Pancytopenia, hyperpigmentation, small stature, congenital abnormalities, and predisposition to neoplasia characterize Fanconi anemia (FA). The clinical phenotype is extremely variable, therefore the diagnosis is frequently delayed until the pancytopenia appears, making diagnosis difficult on the basis of clinical manifestations alone. Hypersensitivity of FA cells to the clastogenic effect of diepoxybutane (DEB) provides a unique marker for the diagnosis before the beginning of hematological manifestations. Our aim in this study was to detect FA in children with atypical manifestations to define which conditions should be routinely included in the DEB test screening. We performed the chromosomal breakage test in 34 patients with probable FA and 83 patients with clinical conditions that could suggest FA, but are not usually screened by the DEB test: 20 patients with aplastic anemia, 20 patients with VACTERL association, 20 with radial ray abnormalities, 7 with tracheo‐esophageal fistulae, 12 with anal atresia, and 4 with myelodysplastic syndrome. We found 18 DEB‐positive patients: 12 were in the group of probable FA and 6 in the other groups. Among the last ones: three were included because of aplastic anemia, without any other sign of FA, however when re‐examined, other anomalies were detected. The third patient had anal atresia, renal hypoplasia, pre‐axial polydactyly, and normal blood cell counts and was diagnosed as having VACTERL association. The other two patients lacking physical or hematological signs were identified among the group of radial ray abnormalities. Thus, our results highlight the need to increase the number of abnormalities indicating need for a DEB test. Delay in the diagnosis of FA may have serious consequences for the patients and their family members.

Homologous recombination (HR)-deficient cancers are sensitive to poly-ADP ribose polymerase inhibitors (PARPi), which have shown clinical efficacy in the treatment of high-grade serous cancers (HGSC). However, the majority of patients will relapse, and acquired PARPi resistance is emerging as a pressing clinical problem. Here we generated seven single-cell clones with acquired PARPi resistance derived from a PARPi-sensitive TP53−/− and BRCA1−/− epithelial cell line generated using CRISPR/Cas9. These clones showed diverse resistance mechanisms, and some clones presented with multiple mechanisms of resistance at the same time. Genomic analysis of the clones revealed unique transcriptional and mutational profiles and increased genomic instability in comparison with a PARPi-sensitive cell line. Clonal evolutionary analyses suggested that acquired PARPi resistance arose via clonal selection from an intrinsically unstable and heterogenous cell population in the sensitive cell line, which contained preexisting drug-tolerant cells. Similarly, clonal and spatial heterogeneity in tumor biopsies from a clinical patient with BRCA1-mutant HGSC with acquired PARPi resistance was observed. In an imaging-based drug screening, the clones showed heterogenous responses to targeted therapeutic agents, indicating that not all PARPi-resistant clones can be targeted with just one therapy. Furthermore, PARPi-resistant clones showed mechanism-dependent vulnerabilities to the selected agents, demonstrating that a deeper understanding on the mechanisms of resistance could lead to improved targeting and biomarkers for HGSC with acquired PARPi resistance. Significance: This study shows that BRCA1-deficient cells can give rise to multiple genomically and functionally heterogenous PARPi-resistant clones, which are associated with various vulnerabilities that can be targeted in a mechanism-specific manner.

Anticancer regimens for Hodgkin lymphoma (HL) patients include highly genotoxic drugs that have been very successful in killing tumor cells and providing a 90% disease-free survival at five years. However, some of these treatments do not have a specific cell target, damaging both cancerous and normal cells. Thus, HL survivors have a high risk of developing new primary cancers, both hematologic and solid tumors, which have been related to treatment. Several studies have shown that after treatment, HL patients and survivors present persistent chromosomal instability, including nonclonal chromosomal aberrations. The frequency and type of chromosomal abnormalities appear to depend on the type of therapy and the cell type examined. For example, MOPP chemotherapy affects hematopoietic and germ stem cells leading to long-term genotoxic effects and azoospermia, while ABVD chemotherapy affects transiently sperm cells, with most of the patients showing recovery of spermatogenesis. Both regimens have long-term effects in somatic cells, presenting nonclonal chromosomal aberrations and genomic chaos in a fraction of noncancerous cells. This is a source of karyotypic heterogeneity that could eventually generate a more stable population acquiring clonal chromosomal aberrations and leading towards the development of a new cancer.

In countries where comparative genomic hybridization arrays (aCGH) and next generation sequencing are not widely available due to accessibility and economic constraints, conventional 400–500-band karyotyping is the first-line choice for the etiological diagnosis of patients with congenital malformations and intellectual disability. Conventional karyotype analysis can rule out chromosomal alterations greater than 10 Mb. However, some large structural abnormalities, such as derivative chromosomes, may go undetected when the analysis is performed at less than a 550-band resolution and the size and banding pattern of the interchanged segments are similar. Derivatives frequently originate from inter-chromosomal exchanges and sometimes are inherited from a parent who carries a reciprocal translocation. We present two cases with derivative chromosomes involving a 9.1 Mb 5p deletion/14.8 Mb 10p duplication in the first patient and a 19.9 Mb 5p deletion/ 18.5 Mb 9p duplication in the second patient. These long chromosomal imbalances were ascertained by aCGH but not by conventional cytogenetics. Both patients presented with a deletion of the Cri du chat syndrome region and a duplication of another genomic region. Each patient had a unique clinical picture, and although they presented some features of Cri du chat syndrome, the phenotype did not conclusively point towards this diagnosis, although a chromosomopathy was suspected. These cases highlight the fundamental role of the clinical suspicion in guiding the approach for the etiological diagnosis of patients. Molecular cytogenetics techniques, such as aCGH, should be considered when the clinician suspects the presence of a chromosomal imbalance in spite of a normal karyotype.

Variation in the location of the 15p region D15Z1 is recognized as a polymorphism in several human populations. We used high-stringency Fluorescence In Situ Hybridization (FISH) to detect D15Z1 in a Mexican cohort. Here, we report the presence of extra D15Z1 sequences on the p-arm of acrocentric chromosomes other than 15 in two groups of Mexican couples, one with healthy offspring (n = 75) and the other with aneuploid offspring (n = 87), mainly trisomy 21. The additional D15Z1 polymorphism was significantly increased in individuals with aneuploid offspring (26.4%), in comparison to individuals with healthy offspring (14%). The most frequent acceptor chromosome of D15Z1 was chromosome 13p, followed by 14p, and finally, 21p. Our results show an overall frequency of 21.6% of this polymorphism in the Mexican population and suggest that its presence might be associated with the mis-segregation of other acrocentric chromosomes and aneuploid offspring. The high frequency of the polymorphism of the D15Z1 sequence on acrocentric chromosomes other than 15 suggests a sequence homogenization of the acrocentric p arms, related to the important function of the centromere and the nucleolar organization region, which flank satellite III DNA.