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PubMed1994

An interstitial deletion of proximal 8q (q11-q13) in a girl with Silver-Russell syndrome-like features.

Silver-Russell syndrome (SRS) is characterized by pre- and postnatal growth retardation, a fine, triangular face, a high frontal hairline and prominent forehead, clinodactyly of the fifth fingers, and sometimes asymmetry of face, trunk and extremities. In a 10-year-old girl referred for SRS, cytogenetic examination disclosed a microdeletion of band 8q12. Dosage analysis of Southern blots hybridized to 8q markers revealed a deletion of three loci: MOS, D8S96 and D8S108, all mapping to 8q11-q12, however the deletion did not include PLAT (8q12-q11). PCR analysis of the D8S166 microsatellite (8q11-q12) showed the lack of paternal inheritance, indicating that the deletion occurred in the paternal chromosome. The patient showed prenatal and postnatal growth retardation, mild developmental delay, microcephaly, a triangular face with high frontal hairline, shallow supraorbital ridges, hypoplastic alae nasi, small and prominent ears, prominent lateral palatine ridges, clinodactyly and brachymesophalangy of the fifth fingers. There were normal female genitalia and no asymmetry or detectable malformations. Screening of 19 other patients with the SRS for a similar cytogenetic and/or molecular deletion at 8q12 and for uniparental disomy 8 was negative. However, 8q12 still remains as one potential locus for a gene whose mutations may cause the clinical findings of SRS and which could be included in a larger deletion in a proband who has additional mild mental retardation.

Blotting, Southern↗
PubMed1995

[The human genome--chromosome 15].

The Prader-Willi syndrome (PWS) with Angelman's syndrome form a pair known above all due to problems of genetic imprinting and uniparental disomy. Both phenomena drew attention to the importance of control of expression of different alleles and their genetic origin. The causes of the two syndromes have not been elucidated unequivocally so far. In case of the PWS, at least, there is the possibility of a gene of the protein carrier of a small nuclear ribonucleic acid described as SNRPN. In case of Marfan's syndrome the responsible gene is the fibrillin gene (FNB1) with the locus on area 15q21. The mentioned gene participates probably also in diseases caused by a change of the vascular wall (aneurysm) and in prolapse of the mitral valves. On the 15th chromosome are several representatives of the family of genes of cytochrome P450 the products of which play a part in the metabolism of exogenous substances, incl. pharmaceutical ones. Their activity is part of the natural sensitivity or resistance to some chemical cancerogens. The postscriptis devoted to the assumed locus of dyslexia DLX1.

Chromosomes, Human, Pair 15↗
PubMed1995

Trisomy 9 mosaicism in a child with a tethered cord.

A two and a half-year-old girl was diagnosed with trisomy 9 mosaicism that was detected in 22% of skin fibroblasts but was not evident in blood. This child manifests some clinical features not previously reported in trisomy 9 mosaicism including a thoracic syringomyelia and a tethered cord due to an extradural lipoma with intradural involvement. DNA analysis showed that she did not have uniparental disomy in her dominant disomic cell line.

Child, Preschool↗
PubMed1995

Maintenance of normal imprinting of H19 and IGF2 genes in neuroblastoma.

H19 and insulin-like growth factor II (IGF2) are among a few genes which have been confirmed to be imprinted in normal human embryonal tissues. This results in monoallelic expression of maternal H19 and paternal IGF2. Loss of imprinting of these genes producing biallelic expression has been observed in Wilm's tumor and embryonal rhabdomyosarcoma, suggesting that an epigenetic change of DNA, in addition to a genetic change in oncogene(s) and/or tumor suppressor gene(s), may be involved in the development of these childhood cancers. Neuroblastoma, which is an embryonal tumor originating from neural crest-derived cells, occasionally occurs in individuals with the Beckwith-Wiedemann syndrome; Wilm's tumor and embryonal rhabdomyosarcoma occur even more frequently in the Beckwith-Wiedemann syndrome; and paternal uniparental disomy of H19 and IGF2 loci (chromosome 11p15) is present in the Beckwith-Wiedemann syndrome. Furthermore, neuroblastoma cell lines express IGF2, and autocrine/paracrine effects of IGF2 have been demonstrated in these cells. Thus, we examined for imprinting of both H19 and IGF2 in primary untreated neuroblastomas using the RsaI and ApaI polymorphisms within these genes, respectively. Seven of 15 tumors were informative for H19 and for IGF2, and all of these cases showed monoallelic expression of both of these genes. These results indicate that loss of imprinting of H19 and IGF2 does not occur in neuroblastomas.

Base Sequence↗
PubMed1995

Coordinate regulation of Igf-2 and H19 in cultured cells.

The insulin-like growth factor 2 (Igf-2) and H19 genes are physically linked on mouse distal chromosome 7 and are reciprocally imprinted. We investigated the molecular basis of the parental imprints in somatic cell cultures derived from normal embryos or from their littermates with maternal uniparental disomy for distal chromosome 7 (MatDi7). In normal cells, the two genes appeared to respond to similar regulatory factor(s), since both genes were coordinately up-regulated upon growth arrest and cell clones which had lost expression of one gene had lost expression of the other. However, in a clone of MatDi7 cells (MatDi7 1-1a), which spontaneously began to express the maternally derived copy of Igf-2, Igf-2 and H19 were not coordinately regulated. MatDi7 1-1a cells showed de novo methylation of sites upstream of Igf-2 and also within the H19 promoter, epigenetic modifications normally seen only on the paternal chromosome. The data provide new experimental evidence for previously hypothesized mechanisms suggesting that Igf-2 and H19 are coordinately regulated.

Animals↗
PubMed1995

Molecular studies of chromosomal mosaicism: relative frequency of chromosome gain or loss and possible role of cell selection.

Studies of uniparental disomy and origin of nonmosaic trisomies indicate that both gain and loss of a chromosome can occur after fertilization. It is therefore of interest to determine both the relative frequency with which gain or loss can contribute to chromosomal mosaicism and whether these frequencies are influenced by selective factors. Thirty-two mosaic cases were examined with molecular markers, to try to determine which was the primary and which was the secondary cell line: 16 cases of disomy/trisomy mosaicism (5 trisomy 8, 2 trisomy 13, 1 trisomy 18, 4 trisomy 21, and 4 involving the X chromosome), 14 cases of 45,X/46,XX, and 2 cases of 45,X/47,XXX. Of the 14 cases of mosaic 45,X/46,XX, chromosome loss from a normal disomic fertilization predominated, supporting the hypothesis that 45,X might be compatible with survival only when the 45,X cell line arises relatively late in development. Most cases of disomy/trisomy mosaicism involving chromosomes 13, 18, 21, and X were also frequently associated with somatic loss of one (or more) chromosome, in these cases from a trisomic fertilization. By contrast, four of the five trisomy 8 cases were consistent with a somatic gain of a chromosome 8 during development from a normal zygote. It is possible that survival of trisomy 8 is also much more likely when the aneuploid cell line arises relatively late in development.

Aneuploidy↗
PubMed1994

Family studies in Prader-Willi syndrome.

Clinical, cytogenetic and molecular studies have been undertaken in the families of 52 probands with Prader-Willi syndrome. The maternal age at the birth of a proband with a deletion in 15p11q13 was on average 8 years less than that of the mothers of probands with uniparental disomy (UPD), the paternal age was on average 7 years less. Seven probands with UPD were all female, as were 7 patients who had neither a detectable chromosomal abnormality nor UPD. Cytogenetic and molecular polymorphisms in proximal chromosome 15 indicated that for probands with a 15q11q13 deletion, inheritance of both the maternal and the intact paternal homologue is random in their unaffected sublings. Pigmentation studies suggest that probands who have a deletion in 15q11q13 have lighter colouring than other family members implying that D15S12 may not be imprinted.

Adult↗
PubMed1994

Paternal isodisomy for chromosome 7 is compatible with normal growth and development in a patient with congenital chloride diarrhea.

Uniparental disomy for maternal chromosome 7 has been described in three patients with recessive disorders. Short stature in each of these patients has been explained by the effect of imprinting of growth-related genes on maternal chromosome 7. Alternatively, although less likely, all these patients may be homozygous for a rare recessive mutation. Here we report both paternal isodisomy for chromosome 7 and normal growth in a patient with a recessive disorder, congenital chloride diarrhea. She had inherited only paternal alleles at 10 loci and was homozygous for another 10 chromosome 7 loci studied. Her physical status and laboratory tests were normal except for a mild high-frequency sensorineural hearing loss. As the patient has normal stature, it is likely that the paternal chromosome 7 lacks the suggested maternal imprinting effect on growth. Paternal isodisomy for human chromosome 7 may have no phenotypic effect on growth.

Adult↗
PubMed1993

From the clinic to the research laboratory. The role of the clinician in molecular genetic studies.

BACKGROUND: The first physician to examine a patient with a genetic disorder or birth defect is usually a specialist in a field other than genetics. The presentation of certain categories of patients of particular interest to molecular genetics research may be distinct. The recognition of these patients by clinicians is fundamental to the study of genetic disorders at the DNA level. OBSERVATIONS: Neurofibromatosis type 1 is a paradigm for how the study of a single genetic disease and its multiple molecular features has been facilitated by the use of various categories of patients. Other examples of interest to dermatologists, surgeons, and other specialists are discussed to demonstrate how the identification of key patients was instrumental in studies of gene localization and subsequent cloning, gene clusters or contiguous gene deletion syndromes, or mutation phenomena such as imprinting, uniparental disomy, and gonadal mosaicism. The molecular researcher has limited access to surgical specimens, and the donation of skin, tumor, and other tissues may lead to increased knowledge of new mutations in somatic mosaicism, or loss of heterozygosity of tumor suppression genes in cancer. CONCLUSIONS: Guidelines are suggested to alert the physician to each of these categories of individuals with unusual presentation, as well as to recognize that the study of families with rare disorders may enable scientists to locate the responsible genes. The teamwork of clinician and molecular researcher is essential for the advancement of our understanding of DNA mechanisms in genetic disease. The ethics involved in referral of patients to molecular genetic research studies are discussed.

Chromosome Aberrations↗
PubMed1993

[DNA-based diagnosis of Angelman syndrome and Prader-Willi syndrome].

A molecular-genetic study was performed in 61 patients with Angelman syndrome (AS) and 14 patients with Prader-Willi syndrome (PWS). Southern blot analyses and/or PCR-mediated dinucleotide repeat polymorphism (DNRP) analyses revealed that 67% of AS patients have DNA deletions ranging from D15S9 to D15S12 loci. An exception was 3 sib cases whose deletion involved only 2 loci, D15S10 and GABRB3. The parental origin of the deletions in AS patients were exclusively maternal. No uniparental disomy (UPD) was found in our AS patient series, suggesting that UPD in AS is infrequent than that in PWS. Molecular deletions were observed in 6 of the 14 PWS patients. In order to develop a simple, reliable DNA-based diagnostic method, I adopted PCR-mediated DNRPs as genetic markers for the detection of deletions and/or parental origin of chromosomes 15 in AS and/or PWS patients. This method gave useful diagnostic information in 33 (89%) of 37 AS patients and 12 (86%) of 14 PWS patients, indicating no big difference from the information obtained with Southern blot analysis. Furthermore, since this DNRP method dose not require radioisotopes, it may be a first-choice, alternative way when diagnosing AS or PWS patients.

Adult↗
PubMed1993

The effect of confined placental mosaicism on development of the human aneuploid conceptus.

The rate of meiotic errors in gametogenesis is high, resulting in approximately 30% of cleaving embryos with chromosomal defect. In addition, mitotic errors occur commonly in chromosomally normal and abnormal embryos. The most likely outcome of the mitotic error is CPM. Mitotic mutation in trisomic blastocysts may lead to diploid/trisomic trophoblast with intrauterine survival of the trisomic fetus or may result in a diploid fetus supported by a trisomic placenta. The outcome of pregnancies with a trisomic placenta and diploid fetus largely depends on the specific chromosome involved and on the presence or absence of uniparental disomy in the fetus.

Aneuploidy↗
PubMed1994

A somatic origin of homologous Robertsonian translocations and isochromosomes.

One t(14q14q), three t(15q15q), two t(21q21q), and two t(22q22q) nonmosaic, apparently balanced, de novo Robertsonian translocation cases were investigated with polymorphic markers to establish the origin of the translocated chromosomes. Four cases had results indicative of an isochromosome: one t(14q14q) case with mild mental retardation and maternal uniparental disomy (UPD) for chromosome 14, one t(15q15q) case with the Prader-Willi syndrome and UPD(15), a phenotypically normal carrier of t(22q22q) with maternal UPD(22), and a phenotypically normal t(21q21q) case of paternal UPD(21). All UPD cases showed complete homozygosity throughout the involved chromosome, which is supportive of a postmeiotic origin. In the remaining four cases, maternal and paternal inheritance of the involved chromosome was found, which unambiguously implies a somatic origin. One t(15q15q) female had a child with a ring chromosome 15, which was also of probable postmeiotic origin as recombination between grandparental haplotypes had occurred prior to ring formation. UPD might be expected to result from de novo Robertsonian translocations of meiotic origin; however, all de novo homologous translocation cases, so far reported, with UPD of chromosomes 14, 15, 21, or 22 have been isochromosomes. These data provide the first direct evidence that nonmosaic Robertsonian translocations, as well as isochromosomes, are commonly the result of a mitotic exchange.

Aneuploidy↗
PubMed1993

De novo microdeletion on an inherited Robertsonian translocation chromosome: a cause for dysmorphism in the apparently balanced translocation carrier.

Robertsonian translocations are usually ascertained through abnormal children, making proposed phenotypic effects of apparently balanced translocations difficult to study in an unbiased way. From molecular genetic studies, though, some apparently balanced rearrangements are now known to be associated with phenotypic abnormalities resulting from uniparental disomy. Molecular explanations for other cases in which abnormality is seen in a balanced translocation carrier are being sought. In the present paper, an infant is described who has retarded growth, developmental delay, gross muscular hypotonia, slender habitus, frontal bossing, micrognathia, hooked nose, abundant wispy hair, and blue sclerae. Cytogenetically, she appeared to be a carrier of a balanced, paternally derived 14;21 Robertsonian translocation. Analysis of DNA polymorphisms showed that she had no paternal allele at the D14S13 locus (14q32). Study of additional DNA markers within 14q32 revealed that her previously undescribed phenotype results from an interstitial microdeletion within 14q32. Fluorescent in situ hybridization was used to show that this microdeletion had occurred de novo on the Robertsonian translocation chromosome. These observations may reactivate old suspicions of a causal association between Robertsonian translocations and de novo rearrangements in offspring; a systematic search for similar subcytogenetic rearrangements in other families, in which there are phenotypically abnormal children with apparently balanced translocations, may be fruitful. The clinical and molecular genetic data presented also define a new contiguous gene syndrome due to interstitial 14q32 deletion.

Abnormalities, Multiple↗
PubMed1993

Nondisjunction of chromosome 15: origin and recombination.

Thirty-two cases of uniparental disomy (UPD), ascertained from Prader-Willi syndrome patients (N = 27) and Angelman syndrome patients (N = 5), are used to investigate the pattern of recombination associated with nondisjunction of chromosome 15. In addition, the meiotic stage of nondisjunction is inferred by using markers mapping near the centromere. Two basic approaches to the analysis of recombination are utilized. Standard methods of centromere mapping are employed to determine the level of recombination in specific pairwise intervals along the chromosome. This method shows a significant reduction in recombination for two of five intervals examined. Second, the observed frequency of each recombinant class (i.e., zero, one, two, three, or more observable crossovers) is compared with expected values. This is useful for testing whether the reduction in recombination can be attributed solely to a proportion of cases with no recombination at all (because of asynapsis), with the remaining groups showing normal recombination (or even excess recombination), or whether recombination is uniformly reduced. Analysis of maternal UPD(15) data shows a slight reduction in the multiple-recombinant classes, with a corresponding increase in both the zero- and one-recombinant classes over expected values. The majority, more than 82%, of the extra chromosomes in maternal UPD(15) cases are due to meiotic I nondisjunction events. In contrast, most paternal UPD(15) cases so far examined appear to have a postzygotic origin of the extra paternal chromosome.

Aneuploidy↗
PubMed1993

[The GABAA receptor beta 3-subunit gene (GABRB3) as a candidate responsible for central nerve disturbances in Angelman syndrome (AS)].

AS is characterized by severe mental retardation, seizures, ataxic gait and easily evoked laughter. About 70 approximately 80% of AS patients have a chromosomal/molecular deletion at 15 q11-q13, occurring exclusively in the maternally-derived chromosome 15. There have been 4 AS patients whose chromosomes 15 are paternal uniparental disomy. This biased parent-of-origin suggests that genomic imprinting may play a role in the occurrence of the syndrome. GABRB3 is located at 15 q11-q13. GABAA is a main inhibitory neurotransmitter in the central nervous system (CNS) and functions through its receptor. The beta 3 subunit, one of the components of the receptor, is present in the telephalonal cortex, hippocampus, thalamus and cerebellum, and a peak GABRB3 expression is observed during embryogenesis. This indicates that GABRB3 plays a role in CNS development, suppression of seizures and behavioral control. Since GABRB3 is encompassed within the smallest deletion among AS patients, it becomes a candidate responsible for the central nerve disturbances in AS. This smallest deletion was found in 3 AS sibs, their phenotypically normal mother and maternal grandfather in a family, suggesting that the paternally-derived deletion has no phenotypical effect in the offspring but the maternally-derived one. However, recent studies demonstrated that the mouse Gabrb3 is not involved in imprinting. The confirmation of GABRB3 to be the AS gene needs to provide direct evidence of its imprinting. Our preliminary study showed that GABRB3 was not expressed in hydatidiform mole that is composed only of the paternal genome, while it was expressed fully in normal villous tissue, suggesting that GABRB3 is paternally imprinted.(ABSTRACT TRUNCATED AT 250 WORDS)

Angelman Syndrome↗
PubMed1996

Familial cryptic translocation resulting in Angelman syndrome:implications for imprinting or location of the Angelman gene?

Angelman syndrome (AS) is associated with a loss of maternal genetic information, which typically occurs as a result of a deletion at 15q11-q13 or paternal uniparental disomy of chromosome 15. We report a patient with AS as a result of an unbalanced cryptic translocation whose breakpoint, at 15q11.2, falls within this region. The proband was diagnosed clinically as having Angelman syndrome, but without a detectable cytogenetic deletion, by using high-resolution G-banding. FISH detected a deletion of D15S11 (IR4-3R), with an intact GABRB3 locus. Subsequent studies of the proband's mother and sister detected a cryptic reciprocal translocation between chromosomes 14 and 15 with the breakpoint being between SNRPN and D15S10 (3- 21). The proband was found to have inherited an unbalanced form, being monosomic from 15pter through SNRPN and trisomic for 14pter to 14q11.2. DNA methylation studies showed that the proband had a paternal-only DNA methylation pattern at SNRPN, D15S63 (PW71), and ZNF127. The mother and unaffected sister, both having the balanced translocation, demonstrated normal DNA methylation patterns at all three loci. These data suggest that the gene for AS most likely lies proximal to D15S10, in contrast to the previously published position, although a less likely possibility is that the maternally inherited imprinting center acts in trans in the unaffected balanced translocation carrier sister.

Angelman Syndrome↗
PubMedDate not supplied

[Genomic imprinting and human pathology. 2].

Genetic imprinting does occur in humans. This is manifest at the level of the genome, the individual chromosome or subcromosomal region, and the single locus. Genomic imprinting is manifest in the developmental defects of hydatiform mole, teratoma and triploidy. Chromosomal imprinting effects are revealed when uniparental disomy or deletion occur as costitutional aberration or in tumural tissues. Evidence at the single gene level comes from an increasing number of autosomal dominant genetic diseases. This part of the paper will briefly review the importance of imprinting in the contest of human genetic diseases.

Adult↗
PubMed1996

Complete paternal isodisomy for chromosome 8 unmasked by lipoprotein lipase deficiency.

Uniparental disomy (UPD)-the inheritance of two homologous chromosomes from a single parent-may be unmasked in humans by the unexpected appearance of developmental abnormalities, genetic disorders resulting from genomic imprinting, or recessive traits. Here we report a female patient with familial chylomicronemia resulting from complete lipoprotein-lipase (LPL) deficiency due to homozygosity for a frameshift mutation in exon 2 of the LPL gene. She was the normal term product of an unremarkable pregnancy and had shown normal development until her current age of 5.5 years. The father (age 33 years) and the mother (age 24 years) were unrelated and healthy, with no family history of stillbirths or malformations. The father was a heterozygous carrier of the mutation, whereas no mutation in the LPL gene was detected in the mother. Southern blotting did not reveal any LPL gene rearrangement in the proband or her parents. The proband was homozygous for 17 informative markers spanning both arms of chromosome 8 and specifically for the haplotype containing the paternally derived LPL gene. This shows that homozygosity for the defective mutation in the LPL gene resulted from a complete paternal isodisomy for chromosome 8. This is the first report of UPD for chromosome 8 unmasked by LPL deficiency and suggests that normal development can occur with two paternally derived copies of human chromosome 8.

Adult↗