Partial trisomy 11,46,XX,-3,-20, + der3, + der20,t(3:11:20), resulting from a complex maternal rearrangement of chromosomes 3, 11, 20

Tandem duplication of 11p12-p13 in a child with borderline development delay and eye abnormalities: dose effect of the PAX6 gene product?

We report on a girl with a duplication of chromosome band 11p12-->13, which includes the Wilms tumor gene (WT1) and the aniridia gene (PAX6). The girl had borderline developmental delay, mild facial anomalies, and eye abnormalities. Eye findings were also present in most of the 11 other published cases with partial trisomy 11p, including 11p12-->13. Recently, it was shown that introduction of additional copies of the PAX6 gene into mice caused very variable eye abnormalities. Therefore, a PAX6 gene dosage effect is likely to be present in mice and humans. The central nervous system may be less sensitive to an altered PAX6 gene dosage, which is consistent with the borderline developmental delay in the present patient. Urogenital abnormalities were absent in this patient and in most of the other patients with partial trisomy of 11p. Therefore, the effect of a WT1 gene duplication on the embryological development of the urogenital tract remains uncertain.

Paternally inherited duplications of 11p15.5 and Beckwith-Wiedemann syndrome

We present a three generation family in which a father and son have a balanced chromosome translocation between the short arms of chromosomes 5 and 11 (karyotype 46,XY,t(5;11)(p15.3;p15.3)). Two family members have inherited the unbalanced products of this translocation and are trisomic for chromosome 11p15.3-->pter and monosomic for chromosome 5p15.3-->pter (karyotype 46,XY,der(5)t(5;11)(p15.3;p15.3)pat). Paternally derived duplications of 11p15.5 are associated with Beckwith-Wiedemann syndrome (BWS) and both family members trisomic for 11p15.5 had prenatal overgrowth (birth weights >97th centile), macroglossia, coarse facial features, and broad hands. We review the clinical features of BWS patients who have a paternally derived duplication of 11p15.5 and provide evidence for a distinct pattern of dysmorphic features in those with this chromosome duplication. Interestingly, our family is the fifth unrelated family to be reported with a balanced reciprocal translocation between the short arms of chromosomes 5 and 11. The apparently non-random nature of this particular chromosome translocation is suggestive of sequence homology between the two chromosome regions involved in the translocation.

Influence of PAX6 gene dosage on development: overexpression causes severe eye abnormalities

Aniridia in man and Small eye in mice are semidominant developmental disorders caused by mutations within the paired box gene PAX6. Whereas heterozygotes suffer from iris hypoplasia, homozygous mice lack eyes and nasal cavities and exhibit brain abnormalities. To investigate the role of gene dosage in more detail, we have generated yeast artificial chromosome transgenic mice carrying the human PAX6 locus. When crossed onto the Small eye background, the transgene rescues the mutant phenotype. Strikingly, mice carrying multiple copies on a wild-type background show specific developmental abnormalities of the eye, but not of other tissues expressing the gene. Thus, at least five different eye phenotypes are associated with changes in PAX6 expression. We provide evidence that not only reduced, but also increased levels of transcriptional regulators can cause developmental defects.

Deletion of chromosome 3 and a 3;20 reciprocal translocation demonstrated by chromosome painting

The combined use of high resolution banding and chromosome painting techniques allowed us to identify a reciprocal translocation involving chromosomes 3 and 20 and simultaneous interstitial deletion of chromosome 3 in a patient with several minor anomalies of the face and hands. His karyotype is described as 46,XY,t(3;20) (p14.2;p12.2),del(3)(p11-p14.1).

Molecular analysis of a complex chromosomal rearrangement and a review of familial cases

A complex chromosome rearrangement (CCR) involving chromosomes 7, 8, and 13 was detected in a phenotypically normal woman ascertained through her mentally retarded son with abnormal phenotype. He had a karyotype with 47 chromosomes including an extra der(13). In initial banding studies the CCR in the mother was interpreted as a three-way translocation. Fluorescence in situ hybridization with whole chromosome libraries and a telomere-specific probe was used to better characterize the rearrangement. Combined data allowed us to reinterpret the CCR as a translocation and an insertion. A review of 35 familial CCRs involving at least three chromosomes led to the following observations: 1) familial CCRs tend to have fewer chromosomes involved and fewer break-points than do de novo CCRs; 2) familial transmission is mainly observed through female carriers although the origin of de novo cases is paternal; 3) an apparent excess of balanced female carriers among the offspring of index carriers was noted; and 4) meiotic segregation resulting in malformed liveborn infants is most frequently due to adjacent-1 segregation, followed by 4:2 segregation; no adjacent-2 segregation was observed.

A balanced complex chromosomal rearrangement (BCCR) with phenotypic effect

The authors report on a case of balanced complex chromosomal rearrangement (BCCR) with phenotypic effect, describe the dysmorphisms and malformations observed, and discuss the various pathogenetic mechanisms. On the basis of these considerations, they underline the need for careful reporting of examined cases, distinguishing the characteristic signs from dysmorphisms that are described in several other chromosomal aberrations as well. Finally, they stress the importance of a more precise description of BCCRs for the purpose, among others, of a correct formulation of reproductive risk.

Reproductive risks for carriers of complex chromosome rearrangements: analysis of 25 families

We have determined the empirical reproductive risks for heterozygous carriers of complex chromosome rearrangements (CCRs). CCRs are structural rearrangements involving at least three chromosomes and three or more chromosomal breakpoints. Pregnancy outcome, the frequency and type of chromosomal imbalance in the offspring, and the localization and distribution of chromosome breakpoints were analyzed in 25 CCR families ascertained by the birth of a malformed child or repeated spontaneous abortions. This study included two newly ascertained familial CCRs and a total of 67 informative pregnancies. Analysis of the data, after correction for ascertainment bias, showed that the incidence of spontaneous abortions in CCR families was 48.3%. Approximately one in ten pregnancies and 18.4% of all live births to CCR carriers resulted in phenotypically abnormal offspring. One-half of all CCR carrier liveborn offspring were also CCR carriers. There was a 53.7% incidence of an abnormal pregnancy outcome to CCR carriers. We failed to detect any evidence for a non-random involvement of specific chromosomes in CCRs. However, we did observe a non-random distribution of specific breakpoints at sites 1q25, 4q13, 6q27, 7p14, 9q12, 11p11, 11p15, 12q21, 13q31, and 18q21.

Prenatal diagnosis and follow up of a child with a complex chromosome rearrangement

A case of de novo, apparently balanced, three way exchange by translocation plus a pericentric inversion is described. The karyotype is 46,XX,t(6;11)(p21;q21),t(11;21) (q21;p13),inv(6)(p21q11) and was ascertained through second trimester amniocentesis. The structural rearrangements appear balanced. The child was phenotypically normal at birth. Growth and motor development were normal until 30 months, at which time linear growth dropped below the 5th centile. In addition, there was delayed speech development at 2 years of age. As far as we can determine, this is the first report of a three chromosome exchange including a pericentric inversion ascertained through genetic amniocentesis.

Analysis of spreading of inactivation in eight X autosome translocations utilizing the high resolution RBG technique

Eight X autosome translocations were studied with replication banding to localize spreading of late replication into the autosomal segments. Partial spreading into the autosomal segment was seen in four translocations and no spreading of late replication was seen in four translocations. In those translocations with partial spreading of late replication into the autosomal segment, late replication did not always spread continuously from the X chromosome breakpoint throughout the autosome. Instead, it appeared to skip some bands and affect others. The data on the pattern of replication, taken to indicate also a spread of inactivation into these autosomal segments, correlated well with the clinical data in most cases and suggest that spreading of late replication is often incomplete and may be discontinuous.

Familial complex autosomal translocations involving chromosomes 7, 8, and 9 exhibiting male and female transmission with segregation and recombination

A family showing a complex translocation between chromosomes 7, 8, and 9 with breakpoints at 7q21, 7q33, 8p23, and 9p23 is described. The proband had been referred because of repeated spontaneous abortions. This is only the second family to be ascertained in this way. Twenty-three other cases of complex translocations are briefly reviewed, eight of which were de novo in origin and 15 familial. All but one of the familial cases showed maternal transmission only. The present family shows both maternal and paternal transmission and is thought to be the first exhibiting recombination from a male carrier. The origin and transmission of the complex translocation is followed through three generations.

De novo translocation heterozygote with three reciprocal translocations

An extremely rare case of a child with three balanced reciprocal translocations involving six different autosomes is described. These abnormalities have apparently arisen de novo and seem to have only relatively minor phenotypic effects. The meiotic possibilities are discussed and cytogenetic markers suggest that the damage may have occurred in a paternal gamete.

Abnormality of chromosome 11 in patients with features of Beckwith-Wiedemann syndrome

Two unrelated children with features of Beckwith-Wiedemann syndrome have been found to have partial duplication of chromosome 11p. A review of six other reported cases of partial duplication of 11 p revealed features of this syndrome not previously recognized. We suggest that karyotype studies with banding techniques should be done in children with features of Beckwith-Wiedemann syndrome and developmental delay or retardation.

A complex rearrangement involving three autosomes in a phenotypically normal male presenting with sterility

This paper reports a rearrangement involving three autosomes: 11, 12, and 21. The translocation carrier, a 31-year-old azoospermic male, is phenotypically normal.

Duplication 11p11.3 leads to 14.1 to meiotic crossing--over

An infant with macular dysfunction, cleft lip and palate, and developmental delay was shown to have an inverted duplication of 11p11.3 leads to p14.1 on the basis of meiotic recombination subsequent to an intrachromosomal "shift" in his mother. A half-sister had previously been shown [3] to have the reciprocal recombinant with resultant deletion of 11p11.3 leads to 11p14.1.

A woman carrier of two apparently unrelated reciprocal translocations: prenatal diagnosis of normal karyotype in the foetus

Two reciprocal balanced translocations involving chromosomes 2, 9, 12, and 18 were found in the karyotype of a woman with a child showing several congenital malformations at birth. Prenatal cytogenetic diagnosis, performed when a second pregnancy occurred, showed a normal chromosome constitution in the foetus.