Recurrent adjacent-2 segregation of a familial t(14;21)(q11.2;q11.2): phenotypic comparison of two brothers and a paternal aunt inheriting the der(14).

A 14-year-old boy was referred for a genetics evaluation after high-resolution chromosome analysis showed a small amount of extra material in the proximal long arm of chromosome 21. Five years prior, his karyotype analysis was interpreted as normal with a variant chromosome 21. The patient has short palpebral fissures, strabismus, flat antihelices of the ears, long thumbs with bilaterally absent interphalangeal creases, proximal bilateral 3/4 syndactyly, small testes, hypotonia, mental retardation, and speech problems. He has significant depression and behavioral problems including hyperactivity, aggression, and impulsivity. His 8-year-old brother has more severe behavioral disturbances and depression, but less significant mental retardation. A paternal aunt has mental retardation, is unusually docile, and appears similar to our patient. Chromosome analysis and fluorescence in situ hybridization (FISH) whole chromosome paint of chromosome 21 showed that the patient's father carries a "cryptic" balanced translocation, 46,XY, t(14;21)(q11.2;q11.2), as does the patient's paternal grandmother. Uniparental disomy studies using seven informative polymorphic nucleotide repeat markers from 14q and 21q confirmed biparental inheritance of the number 14 and 21 chromosomes for each brother, and indicate that they and the paternal aunt, all of whom inherited the der(14), are monosomic for proximal 21q and trisomic for proximal 14q. These karyotypes arose through an adjacent-2 segregation in the father on two occasions, and from the paternal grandmother on one occasion. This family is an example of recurrent malsegregation with translocations involving the acrocentrics.

Recurring chromosomal abnormalities in leukemia in PML-RARA transgenic mice parallel human acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is characterized by the t(15;17)(q22;q11.2), which results in the PML-RARA fusion gene. In previous studies, we demonstrated that expression of a human PML-RARA complementary DNA in murine granulocyte precursor cells initiated the development of leukemia. However, leukemogenesis by PML-RARA required additional genetic alterations. To identify genetic changes that cooperate with PML-RARA in leukemogenesis, we performed spectral karyotyping analysis of myeloid leukemias from hMRP8-PML-RARA mice (11 cases) and from mice coexpressing PML-RARA and BCL2 (8 cases). Clonal abnormalities were detected in 18 of 19 cases (95%). Recurring numerical abnormalities identified in these murine leukemias included +15 (15 cases, 79%); loss of a sex chromosome (12 cases, 63%); +8 (10 cases, 53%); +10 (9 cases, 47%); +4, +7, or +14 (8 cases each, 42%); +16 (7 cases, 37%); and +6 (5 cases, 26%). In a series of 965 patients with APL, we identified secondary abnormalities in 368 (38%). The most common recurring abnormalities were +8 or partial trisomy of 8q (120 patients, 12.4%) and ider(17) t(15;17) (42 patients, 4.4%). The critical consequence of +8 in human leukemias appears to be the gain of 8q24, which is syntenic to mouse 15. Thus, our results suggest that PML-RARA-initiated murine leukemia is associated with a defined spectrum of genetic changes, and that these secondary mutations recapitulate, in part, the cytogenetic abnormalities found in human APL.