Genetic heterogeneity in families with hereditary multiple exostoses

We have carried out a linkage analysis on 11 families segregating gene(s) for hereditary multiple exostoses (EXT). Four highly informative, short tandem-repeat (STR) markers that have been physically mapped to an interval surrounding the Langer-Giedion chromosomal region (8q24.11-q24.13) were used in a multipoint linkage analysis. Significant evidence for linkage of EXT with genetic heterogeneity was found. A model of heterogeneity with linkage of the disease gene to the STR markers in 70% of the families (with a 95% confidence interval of 26%-96%) produced a maximum LOD score of 8.11, with the most likely position of EXT between D8S85 and D8S199. Thus there are at least two genes that are capable of causing hereditary multiple exostoses, one in the Langer-Giedion region and one at another, unlinked location.

Molecular characterization of the gene encoding the gamma subunit of the human skeletal muscle 1,4-dihydropyridine-sensitive Ca2+ channel (CACNLG), cDNA sequence, gene structure, and chromosomal location

cDNA clones of the gamma subunit of the skeletal muscle 1,4-dihydropyridine-sensitive voltage-dependent Ca2+ channel were isolated from a human fetal skeletal muscle cDNA library using the rabbit gamma cDNA as a probe. The DNA sequence of the entire human cDNA was determined. Cosmids that contained the human gamma gene were isolated and used to determine the genomic organization of the coding sequences. Four exons were identified, spanning 12.5 kilobases of DNA. Reverse-transcribed polymerase chain reaction analysis detected the gamma transcript in human and mouse skeletal muscle RNAs, but not in RNA from human brain or cardiac muscle or from mouse brain, cardiac muscle, spleen, kidney, liver, or stomach. A polymorphic dinucleotide repeat within the gamma gene was identified. This repeat was used to type a subset of the Centre d'Etude du Polymorphisme Humain families. Linkage analysis indicates that the gamma gene is tightly linked (Z = 12.94, theta = 0.001) to growth hormone at chromosome 17q23, a region that also contains the adult skeletal muscle Na+ channel.

Application of DNA analysis in a population-screening program for neonatal diagnosis of cystic fibrosis (CF): comparison of screening protocols

We compare two protocols for newborn screening for cystic fibrosis (CF). The first uses the immunoreactive trypsinogen (IRT) assay with a cutoff of > or = 180 ng/ml and a sweat test to identify CF patients. The second uses the IRT assay with a 100 ng/ml cutoff in conjunction with direct analysis for the delta F508 CF transmembrane conductance regulator (CFTR) mutation in a two-tiered (i.e., IRT/DNA) protocol, followed by a sweat test. We screened 220,865 newborns from Wisconsin for CF, using the IRT protocol identifying 369 infants with an elevated IRT, of whom 46 were found to have CF. Another 7 CF patients were identified who had a false-negative IRT level. The CF incidence in the white population was 1 in 3,431 (carrier incidence of 1 in 30). The IRT protocol had a sensitivity of 87% and a positive predictive value of 12.5%. We subsequently used the IRT/DNA protocol to screen 21,258 infants. Of 518 infants with an IRT level > or = 100 ng/ml, 24 carried at least one copy of the delta F508 CFTR mutation, and 4 of these infants were found to have CF, yielding a positive predictive value for this protocol of 16.7%. Direct comparison of the positive predictive value of the two protocols is not valid, because of the different populations screened. However, had the IRT protocol been used on the IRT/DNA cohort, 50 infants, including the 4 with CF, would have received sweat tests, yielding a positive predictive value of 8%. Because of the small sample size, this positive predictive value is not significantly different from that obtained for the IRT/DNA test. However, from a practical point of view the IRT/DNA approach does decrease considerably the number of sweat tests that must be undertaken. The number of false positives for the IRT protocol (46 in 21,258) is increased significantly compared with that for the IRT/DNA approach (20 in 21,258; P < .001). The incidence of delta F508 carriers detected in cohorts with an elevated IRT level was increased compared with the incidence in the general population. The direct costs for the IRT/DNA approach (100 ng/ml) were $11,374 per CF patient detected, compared with $10,187 per CF patient detected for the IRT protocol. Therefore, we conclude that the IRT/DNA approach to CF newborn screening decreases the number of false-positive subjects contacted, without a significant increase in cost.

Refined genetic localization for central core disease

Central core disease (CCO) is an autosomal dominant myopathy clinically distinct from malignant hyperthermia (MHS). In a large kindred in which the gene for CCO is segregating, two-point linkage analysis gave a maximum lod score, between the central core disease locus (CCO) and the ryanodine receptor locus (RYR1), of 11.8, with no recombination. Mutation within RYR1 is responsible for MHS, and RYR1 is also a candidate locus for CCO. A combination of physical mapping using a radiation-induced human-hamster hybrid panel and of multipoint linkage analysis using the Centre d'Etude du Polymorphisme Humain families established the marker order and sex-average map distances (in centimorgans) on the background map as D19S75-(5.2)-D19S9-(3.4)-D19S191-(2.2)-RYR1-(1.7)-D19S190-(1.6)-D19S47-(2.0)- CYP2B. Recombination was observed between CCO and the markers flanking RYR1. These linkage data are consistent with the hypothesis that CCO and RYR1 are allelic. The most likely position for CCO is near RYR1, with a multipoint lod score of 11.4, in 19q13.1 between D19S191 and D19S190, within the same interval as MHS (RYR1).

Assignment of the human gene for the alpha 1 subunit of the skeletal muscle DHP-sensitive Ca2+ channel (CACNL1A3) to chromosome 1q31-q32

A human clone corresponding to the gene encoding the alpha 1 subunit of the skeletal muscle dihydropyridine-sensitive calcium channel (CACNL1A3) has been isolated and partially sequenced. Oligonucleotides based on this sequence were used in a polymerase chain reaction to amplify specifically the human gene in human-rodent somatic cell hybrids, allowing the assignment of CACNL1A3 to chromosome 1. A polymorphic dinucleotide repeat also was identified in the human clone and using PCR was typed on a subset of the CEPH families. Multipoint linkage analysis places the CACNL1A3 gene between D1S52 and D1S70, on chromosome 1q31-q32.

Assignment of the human gene for the beta subunit of the voltage-dependent calcium channel (CACNLB1) to chromosome 17 using somatic cell hybrids and linkage mapping

A human clone containing a portion of the gene encoding several isoforms of the beta 1 subunit of voltage-dependent calcium channels was isolated and partially sequenced. The gene was mapped to chromosome 17 using the polymerase chain reaction with oligonucleotides that allowed the specific amplification of the human sequence in the human-rodent hybrids. A polymorphic dinucleotide repeat was identified within the gene and typed on a subset of the CEPH families. Using multipoint linkage analysis the most likely location of the beta 1 subunit gene is between D17S36 and NGFR on chromosome 17q11.2-q22.

Skeletal muscle and brain isoforms of a beta-subunit of human voltage-dependent calcium channels are encoded by a single gene

Clones of the beta 1-subunit of the voltage-dependent calcium channel (VDCC) from human skeletal muscle and hippocampus cDNA libraries, and from human genomic libraries, were isolated using a human skeletal muscle beta 1 cDNA probe generated by polymerase chain reaction. The skeletal muscle beta 1 cDNA (beta 1M) encodes a protein of 523 amino acids that is 97% identical to the rabbit skeletal muscle beta-subunit. Two different cDNAs, beta 1B1 and beta 1B2, were obtained from the human hippocampus library. The beta 1B1 transcript encodes a protein of 478 amino acids that is identical to the skeletal muscle beta-subunit (beta 1M), except for an internal region of 52 amino acids. The beta 1B2 transcript encodes a protein of 596 amino acids. The beta 1B2 polypeptide is identical to the beta 1B1 polypeptide at amino acids 1-444; however, it has a unique 152 amino acid carboxyl terminus. Like beta 1B1, it differs from beta 1M at the internal 52 amino acids. Analysis of the beta 1 gene structure demonstrates that these three cDNAs represent transcripts encoded by a single beta 1 gene. Transcripts from the beta 1 gene were detected in RNA from skeletal muscle, heart, spleen, and brain, but not in RNA from liver, stomach, or kidney.

A cysteine-for-arginine substitution (R614C) in the human skeletal muscle calcium release channel cosegregates with malignant hyperthermia

A point mutation in the human gene for the skeletal muscle calcium release channel (ryanodine receptor [RYR1]) correlates with inheritance of malignant hyperthermia in a family of Northern European descent. The substitution of thymine for cytosine at position 1840 of the RYR1 transcript results in a cysteine-for-arginine substitution at position 614 (R614C) of the amino acid sequence. The mutation was absent in 59 normal individuals from the general population, in 61 additional unrelated malignant hyperthermia-susceptible patients, and in 18 patients with malignant hyperthermia associated with other inherited or congenital diseases. Together with reports of an equivalent mutation in six susceptible pig strains and an identical mutation in one other human pedigree, these findings suggest that the cysteine-for-arginine mutation represents a shared calcium release channel pathogenesis between porcine malignant hyperthermia and a subset of mutations responsible for the human malignant hyperthermia syndrome.

Dinucleotide repeat polymorphism at the RYR1 locus (19q13.1)

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Assignment of the human gene for the alpha 1 subunit of the cardiac DHP-sensitive Ca2+ channel (CCHL1A1) to chromosome 12p12-pter

A human clone corresponding to the gene encoding the alpha 1 subunit of the cardiac dihydropyridine-sensitive calcium channel (CCHL1A1) has been isolated and partially sequenced. Oligonucleotides based on the human sequence were constructed and used in the polymerase chain reaction to amplify specifically this human gene in human-rodent somatic cell hybrids. Using somatic cell hybrids that contained defined regions of human chromosome 12, the human alpha 1 subunit of the cardiac dihydropyridine-sensitive calcium channel has been assigned to the short arm of chromosome 12 in the interval 12p12-pter.

Waisman syndrome, a human X-linked recessive basal ganglia disorder with mental retardation: localization to Xq27.3-qter

Linkage of the gene responsible for an X-linked early onset parkinsonism disorder with mental retardation (McKusick 311510) to DNA probes that detect restriction fragment length polymorphisms is described. The disease gene is linked to the F8C gene, and to DNA probes detecting polymorphic loci DXS52, DXS15, DXS134, and DXS374 with maximum lod scores at theta = 0 of 5.08, 5.19, 5.00, 5.03, and 4.46, respectively. Multipoint linkage analysis gives a maximum multipoint lod score of 6.75 at the F8C gene. This places the disease gene in chromosomal region Xq27.3-qter.

Current issues in neonatal screening for cystic fibrosis and implications of the CF gene discovery

Many questions remain regarding the efficacy, toxicity, and costs of CF neonatal screening. It would be premature, in our opinion, to implement mass population screening of newborns for CF until the benefits and risks have been fully defined, and an adequate and logistically feasible testing system developed and/or highly effective therapy for CF lung disease becomes available. In addition, the ethical issues described herein need to be resolved. This pertains not only to the CF patient but also the heterozygote carrier. These reservations notwithstanding, the discovery of the CF gene should have a favorable impact both directly and indirectly on neonatal screening for the disease. Mutation analysis coupled to IRT testing seems most attractive at this time, at least on a research basis, but primary molecular diagnostic procedures might supervene in the future, particularly if they are financially feasible.

Regulatory elements in the introns of the human HPRT gene are necessary for its expression in embryonic stem cells

We have examined the expression of transfected human hypoxanthine phosphoribosyltransferase minigenes (HPRT) in mouse embryonic stem (ES) cells. cDNA constructs of this gene that have been successfully used in somatic cell lines failed to confer hypoxanthine/aminopterin/thymidine (HAT) resistance in ES cells. In contrast, constructs containing introns 1 and 2 from the HPRT gene produced a high frequency of HAT-resistant colonies. This observation allowed us to identify two sequences in these introns that influence expression of the HPRT gene in ES cells. One element, located in intron 2, is required for effective HPRT expression in these cells; the other element, located in intron 1, acts as an enhancer of HPRT expression. Using this information, we have constructed an HPRT minigene that can be used for either positive or negative selection in ES cell experiments. This dual capability allows the design of "in-out" procedures to create subtle changes in target genes by homologous recombination with the aid of this selectable minigene.

Regulated expression of genes inserted at the human chromosomal beta-globin locus by homologous recombination

We have examined the effect of the site of integration on the expression of cloned genes introduced into cultured erythroid cells. Smithies et al. [Smithies, O., Gregg, R.G., Boggs, S.S., Koralewski, M.A. & Kucherlapati, R.S. (1985) Nature (London) 317, 230-234] reported the targeted integration of DNA into the human beta-globin locus on chromosome 11 in a mouse erythroleukemia-human cell hybrid. These hybrid cells can undergo erythroid differentiation leading to greatly increased mouse and human beta-globin synthesis. By transfection of these hybrid cells with a plasmid carrying a modified human beta-globin gene and a foreign gene composed of the coding sequence of the bacterial neomycin-resistance gene linked to simian virus 40 transcription signals (SVneo), cells were obtained in which the two genes are integrated at the beta-globin locus on human chromosome 11 or at random sites. When we examined the response of the integrated genes to cell differentiation, we found that the genes inserted at the beta-globin locus were induced during differentiation, whereas randomly positioned copies were not induced. Even the foreign SVneo gene was inducible when it had been integrated at the beta-globin locus. The results show that genes introduced at the beta-globin locus acquire some of the regulatory properties of globin genes during erythroid differentiation.

Targetted correction of a mutant HPRT gene in mouse embryonic stem cells

Two recent developments suggest a route to predetermined alterations in mammalian germlines. These are, first, the characterization of mouse embryonic stem (ES) cells that can still enter the germline after genetic manipulation in culture and second, the demonstration that homologous recombination between a native target chromosomal gene and exogenous DAN can be used in culture to modify specifically the target locus. We here use gene targetting functionally to correct the mutant hypoxanthine-guanine phosphoribosyl transferase (HPRT) gene in the ES cell line which has previously been isolated and used to produce an HPRT-deficient mouse. This modification of a chosen gene in pluripotent ES cells demonstrates the feasibility of this route to manipulating mammalian genomes in predetermined ways.

Hepatic cholesterol synthesis and hydroxymethylglutaryl CoA reductase activity after injection of methylazoxymethanol acetate

Cholesterol synthesis and 3-hydroxy-3-methylglutaryl CoA reductase (HMG-CoA reductase) in the liver of rats at various times (7, 22, 45 and 314 days) after injection with the carcinogen, methylazoxymethanol acetate (MAMA) is reported. Seven days after treatment, an increase in both cholesterol synthesis and HMG-CoA reductase activity was observed. Elevated HMG-CoA reductase activity and reduced dietary feedback was present 22 days after carcinogen. Cholesterol synthesis was normal at this time but dietary cholesterol failed to significantly reduce synthesis. Forty-five days after carcinogen both cholesterol synthesis and HMG-CoA reductase activity had returned to normal. Both parameters were normal 314 days after carcinogen. The enzyme gamma-glutamyl transferase was also elevated at 7, 22 and 314 days. These results indicate that HMG-CoA reductase activity and cholesterol synthesis exhibit different regulatory characteristics during the early stages of hepatocarcinogenesis initiated by MAMA injection.

Efficient transformation and frequent single-site, single-copy insertion of DNA can be obtained in mouse erythroleukemia cells transformed by electroporation

Electroporation has recently been shown to have advantages over the commonly used method of calcium phosphate precipitation for obtaining DNA-mediated transformation of certain types of cells. Although mouse erythroleukemia cells and other cells of hematopoietic origin are not transformed at useful frequencies by calcium phosphate-DNA precipitation methods, we obtained high frequencies of transformation (approximately 10(-5)) of these cells with electroporation. Even higher transformation frequencies (approximately 10(-3)) were obtained with human fibroblasts. Another advantage of electroporation was found when analysis of Southern blots of DNA from 243 transformed erythroleukemia cell colonies indicated that, under appropriate conditions, about 79% of the transformed cells had the exogenous DNA integrated in single copies at single sites. Under conditions of higher DNA and lower cell concentrations using fibroblasts, cotransformation was obtained with two plasmids that confer HAT or G418 resistance when integrated into cellular DNA. About 23% of the transformed cells developed both types of resistance. We describe a simple, inexpensive apparatus for carrying out electroporation.