Report of the committee on the genetic-constitution of chromosomes 1 and 2

Influence of C4 null alleles on C4 activation in systemic lupus erythematosus

Deficiencies of early components of the classical complement pathway are known to be associated with systemic lupus erythematosus (SLE). C4 null alleles, C4A Q0 and C4B Q0, are prime candidates for the major histocompatibility complex associated factor which determines susceptibility to SLE. There is poor correlation, however, between the presence of low concentrations of C4 and possession of C4 null alleles, and thus the basis of the association between C4A Q0, C4B Q0 and SLE remains obscure. The possibility that activation of C4 may be related to the possession of C4 null alleles was examined. C4 phenotypes were investigated, and C4 concentration and activation were estimated in patients with SLE. C4 activation was determined by measuring the concentration of C4d--a split product of C4. Twenty five of 35 patients had C4 phenotypes which include null alleles. No association between low C4 concentrations and C4 null alleles was found, but a significant association between low C4d concentrations and C4 phenotypes including null alleles, particularly those with C4A Q0, was noted. No correlation between concentrations of C4 and C4d was found. These results show an influence of C4 null alleles on the activation of the C4 molecule, which is independent of the concentration of C4. The possession of silent genes coding for C4 null alleles might predispose to SLE by conditioning poor C4 activation, a critical event for the clearance of immune complexes mediated by the classical complement pathway.

A genetic linkage map of 27 markers on human chromosome 21

We have constructed a genetic linkage map of the long arm of human chromosome 21 comprising 27 DNA markers. This map is an updated version of that reported earlier by group (1989, Genomics 4: 579-591), which contained 17 DNA markers. The current markers consist of 10 genes and 17 anonymous sequences. Traditional methods (restriction fragment length polymorphisms) were used to map 25 of these markers, whereas 2 markers were studied by polymerase chain reaction amplification of (GT)n dinucleotide repeats. Linkage analysis was performed on 40 CEPH families using the computer program packages LINKAGE, CRI-MAP, and MAPMAKER. Recombination rates were significantly different between the sexes, with the male map being 132 cM and the female map being 161 cM, assuming Kosambi interference and a variable ratio of sex difference in recombination. Approximately one-half of the crossovers in either sex occur distally, in terminal band 21q22.3, which also contains 16 of the markers studied. The average distance between adjacent markers was 6 cM.

Myogenin is in an evolutionarily conserved linkage group on human chromosome 1q31-q41 and unlinked to other mapped muscle regulatory factor genes

Myogenin is a member of a family of muscle-specific regulatory factors which includes MyoD1, Myf-5, and Myf-6 (also called MRF4 and herculin). Extensive regions of sequence homology in genes for these three factors suggest duplication events associated with their evolution. In the present study, the chromosomal location of the myogenin gene in humans (MYOG), mice (Myog), and Chinese hamsters (MYOG) was determined using in situ hybridization to human metaphase chromosomes as well as segregation analysis among interspecific somatic cell hybrid panels and interspecific backcrossed mice. We localize the gene encoding myogenin to human chromosome 1q31-q41 within a linkage group homologous with a region on mouse chromosome 1 and Chinese hamster chromosome 5. The results verify the nonlinkage of MYOG to MYOD1, MYF5, and MYF6 genes and indicate that events associated with the duplication of MYOG with respect to MYOD1, MYF5, or MYF6 loci were not chromosome-wide.

A detailed multipoint gene map of chromosome 1q

Utilizing genotyping data for 23 markers, we have constructed a 21-locus multipoint genetic map of the long arm of chromosome 1. Five new RFLPs are reported. The map integrates anonymous loci from previous primary linkage maps and incorporates markers for 10 coding sequences. These markers form a continuous linkage group of 85 cM in males and 141 cM in females. The map was constructed employing the LINKAGE and CRIMAP computational methodologies via a stepwise algorithm.

An erythrocyte glycoprotein of apparent Mr 60,000 expresses the Sc1 and Sc2 antigens

Immunoblotting with human anti-Sc1 and anti-Sc2 locates the Sc1 and Sc2 antigens to an erythrocyte membrane glycoprotein of apparent Mr 60,000. The antigens are destroyed by pronase, and require intact disulphide bonds for expression. A proportion of the molecules carrying the Sc1 and Sc2 antigens are associated with red cell cytoskeleton preparations. Treatment of intact cells with an Endo F preparation resulted in the loss of the Sc2 antigen but not the Sc1 antigen, suggesting that the Sc2 antigen is dependent on the presence of one or more complex N-glycans for its expression.

Twenty loci form a continuous linkage map of markers for human chromosome 2

We have used a combination of 20 DNA markers and 1 protein electromorph, defining 20 loci, to construct a genetic linkage map of chromosome 2. These markers form a continuous linkage group of 306 cM in males and 529 cM in females. Female map distances varied from approximately twofold higher to equivalence from those of males across the map. Among the DNA markers are six well-distributed, highly polymorphic markers reflecting loci that contain a variable number of tandem repeats that will be highly efficient anchor points for the eventual application of this map to studies of human genetic disease.

Definition of mouse chromosome 1 and 3 gene linkage groups that are conserved on human chromosome 1: evidence that a conserved linkage group spans the centromere of human chromosome 1

Comparative mapping between the human and the mouse genomes allows characterization of linkage groups that have been conserved over evolution. In this study, genes previously localized to adjacent regions of human chromosome 1 were mapped to discrete regions on distal mouse chromosomes 1 and 3 using an interspecific cross. Linkage analysis in mouse defined two groups in which the gene order appears to be the same as that in humans: 15 genes localized between human chromosome 1q21 and 1q32 were found to span 29.5 cM on distal mouse chromosome 1; 6 genes localized between human chromosome 1q21 and 1p22 spanned 15.6 cM on distal mouse chromosome 3. These data suggest that gene order within large chromosome segments may remain stable over long periods of evolution and that the position of the centromere may reflect a late event in the evolution of higher eukaryotic organisms. These studies provide a model for examination of specific evolutionary events.

Exclusion of the dysplastic nevus syndrome (DNS) locus from the short arm of chromosome 1 by linkage studies in Dutch families

Familial dysplastic nevus syndrome (DNS) is an autosomal dominant premalignant condition characterized by multiple large moles of variable size and color and a strongly increased risk for cutaneous malignant melanoma. In order to determine the chromosomal localization of the DNS gene, linkage studies were initiated in six large Dutch families. No support was obtained for linkage between the loci for DNS and the rhesus blood group on chromosome 1. Data from additional markers (DNF15S1, D1Z2, FUCA1, D1S17, D1S57, and PGM1) make it possible to exclude the DNS gene from the short arm of chromosome 1 in these Dutch families.

MAP, an expert system for multiple pairwise linkage analysis

The logic of a program for multiple pairwise linkage analysis under interference is set forth, including a seriation algorithm to obtain a trial order, a mapping bootstrap to improve the trial order, and three procedures for quality control to detect mistyping. This approach is compared with multipoint analysis under null interference, which substantially overestimates map length and cannot incorporate a variety of data.

A genetic linkage map of 17 markers on human chromosome 21

We have constructed a genetic linkage map of 17 markers on the long arm of human chromosome 21, including six genes and two anonymous loci with a variable number of tandem repeats. The estimated length of the map is 103 cM in males and 140 cM in females, assuming Kosambi interference. Recombination in females was approximately twice that in males between proximal markers. However, over half of the recombination events in either sex occur distally, in 21q22.3, although this region accounts for only about 15% of the physical length of chromosome 21.

Linkage between serum cholinesterase 2 (CHE2) and gamma-crystallin gene cluster (CRYG): assignment to chromosome 2

Serum cholinesterase 2 (CHE2) was examined in a Danish material of normal families that has been tested earlier for 70-78 classical marker systems and 25 RFLP systems. DNA for RFLP typing was provided by transforming 16-year-old frozen lymphocytes. The frequency of allele CHE2*C5+ in the Danish population was found to be 0.0430. The highest lod score was between CHE2 and the gamma-crystallin gene cluster (CRYG) (zeta = 4.21 at theta = 0.00 in females). The scores were from a single family with 15 children. CHE2 may, accordingly, be assigned to the location of CRYG: chromosome 2, bands q33-q35.

The genes for apolipoprotein all (APOA2) and the Duffy blood group (FY) are linked on chromosome 1 in man

We have cloned a cDNA probe for human apolipoprotein AII and used it to analyze linkage relationships on chromosome 1. We found no recombinations between APOA2 and the gene coding for the Duffy blood group antigens (FY) in the 19 meioses examined. Our maximal lod score is 4.2 at zero recombination rate. K. Berg (1987, Cytogenet. Cell Genet. 46:579) found a maximal score of 2.5 at recombination fraction 0.14 in 54 meioses. When results from both studies are combined, the most likely distance between FY and APOA2 is about 10% recombination with a combined lod score of 5.6 for both sexes.

Absence of linkage of hereditary motor and sensory neuropathy type I to chromosome 1 markers

Although one large family with hereditary motor and sensory neuropathy (HMSN) type I that showed linkage to the Duffy blood group (FY) on chromosome 1 has previously been reported, we have failed to find evidence for such linkage after examining 14 markers from chromosome 1 in 12 pedigrees. We have excluded linkage between HMSN I and FY up to theta = 0.15 (lod = -3.01) and also between HMSN I and markers flanking FY; amylase (AMY), polymorphic urinary mucin (PUM), serum amyloid protein (APCS), and alpha-spectrin (SPTA). We have excluded HMSN I from 70 cM around this linkage group. Other markers examined were MS1, oncogene L-myc (MYCL), beta-subunit of nerve growth factor (NGFB), oncogene N-ras (NRAS), glucocerebrosidase (GBA), apolipoprotein AII (APOA2), antithrombin III (AT3), renin (REN), and MS32. These cover both the long and the short arms of chromosome 1 in addition to the centromeric region and yielded no evidence of linkage to HMSN I. Two-point lod scores between these markers are also presented. It is possible that there are two or more loci for HMSN I and it will be necessary to obtain significant lod scores from individual families to resolve this issue. This is increasingly possible now that hypervariable genetic markers such as PUM are available.

Sublocalization of the human protein C gene on chromosome 2q13-q14

The localization of human protein C gene on chromosome 2 was investigated by in situ hybridization using a partial cDNA for protein C. Silver-grain analysis indicates that the protein C gene is located on 2q13-q14.

Twenty-eight loci form a continuous linkage map of markers for human chromosome 1

We have used a combination of 30 serological, protein electromorphic, and DNA markers defining 28 loci to construct a linkage map of chromosome 1. These markers form a continuous linkage group of 320 cM in males and 608 cM in females; female genetic distances were on average twofold higher than those of males across the map. Among the DNA markers are 10 highly polymorphic markers reflecting loci that contain a variable number of tandem repeats, well distributed over the length of the chromosome, that will be highly efficient anchor points for application of this map to studies of human genetic disease.

Structure and chromosomal localization of the functional intronless human JUN protooncogene

The JUN protooncogene encodes a protein that is functionally and biochemically identical to the transcription factor AP-1 (activator protein 1). To understand the structure and regulation of this important gene, a genomic clone of human JUN was isolated and its primary structure and transcription pattern were determined. Most surprisingly, the sequence of the genomic clone was found to be contiguous with the sequence of the JUN cDNA, suggesting that it lacks introns. RNase protection experiments confirm that JUN is an intronless gene that yields several transcripts due to 5' and 3' heterogeneities. Transfection experiments show that the cloned gene is functional, as it encodes a trans-acting factor that stimulates transcription of AP-1-dependent reporter gene. In situ hybridization was used to map JUN to chromosomal region 1p31-32. Interestingly, this region is frequently deleted in neuroblastomas, suggesting that elimination of AP-1 may play an important role in the pathogenesis of this disease.

Linkage between the expressed hypervariable gene locus PUM and the gene coding for the Duffy blood group FY

Linkage is reported between the expressed hypervariable gene locus PUM and the gene coding for the Duffy blood group FY, with a maximum lod score of 4 at theta = 0. Linkage can be excluded between PUM and PEPC at a distance of 10 cM.

Multipoint mapping and the emperor's clothes

On the hypothesis of no interference, pedigree probabilities for segregating loci considered simultaneously factor into pairwise probabilities, and multipoint mapping reduces to multiple pairwise mapping. Under these conditions, use of a computer program such as linkage or mapmaker entails no gain but substantial loss (measured as map distortion, wasted data, concealed evidence, redundant calculation and exaggerated multiple recombination) by comparison with maps based on lod scores. This is illustrated by the current maps of chromosomes 1 and 2.

Regional chromosomal localisation of APOA2 to 1q21-1q23

Using in situ hybridisation, we have mapped APOA2 to the 1q21-1q23 region of chromosome 1. DNA hybridisation to somatic cell hybrids made from cells carrying a balanced translocation between X and 1 confirms the localisation as proximal to 1q23. This was further confirmed by the presence of two polymorphic alleles in a cell line carrying a deletion of 1q25-1q32.