Prader-Willi syndrome with an unusually large 15q deletion due to an unbalanced translocation t(4;15)

Prader-Willi syndrome (PWS) is a neurobehavioral disorder caused by deletions in the 15q11-q13 region, by maternal uniparental disomy of chromosome 15 or by imprinting defects. Structural rearrangements of chromosome 15 have been described in about 5% of the patients with typical or atypical PWS phenotype. An 8-year-old boy with a clinical diagnosis of PWS, severe neurodevelopmental delay, absence of speech and mental retardation was studied by cytogenetic and molecular techniques, and an unbalanced de novo karyotype 45,XY,der(4)t(4;15)(q35;q14),-15 was detected after GTG-banding. The patient was diagnosed by SNURF-SNRPN exon 1 methylation assay, and the extent of the deletions on chromosomes 4 and 15 was investigated by microsatellite analysis of markers located in 4qter and 15q13-q14 regions. The deletion of chromosome 4q was distal to D4S1652, and that of chromosome 15 was located between D15S1043 and D15S1010. Our patient's severely affected phenotype could be due to the extent of the deletion, larger than usually seen in PWS patients, although the unbalance of the derivative chromosome 4 cannot be ruled out as another possible cause. The breakpoint was located in the subtelomeric region, very close to the telomere, a region that has been described as having the lowest gene concentrations in the human genome.     

The Prader-Willi syndrome and 15-15 translocation]

The association of the Willi-Prader syndrome and a t(15q15q) is reported. This, in conjunction with an earlier report of this association, suggests that a gene related to the Willi-Prader syndrome may be present on chromosome 15.     

Familial translocation t(10;21)(q22;q22)

Summary A family is described with a translocation t(10;21)(q22;q22) transmitted through three generations. This family was studied for the apparition of several miscarriages and two sisters with multiple malformations. Both children had a probably partial trisomy of chromosome 10 and a monosomy of chromosome 21 due to a maternal adjacent-2 meiotic segregation.     

Molecular characterisation of the t(1;15)(p22;q22) translocation in the prostate cancer cell line LNCaP

Although chromosome translocations are well-documented recurrent events in hematological malignancies and soft tissue sarcomas, their significance in carcinomas is less clear. We report here the molecular characterization of the reciprocal translocation t(1;15)(p22;q22) in the prostate carcinoma cell line, LNCaP. The chromosome 1 breakpoint was localized to a single BAC clone, RP11-290M5, by sequential FISH analysis of clones selected from the NCBI chromosome 1 map. This was further refined to a 580-bp region by Southern blot analysis. A 2.85-kb fragment spanning the der(1) breakpoint was amplified by long-range inverse PCR. The breakpoint on chromosome 1 was shown to lie between the CYR61 and the DDAH1 genes with the der(1) junctional sequence linking the CYR61 gene to the TSPAN3 (TM4SF8) gene on chromosome 15. Confirmatory PCR and FISH mapping of the der(15) showed loss of chromosome material proximal to the breakpoint on chromosome 15, containing the PSTPIP1 and RCN2 genes. On the available evidence we conclude that this translocation does not result in an in-frame gene fusion. Comparative expressed sequence hybridization (CESH) and comparative genomic hybridization (CGH) analysis, showed relative down-regulation of gene expression surrounding the breakpoint, but no gross change in genomic copy number. Real-time quantitative RT-PCR for genes around the breakpoint supported the CESH data. Therefore, here we may have revealed a gene down-regulation mechanism associated with a chromosome translocation, either through small deletion at the breakpoint or through another means of chromosome domain related gene regulation.     

AT-rich palindromes mediate the constitutional t(11;22) translocation

The constitutional t(11;22) translocation is the only known recurrent non-Robertsonian translocation in humans. Offspring are susceptible to der(22) syndrome, a severe congenital anomaly disorder caused by 3&rcolon;1 meiotic nondisjunction events. We previously localized the t(11;22) translocation breakpoint to a region on 22q11 within a low-copy repeat termed "LCR22" and within an AT-rich repeat on 11q23. The LCR22s are implicated in mediating different rearrangements on 22q11, leading to velocardiofacial syndrome/DiGeorge syndrome and cat-eye syndrome by homologous recombination mechanisms. The LCR22s contain AT-rich repetitive sequences, suggesting that such repeats may mediate the t(11;22) translocation. To determine the molecular basis of the translocation, we cloned and sequenced the t(11;22) breakpoint in the derivative 11 and 22 chromosomes in 13 unrelated carriers, including two de novo cases and der(22) syndrome offspring. We found that, in all cases examined, the reciprocal exchange occurred between similar AT-rich repeats on both chromosomes 11q23 and 22q11. To understand the mechanism, we examined the sequence of the breakpoint intervals in the derivative chromosomes and compared this with the deduced normal chromosomal sequence. A palindromic AT-rich sequence with a near-perfect hairpin could form, by intrastrand base-pairing, on the parental chromosomes. The sequence of the breakpoint junction in both derivatives indicates that the exchange events occurred at the center of symmetry of the palindromes, and this resulted in small, overlapping staggered deletions in this region among the different carriers. On the basis of previous studies performed in diverse organisms, we hypothesize that double-strand breaks may occur in the center of the palindrome, the tip of the putative hairpin, leading to illegitimate recombination events between similar AT-rich sequences on chromosomes 11 and 22, resulting in deletions and loss of the palindrome, which then could stabilize the DNA structure.     

Sotos syndrome with a balanced reciprocal translocation t(2;12)(q33.3;q15)

A balanced reciprocal translocation, 46,XY, t(2;12), was detected in a male infant who had the characteristic features of Sotos syndrome. His father's karyotype was normal, but his mother and an older brother had the same chromosomal abnormality without a history or clinical features of Sotos syndrome.     

Unbalanced reciprocal translocations in cases of Prader-Willi syndrome

Summary A case of Prader-Willi syndrome (PWS) associated with a de novo unbalanced 15q;17q reciprocal translocation presumptively resulting from the tertiary monosomic form of 3:1 meiotic disjunction is described. Twenty-three similar unbalanced translocations have been identified from the literature. The 24 karyotypes are characterised by having 45 chromosomes, monosomy for the pericentromeric region of chromosome 15 (range pter»q11 to q21), and little monosomy of the recipient (non-15) chromosome. Two-thirds of the cases with these karyotypes have phenotypic features of PWS. It seems probable that (i) where unbalanced reciprocal translocations are associated with PWS, they will almost invariably be presumptive segregants of the tertiary monosomic form of 3:1 disjunction and (ii) the majority of cases found with this type of karyotype, particularly it appears when de novo in origin, will be associated with phenotypic features of PWS.     

Unbalanced 1q whole-arm translocation resulting in der(14)t(1;14)(q11-12;p11) in myelodysplastic syndrome

Unbalanced whole-arm translocations (WATs) of the long arm of chromosome 1, resulting in complete trisomy 1q, are chromosomal abnormalities detectable in both solid tumors and hematologic neoplasms. Among the WATs of 1q to acrocentric chromosomes, a few patients with der(1;15) described as a dicentric chromosome have been reported so far, whereas cases of der(1;14) are much rarer. We report on a case of der(1;14) detected as single anomaly in a patient with myelodysplastic syndrome. The aim of our work was to investigate the breakpoints of the (1;14) translocation leading to the der(1;14). Fluorescence in situ hybridization (FISH) experiments have been performed on chromosome preparations from bone marrow aspirate, using specific centromeric probes of both chromosomes, as well as a probe mapping to 1q11 band. FISH results showed that in our patient the derivative chromosome was monocentric with a unique centromere derived from chromosome 14. The breakpoints of the translocation were located in the short arm of chromosome 14 and in the long arm of chromosome 1, between the alphoid D1Z5 and the satellite II domains. The 1q breakpoint was within the pericentromeric region of chromosome 1, which is notoriously an unstable chromosomal region, involved in different chromosomal rearrangements.     

Familial unbalanced translocation t(8;15)(p23.3;q11) with uniparental disomy in Angelman syndrome

A 29-year-old male with Angelman syndrome and an unbalanced reciprocal translocation, 45,XY,-8,-15,+der(8),t(8;15)(p23.3;q11)pat, was evaluated with DNA studies. These showed the underlying mechanism to be paternal uniparental disomy. This is the second case reported of Angelman syndrome that has resulted from a familial unbalanced reciprocal translocation.     

A Y/15 translocation in a 45,X male with Prader-Willi syndrome

We report a male neonate with a 45 X karyotype; the long arm of a chromosome 15 was translocated onto the proximal long arm of the Y chromosome. Breakpoints were identified by in situ fluorescence hybridization (FISH) on the proximal 15q13 and Yq11.2. The derivative chromosome has no primary centromere. Clinical features were compatible with Prader-Willi syndrome. This is the first report case ofmonosomy 15q and Yq deletion with Prader-Willi syndrome.     

Trisomie 10 partielle par translocation familiale t(1;10) (q44;q22)

Résumé Chez une enfant anormale, on observe un excès de matériel chromosomique sur la paire 1:1q+, et une translocation t(1q+;10q-) est dépistée dans la famille.L'analyse du caryotype après «dénaturation thermique ménagée» a permis d'individualiser le chromosome C anormal (10q-), de définir l'emplacement exact des points de cassure et de lier essentiellement l'état pathologique du patient à une trisomie partielle du bras long du chromosome 10.Cette trisomie se traduit principalement par une arriération mentale, une hypotrophie, des anomalies oculaires, une fente palatine, une mal-implantation des oreilles, un micrognathisme, des anomalies du squelette et une cardiopathie.

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Partial trisomy 10 due to hereditary translocation t(1;10) (q44;q22)

Summary A chromosome 1q+was observed in an abnormal girl. A balanced t(1q+;10q-) was found in the family.Application of a controlled thermic denaturation technique allowed recognition of the abnormal C as a 10q-and localization of the break points (1q44 and 10q22).The partial trisomy 10q of the proband had induced mental retardation, severe retardation of growth, ocular anomalies, agenesis of the palate, low implantation of the ears, micrognathia bone anomalies and cardiac malformation.

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Zusammenfassung Bei einem Mädchen mit Mißbildungen wurde ein Chromosom 1q+beobachtet. Eine balancierte t(1q+, 10q-) fand sich in der Familie.Die Identifikation des abnormen C als 10q- wurde durch Anwendung kontrollierter Wärmedenaturierung erreicht; auf diesem Wege wurden auch die Bruchpunkte identifiziert.Die partielle Trisomie 10q hatte bei dem Probanden einen geistigen Entwicklungsrückstand, eine schwere Wachstumsstörung, Augenanomalien, Fehlen des Gaumens, tief ansetzende Ohren, eine Mikrognathie, Knochenanomalien und eine Herzmißbildung zur Folge.

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Chargée de Recherche I.N.S.E.R.M. Chef de Service à l'Institut Pasteur de Lyon.

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Chargés de Recherche C.N.R.S.     

Supernumerary chromosome der(22)t(11;22): Emanuel syndrome associates with novel features

Emanuel syndrome results from +der(22)t(11q23;22q11). Cleft palate, ear anomalies, heart defects, genital anomalies, hypotonia, and mental retardation are the main features of the syndrome. We report a nine-year-old boy with the t(11;22)(q23;q11) chromosome, transmitted in an unbalanced fashion from his mother, and originated in the maternal grandmother's meiosis. In addition to mental retardation, hypotonia, craniofacial anomalies, and cryptorchidism, he has novel findings such as, joint hyperextensibility, left liver lobe agenesis, left sided malposition of the gallbladder and pancreas hypoplasia. This is the first report associating these features with Emanuel syndrome.     

Unstable familial translocations: A t(11;22)mat inherited as a t(11;15).

Unusual inheritance of a reciprocal translocation, t(11;22)(p11;p12)mat was discovered in a family with one daughter having a different translocation, t(11;15)(p11;p12). Another daughter inherited the same translocation as her mother. The breakpoints through the nucleolar organizing regions (NORs) of chromosomes 15 and 22 were determined by silver staining. A review of the literature has demonstrated that such unstable familial translocations are very rare and can occur either in mitosis or meiosis. They usually involve exchanges between centromeres, telomeres, or NORs.     

The constitutional t(17;22): another translocation mediated by palindromic AT-rich repeats

We have demonstrated that the breakpoints of the constitutional t(11;22) are located at palindromic AT-rich repeats (PATRRs) on 11q23 and 22q11. As a mechanism for this recurrent translocation, we proposed that the PATRR forms a cruciform structure that induces the genomic instability leading to the rearrangement. A patient with neurofibromatosis type 1 (NF1) had previously been found to have a constitutional t(17;22) disrupting the NF1 gene on 17q11. We have localized the breakpoint on 22q11 within the 22q11-specific low-copy repeat where the breakpoints of the constitutional t(11;22)s reside, implying a similar palindrome-mediated mechanism for generation of the t(17;22). The NF1 gene contains a 195-bp PATRR within intron 31. We have isolated the junction fragments from both the der(17) and the der(22). The breakpoint on 17q11 is close to the center of the PATRR. A published breakpoint of an additional NF1-afflicted patient with a constitutional t(17;22) is also located close to the center of the same PATRR. Our data lend additional support to the hypothesis that PATRR-mediated genomic instability can lead to a variety of translocations.