Mapping around the Xq13.1 breakpoints of two X/A translocations in hypohidrotic ectodermal dysplasia (EDA) female patients.

Cellular hybrids were obtained from a t(X;12) identified in a female patient with hypohidrotic ectodermal dysplasia (EDA). This rearrangement had the same Xq13.1 cytogenetic breakpoint as a t(X;9) found in a previously observed EDA patient. A comparative analysis of these two rearrangements with nine probes was performed at the molecular level. These probes could define three subregions: three are proximal, two are distal, and four are between the two breakpoints. These last probes should prove useful for cloning the gene.

Increased SOD1 enzymatic activity and gene modifications in orangutans: evolutionary implications.

Superoxide dismutase CuZn (SOD1) enzymatic activity was measured in five orangutans (Pongo pygmaeus, PPY) and compared to that of man, chimpanzee, and gorilla. It was found to be increased by a factor of two in one orangutan (Ralfina) and by a factor of 1.5 in the four others. In situ hybridization of the SOD1 cDNA human probe showed a heterozygous intra-chromosomal rearrangement of pair PPY XXI, possibly an insertion, in Ralfina. Southern blotting showed that the SOD1 gene is modified in the three orangutans that were investigated and that a further modification of the 5'-end of the gene had occurred in Ralfina. The evolutionary implications of these observations are discussed.

Physical map around the retinoblastoma gene: possible genomic imprinting suggested by NruI digestion.

A long-range restriction map constructed around the retinoblastoma (RB) gene by means of PFGE analysis allowed further definition of chromosomal rearrangements with a breakpoint within the gene, as well as of submicroscopic deletions. A serendipitous observation was that the NruI restriction pattern differs according to the parental origin of the rearrangement.

Molecular detection of constitutional deletions in patients with retinoblastoma.

The recent cloning of the retinoblastoma (RB) gene as well as the identification of intragenic polymorphisms afford the necessary tools for the analysis of rearrangements using molecular hybridization. We searched for constitutional deletions by Southern blotting in 67 independent patients with normal karyotype comprising 15 familial and 52 sporadic cases. Among the latter, 33 were bilaterally and 19 unilaterally affected. We detected 6 deletions using cDNA probes covering almost all of the RB gene, as well as a genomic probe of the 5' part of the gene. With this approach, the incidence of detectable deletions was around 10%. No hot spots for deletion breakpoints were found. Asymptomatic carriers were detected in 2 families. The effectiveness of genetic counselling was largely improved by this approach.

The malignant primate?

Speciation and carcinogenesis result from genomic instability at the gametic or at the somatic levels. After an infinity of trials they occur, by chromosome rearrangements, in single individuals or in single cells and evolve by similar chromosomal or clonal evolutions. Loss of heterozygosity for the first event is essential in both processes: in evolution, a chromosomal rearrangement, a pericentric inversion or a Robertsonian fusion, must become homozygous to ensure a reproductive barrier for a new species; Knudson's two-event sequence is a similar situation in cancer. Position effect is equally important: we have shown overexpression of the SOD1 gene in the orangutan phylum probably by an intrachromosomal rearrangement; the t(9;22) in CML acts by typical position effect. Parental imprinting underlies the evolution of genome function and the unset of certain cancers. Evolution and malignancy are interweaved by viruses and oncogenes since the dawn of life. Cancer uses its intelligence to expand and to destroy the other tissues, using subtle metabolic pathways and a variety of tricks to metastasize other cells. It always wins but saws the branch on which it sits. Mankind also grows exponentially, killing thousands of other species, poisoning the oceans and soft waters, polluting the atmosphere, all for his egoistic needs. Man also travels and metastasizes other Earths. He modifies his genome or that of other species, and develops new technologies for his reproduction. He can destroy the planet in an eyeblink. To be or not to be the malignant primate, that will be the dilemma for the 21st Century.

[Genetics and genetic counseling: the retinoblastoma case]. / Génétique et conseil génétique: le cas du rétinoblastome.

Forty-percent of retinoblastomas are due to a mutation inherited as an autosomal dominant trait with a high penetrance. Cytogenetic forms of retinoblastoma have led to the location of the gene, to the identification of numerous chromosome 13 specific DNA polymorphisms, and to the cloning of the gene. Intragenic DNA polymorphisms are now known. Using Southern blot hybridization, study of the mutation is possible either by direct analysis or by an indirect approach using linkage with polymorphic genetic markers. The majority of cases cannot be examined by these techniques. Their value and limits are discussed.

Autosomal mendelian disorders and microcytogenetics.

The development of cytogenetic high resolution banding techniques has allowed the observation of specific chromosome rearrangements--i.e. microdeletions, translocations--in patients with morbid conditions suspected to have a genetic component but for which a precise etiology had not, or rarely, been recognized. The most striking examples are retinoblastoma, the WAGR complex, Beckwith-Wiedemann syndrome, Langer-Giedion syndrome, Prader-Willi syndrome, Miller-Dieker syndrome and others, which thus could be mapped to the genome. Molecular technology further allowed in a number of cases cloning of the genes proper or of linked DNA polymorphisms permitting genetic counseling.

[Prenatal diagnosis of various hereditary blinding diseases]. / Diagnostic anténatal de certaines maladies héréditaires cécitantes.

The availability of more and more reliable obstetrical echographies makes now possible to screen fetuses for microphtalmies and anophtalmies. More over, by mean of linkage studies with DNA markers within a family, we can identify the women who will transmit X-linked diseases, and realize a prenatal diagnosis. This technology can be applied to the following ophthalmological diseases: the X-linked retinoschisis, the choroideremia, the ocular albinism, the Noorie disease, and recently the retinoblastoma. From now on, the use of such a technology which makes it possible to detect ophthalmological diseases in the fetuses, is posing ethical problems especially in case of diseases without any survival prognosis involvement.

Rett phenotype with X/autosome translocation: possible mapping to the short arm of chromosome X.

Rett syndrome (RS) was diagnosed in a girl with a t(X;22) (p11.22;p11). This translocation was also present in her unaffected mother and her sister affected by a neurological disorder compatible with a "forme fruste" of RS. Different etiological mechanisms are considered: gene disruption, X inactivation disturbance, metabolic interference. Whatever this may be, the localization of a RS related gene to the short arm of chromosome X is likely.

[Chromosome abnormalities of the fertilized human egg]. / Anomalies chromosomiques de l'oeuf humain fécondé.

In vitro fertilization enabled the study of lethal (parthenogenesis) or sublethal (triploidy, monosomy and trisomy) chromosomal abnormalities in man. According to the literature, 23 to 71% of preimplantation embryos carry a chromosomal defect. Various factors, such as delayed fertilization, early embryo fragmentation or elevated maternal age (greater than 35 years) are related to an increase in the incidence of chromosomal aberrations. These data reinforce the debate on a preimplantation genetic diagnosis in order to select for transfer only viable and apparently normal embryos.

Cytogenetic analysis and developmental capacity of normal and abnormal embryos after IVF.

Chromosome abnormalities represent the major cause of pre- and post-implantation embryo wastage. Indeed, 29% of embryos produced by in-vitro fertilization have an abnormal karyotype. Parthenogenesis (1.6% of the cases) and triploidy (6.4%) are the only abnormalities detectable 17 h after insemination. A total of 23% of activated oocytes with a single pronucleus (1 PN) and 18% of fertilized eggs with three pronuclei (three PN) remained uncleaved, compared with 4% for diploid eggs. The rate of cleavage for parthenogenes is not different from normal eggs. On the contrary, we observed that 29% of three PN-eggs reached the 5- to 8-cell stage 42 h after insemination when compared to 15% for diploids mainly due to a direct division of 56% of three PN-eggs in three cells. A model of development for triploid eggs is proposed, taking into account physiological and cytogenetic observations. The quality of embryos expressed in terms of morphology did not show any difference between embryos proceeding from parthenogenes or diploid eggs. On the contrary, the rate of fragmentation is decreased for triploid (3%) compared with diploid (13%) or activated (17%) embryos. Embryos resulting from one, two, three or four pronucleate ova display different developmental capacities during 5 days' culture in vitro.

X-linked hypohidrotic ectodermal dysplasia and t(X;12) in a female.

A female patient with features of hypohidrotic ectodermal dysplasia (HED) was found to be a carrier of a de novo t(X;12) with a breakpoint in Xq13.1. This is the second instance of an X/autosome translocation, with apparently the same X breakpoint, reported in HED.

Multibranched chromosomes in the ICF syndrome: immunodeficiency, centromeric instability, and facial anomalies.

A new patient with the rare ICF syndrome (immunodeficiency, centromeric heterochromatin instability, and facial anomalies) is reported. The six patients previously reported in the literature are reviewed. The main clinical and cytogenetic characteristics of the syndrome are discussed.

Incontinentia pigmenti and X-autosome translocations. Non-isotopic in situ hybridization with an X-centromere-specific probe (pSV2X5) reveals a possible X-centromeric breakpoint in one of five published cases.

Incontinentia pigmenti (IP) is a rare X-linked disease with marked female-to-female transmission and a dominant pattern of inheritance. Reports of six unrelated females with IP and X-autosomal translocations, all with the X breakpoint at Xp11, and an additional report of a female with IP and a 45,X/46,X,r(X) karyotype suggests that this may be the locus for the IP gene. When four of these cases, including the r(X), were re-examined with a non-isotopic in situ hybridization technique and an X centromere-specific probe (pSV2X5), the Xp11 breakpoint was confirmed. However, results from a fifth reported case, t(X;17), showed that the X breakpoint was within the centromeric alphoid repetitive sequences recognized by the probe pSV2X5. As the clinical presentation of this patient was consistent with the IP phenotype and diagnosis, the centromeric position of the X-chromosome breakpoint raises several questions with respect to the homogeneity of the Xp11 locus for IP.

Molecular definition of the 11p15.5 region involved in Beckwith-Wiedemann syndrome and probably in predisposition to adrenocortical carcinoma.

To define more precisely, in molecular terms, the region involved in Beckwith-Wiedemann syndrome (BWS), we have studied patients with BWS and a constitutional duplication of 11p15 using eight 11p15 markers. In the first case with a de novo duplication and extra material on 11p, the region spanning pter to CALCA, excluded, was duplicated. In the second case, the rearrangement was characterized using somatic cell hybrids established with lymphocytes from the father who carried a balanced translocation t(11;18)(p15.4;p11.1). The breakpoint lay exactly in the same region. It could thus be inferred that the two sons, who were the first cases reported of BWS with dup11p15 and adrenocortical carcinoma (ADCC), carried a duplication similar to that observed in the first case. Together with evidence for specific somatic chromosomal events leading to loss of 11p15 alleles in familial cases of ADCC, it can be hypothesized that a gene involved in predisposition to ADCC maps to region 11p15.5.

The decrease of catalase or esterase D activity in patients with microdeletions of 11p or 13q does not increase their radiosensitivity.

Lymphocyte cultures from patients affected by retinoblastoma (Rb), with or without a microdeletion of chromosome 13, and Wilms tumor (WT), with a microdeletion of chromosome 11p where exposed to gamma-ray radiation during S and G2 phases. Chromatid and chromosome lesions were scored and compared to those observed in controls. No significant differences were detected, neither between patients and controls, nor between patients carrying or not a microdeletion. This lack of difference was unexpected since the genes for catalase and esterase D, also called S-formyl glutathione hydrolase, which are two detoxication enzymes, are deleted in case of microdeletion of 11p and 13q, respectively.

Incontinentia pigmenti: Xp breakpoint is not the same in a case of r(X) and in X/autosome translocations.

X-specific DNA probes were used to characterize the r(X) of a 45,X/46,X,r(X) female patient with Incontinentia pigmenti. It was found to be of maternal origin. Breakpoints were shown to be in or distal to p11.22 and between q12.2 and q13.1. When considering all known cases of Incontinentia pigmenti and X rearrangements at least four different break sites on the X have been shown.