Linkage analysis of the murine interferon alpha locus (Ifa) on chromosome 4

We performed linkage analysis of the murine interferon alpha gene cluster, Ifa, with three different marker genes on chromosome 4: the major urinary protein locus (Mup-1), the brown locus (b) and the misty locus (m). The gene order (from centromere) with intervening percent recombination derived from a first three-point cross is Mup-1--13.6 (+/- 3.6)--Ifa--7.9 (+/- 2.8)--m and from a second three-point cross Mup-1--1.7 (+/- 1.7)--b--3.5 (+/- 2.4)--Ifa. The combined results indicate that the gene order, from the centromere, is Mup-1--b--Ifa--m.     

Linkage analysis of the murine Hyal-1 locus on chromosome 9

We have recently described a new locus, Hyal-1, which determines hyaluronidase variants in mouse serum. On the basis of segregation in recombinant inbred and congenic strains, Hyal-1 was tentatively assigned to chromosome 9 (Fiszer-Szafarz and De Maeyer, '89). In the present study we have performed a linkage analysis of Hyal-1 using 156 backcross progeny of an interspecies cross of laboratory mice and Mus Spretus. Linkage was tested to two anchor loci on chromosome 9: d (dilute, a coat color locus) and Bgl-s (a locus controlling beta-galactosidase activity). The gene order (from centromere) with intervening percentage recombination is d-16.6 (+/- 2.9)-Hyal-1-10.9 (+/- 2.4)-Bgl-s, indicating close linkage to H-7 and Fv-2.     

The Mos proto-oncogene maps near the centromere on mouse chromosome 4

The Mos proto-oncogene, the cellular homolog of the transforming gene of Moloney murine sarcoma virus, was originally assigned to mouse chromosome 4 using independent panels of mouse/hamster somatic cell hybrids. By in situ hybridization to metaphase chromosomes and standard genetic backcrosses, we have confirmed this assignment and determined that Mos maps near the centromere in a region devoid of other markers. We have also identified a restriction fragment length polymorphism (RFLP) that defines two alleles of the Mos locus in selected inbred strains of laboratory mice. Using the RFLP, we determined the strain distribution pattern for the Mos gene in three sets of recombinant inbred strains and in five strains congenic for histocompatibility antigen genes localized on chromosome 4. These results establish Mos as a useful marker in a poorly characterized region of the mouse genome. In addition, these results will facilitate the genetic analysis of the Mos locus.     

Linkage studies between polymorphic markers on chromosome 4 and cystic fibrosis

Summary It has been suggested that a protein factor causing ciliary dyskinesis is a marker for the basic defect causing cystic fibrosis (CF), and that the structural gene for this protein may be (amongst others) on human chromosome 4. We have isolated two DNA sequences mapping to chromosome 4 which show restriction fragment length polymorphisms (RFLPs), and have followed their segregation in families in which cystic fibrosis occurs. Elevent families with a total of 30 children with CF and ten unaffected sibs were studied. We have also followed the inheritance of RFLPs revealed by two probes mapping to chromosome 4 and obtained from another laboratory, polymorphisms revealed by cloned coding sequences for albumin and fibrinogen, and the inheritance of the MNS blood group. Although the level of albumin is altered in children with CF, the gene does not segregate with CF, and therefore albumin can be excluded as the site of the basic defect. Tight linkage with CF was not found with any of the seven markers investigated, and therefore, assuming that the markers (excepting MNS and fibrinogen) are unlinked to one another, approximately half of the total genetic length of chromosome 4 may be excluded.     

Linkage analysis of von Recklinghausen neurofibromatosis to DNA markers on chromosome 17

Several recent studies indicate that the von Recklinghausen neurofibromatosis (NF1) gene is located near the centromere of chromosome 17 in some families. However, variable expressivity and a very high mutation rate suggest that defects at several different loci could result in phenotypes categorized as NF1. In order to assess this possibility and to map the NF1 gene more precisely, we have used two polymorphic DNA markers from chromosome 17 to screen several pedigrees for linkage to NF1. We ascertained a large Caucasian pedigree (33 individuals sampled, 17 NF1 affected) as well as eight smaller pedigrees and nuclear families (50 individuals sampled, 30 NF1 affected). Here, we report strong evidence of linkage of NF1 to the centromeric marker D17Z1 (maximum lod = 4.42) and a weaker suggestion of linkage to the ERBA1 oncogene (maximum lod = 0.57), both at a recombination fraction of zero. Since obligate cross-overs with NF1 were not observed for either marker in any of the informative families tested, the possibility of NF1 locus heterogeneity is not supported.     

Linkage of loci affecting a murine liver protein and arylsulfatase B to chromosome 13

As-1 is the putative structural locus for murine arylsulfatase B, and Lth-1 determines the presence or absence of a 35 000 dalton acidic liver protein. As-1 and Lth-1 were found to be closely linked using recombinant inbred (RI) strains. Both loci were found to have been cotransferred with the pearl (pe) coat color mutation (chromosome 13) in the B6.C3H pe/pe congenic strain. The linkage relationships between pe, Lth-1, and As-1 were further defined in a backcross. On the basis of the RI data, the congenic strain result, and the backcross data, the following genetic distances were estimated: pe--As-1, 7.1 +/- 4.0 cM; As-1--Lth-1, 2.5 +/- 1.0 cM; and pe--Lth-1, less than 6.9 cM. As-1 and Lth-1 are the first biochemically defined loci to be added to the chromosome 13 linkage map.     

Linkage of aspartylglucosaminuria (AGU) to marker loci on the long arm of chromosome 4

Summary Aspartylglucosaminuria (AGU) is caused by deficient activity of the enzyme aspartylglucosaminidase (AGA). The structural gene for AGA has been assigned to the region 4q21-qter of chromosome 4. We have studied the map position of the AGU locus in relation to other marker loci on the long arm of chromosome 4 using linkage analyses. Restriction fragment length polymorphism alleles for the ADH2, ADH3, EGF, FG and FG loci and blood group antigenes for the MNS locus were determined in a panel of 12 Finnish AGU families. The heterozygous family members were identified by reduced activity of AGA in lymphocytes. Linkage studies were performed using both pairwise and multipoint analyses. Loose linkage of the AGU locus to the FG and MNS loci was observed ( = 1.16, = 1.39, respectively). Multipoint analysis to the fixed map [ADH-(0.03)-EGF-(0.35)-FG-(0.11)-MNS] suggests that the location of the AGU locus is 0.05–0.30 recombination units distal to MNS ( = 3.03). The order cen-ADH-EGF-FG-MNS-AGU is 35 times more likely than the next best order cen-ADH-EGF-AGU-FG-MNS.     

Linkage mapping of serotonin transporter protein gene SLC6A4 on chromosome 17

Abnormalities in monoamine metabolism, including serotonin metabolism, have been implicated in the pathophysiology of affective disorders, schizophrenia, suicide, and other psychiatric disorders. Serotonin transporter protein (SERT) allows neurons to retrieve serotonin that has been released into a synapse. SERT is a site of action for several drugs with CMS effects, including both therapeutic agents (e.g., antidepressants) and drugs of abuse (e.g., cocaine). This gene had previously been physically mapped to chromosome 17. We used a PCR product corresponding to the 3 untranslated region of the gene as a probe to identify restriction fragment length polymorphism (RFLP), which we then used to establish that the SLC6A4, genetic locus for SERT, is near 17q12 and probably flanked by D17S58 and D17S73 (a location consistent with observed crossovers). These data should be useful for linkage studies of neuropsychiatric disorders. (Joyce et al. 1993). Neurotransmitter reuptake sites (including also the norepinephrine transporter protein and the dopamine transporter protein) are logical candidate genes for susceptibility to psychiatric illness. We have previously (Gelernter et al. 1993) mapped the norepinephrine transporter protein to chromosome 16q21. We describe here linkage mapping of the serotonin transporter protein gene (gene symbol SLC6A4, for solute carrier family 6 (neurotransporter, serotonin), member 4), which was cloned in 1991 (Blakely et al. 1991; Hoffman et al. 1991) and previously assigned to chromosome 17, most likely to band 17q11.2, by in situ hybridization (Ramamoorthy et al. 1993). Our linkage results confirm the initial mapping of SLC6A4 and place it in the linkage map of proximal 17q.     

Linkage analysis of familial Alzheimer disease, using chromosome 21 markers

Chromosome 21 markers were tested for linkage to familial Alzheimer disease (FAD) in 48 kindreds. These families had multiple cases of Alzheimer disease (AD) in 2 or more generations with family age-at-onset means (M) ranging from 41 to 83 years. Included in this group are seven Volga German families which are thought to be genetically homogeneous with respect to FAD. Autopsy documentation of AD was available for 32 families. Linkage to the 21 q11-q21 region was tested using D21S16, D21S13, D21S110, D21S1/S11, and the APP gene as genetic markers. When linkage results for all the families were summed, the LOD scores for these markers were consistently negative and the entire region was formally excluded. Linkage results were also summed for the following family groups; late-onset (M greater than 60), early-onset (M less than or equal to 60), Volga Germans (M = 56), and early-onset non-Volga Germans (M less than or equal to 60). For the first three groups, LOD scores were negative for this region. For the early-onset non-Volga German group (six families), small positive LOD scores of Zmax = 0.78 (recombination fraction theta = .15), Zmax = 0.27 (theta = .15), and Zmax = 0.64 (theta = .0), were observed for D21S13, D21S16, and D21S110, respectively. The remainder of the long arm of chromosome 21 was tested for linkage to FAD using seven markers spanning the q22 region. Results for these markers were also predominantly negative. Thus it is highly unlikely that a chromosome 21 gene is responsible for late-onset FAD and at least some forms of early-onset FAD represented by the Volga German kindreds.     

Functional analysis of mutations on murine chromosome 17 using tertiary trisomy

Analysis of the functional nature of mutations can be based on their manifestation in organisms with a deletion or a duplication of a particular chromosome segment. With the use of reciprocal translocation T(16;17)43H it is feasible to produce mice with tertiary trisomy for proximal region of chromosome 17. The mutations on chromosome 17 we tested included brachyury (T), hairpin tail (Thp), kinky (Fuki), quaking (qk), tufted (tf), as well as tct (t-complex tail interaction) and tcl (t complex lethal), that are specific for t haplotypes. The set of dominant and recessive mutations was assigned to two groups, one obligatory manifesting itself in the phenotype independently of the number of normal alleles in di- and trisomics, and the other facultative, phenotypically manifesting itself, depending upon the dosage of mutant alleles. A model was derived from analysis of the interaction of the T and Thp mutations with t haplotypes which is to explain the morphogenetic effects of the mutations observed in mice of different genotypes. The tir gene is postulated to reside on chromosome 17 within its framework. It is suggested that the gene dosage ratio at the tir and tct loci determines tail length.     

Structure and chromosome mapping of the human SIX4 and murine Six4 genes

Six4, a member of the homeobox gene subfamily (Six), is expressed in a developmentally regulated fashion, and supposed to be involved in embryogenesis. We cloned the human SIX4 and murine Six4 genomic DNAs and determined their structures. The structure, including the 5' upstream region of both genes, was well conserved suggesting the conserved function and regulation of these genes. Human SIX4 was mapped to chromosome 14q23.     

Linkage of the mouse LDL receptor gene on chromosome 9

We identified restriction fragment length variants of the mouse low-density lipoprotein receptor gene and used these to map the gene, designated Ldlr, to the proximal region of chromosome 9. An interspecific backcross between strains MEV and CAST/Ei yielded the following gene order and distances in centimorgans: Ldlr-18.8 +/- 5.6-Apoa-4-7.3 +/- 3.5-Mpi-1-10.2 +/- 3.9-Emv-3 or dilute. Analysis of recombinant inbred strains also indicated that Ldlr is tightly linked to a previously unmapped retroviral marker, Xmmv-67.