Retinoblastoma in a boy with a de novo mutation of a 13/18 translocation: The assumption that the retinoblastoma locus is at 13q141, particularly at the distal portion of it

Summary In serial cytogenetic examinations of peripheral lymphocytes from retinoblastoma patients, we found a patient with sporadic bilateral retinoblastoma with a de novo mutation of a 13/18 translocation, with their respective breakpoints at 13q141 and 18q122. The simultaneous de novo occurrence of retinoblastoma and the chromosomal rearrangement involving 13q14 in the proband suggests that the gene locus for retinoblastoma is at 13q141, particularly at the distal portion of it. Deletion mapping data are compatible with this suggestion.     

A case of (13q;18q) translocation with proximal 13q monosomy

Summary A case of partial monosomy of the 13p terminal to 13q12, associated with a de novo 13/18 translocation, is reported. The symptoms appeared to be derived from both 18q- and partial monosomy 13, the latter giving rise to: high arched palate, epicanthus, antimongolian slant, small eye fissure, flat nasal bridge, hypoplastic helix, and large clitoris. Serum Ig-A and Ig-M levels were normal in our case.     

Detection of a de novo R1066H mutation in an Italian patient affected by cystic fibrosis

Search for mutations in a cystic fibrosis patient, compound heterozygous for 1717–1G→A and another uncharacterized molecular defect, revealed the presence of a de novo R1066H mutation on the affected chromosome of paternal origin. Three additional rare mutations (R1066C, R1066S and R1066L), occurring at the CpG dinucleotide at position 3328–3329 of the cystic fibrosis transmembrane conductance regulator gene, have so far been reported. The identification of a R1066H de novo mutation further suggests that this dinucleotide may constitute a mutational hotspot. Received: 10 November 1995 / Revised: 18 January 1996     

Mesomelic form of chondrodysplasia and congenital glaucoma associated with de novo translocation (13;18)(q14;q23)

Mesomelic form of chondrodysplasia and congenital glaucoma associated with de novo translocation (13;18)(q14:q23): Mesomelic dysplasias are characterized by limb shortening most prominent of the middle segment of the extremities (forearm and lower leg). In addition to several syndromic forms a few patients with sporadic or familial forms and without precise nosological classification have been reported so far. In this report we present a young female with disproportionate mesomelic dwarfism, dysmorphic facial features, bilateral glaucoma, patent ductus arteriosus, low and hoarse voice, and generalized muscular hypotonia. At the age of 2.5 years mental development is normal. High resolution G-banded chromosome studies revealed a de novo reciprocal translocation with karyotype 46,XX t (13;18)(q14;q23). The concurrence of this de novo autosomal translocation with this distinct phenotype supports the hypothesis that disruption of (a) gene(s) at the translocation breakpoints causes this unusual, apparently new form of skeletal chondrodysplasia.     

Molecular mapping of a translocation breakpoint at 14q13 in a patient with mirror-image polydactyly of hands and feet

Mirror hands and feet (MIM, 135750) is a rare congenital anomaly, and mirror-image polydactyly is considered to be a variant of mirror hands and feet. To our knowledge, seven patients with the disorder have been reported in the literature. Parent-to-child transmission was reported in two families, which may indicate a single-gene defect inherited in an autosomal dominant fashion. We had previously encountered a boy with mirror-image polydactyly whose karyotype showed 46,XY,t(2;14) (p23.3;q13) de novo. We hypothesized that at least one of the putative genes responsible for the determination of an anterior-posterior limb pattern is disrupted by a translocation breakpoint. In this study, we identified a yeast artificial chromosome clone spanning a translocation breakpoint at 14q13, and the breakpoint was confirmed to be located between two loci, AFM200ZH4 and D14S306, within a genetic distance of 0.6 cM. Received: 25 September 1996 / Revised: 6 December 1996     

Factors to consider in using [U-C]palmitate for analysis of sphingolipid biosynthesis by tandem mass spectrometry

This study describes the use of a stable-isotope labeled precursor ([U-13C]palmitate) to analyze de novo sphingolipid biosynthesis by tandem mass spectrometry. It also describes factors to consider in interpreting the data, including the isotope's location (13C appears in three isotopomers and isotopologues: [M + 16] for the sphingoid base or N-acyl fatty acid, and [M + 32] for both); the isotopic enrichment of palmitoyl-CoA; and its elongation, desaturation, and incorporation into N-acyl-sphingolipids. For HEK293 cells incubated with 0.1 mM [U-13C]palmitic acid, ～60% of the total palmitoyl-CoA was 13C-labeled by 3 h (which was near isotopic equilibrium); with this correction, the rates of de novo biosynthesis of C16:0-ceramide, C16:0-monohexosylceramide, and C16:0-sphingomyelins were 62 ± 3, 13 ± 2, and 60 ± 11 pmol/h per mg protein, respectively, which are consistent with an estimated rate of appearance of C16:0-ceramide using exponential growth modeling (119 ± 11 pmol/h per mg protein). Including estimates for the very long-chain fatty acyl-CoAs, the overall rate of sphingolipid biosynthesis can be estimated to be at least ～1.6-fold higher. Thus, consideration of these factors gives a more accurate picture of de novo sphingolipid biosynthesis than has been possible to-date, while acknowledging that there are inherent limitations to such approximations.     

Species pattern of phosphatidic acid, diacylglycerol, CDP-diacylglycerol and phosphatidylglycerol synthesized de novo in rat liver mitochondria

Rat liver mitochondria were incubated with [3H]glycerol 3-phosphate, ATP, CTP and coenzyme A allowing acylatin of glycerophosphate with endogenous fatty acids and the further conversion of labelled phosphatidic acid (PA) to diacylglycerol (DG), CDP-diacylglycerol (CDP-DG) and phosphatidylglycerol (PG). In these glycerolipids, the distribution of label among the individual molecular species was found to be similar, with 16:0-18:1, 16:0-18:2 and 18:0-18:2/16:0-16:0 being the main species. It was concluded that mitochondrial enzymes involved in the de novo synthesis of these glycerolipids exhibited no acyl selectivity for their substrates. The pattern of molecular species of mitochondrial PA, DG and CDP-DG closely approached that of the same glycerolipids synthesized de novo in isolated rat liver microsomes.     

Fragile site and interstitial telomere repeat sequences at the fusion point of a de novo (Y;13) translocation

We describe a novel fragile site in a rearranged chromosome, associated with the presence of telomeric repeat sequences at the fusion point of a translocation between chromosomes 13 and Y. The case reported in this study shows a de novo (Y;13) translocation, which appears to represent fusion of an apparently intact chromosome Y with a chromosome 13 that has lost only part of its short arm. Ten percent of the cells show a normal karyotype without the (Y;13) translocation. Molecular cytogenetic studies of the derived Y;13 chromosome revealed three hybridization sites of the telomeric probes – one at each end and one at the breakpoint junction. A fragile site is also observed in the intrachromosomic telomeric region. This coincidence suggests that the telomere repeat sequences (TTAGGG)n, when present at an interstitial chromosomal location, can promote the formation of a novel fragile site. Received: 15 November 1995 / Revised: 6 March 1996     

Tetrasomy 18p de novo: Identification by FISH with conventional and microdissection probes and analysis of parental origin and formation by short sequence repeat typing

We report a de novo supernumerary isochromosome 18p in a child with tetrasomy 18p, analyzed by a straightforward combination of cytogenetic and molecular cytogenetic methods. The diagnostic procedure consisted of standard banding techniques and fluorescence in situ hybridization (FISH) with centromere and library DNA probes for chromosome 18, and 18p-specific FISH probes prepared by chromosome microdissection and in vitro amplification. The maternal origin as well as the most probable cell stages of formation of the supernumerary isochromosome were determined by typing of short sequence repeats (SSRs). The pattern of allelic distribution suggests a nondisjunction during meiosis followed by a centromeric misdivision in an early postzygotic mitosis as the most probable mode of isochromosome 18p formation. The combination of the applied methods represents a powerful tool to investigate the nature and the origin of de novo marker chromosomes. Received: 28 August 1995 / Revised: 3 November 1995; 20 December 1995     

High rate of detection of 13q14 deletion mosaicism among retinoblastoma patients (using more extensive methods)

Summary Using a cell population with a high proportion of early mitotic cells and by examining more cells derived from peripheral lymphocytes, we found three cases with a 13q14 deletion mosaicism among fifteen retinoblastoma patients; one with a de novo 13/18 balanced translocation, and another with a monosomy 13(q13»q21.2 or 21.3). The three patients with a 13q14 deletion mosaicism had sporadic retinoblastoma (two had bilateral and one unilateral retinoblastoma). The results indicate that 13q14 deletion mosaicism plays a major role in the etiology of this tumor.     

Comparative genomic hybridization reveals a partial de novo trisomy 6q23-qter in an infant with congenital malformations: delineation of the phenotype

We report the use of comparative genomic hybridization (CGH) to define the origin of a small extra segment (unidentifiable by classical cytogenetics) present in a de novo add(13)q34 chromosome that we found in the karyotype of a newly born boy with congenital heart defects, brain anomalies and dysmorphic signs. Initial investigation with fluorescence in situ hybridization (FISH) and a chromosome-13-specific library revealed that the excess material was not derived from chromosome 13. To uncover the origin of the unknown chromosome material, CGH was carried out on DNA isolated from blood lymphocytes of the patient. By using a conventional fluorescence microscope with no digital imaging devices, a single distinct region with gain of fluorescent intensity was observed on distal chromosome 6q. Confirmation of this finding by FISH with a chromosome-6-specific paint and a subtelomeric yeast artificial chromosome clone from 6q26-q27, in combination with the band morphology of the small extra chromosomal segment, allowed us to diagnose the additional material as being derived from chromosome 6q23-qter. FISH with a telomere 13q probe detected a terminal deletion of 13q34-qter on the derivative chromosome 13, indicating that the der(13) was a result of a translocation event. Genotyping of the hypervariable apolipoprotein (a) gene, which lies within 6q26-q27, showed that the additional chromosome 6 material was inherited from the mother. The karyotype of the proposita is therefore: 46,XY,-13,+der(13)t(6;13)(q23;q34) de novo (mat). Our results confirm the usefulness of CGH as an attractive alternative method for the characterization of constitutional small genetic imbalances and contribute to the delineation of the trisomy 6q23-qter phenotype. Received: 26 November 1996 / Revised: 2 January 1997     

Kinetic analyses of liver phosphatidylcholine and phosphatidylethanolamine biosynthesis using (13)C NMR spectroscopy

Choline and ethanolamine are substrates for de novo synthesis of phosphatidylcholine (PtdC) and phosphatidylethanolamine (PtdE) through the CDP-choline and CDP-ethanolamine pathways. In liver, PtdE can also be converted to PtdC by PtdE N-methyltransferase (PEMT). We investigated these kinetics in rat liver during a 60 min infusion with (13)C-labeled choline and ethanolamine. NMR analyses of liver extracts provided concentrations and (13)C enrichments of phosphocholine (Pcho), phosphoethanolamine (Peth), PtdC, and PtdE. Kinetic models showed that the de novo and PEMT pathways are 'channeled' processes. The intermediary metabolites directly derived from exogenous choline and ethanolamine do not completely mix with the intracellular pools, but are preferentially used for phospholipid synthesis. Of the newly synthesized PtdC, about 70% was derived de novo and 30% was by PEMT. PtdC and PtdE de novo syntheses displayed different kinetics. A simple model assuming constant fluxes yielded a modest fit to the data; allowing upregulated fluxes significantly improved the fit. The ethanolamine-to-Peth flux exceeded choline-to-Pcho, and the rate of PtdE synthesis (1.04 micromol/h/g liver) was 2-3 times greater than that of PtdC de novo synthesis. The metabolic pathway information provided by these studies makes the NMR method superior to earlier radioisotope studies.     

Prenatal diagnosis of a de novo satellited chromosome 18 (18ps) associated with 18p deletion

De novo satellited non-acrocentric chromosomes are very rare findings in prenatal diagnosis. Here we report the first case of a de novo 18ps, associated with del(18p), detected at prenatal diagnosis. A 37 years old woman underwent Chorionic Villus Sampling (CVS) for advanced maternal age. Cytogenetic analysis on direct CVS preparation (CVSc) revealed a male karyotype with a nonfamilial satellited 18ps and a reciprocal translocation t(17;19)(P11.1;q11) of maternal origin. The mesenchimal CVS culture (CVSm) showed a mosaic of cell lines with various involvement of chromosome 18: 18ps [36/70]/ r(18) [25/70]/ del(18p) [3/70]/ -18 [6/70]. Amniotic fluid cells (AFC) confirmed the homogeneous karyotype found at CVSc. The molecular cytogenetic characterization, performed on AFC, allowed the following diagnosis: 46,XY, +15, dic(15;18)(p11.1;p11.2), t(17;19)(p11.1;q11)mat. ish dic(15;18)(tel 18p-, D15Z1+, wcp18-, wcp 18+, D18Z1+, tel 18q+). The foetal autopsy disclosed subtle facial dysmorphisms and corpus callosum hypoplasia. In case of prenatal detection of de novo terminal ectopic NORs an accurate cytogenetic and molecular analysis should be performed in order to rule out subtle unbalancements.     

Kinetic analyses of liver phosphatidylcholine and phosphatidylethanolamine biosynthesis using 13C NMR spectroscopy

Choline and ethanolamine are substrates for de novo synthesis of phosphatidylcholine (PtdC) and phosphatidylethanolamine (PtdE) through the CDP-choline and CDP-ethanolamine pathways. In liver, PtdE can also be converted to PtdC by PtdE N-methyltransferase (PEMT). We investigated these kinetics in rat liver during a 60 min infusion with ¹³C-labeled choline and ethanolamine. NMR analyses of liver extracts provided concentrations and ¹³C enrichments of phosphocholine (Pcho), phosphoethanolamine (Peth), PtdC, and PtdE. Kinetic models showed that the de novo and PEMT pathways are ‘channeled’ processes. The intermediary metabolites directly derived from exogenous choline and ethanolamine do not completely mix with the intracellular pools, but are preferentially used for phospholipid synthesis. Of the newly synthesized PtdC, about 70% was derived de novo and 30% was by PEMT. PtdC and PtdE de novo syntheses displayed different kinetics. A simple model assuming constant fluxes yielded a modest fit to the data; allowing upregulated fluxes significantly improved the fit. The ethanolamine-to-Peth flux exceeded choline-to-Pcho, and the rate of PtdE synthesis (1.04 μmol/h/g liver) was 2–3 times greater than that of PtdC de novo synthesis. The metabolic pathway information provided by these studies makes the NMR method superior to earlier radioisotope studies.     

De novo isochromosome 18p in a female dysmorphic child

Isochromosome 18p results in tetrasomy 18p. Most of the i(18p) cases reported so far in the literature are sporadic due to de novo formation, while familial and mosaic cases are infrequent. It is a rare chromosomal abnormality, occurring once in every 140,000 livebirths, affecting males and females equally. In the present investigation, we report a de novo i(18p) in a female dysmorphic child. The small metacentric marker chromosome was confirmed as i(18p) in the proband by cytogenetic and FISH analysis [47,XX+i(18p)]. Cytogenetic investigations in the family members revealed normal chromosome numbers, indicating the case as a de novo event of i(18p) formation. It could be due to the somewhat advanced maternal age (32 years) and/or expression of recessive genes in the proband, who is the progeny of consanguineous marriage, which could have led to misdivision and nondisjunction of chromosome 18 in meiosis I, followed by failure in the chromatid separation of 18p in meiosis II and by inverted duplication.     

Complex chromosomal rearrangement involving chromosomes 11, 13, 14 and 18 resulting in monosomy for 13q32----qter

A five-year-old boy with speech delay, minor facial abnormalities and borderline psychomotor retardation was found to have a complex de novo double translocation involving four chromosomes resulting in monosomy for the segment 13q32----qter. Chromosomes involved were 11, 13, 14, and 18. The translocation between chromosome 11 and 13 was unbalanced with the loss of the segment 13q32----qter. The second translocation between 14 and 18 was apparently balanced.     

Submicroscopic terminal deletions and duplications in retarded patients with unclassified malformation syndromes

Unbalanced submicroscopic subtelomeric chromosomal rearrangements represent a significant cause of unexplained moderate to severe mental retardation with and without phenotypic abnormalities. We investigated 254 patients (102 from Zürich, 152 from Liège) for unbalanced subtelomeric rearrangements by using fluorescence in situ hybridisation with probes mapping to 41 subtelomeric regions. Mental retardation combined with a pattern of dysmorphic features, with or without major malformations, and growth retardation and a normal karyotype by conventional G-banding were the criteria of inclusion. Selection criteria were more restrictive for the Zürich series in terms of clinical and cytogenetic pre-investigation. We found 13 unbalanced rearrangements and two further aberrations, which, following the investigation of other family members, had to be considered as variants without influence on the phenotype. The significant aberrations included three de novo deletions (two of 1pter, one of 5pter), three de novo duplications (8pter, 9pter, Xpter), one de novo deletion 13qter-duplication 4qter, and five familial submicroscopic translocations [(1q;18p), (2q;4p), (2p;7q), (3p;22q), (4q;10q), (12p;22q)], most of them with several unbalanced offspring with deletion-duplication. Although the incidence of abnormal results was higher (10/152) in the Liège versus the Zürich series (3/102), similar selection criteria in Zürich as in Liège would have resulted in an incidence of 7/106 and thus similar figures. In our series, submicroscopic unbalanced rearrangements explain the phenotype in 13/254 study probands. The most important selection criterion seems to be the presence of more than one affected member in a family. An examination of subtelomeric segments should be included in the diagnostic work-up of patients with unexplained mental retardation combined with physical abnormalities, when a careful conventional examination of banded chromosomes has yielded a normal result and a thorough clinical examination does not lead to another classification. The proportion of abnormal findings depends strongly on selection criteria: more stringent selection can eliminate some examinations but necessitates a high workload for experienced clinical geneticists. Once the costs and workload of screening are reduced, less selective approaches might finally be more cost-effective.     

A novel double nucleotide substitution in the HMG box of the SRY gene associated with Swyer syndrome

We describe a novel double nucleotide substitution in the SRY gene of a 46,XY female with gonadal dysgenesis or Swyer syndrome. The SRY sequence was analysed by both the single-strand conformational polymorphism assay and direct DNA sequencing of products from the polymerase chain reaction. A double nucleotide substitution was identified at codon 18 of the conserved HMG box motif, causing an arginine to asparagine amino-acid substitution. The altered residue is situated in the high mobility group (HMG)-related box of the SRY protein, a potential DNA-binding domain. Since the mutation abolishes one HhaI recognition site, the results were confirmed by HhaI restriction mapping. No other mutations were found in the remaining regions of the gene. The corresponding DNA region from the patient’s brother was analysed and found to be normal. We conclude that the SRY mutation in the reported XY female occurred de novo and is associated with sex reversal. Received: 16 December 1996 / Accepted: 5 May 1997     

The importance of the stearoyl-CoA desaturase system in octadecenoate metabolism in the Morris hepatoma 7288C

The sources of octadecenoic acid (18:1) and the importance of the stearoyl-CoA desaturase system in maintaining elevated levels of this fatty acid in the Morris hepatoma 7288C have been investigated. Sterculic acid, an inhibitor of the stearoyl-CoA desaturase system, when added to the culture medium, inhibited the production of monoenoic fatty acids through de novo synthesis by 90% while the production of saturated fatty acids and cholesterol was unaffected. Sterculic acid also inhibited 18:1 formation through desaturation of exogenous stearate (18:0) by 80%. These results indicate that the stearoyl-CoA desaturase system is responsible for most, if not all, of the 18:1 produced within these cells and that an alternate, sterculic acid-insensitive, pathway for 18:1 biosynthesis is not functioning in this cell line. Measurements of fatty acid synthesis, using 3H2O, show that de novo synthesis accounts for approx. 30% of the cellular 16:1 and 18:1 mass, while contributing 63% and 95% of the stearate and palmitate mass, respectively. Cells grown in the presence of sterculic acid displayed a 50% decrease in 18:1 levels while levels of both palmitate and stearate increased. These effects were maximal at 20-30 microM sterculate. Polyunsaturate levels were unaffected. The 50% decrease in 18:1 levels in treated cells could be completely accounted for by the inhibition of de novo 18:1 biosynthesis and the inhibition of exogenous 18:0 desaturation. This enzyme system, although low in activity when measured in this tissue, is responsible for a major portion of the 18:1 observed in these cells.     

Parental origin of germ-line and somatic mutations in the retinoblastoma gene

Segregation analysis of polymorphic sites within the retinoblastoma (RB) gene and on chromosome 13, as well as the parental origin of the lost allele in the tumor, were analyzed in 24 families with RB patients. Four mutant alleles transmitted through the germ-line and seven de novo germ-line mutant alleles were identified in 11 patients with hereditary RB. Segregation analysis within the RB gene and on chromosome 13 was useful for DNA diagnosis of susceptibility to RB in relatives of hereditary patients, even if mutations were not identified. All seven de novo germ-line mutant alleles were paternally derived. The bias toward the paternal allele for de novo germ-line mutations of the RB gene was statistically significant. Seven paternal alleles and six maternal alleles were lost in 13 non-hereditary RB tumors with no bias in the parental origin of the somatic allele loss. These results suggest that the physical environment or a deficiency in DNA repair during spermatogenesis may be associated with significant risk factors for de novo germ-line mutations.