Constance K. Stein

Direct correlation between FRA3B expression and cigarette smoking

Cytogenetic deletions and/or loss of heterozygosity (LOH) of the short arm of chromosome 3, often with a break at 3p14, are well documented in lung tumors. The coincidence of a chromosomal fragile site, FRA3B, at a common chromosomal breakpoint in lung cancer has suggested that fragility at this site may predispose to breakage that could contribute to multistep carcinogenesis. This idea is supported by the more recent finding that FRA3B maps within the FHIT (fragile histadine triad) gene, and that aberrant transcripts and genomic deletions of FHIT/FRA3B occur in a variety of tumors including lung tumors. To determine whether some individuals have increased fragility of FRA3B that might increase the risk for breakage or deletion in 3p14.2, fragile site expression was examined in smokers, nonsmokers, and small cell lung cancer (SCLC) patients. The data clearly show that active smokers exhibit a significantly higher frequency of fragile site expression, including FRA3B, compared to that of nonsmokers and patients diagnosed with SCLC who have stopped smoking. These results suggest that active tobacco exposure increases chromosome fragile site expression, and that this fragility is transient and reversible. The data support the hypothesis that exposure to tobacco carcinogens increases the potential for chromosome breakage at fragile sites.

Molecular delineation of deletions on 2q37.3 in three cases with an Albright hereditary osteodystrophy‐like phenotype

A minority of the reported cases of terminal 2q37 deletion clinically resemble Albright hereditary osteodystrophy (AHO)/pseudopseudohypoparathyroidism and have only mild‐to‐moderate mental retardation. Our molecular and cytogenetic fluorescence in situ hybridization (FISH) findings on an additional three patients further reduce the size of the minimal critical region deleted in this syndrome to about 3 Mb. This region includes the G‐protein‐coupled receptor 35 (GPR35), glypican 1 (GPC1), and serine/threonine protein kinase 25 (STK25) genes on 2q37.3. We have further defined several polymorphic variants within the coding region and flanking regions of GPR35 gene, which could potentially be useful for rapid detection of GPR35 gene deletion. We postulate that the absence of GPR35 may, at least partly, account for the phenotypic resemblance to the AHO. We also believe that the deletion of GPR35 could be responsible for the entity brachydactyly mental retardation syndrome (OMIM #600430), which was coined based on the above minority of patients with terminal 2q37 deletion. We recommend that every patient with AHO phenotype should undergo 2q subtelomeric FISH screen and subsequently a molecular study on the GPR35 gene. GPC1 and/or STK25 haploinsufficiency may also contribute to the AHO‐like phenotype.

Hypomorphic PCNA mutation underlies a human DNA repair disorder

Numerous human disorders, including Cockayne syndrome, UV-sensitive syndrome, xeroderma pigmentosum, and trichothiodystrophy, result from the mutation of genes encoding molecules important for nucleotide excision repair. Here, we describe a syndrome in which the cardinal clinical features include short stature, hearing loss, premature aging, telangiectasia, neurodegeneration, and photosensitivity, resulting from a homozygous missense (p.Ser228Ile) sequence alteration of the proliferating cell nuclear antigen (PCNA). PCNA is a highly conserved sliding clamp protein essential for DNA replication and repair. Due to this fundamental role, mutations in PCNA that profoundly impair protein function would be incompatible with life. Interestingly, while the p.Ser228Ile alteration appeared to have no effect on protein levels or DNA replication, patient cells exhibited marked abnormalities in response to UV irradiation, displaying substantial reductions in both UV survival and RNA synthesis recovery. The p.Ser228Ile change also profoundly altered PCNAs interaction with Flap endonuclease 1 and DNA Ligase 1, DNA metabolism enzymes. Together, our findings detail a mutation of PCNA in humans associated with a neurodegenerative phenotype, displaying clinical and molecular features common to other DNA repair disorders, which we showed to be attributable to a hypomorphic amino acid alteration.

Interstitial 6q deletion and Prader-Willi-like phenotype

A third case of an interstitial deletion of the long arm of chromosome 6 with clinical features mimicking Prader‐Willi syndrome (PWS) is presented. Although preliminary clinical evaluation in each case suggested PWS, further review revealed that the features in all three cases are not completely compatible with the characteristic findings in Prader‐Willi syndrome. Furthermore, the deletions in the three cases do not show a consistent region of overlap. Consequently, no particular band or region in 6q can be defined as associated widi obesity. However, our findings confirm the suggestion of Villa et al. in 1995, that individuals with a PWS phenotype who are cytogenetically and molecularly negative for a deletion of 15q11‐q13 should be examined for a deletion of 6q.

Delineation of 14q32.3 deletion syndrome.

A patient with a 14q32.3 terminal band deletion and cat cry is reported. Review of four other 14q32.3 deletion cases suggests the possible presence of a recognisable 14q32.3 terminal deletion syndrome, which is characterised by (1) apparently postnatal onset of small head size in comparison to body size, (2) high forehead with lateral hypertrichosis, (3) epicanthic folds, (4) broad nasal bridge, (5) high arched palate, (6) single palmar crease, and (7) mild to moderate developmental delay. Although none of the above seven features in unique to this syndrome, and indeed are quite common in other chromosomal disorders or genetic syndromes, patients with a terminal 14q32.3 deletion do show a recognisable facial gestalt. Interestingly, unlike ring chromosome 14, the 14q32.3 terminal deletion has rarely been reported, possibly because it is harder to detect, and an optimal chromosome preparation is required for its identification.

Molecular characterization of an EWSR1–POU5F1 fusion associated with a t(6;22) in an undifferentiated soft tissue sarcoma

We report a soft tissue sarcoma from the thigh with morphologic features resembling Ewing sarcoma, clear cell sarcoma, and myoepithelial tumor of soft tissue. In addition, the genetic and immunohistochemical findings do not correspond to any established pattern, so the tumor does not clearly fit into any one classification. The karyotype analysis revealed a rare chromosomal rearrangement, t(6;22)(p22;q12), that previously has been reported in bone and epithelial tumors. Molecular studies confirmed the presence of an EWSR1-POU5F1 fusion creating a chimeric gene with the N-terminal transcriptional activation domain of EWSR1 and the C-terminal POU DNA binding domain of POU5F1. This report is novel in that to our knowledge, it is the first complete molecular characterization of an EWSR1-POU5F1 fusion in a soft tissue sarcoma. Evaluation of existing data on the known EWSR1-POU5F1 tumors suggests that the fusion gene functions in a wide variety of cell types and may modify the differentiation state of cells, resulting in susceptibility to tumorigenesis.

Newly described translocation (18;19)(q23;q13.2) in abdominal wall soft-tissue tumor resembling Ewing sarcoma/primitive neuroectodermal tumor

From a morphologic standpoint, Ewing sarcoma (EWS) is one of a number of pediatric malignancies that are characterized by sheets of small, round, blue cells. Ewing sarcoma can usually be differentiated from other small round blue cell tumors by the presence of a gene rearrangement having a consistent breakpoint within the Ewing sarcoma gene (EWSR1) at 22q12. Although the most common translocation partner is FLI1, located at 11q24, there is a growing list of alternate rearrangements involving different loci. We describe the first example of a soft-tissue sarcoma morphologically and immunohistochemically similar to Ewing sarcoma, but with a novel t(18;19)(q23;q13.2).

“Zwilling” versus “Tai Chi” configuration of double‐sized ring chromosome

Karyotype study of a newborn infant with clinical features of Down syndrome revealed a large ring chromosome replacing one of the chromosomes 21 in the majority of metaphase spreads. The G-banding pattern of this large ring chromosome suggested a double-sized ring chromosome 21 (Fig. 1A) in which the two halves of the ring are mirror images of each other, reminiscent of the ‘‘Zwilling’’ (twins) logo of the renowned brand name of high carbon stainless steel kitchen knifes from Henckel (Fig. 1B). Some of the cells only had 45 chromosomes without the ring and few others showed a quadruple-sized ring (Fig. 1C). The C-banding proved the two centromeres are located close to each other (Fig. 1D), and fluorescence in-situ hybridization (FISH) using the Down syndrome critical region probe (D21S259, D21S341, and D21S342, Vysis, Inc., Downers Grove, IL) also showed two signals adjacent to each other on the double-sized ring chromosome (Fig. 2A). FISH using a chromosome 21 subtelomere probe showed a single signal on one chromosome 21 and a pair of closely associated signals for the ring 21. This indicates that the break in the long arm occurred distal to the subtelomere region resulting in probable loss of some telomeric sequences and ring fusion within the remaining telomere region. Interphase FISH indicated the majority of nuclei (219/300 or 73%) to have three signals with two of them close to each other (Fig. 2B). Less than 10% (26/300) had only one signal, and 17% seemed to equivocally show more than three signals. The presence of cells without a ring and cells with more than three signals suggested this ring chromosome is unstable, a common feature of dicentric ring chromosomes [McClintock, 1938; Hoo et al., 1974]. A double-sized ring chromosome is usually derived from a single-sized ring chromosome following a sister-chromatid exchange in mitosis [Hoo et al., 1974]. The double-sized ring chromosome generated from this mechanism has an inverted, opposite or reverse mirror image of the banding patterns of the two halves of the doublesized ring chromosome reminiscent of a ‘‘Tai Chi’’ symbol (Fig. 3A,B).