Jacqueline R. Batanian

Acute megakaryoblastic leukemia after transient myeloproliferative disorder with clonal karyotype evolution in a phenotypically normal neonate.

We report a case of transient myeloproliferative disorder (TMD) in a neonate without features of Down syndrome (DS) with clonal karyotype evolution, after apparent spontaneous resolution of TMD, but eventually progressing to acute megakaryoblastic leukemia (AMKL). The patient had petechiae, thrombocytopenia, and blastemia. Trisomy 21 with a satellited Y chromosome (Yqs) was found in proliferating blasts. A stimulated peripheral blood culture confirmed the constitutional origin of the Yqs, but did not reveal the presence of any trisomic 21 cell. By the age of 3 months, clonal chromosome evolution in the form of an interstitial deletion of the long-arm of chromosome 13 [del(13)(q13q31)] was detected along with trisomy 21 in unstimulated bone marrow cultures. However, remission was achieved without treatment at the age of 4 months. Trisomy 21 and del(13)(q13q31) were not identified in either cytogenetics or fluorescence in situ hybridization studies at that time. The child was asymptomatic until the age of 20 months when anemia and thrombocytopenia prompted a bone marrow biopsy, revealing changes consistent with AMKL. The remission proceeded by clonal karyotype evolution in a neonate with TMD demonstrates that clonal karyotype evolution does not indicate an immediately progressive disease. However, the development of AMKL after TMD in this case illustrates the increased risk for leukemia in TMD cases, even without DS. The gradual clonal evolution of the blasts in our patient suggests that “multiple hits” oncogenesis applies to TMD progression to acute leukemia.

Aberrant SP-B mRNA in lung tissue of patients with congenital alveolar proteinosis (CAP).

Mutations in the surfactant protein (SP)‐B gene are responsible for SP‐B deficiency in congenital alveolar proteinosis (CAP) (Nogee et al. J Clin Invest 1994: 93: 1860–1883; Lin et al. Mol Genet Metab 1998: 64: 25–35; Klein et al. Pediatrics 1998: 132: 244–248; Ballard et al. Pediatrics 1995: 96: 1046–1052). The multigenerational consanguineous pedigree under study does not carry any of the known mutations, although this pedigree had 14 infant deaths following respiratory distress at birth. Immunostaining of the lungs from three such infants revealed decreased or absent SP‐B. By sequencing of SP‐B exons, exon–intron junctions, and the 5′ and 3′ flanking regions, nine polymorphisms were found in this pedigree, but none of them could explain the observed SP‐B deficiency. Further analysis of SP‐B mRNA by reverse transcription‐polymerase chain reaction from paraffin‐embedded lung tissue of CAP patients showed that SP‐B mRNA is not intact. Although the sequence of mRNA from exon 1–exon 7 and from exon 8–exon 10 could be amplified, the region between exons 7 and 8 could not. From fluorescence in situ hybridization of the short arm of chromosome 2p, only 2 signals were identified, eliminating the possibility of translocation as the cause of the SP‐B mRNA aberrance. Although the nature of the genetic basis of SP‐B deficiency in this family is currently unknown, the existence of aberrant SP‐B mRNA may, at least in part, be responsible for the SP‐B deficiency in this pedigree.

Familial complex chromosome rearrangement giving rise to balanced and unbalanced recombination products.

We report on a family ascertained through a 14-month-old girl with a terminal deletion of chromosome 8p23.1. Analysis of the karyotype of other relatives showed that the mother is the carrier of a balanced complex 4-break chromosome rearrangement, which she and her brother inherited from their father following recombination. This complex chromosome rearrangement (CCR) was confirmed by fluorescence in-situ hybridization (FISH) using libraries for chromosomes 1, 8, and 9, and telomeric probes for the long arm of chromosome 9. The karyotype of the maternal grandfather was 46,XY,t(1;8) (p31;q21.1),t(8;9) (p23.1;q34). The karyotype of his daughter is 46,XX,rec(8)t(1;8) (p31;q21.1)t(8;9)(p23.1;q34)pat. The karyotype of the proposita is 46,XX,rec(8)t(8;9) (p23.1;q34)mat, and that of her abnormal elder sister is 46,XX,t(1;8)(p31;q21.1)rec(8) t(8;9) (p23.1;q34)mat,der(9)t(8;9) (p23.1;q34) mat. Unbalanced segregation and/or recombination during maternal meiosis gave rise to the two abnormal sisters, one effectively with 8p trisomy and the other with monosomy for that same 8p segment. To our knowledge, this is the first case of a familial CCR giving rise to unbalanced recombination products.

EWS/FLI-1 fusion signal inserted into chromosome 11 in one patient with morphologic features of Ewing sarcoma, but lacking t(11;22)

A reciprocal t(11;22)(q24;q12) is found in 85% of Ewing sarcomas (ES) cases. We report a case of a child with ES, in whom trisomy 8 was observed as the sole chromosomal abnormality. Fluorescence in situ hybridization---using a set of probes that localize to 22q12 (EWS) and 11q24 (FLI-1) and usually show the translocation as fusion (red-green) signal on der(22)---showed a fusion signal on der(11) suggesting an insertion as the mechanism that led to the EWS-FLI-1 gene rearrangement. Reverse transcriptase-polymerase chain reaction studies revealed the presence of two EWS/FLI1 fusion gene products.

Case of lipoblastoma with two derivative chromosomes 8 containing homogeneously staining-like regions and a review of the literature: lipoblastoma and chromosome 8

We report a case of a lipoblastoma in a 10-month-old girl in which the cytogenetic aberration showed a homogeneously staining-like region (hsr) within two derivative chromosomes 8. There was a loss of one normal copy of chromosome 8 and gain of two identical derivative chromosomes 8 with the karyotype designation 47,XX,psu idic(8)(pter-->q12 approximately 13::hsr::q12 approximately 13-->pter),+psu idic (8)(pter-->q12 approximately 13::hsr::q12 approximately 13-->pter). This is the first report of a chromosomal aberration of this type seen in lipoblastoma.

Preferential involvement of the short arm in chromosome 8‐derived supernumerary markers and ring as identified by chromosome arm painting

We report on the use of fluorescence in situ hybridization (FISH) with specific chromosome 8 arm painting to characterize further small supernumerary chromosome 8-derived markers/rings (SMC/SRC) identified in three patients. Two patients (patients 1 and 2) who carried the marker (SMC) were evaluated because of mental retardation and minor facial anomalies. The patient (patient 3) who carried the ring (SRC) had ventriculomegaly. Parental blood chromosomes of patients 2 and 3 were normal and unavailable on patient 1. The identification of the SMC/SRC was first characterized by FISH specific alpha-repeat centromeric probes, second by FISH whole chromosome painting (WCP), and finally by FISH chromosome arm painting (CAP). The latter showed involvement of only the short arm of chromosome 8 in all three SMC/SRC cases, suggesting a U-type exchange mechanism.

Trisomy 15 Is Frequently Observed as a Minor Clone in Patients with Anemia/ MDS/ NHL and as a Major Clone in Patients with AML

Trisomy 15 as the sole karyotypic aberration is an uncommon clonal cytogenetic aberration in hematological malignancies, making its significance unclear. Previous studies have reported relations of trisomy 15 with low-grade myelodysplasia or a benign age-related phenomenon associated with loss of the Y chromosome. To define the significance of trisomy 15, we conducted a retrospective study of all examples of trisomy 15 accessed in our laboratories. Trisomy 15 was observed as a clonal abnormality (> or =2 cells) in 17 cases and nonclonal (single cell) in 9 cases. The majority of cases (14/17 clonal cases) had a minor clone (5-35% of metaphase cells) of trisomy 15. The minority of cases (3/17) had a major clone (80-95% of metaphase cells) of trisomy 15. Two of these 3 cases were diagnosed as having acute myelocytic leukemia. Fluorescence in-situ hybridization (FISH) with the use of a chromosome 15-specific alpha-satellite probe was performed on 3 of 17 clonal cases and on 3 of 9 nonclonal cases. FISH results revealed the presence of a minor clone (from 3 to 5 of 700 interphase cells) in 5 of them, 2 of which had trisomy 15 in 20% of metaphase cells. These results may indicate that the 20% of trisomy 15 are very likely an overrepresentation of a very minor clone that could be transitory. In summary, the analysis of our cytogenetic and FISH results revealed the presence of two types of trisomy 15 clones: a minor clone that could be transitory or indolent and a major clone that could be of a neoplastic nature.

Increased STAG2 dosage defines a novel cohesinopathy with intellectual disability and behavioral problems

Next generation genomic technologies have made a significant contribution to the understanding of the genetic architecture of human neurodevelopmental disorders. Copy number variants (CNVs) play an important role in the genetics of intellectual disability (ID). For many CNVs, and copy number gains in particular, the responsible dosage-sensitive gene(s) have been hard to identify. We have collected 18 different interstitial microduplications and 1 microtriplication of Xq25. There were 15 affected individuals from 6 different families and 13 singleton cases, 28 affected males in total. The critical overlapping region involved the STAG2 gene, which codes for a subunit of the cohesin complex that regulates cohesion of sister chromatids and gene transcription. We demonstrate that STAG2 is the dosage-sensitive gene within these CNVs, as gains of STAG2 mRNA and protein dysregulate disease-relevant neuronal gene networks in cells derived from affected individuals. We also show that STAG2 gains result in increased expression of OPHN1, a known X-chromosome ID gene. Overall, we define a novel cohesinopathy due to copy number gain of Xq25 and STAG2 in particular.

Oculo-auriculo-vertebral spectrum, cat eye, and distal 22q11 microdeletion syndromes: a unique double rearrangement.

An array‐CGH on 19‐year‐old male showed a proximal 1.11 Mb duplication and a distal 1.7 Mb deletion of 22q11.2 regions flanking the Velocardiofacial/DiGeorge syndrome region that remained intact. FISH analyses revealed both abnormalities to be on the same homolog 22. This double rearrangement lead to the co‐existence of two syndromes: Cat eye and distal 22q11.2 microdeletion syndromes with a rare associated phenotype of oculo‐auriculo‐vertebral spectrum (OAVS). A review of the literature indicates that this is the second report of a proximal duplication and the fifth report of a distal deletion and OAVS suggestive of a possible OAVS candidate gene in this region.

Two unbalanced translocations involving a common 6p25 region in two XY female patients

We report two 46,XY female patients with two different de novo unbalanced translocations, each involving the chromosomal region 6p25. The patient with a 46,XY,der(6)t(X;6)(p21.2;p25) karyotype had a sex reversal phenotype. The patient with a 46,XY,der(13)t(6;13)(p25;q33) karyotype had a male pseudohermaphrodite phenotype. Multi‐paint fluorescent in situ hybridization was performed to determine the origin of the derivative material on 6p and 13q. The association of abnormalities of the 6p25 region with either an Xp duplication or a 13q deletion is reported here for the first time.