations leading to partial short arm trisomies through 2:2 disjunction and adjacent-1 segregation (25-29%). They were lower for translocations leading to complete short arm trisomies through the same disjunction/segregation mechanism (5-17%). Low risks were obtained for translocations, leading through 3:1 disjunction to unbalanced offspring (about 2%). For 2:2 disjunction and adjacent-2 segregation and for 3:1 disjunction the risk is significantly lower for male than for female carriers.--The frequency of balanced karyotypes compared with normal karyotypes deviated among the phenotypically normal offspring of parental carriers from the theoretical 1:1 ratio, both for translocations ascertained through trisomy 12p and trisomy 10p.--It was demonstrated that the genetic risk for reciprocal translocations depends exclusively on (1) the degree of possibly resulting genetic imbalance and (2) the probability of the disjunction/segregation mechanism leading to this type of imbalance. Both factors can be predicted from the position of breakpoints.--The precision of breakpoint localizations and its impact on the risk estimation are also considered.--Finally, general rules for genetic counselling of families with reciprocal translocations are indicated.

Trisomy 9p with i(9p) and t(9q18p)

The trisomy 9p syndrome in a 2-year-old girl with moderate mental retardation is presented. She has a unique karyotype with a de novo isochromosome 9p and a translocation between 9q and 18p.