Fine mapping of thymus enlargement gene 1 (Ten1) in BUF/Mna rats

Two polymeric autosomal loci, Ten1 and Ten2, regulate thymus enlargement in BUF/Mna (B) rats. Previously, we mapped Ten1 on chromosome (Chr) 1 to a 20 cM region between Myl2 and D1Mgh11, and Ten2 on Chr 13. To further characterize the precise position of Ten1, 34 and 37 microsatellite markers, that have a polymorphism between the B and WYK (W) and between the B and MITE (M) strains, were used for linkage analysis of thymus enlargement in 105 (WBF1 x B) blackcross (BC) and 78 (B x BMF1) BC rats, respectively. Our data showed that the D1Rat168, D1Rat112, D1Rat323, D1Got186, D1Got187 and D1Got188 markers each gave a peak logarithm of odds (LOD) score of 10.68 for linkage to the thymus ratio in (WBF1 x B) BC rats, and that the D1Rat168, D1Rat197, D1Got184, D1Got186 and D1Got188 markers each gave a peak LOD score of 7.82 in (B x BMF1) BC rats. The two LOD score peaks are coincident in the position of the rat genetic map. All of the markers mentioned above are located in the region between Igf2 and D1Mgh11, in which synteny is conserved with human 11q15.5 and the distal end of mouse Chr 7 or with human 11q13 and the proximal end of mouse Chr 19. Genes existing in these regions are discussed as candidate genes for Ten1.     

Iinkage of the athymic nude locus with the myeloperoxidase locus in the rat

In rats of the BUF/Mna strain epithelial thymoma development is regulated by a single autosomal susceptible gene, Tsr-1 . In pre-thymoma stage, BUF/Mna rats have extremely large thymuses, when compared with those of other strains of rats. The large thymus size of this strain is contributed by a thymus-enlargement gene, Ten-1 . On the other hand, reduced thymus size and suppression of thymoma development were found in heterozygous BUF/Mna-rnu/+ rats. Linkage studies between RNU and microsatellite and restriction fragment length polymorphism markers in ([BUFIMna- runl rnu × WKY/NCrj]F1 × WKY/NCrj)- and (WKY/NCrj × [BUF/ Mna-rnu/rnu × WKY/NCrj] F1)- backcross rats have led to the localization of RNU on chromosome 10. The rat homolog of mouse Mpo (myeloperoxidase) was also assigned to the chromosome 10. The gene order on the chromosome was MYHSE (myosin heavy chain of embryonic skeletal muscle) — (1.0 centimorgan [cM]) — SHBG (sex hormone-binding globulin) — (4.0 cM) — RNU (Rowett rat nude) — (10.0cM) — MPO — (13.0 cM) — AEP (anion exchange protein). Conserved linkage of homologous loci mapped to rat chromosome 10 and mouse chromosome 11 supports the hypothesis that the RNU and MPO loci are rat homologs of the mouse nu and Mpo loci.     

Age-related thymic involution in C57BL/6J x DBA/2J recombinant-inbred mice maps to mouse chromosomes 9 and 10

A comprehensive analysis of initial thymus size and involution rate has not been quantitated for different genetic backgrounds of mice, thus genetic linkage analysis of thymic involution has not been possible. Here, we have used a mathematical method to analyze the age-related decline in thymocyte count in C57BL/6 and DBA/2 mice and have observed that thymic involution could be best fit with a negative exponential curve N(t)=beta(0) x exp(-beta(1)t), where t represents the age (day). This regression model was applied to C57BL/6 x DBA/2 (B x D) recombinant inbred strains of mice to identify the genetic loci influencing age-related thymic involution. There was a dramatic genetic effect of B and D alleles on thymocyte count at young age and the age-related thymic involution rate. The strongest quantitative trait loci (QTL) influencing the rate of thymic involution were mapped to mouse chromosome (Chr) 9 (D9Mit20 at 62 cM) and Chr 10 (D10Mit61 at 32 cM). The strongest QTLs influencing the initial thymocyte count were mapped to ChrX (DXMit324 at 26.5 cM) and Chr 3 (D3Mit127 at 70.3 cM). The present study suggests that the initial thymus size and the rate of thymic involution may be influenced by a relatively small number of genetic loci.     

Genetic regulation of thymic involution

In this review, we have summarized our work using combined complex statistical genetics, bioinformatics, and functional genomics to determine the genetic basis of the age-related thymic involution in C57BL/6J X DBA/2J recombinant inbred mice and the parental B6 and D2 mice. We have shown that these mice provided a valuable genetic model that can permit resampling of thymuses from different aged but genetically identical animals and determination of the relative significance of age-associated changes in the thymus. Our results suggest that the quantitative trait loci (QTL) regulating the Con A-induced thymocyte proliferative response were mapped to mouse chromosome Chr 11 (D11Mit51 at 18 cM), a region that harbors the IL-12b gene. The importance of IL-12b in maintaining thymic integrity and function during the aging process was confirmed by a more rapid involution of the thymus in IL-12b knockout (IL-12b-/-) mice compared to wild-type (WT) mice. Functionally, IL-12 provided a strong synergistic effect to augment the IL-7 or IL-2 induced thymocyte proliferative response, especially in both aged WT and IL-12b-/- mice, but not in normal young mice. In contract to the proliferative response, the age-related decline in the total number of thymocytes was determined at different age, and mapped to loci on Chr 9, 62 cM and Chr 10, 32 cM. Using matrix-assisted laser desorption/ionisation-time of flight-mass spectrometry (MALDI-TOF-MS), increased expression of peroxiredoxin was found to be correlated with thymic involution. Our results suggest the possibility to identify the complex molecular network that can be associated with the regulation of thymic involution in aged mice using a high-dimensional functional genomics approach.     

Genetic heterogeneity of dominantly inherited olivopontocerebellar atrophy (OPCA) in the Japanese: Linkage study of two pedigrees and evidence for the disease locus on chromosome 12q (SCA2)

Summary We did a linkage study of 2 multigenerational pedigrees with dominant olivopontocerebellar atrophy (OPCA) other than SCA1, with chromosome 12q microsatellites. Multipoint linkage analysis led to the conclusion that the disease locus locates within the 6.2 cM interval between IGF1 and D12S84/D12S105. This result coincides with that of Cuban ataxia pedigrees designated as SCA2. Our study provides genetic evidence that dominant OPCA in the Japanese consists of at least two genetically different disorders: SCA1 and SCA2.     

Finer linkage mapping of a primary hip osteoarthritis susceptibility locus on chromosome 6

Primary osteoarthritis (OA) is a common late-onset disease that exhibits complex genetic transmittance. A previous genome-wide linkage scan of OA affected sibling pair families (ascertained by total joint replacement surgery) identified a region of suggestive linkage on chromosome 6, with a maximum multipoint-LOD score (MLS) of 2.9 in 194 families containing sibling pairs concordant for total hip replacement (THR-families). However, up to 50 cM of the chromosome had a multipoint-LOD score >2.0, indicating that the susceptibility locus was poorly mapped. We have now genotyped chromosome 6 to a higher density in an expanded cohort of 378 THR-families. We obtained an MLS of 2.8 to an 11.4 cM interval defined by markers D6S452 and 509-8B2, which map between 70.5 to 81.9 cM from the 6p-telomere. Stratification by gender revealed that this linkage was completely accounted for by female THR-families (n=146), with an MLS of 4.0 and with the highest two-point LOD score being 4.6 for marker D6S1573 (75.9 cM). The 11.4 cM interval just encompasses the candidate gene COL9A1 (81.9 cM). We identified and then genotyped twenty common single nucleotide polymorphisms (SNPs) from within COL9A1 in the 146 probands from our female THR-families and in 215 age-matched female controls. No SNP allele, genotype or haplotype demonstrated association to disease. Overall, we have narrowed the chromosome 6 OA susceptibility locus to a point at which linkage disequilibrium/association analysis is feasible, we have demonstrated that this locus is female specific, and found no evidence that COL9A1 encodes for the susceptibility.     

非综合征性耳聋一家系的基因定位

目的：定位1个一级表亲婚配非综合征性耳聋家系的致病基因，为分离该基因奠定基础。方法：先进行X染色体扫查，排除致病基因位于X染色体的可能；随后采用纯合子定位法，进行候选基因分析和常染色体基因组扫查；再对提示与致病基因紧密连锁的位点所在区域进一步分析，确定致病基因所在区域。结果：确认该家系的非综合征性耳聋为常染色体隐性遗传方式，候选基因分析排除25个已知基因是该家系致病基因的可能，而常染色体扫查提示致病基因位于D17S1293附近，进一步分析将其定位于D17S1850和D17S1818之间5．07cM区域。结论：该家系的致病基因定位于17q11.2-12的D17S1850和D17S1818之间5．07cM区域，是新的常染色体隐性遗传非综合征性耳聋致病基因位点。     

Machado Joseph disease maps to the same region of chromosome 14 as the spinocerebellar ataxia type 3 locus.

Machado Joseph disease (MJD) is an autosomal dominantly inherited neuro-degenerative disorder primarily affecting the motor system. It can be divided into three phenotypes based on the variable combination of a range of clinical symptoms including pyramidal and extra-pyramidal features, cerebellar deficits, and distal muscle atrophy. MJD is thought to be caused by mutation of a single gene which has recently been mapped, using genetic linkage analysis, to a 29 cM region on chromosome 14q24.3-q32 in five Japanese families. A second disorder, spinocerebellar ataxia type 3 (SCA3), which has clinical symptoms similar to MJD, has also been linked to the same region of chromosome 14q in two French families. In order to narrow down the region of chromosome 14 which contains the MJD locus and to determine if this region overlaps with the predisposing locus for SCA3, we have performed genetic linkage analysis in seven MJD families, six of Portuguese/Azorean origin and one of Brazilian origin, using nine microsatellite markers mapped to 14q24.3-q32. Our results localise the MJD locus in these families to an 11 cM interval flanked by the markers D14S68 and AFM343vf1. In addition we show that this 11 cM interval maps within the 15 cM interval containing the SCA3 locus, suggesting that these diseases are allelic.     

Linkage of a new locus for autosomal dominant familial spastic paraplegia to chromosome 2p

Autosomal dominant familial spastic paraplegia (ADFSP) is agenetically heterogeneous neurodegenerative disorder characterizedby a spasticity of the lower limbs. A locus causing AD-FSP (FSP1)has been previously mapped to chromosome 14q. We now reportlinkage of a second AD-FSP locus (FSP2) to chromosome 2p21 –p24 In five of seven French families and one large Dutch pedigree.The analysis of recombination events and multipoint linkageplace FSP2 within a 4 cM interval flanked by loci D2S400 andD2S367.     

Refinement of the RP17 locus for autosomal dominant retinitis pigmentosa, construction of a YAC contig and investigation of the candidate gene retinal fascin

The RP17 locus for autosomal dominant retinitis pigmentosa has previously been mapped to chromosome 17q by linkage analysis. Two unrelated South African families are linked to this locus and the identification of key recombination events assigned the RP17 locus to a 10 cM interval on 17q22. The work reported here refines the mapping of the locus from a 10 cM to a 1 cM interval between the microsatellite markers D17S1604 and D17S948. A physical map of this interval was constructed using information from the Whitehead/MIT YAC contig WC 17.8. Sequence-tagged site (STS) content mapping of seven overlapping YACs from this contig was employed in order to build the map. A BAC library was screened to cover a gap in the YAC contig and two positive BACs were identified. Intragenic polymorphisms in the retinal fascin gene provided evidence for the exclusion of this candidate as the RP17 disease gene.     

A locus for autosomal recessive achromatopsia on human chromosome 8q

Autosomal recessive achromatopsia is a rare disorder characterized by total absent color vision, nystagmus, photophobia, and visual impairment, frequently leading to 'legal blindness'. The primary defect is at the photoreceptor level, with retinal cones being absent or defective. The first locus for this disorder was mapped to chromosome 2q11. Here, we confirm the genetic mapping of a locus discovered in our studies of a kindred with Irish ancestry, but no known consanguinity, in which 5 of 12 children are affected. We have mapped the locus in this disorder in this family to chromosome 8q. Available data now narrow the region containing the putative gene to 1.2 cM.     

DFNB74, a novel autosomal recessive nonsyndromic hearing impairment locus on chromosome 12q14.2-q15

Autosomal recessive nonsyndromic hearing impairment (ARNSHI) segregating in three unrelated, large consanguineous Pakistani families (PKDF528, PKDF859 and PKDF326) is linked to markers on chromosome 12q14.2-q15. This novel locus is designated DFNB74 . Maximum two-point limit of detection (LOD) scores of 5.6, 5.7 and 2.6 were estimated for markers D 12 S 313, D 12 S 83 and D 12 S 75 at θ = 0 for recessive deafness segregating in these three families. Haplotype analyses identified a critical linkage interval of 5.35 cM (5.36 Mb) defined by D 12 S 329 at 74.58 cM and D 12 S 313 at 79.93 cM. DFNB74 is the second ARNSHI locus mapped to chromosome 12, but the physical intervals do not overlap with one another. A locus contributing to the early onset, rapidly progressing hearing loss of A/J mice ( ahl4 , age-related hearing loss 4) was reported to map to chromosome 10 in a region of conserved synteny to DFNB74 , suggesting that ahl4 and DFNB74 may be due to mutations of the same gene in these two species.     

Nonallelism for the audiogenic seizure prone (Asp1) and the aryl hydrocarbon receptor (Ahr) loci in mice

Previous studies showed an association between the Ahr locus on Chr 12 and a major gene, Asp1, that influences susceptibility to audiogenic seizures (AGS) in mice. Although the association was thought to involve close linkage, a pleiotropic effect of the Ahr locus on AGS susceptibility was not excluded. Two congenic strains, D2.B6N-Asp1b and the D2N.B6N-Ahrb1, were used to evaluate further the association between the Ahr and Asp1 loci. Both strains are genetically identical to the AGS susceptible DBA/2 (D2) strain except for a small amount of C57BL/6N (B6N) genome surrounding the Ahr locus and encompassing the Asp1 locus. The AGS susceptibility of both congenic strains is similar and significantly lower than that of the D2 strain. We found that the Ahr/Asp1 critical region encompasses 5.5-7.0 cM from the proximal microsatellite marker D12Mit153 to the distal marker D12Mitl12. The D2N.B6N-Ahrb1 expresses B6 alleles for all markers within the critical region, whereas the D2.B6N-Asp1b expresses the B6 allele only at the Asp1 locus. Furthermore, we determined that the D2.B6N-Asp1b mouse expresses both the D2 phenotype and genotype at the Ahr locus, i.e., zoxazolamine paralysis and T to C and G to A transition mutations in the Ahr cDNA at bp sites 3330 and 3336, respectively. We therefore conclude that the Ahr and Asp1 loci are nonallelic and that the Ahr gene is excluded as a candidate for Asp1.     

A newly identified locus for Usher syndrome type I, USH1E, maps to chromosome 21q21

Usher syndrome (USH) is a clinically and genetically heterogeneous disorder characterized by congenital hearing loss combined with retinitis pigmentosa. This dual sensorineural deficiency is transmitted in an autosomal recessive mode. Usher syndrome type I (USH1) is the most severe form. Four loci responsible for USH1 (USH1A, 1B, 1C and 1D) have previously been mapped, among which only the USH1B gene has been cloned. Using homozygosity mapping in a consanguineous family from Morocco, we identified a novel locus for USH1, USH1E, mapping to chromosome band 21q21. The delimited 15 cM interval is flanked by the loci D21S1905 and D21S1913. Subsequent segregation analysis of two families affected by USH1, in which the A, B, C and D loci had been excluded, also excluded the involvement of the USH1E locus, therefore indicating the existence of at least one more locus for USH1.      

Complex genetic control of host susceptibility to coxsackievirus B3-induced myocarditis

The pathogenesis of viral myocarditis is a multifactorial process involving host genetics, viral genetics and the environment in which they interact. We have used a model of infection with coxsackievirus B3 (CVB3) to characterize the contribution of host genetics to viral myocarditis in mice of different genetic backgrounds but with a common H2 haplotype: A/J and B10.A-H2(a). Here we have used Evans blue dye as a quantitative biomarker for susceptibility to CVB3-induced myocarditis in addition to histopathological semiquantitative measures. We have found evidence of linkage between susceptibility to viral myocarditis and three loci. A locus on chromosome 1 centered on D1Mit200 was linked to sarcolemmal disruption in males (P=0.00005), a second locus on chromosome 4 centered on D4Mit81 was also linked to sarcolemmal disruption in males (P=0.0022). A third locus on distal chromosome 3 centered on D3Mit19 was linked to myocardial infiltration, with a logarithm of odds (LOD) score of 4.7 (P=0.0045), as well as sarcolemmal disruption in females (P=0.0015). These results provide strong evidence for the presence of loci contributing to the susceptibility of mice to viral myocarditis.     

The gene for spinal cerebellar ataxia 1 (SCA1) is flanked by two closely linked highly polymorphic microsatellite loci

The gene for one form of autosomal dominant spinal cerebellarataxia (SCA1), Is mapped by linkage to chromosome 6p, very closeto the microsatellite locus D6S89. Eight large Italian kindredssegregating SCA1, as defined by very close linkage to D6S89,were genotyped with five microsatellite markers linked closelyto D6S89, all mapping within a 6 cM Interval on 6p. Multipointlinkage analysis and haplotypes from recombinants map SCA1 betweentwo of these markers, D6S274, and D6S259, 5 – 6 cM apart.A single rare four marker haplotype within this Interval showslinkage disequilibrium with the disease locus in southern Italyand is transmitted with SCA1 In five kindreds originating fromthis area.     

The rat shorn mutation (shn) maps between D7Got143 and D7Rat94

The recessive shorn (shn) mutation in the rat generates an almost complete absence of normal hair. Previous analysis of 85 backcross rats typed for shn-generated hypotrichosis located this marker between the telomere and D7Mgh1 on distal rat Chromosome 7. Here, we present a microsatellite polymorphism analysis of a 184-member backcross panel-including 99 new rats-that places shn within a 2.7cM interval between markers D7Got143 and D7Rat94. In addition, this analysis has allowed meiotic ordering of 18 microsatellite markers-including 10 D7Got markers previously positioned only by radiation reduced hybrid analysis-across the 16.8cM region between D7Mit16 (Cyp2d4) and D7Rat94. Our inability to meiotically separate shn from 8 microsatellite markers (mapped by others over some 2-4cM or more than 40cR of genetic distance) suggests that the shn mutation may result from a chromosomal rearrangement that suppresses recombination throughout this interval.     

Localizaion of the gene for dominant cystoid macular dystrophy on chromosome 7p

In a family with autosomal dominant cystoid macular dystrophy(DCMD) lInkage was detected with the dinucleotide marker D7S435on the short arm of chromosome 7. With markers flanking D7S435,the DCMD locus could be asigned to the interval D7S493-D7S526at 7p15-p21, which spans approximately 20 cM. Three-points lInkageyIelded a maximal lod score of 9.46 and location score of 43.5and suggested that DCMD is 5, 5 cM proximal to D7S493. Recently,a retinitis plgmentosa (RP7) locus has been mapped in roughlythe same area of chromosome 7. Genetic data of both studiesdescribed below, allow a region of overlap between the locationof the DCMD and the RP7 gene between D7S435 and D7S526. Bothgenes being one and the same will further substantiate the closerelationship between macular degeneration and retinitis pIgmentosa.     

中国人群中家族性精神分裂症与1号染色体的连锁分析

目的 探讨中国人群中家族性精神分裂症易感基因1号染色体的分子遗传学关系。方法 用基因组扫描的方法，选择了平均分布在1号染色体上的29个标记，对32个家族性精神分裂症家系样本进行易感基因扫描。结果 参数连锁分析结果,在隐性模型下，多点连锁在262.52cM位置得到最大异质性Lod分为1．70；非参数连锁分析结果，262.52cM位置处理到最大的多点非参数连锁分为1.71(P=0.046)首次是149.70cM位置处得到多点非参数连锁分为1.37(P=0.086)，分别对应于标记D1S206，D1S425位点的位置。结论 进一步支持在染色体1q上可能存在家族性精神分裂症的易感基因。