Single base pair germ-line deletion in the p53 gene in a cancer predisposed family

A family with an aggregation of adrenocortical carcinoma, rhabdomyosarcoma, osteosarcoma, and early onset breast cancer was referred to our laboratory. Because this aggregation was reminiscent of Li-Fraumeni syndrome, germ-line mutation of the p53 tumor suppressor gene was sought in the DNA of two affected members. The highly conserved regions spanning exons 5 to 8 of the p53 gene were screened by a previously validated denaturing gradient gel electrophoresis method. A single base pair deletion at codon 215 was detected in constitutional DNA of the two patients, and in the DNA extracted from an adrenocortical carcinoma tumor specimen of the propositus. This deletion is predicted to lead to the formation of a truncated p53 protein, a relatively rare event in Li-Fraumeni families. The spectrum of tumors observed in this family does not differ markedly from the spectrum observed in families with missense p53 mutations.

Assignment of 112 microsatellite markers to 23 chromosome 11 subregions delineated by somatic hybrids: comparison with the genetic map

Using a panel of 25 somatic cell hybrids, we have regionally localized 112 microsatellite markers generated by Généthon and assigned to chromosome 11. A genetic map of 74 of them was produced using linkage analysis of the eight largest CEPH (Centre d'Etude du Polymorphisme Humain) families. They could be ordered on chromosome 11 with an average distance of 2.1 cM. The tight correlation observed between the genetic order and the physical assignment of these microsatellites reinforces the genetic map data. These newly localized markers identified by the PCR method using a standardized protocol represent useful tools for mapping YAC clones and establishing YAC contigs and for studying genetic diseases or cancers associated with specific genes and/or germinal/somatic rearrangements of chromosome 11.

Myotonic dystrophy: over-expression or/and under-expression? A critical review on a controversial point

Myotonic dystrophy (DM) results from the amplification of an unstable (CTG)n sequence in the 3' untranslated region of the myotonin-protein kinase (MT-PK) gene. The expression of the enlarged allele in DM patients with a number of repeats below or beyond 200, was analysed by three different groups. Two groups showed a decreased or absent expression of mutant alleles in DM adults, in congenitally affected infants (CDM) and in an affected fetus. On the contrary, another group reported the increased expression of the mutated allele in several tissues of a CDM infant. These discrepancies may be explained by the different methods used, the small number of patients, the individuals and tissues used as controls, or reflect the use of primers located in different regions of the MT-PK gene.

Myotonic dystrophy: absence of CTG enlarged transcript in congenital forms, and low expression of the normal allele

Myotonic dystrophy (DM) is an autosomal dominant neuromuscular disease. The mutation has been identified as an unstable trinucleotide CTG repeat in a sequence encoding a putative cAMP-dependent protein kinase. The CTG repeat varies in length between affected siblings, and generally increases through generations in parallel with increasing severity of the disease. Congenital myotonic dystrophy, which represents the most severe phenotype, is exclusively maternally inherited. In this report, we show, by Northern blot analysis, that no mutated enlarged transcript is detectable in a 20-week-old DM fetus and in two congenitally affected infants. Furthermore, in skeletal and cardiac muscle of the DM fetus, we observed by RNA analysis, including Northern blot and RT-PCR, an unexpectedly low expression of the paternal wild type allele. Varying degrees of expression of the mutant and/or the normal allele might therefore account for the characteristic features of the congenital form and the extreme variability of the disease.

Isolation of kidney complementary DNAs down-expressed in Wilms' tumor by a subtractive hybridization approach

We applied a subtractive hybridization approach to isolate genes differentially expressed between mature kidney and Wilms' tumor. We constructed a complementary DNA library from a total mature kidney complementary DNA subtracted by an excess of mRNA from a Wilms' tumor, WAGR4, with a germline deletion of 11p13 and a somatic loss of alleles at 11p15. Six clones presenting a differential pattern of expression, positive with mRNA from the mature kidney and negative with mRNA from the Wilms' tumor WAGR4, were characterized. Among these clones were two as yet unknown expressed sequences (D11S877E and D15S109E) and four sequences from known genes: renal dipeptidase (DPEP1), alpha B-crystallin (CRYA2), uromodulin (UMOD), and plasma glutathione peroxidase (GPX2). The different patterns of expression of these genes in 11 Wilms' tumors, whether or not they are hereditary, reflect the well-documented pathogenetic heterogeneity for Wilms' tumors. We propose that these clones could be helpful for an improved histological characterization of Wilms' tumors.

Two new polymorphisms in the coding sequence of the LDL receptor (LDLR) gene

We identified by polymerase chain reaction/single-strand conformation polymorphism analysis two unreported polymorphisms in the low density lipoprotein receptor gene, located in exons 11 and 15. The exon 15 sequence variation can also be readily detected since it abolishes an MspI site.

Myotonic dystrophy: size- and sex-dependent dynamics of CTG meiotic instability, and somatic mosaicism

Myotonic dystrophy (DM) is a progressive neuromuscular disorder which results from elongations of an unstable (CTG)n repeat, located in the 3' untranslated region of the DM gene. A correlation has been demonstrated between the increase in the repeat number of this sequence and the severity of the disease. However, the clinical status of patients cannot be unambiguously ascertained solely on the basis of the number of CTG repeats. Moreover, the exclusive maternal inheritance of the congenital form remains unexplained. Our observation of differently sized repeats in various DM tissues from the same individual may explain why the size of the mutation observed in lymphocytes does not necessarily correlate with the severity and nature of symptoms. Through a molecular and genetic study of 142 families including 418 DM patients, we have investigated the dynamics of the CTG repeat meiotic instability. A positive correlation between the size of the repeat and the intergenerational enlargement was observed similarly through male and female meioses for < or = 0.5-kb CTG sequences. Beyond 0.5 kb, the intergenerational variation was more important through female meioses, whereas a tendency to compression was observed almost exclusively in male meioses, for > or = 1.5-kb fragments. This implies a size- and sex-dependent meiotic instability. Moreover, segregation analysis supports the hypothesis of a maternal as well as a familial predisposition for the occurrence of the congenital form. Finally, this analysis reveals a significant excess of transmitting grandfathers partially accounted for by increased fertility in affected males.

Pericentric intrachromosomal insertion responsible for recurrence of del(11)(p13p14) in a family

The combined use of qualitative and quantitative analysis of 11p13 polymorphic markers together with chromosomal in situ suppression hybridization (CISS) with biotin labeled probes mapping to 11p allowed us to characterize a complex rearrangement segregating in a family. We detected a pericentric intrachromosomal insertion responsible for recurrence of del(11)(p13p14) in the family: an insertion of brand 11p13-p14 carrying the genes for predisposition to Wilms' tumor, WT1, and for aniridia, AN2, into the long arm of chromosome 11 in 11q13-q14. Asymptomatic balanced carriers were observed over three generations. Classical cytogenetics had failed to detect this anomaly in the balanced carriers, who were first considered to be somatic mosaics for del(11)(p13). Two of these women gave birth to children carrying a deleted chromosome 11, most likely resulting from the loss of the 11p13 band inserted in 11q. Although in both cases the deletion encompassed exactly the same maternally inherited markers, there was a wide variation in clinical expression. One child, with the karyotype 46,XY, del(11)(p13p14), presented the full-blown WAGR syndrome with aniridia, mental retardation, Wilms' tumor, and pseudohermaphroditism, but also had proteinuria and glomerular sclerosis reminiscent of Drash syndrome. In contrast, the other one, a girl with the karyotype 46,XX,del(11)(p13), only had aniridia. Although a specific set of mutational sites has been observed in Drash patients, these findings suggest that the loss of one copy of the WT1 gene can result in similar genital and kidney abnormalities.

Physical and genetic mapping of the dipeptidase gene DPEP1 to 16q24.3

We report the subregional physical and genetic mapping on chromosome 16q of a cDNA clone selected as a potential tumor/growth suppressor sequence. By DNA sequencing and RNA expression pattern, this clone was identified as part of the renal dipeptidase gene (DPEP1). Using somatic cell hybrids carrying either different human chromosomes or chromosome 16 segments, we confirm and refine the physical mapping of DPEP1 to the chromosome 16 subregion q24.3. Two RFLPs, a biallelic polymorphism detected by TaqI and a VNTR detected by BamHI, EcoRI, and BglII, are described. Using the VNTR polymorphism, DPEP1 was shown to be linked to D16S7 with a maximum lod score of 5.8 at a recombination fraction of 0.03.

Genetic exclusion of apo-B gene in recessive abetalipoproteinemia

Abetalipoproteinemia is a recessive genetic disorder of unknown origin, which is characterized by absence of circulating apo-B-containing lipoproteins, malabsorption of intestinal fat, and degenerative neurological and retinal lesions. In this study, four families were analysed for genetic linkage between the abetalipoproteinemia phenotype and the apo-B genotype determined from polymorphisms of XbaI, MsPI, EcoRI and PvuII restriction sites and that of the 3'-minisatellite of the apo-B gene. The results definitively exclude mutation of the apo-B gene as a causal factor of abetalipoproteinemia in three families. Consanguinity of the parents in the fourth family made genotyping less conclusive.

Chromosomal assignment of the uromodulin gene (UMOD) to 16p13.11

We report the chromosomal assignment on chromosome arm 16p of a cDNA clone isolated through its expression in mature kidney and lack of expression in several Wilms tumors. DNA sequencing and analysis of the pattern of RNA expression in different tissues identified this clone as a uromodulin (Tamm-Horsfall glycoprotein, uromucoid; UMOD) sequence. By hybridizing this clone to somatic cell hybrids carrying different human chromosomes or segments of chromosome 16, the gene for UMOD was localized to 16p13.11.

Subregional physical mapping of an alpha B-crystallin sequence and of a new expressed sequence D11S877E to human 11q

We report the regional assignment on Chromosome (Chr) 11q of two cDNA clones selected as sequences expressed in mature kidney and not expressed in Wilms' tumor. Clone T70 was identified as an alpha B-crystallin sequence (CRYA2). CRYA2 has previously been mapped to 11q22.3-23.1 by in situ hybridization. Clone 6.2 represents a new gene expressed in adult and fetal kidney, pancreas, and liver. In order to map sequences corresponding to clone 6.2 and to physically define the boundaries of the localization of CRYA2, we used somatic cell hybrids carrying either different human chromosomes or Chr 11 segments and a cell line established from a patient with an interstitial deletion of region 11q14.3-q22.1. We showed that CRYA2 lies proximal to the 11q23.2 breakpoint defined by the constitutional t(11;22) and distal to the 11q22.1 breakpoint (between D11S388 and D11S35) of a constitutional interstitial deletion. This is in agreement with previous data obtained by in situ hybridization and provides proximal and distal physical benchmarks for this localization. Clone 6.2-related sequence (D11S877E) was assigned to region 11q23.2-q24.2 defined by the breakpoints of the constitutional t(11;22) and of the Ewing's sarcoma neuroepithelioma t(11;22).

Somatic mosaicism for partial paternal isodisomy in Wiedemann-Beckwith syndrome: a post-fertilization event

Genomic imprinting has been implicated in the aetiology of an overgrowth cancer-prone syndrome, the Wiedemann-Beck-with syndrome (WBS). We have demonstrated uniparental disomy (UPD) for paternal chromosome 11p markers in 5 out of 25 sporadic cases (20%). Delineation of the extent of the disomy region may help in understanding the mechanism and the stage, meiotic or mitotic, of disomy formation in this disease and in associated tumours. Our current studies in WBS patients with seventeen 11p and one 11q markers reveal paternal isodisomy, not heterodisomy, in the five cases. For one case we demonstrate unambiguously that partial isodisomy for 11p and somatic mosaicism for UPD resulted from a post-fertilization event. The restriction of isodisomy to part of 11p in another case, and somatic mosaicism for UPD in three other cases, suggest a mitotic recombinational event that must have occurred after fertilization. Mosaic phenotypes reflect the timing of their origin and the fate of the cells involved, as well as the cell-specific pattern of imprinting. Somatic mosaicism for UPD in four cases may thus explain the incomplete forms of WBS. The association of hemihypertrophy in sporadic WBS and even some cases of isolated hemihypertrophy. This is in agreement with a recent report of paternal isodisomy for 11p markers in a patient with hemihypertrophy, Wilms' tumour and adrenocortical carcinoma. Moreover, the risk of developing a tumour seems higher (50%) for patients with paternal 11p UPD than for WBS patients in general (7.5%).

Testing genomic imprinting in Wilm's tumor

Data from 511 cases of Wilms' tumor in France (including 12 familial cases) and 8 pedigrees from the literature were analyzed to test three modifications of Knudson's classical bimutational theory, based on genomic imprinting in Wilms' tumor carcinogenesis. Analysis of data of age at diagnosis and segregation analysis were performed to determine the number of independent events for Wilms' tumor development and to search for a differential role of paternal and maternal alleles. Unexpectedly, we show that only one rare event is required for tumor development in isolated unilateral cases which are considered to be mainly nonhereditary. In familial cases, we observe no effect of the sex of the transmitting parent on either hge at diagnosis or segregation ratio. We show that this could be explained by models of genomic imprinting which assume two nonindependent events, or only one rare genetic event. In bilateral cases we show a bimodality for age at diagnosis which could be due to a mixture of hereditary and nonhereditary cases. This result completely questions the classical assumption according to which all bilateral cases would be hereditary. These findings support the hypothesis that this childhood cancer arises from a variety of etiological pathways and might be useful to find strategies for further molecular investigations.

Beckwith-Wiedemann syndrome, tumourigenesis and imprinting

The concurrent development of cytogenetic, clinical, genetic and molecular studies has led to the recognition that the different hereditary and non-hereditary forms of the Beckwith-Wiedemann syndrome and associated tumours result from an imbalance between maternal and paternal alleles. The most exciting development in the past year was the discovery of uniparental paternal disomy and the increased understanding, arising from studies in the mouse and in hereditary cases, of the role possibly played by imprinting and somatic mosaicism in partial and complete expression of this complex syndrome.

Diagnosis of Duchenne and Becker muscular dystrophies by polymerase chain reaction. A multicenter study

OBJECTIVE--To assess the efficiency, reliability, and ease of use of DNA diagnosis for Duchenne and Becker muscular dystrophies (DMD/BMD) using the polymerase chain reaction (PCR). DESIGN--DNA from the patients was screened for deletion mutations using multiplex PCR, and the results were compared with those obtained by Southern blot analysis. The PCR multiplex reaction detects nine specific "hot-spot" exons in the dystrophin gene while the Southern analysis detects 66 specific dystrophin gene restriction fragments. The multiplex reaction requires 50-fold less DNA than Southern analysis and thus is considerably more sensitive. SETTING--Fourteen university-affiliated and private genetic disease diagnostic laboratories. PATIENTS--Male patients with clinical signs of DMD/BMD. Cases were selected for analysis randomly, without knowledge of whether a deletion was present within the dystrophin gene. MAIN OUTCOME MEASURES--The percentage of cases that were detectable by multiplex PCR in comparison with Southern analysis, the frequency, extent, and location of the detected deletion mutations. In some cases, duplication mutations were monitored. RESULTS--The accuracy of a single PCR multiplex amplification (nine exons) was compared with Southern analysis with 10 cDNA probes that cover the full length of the gene. The multiplex PCR analytic method detected 82% of those deletions detected by Southern analysis methods. In one of 745 analyses, the multiplex method suggested a single exon deletion, which was not confirmed by Southern analysis, representing a false-positive rate of 0.013%. CONCLUSIONS--Multiplex PCR represents a sensitive and accurate method for deletion detection of 46% of all cases of DMD/BMD. The method requires 1 day for analysis, is easy to perform, and does not use radioactive tracers. As such, multiplex PCR represents an efficient and rapid method for prenatal or postnatal diagnosis of DMD/BMD.

Beckwith-Wiedemann syndrome: a demonstration of the mechanisms responsible for the excess of transmitting females

Beckwith-Wiedemann syndrome (BWS) is often associated with embryonal tumours (nephroblastoma, adrenocortical carcinoma, hepatoblastoma, and rhabdomyosarcoma). Several pedigrees have been reported strongly suggesting autosomal dominant inheritance and an excess of transmitting females was noticed in these families. We confirmed this excess using 19 published pedigrees and showed that this excess was for two reasons: first, reduced fecundity in affected males compared to females in a ratio of 1:4.6, and, second, a smaller risk of being affected in a ratio of 1:3 for subjects having inherited the gene from their father. These latter findings suggest genomic imprinting. Furthermore, considering these results together with other observations, such as the parental origin of the 15p15.5 duplication and the existence of uniparental disomy in some sporadic cases, we propose that overgrowth in BWS patients and malignant proliferation in associated tumours reflect an imbalance between paternal and maternal alleles.

A linkage map of 10 loci flanking the Marfan syndrome locus on 15q: results of an International Consortium study

Members of an International Consortium for Linkage Analysis of the Marfan Syndrome (MFS1) have pooled data for joint analysis in an attempt to determine the precise location of the MFS1 gene and the order of 10 DNA markers on 15q. Five laboratories performed a total of 2111 genotypes in 22 families consisting of 225 affected and 248 normal subjects. For each marker a mean of 98 meioses was informative. D15S48 and D15S1 were identified as the closest linked markers with 99% upper confidence intervals of 12% and 13% respectively. We have used the CRI-MAP program to construct the most likely order as: D15S24-D15S25-D15S1-MFS1-D15S48-D15S49+ ++-(D15S45/S51)-(D15S29/S38). Placement of D15S2 in relation to -D15S1-D15S48- cannot be determined with certainty. The genetic map of these markers extends 53.6 cM in males and 65.0 cM in females with a sex averaged map of 60.7 cM. The sex difference was statistically significant (p = 0.005). Linkage heterogeneity between 22 MFS1 families was documented (p = 0.009) necessitating the exclusion of one family from the analysis. However, comparison of the remaining 21 families for two point and multipoint lod scores showed no evidence for linkage heterogeneity of the MFS1 locus.