A case of inverted insertion assessed by R and G banding

Mouse chromosome engineering for modeling human disease

Chromosomal rearrangements are frequently in humans and can be disease-associated or phenotypically neutral. Recent technological advances have led to the discovery of copy-number changes previously undetected by cytogenetic techniques. To understand the genetic consequences of such genomic changes, these mutations need to be modeled in experimentally tractable systems. The mouse is an excellent organism for this analysis because of its biological and genetic similarity to humans, and the ease with which its genome can be manipulated. Through chromosome engineering, defined rearrangements can be introduced into the mouse genome. The resulting mouse models are leading to a better understanding of the molecular and cellular basis of dosage alterations in human disease phenotypes, in turn opening new diagnostic and therapeutic opportunities.

Duplication and deletion of chromosome band 2(p21p22) resulting from a familial interstitial insertion (2;11)(p21;p15)

Routine amniocentesis for advanced maternal age led to the prenatal diagnosis of a fetus with a karyotype of a 46,XX,del(2)(p21p22). At delivery the baby had holoprosencephaly as the major clinical finding, which has been associated with a deletion of band 2p21 in several other case reports. Chromosome studies of the parents showed a normal 46,XY karyotype in the father, and a balanced interstitial insertion 46,XX dir ins (11;2)(p15.1;p21p22) in the mother. Subsequent chromosome studies of other relatives documented a 23-year-old half-brother of the proposita with a partial trisomy for the segment deleted in the proposita. The half-brother showed the derivative chromosome 11 from the mother, resulting in a 46,XY,der(11)dup(2)(p21p22) karyotype. Major clinical findings include short stature, mild developmental delay, and behavior abnormalities. A half-sister of the proposita is also a balanced carrier of the dir ins (11;2) (p15.1;p21p22.2). The association of the deletion chromosome band 2p21 and the clinical finding of holoprosencephaly is further supported by the findings in this family.

Partial trisomy 4p resulting from a balanced intrachromosomal insertion, 4(q313p14p16)

Partial trisomy 4p was found in a child with dysmorphic features. Cytogenetic investigations in the parents revealed an intrachromosomal insertion in the mother, 46,XX,ins (4) (q313p14p16). The proband was trisomic for 4p(p14p16) as a result of a recombination event in the mother's chromosome 4 at meiosis. The clinical features of the proband are compared with those found in the literature.

Three cases of partial trisomy 7q owing to rare structural rearrangements of chromosome 7

Three cases of partial trisomy 7q are described. One case had duplication of region 7q22.1----q31.2 owing to a de novo direct intra-arm intrachromosomal duplication. The other two cases, first cousins, were trisomic for 7q34----qter, resulting from recombination within the inserted segment of a dir ins(7;17)(q34;q23.1q25.3)mat. All three cases had a number of the already recorded manifestations of partial trisomy 7q, namely strabismus, low set ears, depressed nasal bridge, small nose, hypotonia, and mental retardation.

Partial deletion of the short arm of chromosome 3 (3p25----3pter). Further delineation of the clinical phenotype

Clinical descriptions of individuals with partial deletion of the distal short arm of chromosome three have been reported rarely. A characteristic phenotype has been proposed. We present another patient with this cytogenetic abnormality whose physical and developmental features show similarities with, as well as differences from, previously reported cases. This suggests that the clinical phenotype requires further definition. In addition, gene dosage studies were undertaken on several serum proteins in order to try to map the location of the responsible genes on chromosome three.

Pure monosomy and trisomy 2q24.2----q3105 due to an inv ins(7;2)(q21.2;q3105q24.2) segregating in four generations

An inv ins(7;2)(q21.2;q3105q24.2) was found to segregate through four generations of a family. Adjacent-1 segregation aneusomies were ascertained in five patients: three monosomics and two trisomics; and the corresponding syndromes were delineated. The comparative analysis between these and other previously described 2q aneusomic individuals led to the conclusion that a large cleft between first and second toes is a constant feature in monosomy 2q24----q31. No other trait could plausibly be mapped. Risks of 7.9 to 31.6% for aneusomic children and of 26.3% for abortion were estimated in the present family.

Familial balanced insertion (5;10) and monosomy and trisomy (10) (q24.2----q25.3)

The phenotype of a boy with monosomy of a small segment of chromosome (10) (q24.2----q25.3) is described. In his family a balanced insertion (5;10) is found in three generations. Moreover there are two persons who are trisomic for the same small segment of chromosome 10 for which the boy is monosomic.