Analysis of chromosome 1 microsatellite markers and the FHM2-ATP1A2 gene mutations in migraine pedigrees

OBJECTIVES: The aims of the study were: (i) to extend our linkage analysis of chromosome 1q microsatellite markers in predominantly migraine with aura pedigrees and (ii) to test the novel FHM-2 ATP1A2 gene for involvement in these migraine affected pedigrees and a previous pedigree (MF14) showing evidence of linkage of markers to C1q31. METHODS: A chromosome 1 scan (31 markers) was performed in 21 multiplex pedigrees affected predominantly with migraine with aura (MA). The known FHM-2 ATP1A2 gene mutations were tested, by sequencing, for the involvement in MA and migraine without aura (MO) in these pedigrees. Sequencing was performed in the coding areas of the ATP1A2 gene through three MA individuals from MF14. RESULTS: Evidence for linkage was obtained at C1q23 to markers spanning the ATP1A2 gene. However, testing of the known ATP1A2 gene mutations (for FHM) in common migraine probands of pedigrees showing excess allele sharing was negative. Sequencing of the entire coding areas of the gene through all the three MA affected from MF14 was also negative for mutations. DISCUSSION: Microsatellite markers on chromosome 1q23 show evidence of excess allele sharing in MA and some MO pedigrees, suggesting linkage to the common forms of migraine and the presence of a susceptibility gene in this region. The FHM-2 (ATP1A2 gene) does not seem to be involved in the common types of migraine. Despite certain clinical characteristics, the genetic correlation between FHM and familial typical migraine remains unclear. Several candidate genes lie within the C1q23 and C1q31 cytogenetic regions; therefore, further studies are needed.

Association of the NuMA region on chromosome 11q13 with breast cancer susceptibility

The development of breast cancer is a complex process that involves multiple genes at many stages, from initial cell cycle dysregulation to disease progression. To identify genetic variations that influence this process, we conducted a large-scale association study using a collection of German cases and controls and >25,000 SNPs located within 16,000 genes. One of the loci identified was located on chromosome 11q13 [odds ratio (OR)=1.85, P=0.017]. The initial association was subsequently tested in two independent breast cancer collections. In both sample sets, the frequency of the susceptibility allele was increased in the cases (OR=1.6, P=0.01). The susceptibility allele was also associated with an increase in cancer family history (P=0.1). Fine mapping showed that the region of association extends approximately 300 kb and spans several genes, including the gene encoding the nuclear mitotic apparatus protein (NuMA). A nonsynonymous SNP (A794G) in NuMA was identified that showed a stronger association with breast cancer risk than the initial marker SNP (OR=2.8, P=0.005 initial sample; OR=2.1, P=0.002 combined). NuMA is a cell cycle-related protein essential for normal mitosis that is degraded in early apoptosis. NuMA-retinoic acid receptor alpha fusion proteins have been described in acute promyelocytic leukemia. Although the potential functional relevance of the A794G variation requires further biological validation, we conclude that variations in the NuMA gene are likely responsible for the observed increased breast cancer risk.

A typical migraine susceptibility region localizes to chromosome 1q31

Migraine (with and without aura) is a prevalent neurovascular disease that shows strong familial aggregation, although the number of genes involved and the mode of inheritance is not clear. Some insight into the disease has been gained from genetic studies into a rare and very severe migraine subtype known as familial hemiplegic migraine (FHM). In this study, we took a family-based linkage and association approach to investigate the FHM susceptibility region on chromosome 1q31 for involvement in typical migraine susceptibility in affected Australian pedigrees. Initial multipoint ALLEGRO analysis provided strong evidence for linkage of Chrlq31 markers to typical migraine in a large multigenerational pedigree. The 1-LOD* unit support interval for suggestive linkage spanned approximately 18 cM with a maximum allele sharing LOD* score of 3.36 obtained for marker D1S2782 (P=0.00004). Subsequent analysis of an independent sample of 82 affected pedigrees added support to the initial findings with a maximum LOD* of 1.24 (P=0.008). Utilising the independent sample of 82 pedigrees, we also performed a family-based association test. Results of this analysis indicated distortion of allele transmission at marker D1S249 [global chi2 (5) of 15.00, P=0.010] in these pedigrees. These positive linkage and association results will need further confirmation by independent researchers. However, overall they provide good evidence for the existence of a typical migraine locus near these markers on Chrlq3l, and reinforce the idea that an FHM gene in this genomic region may also contribute to susceptibility to the more common forms of migraine.

Chromosome 17 and the inducible nitric oxide synthase gene in human essential hypertension

Essential hypertension is a common multifactorial trait that results in a significantly increased risk for heart attack and stroke. The condition has a genetic basis, although at present the number of genes is unknown. In order to identify such genes, we are utilising a linkage scanning approach using microsatellite markers and affected sibships. Here we provide evidence for the location of at least one hypertension susceptibility locus on chromosome 17. Analysis of 177 affected sibpairs gave evidence for significant excess allele sharing to D17S949 (SPLINK: P=0.0029; MAPMAKER SIBS: P=0.0033; ASPEX: P=0.0061; GENEHUNTER: P=0.0096; ANALYZE (SIBPAIR): P=0.0025) on 17q22–24, with significant allele sharing also indicated for an additional marker, D17S799 (SPLINK: P=0.025; MAPMAKER SIBS: P= 0.025) located close to the centromere. Since these two genomic regions are well separated, our results indicate that there may be more than one chromosome 17 locus affecting human blood pressure. Moreover, further investigation of this chromosome, utilizing a polymorphism within the promoter of the iNOS candidate gene, NOS2A, revealed both increased allele sharing among sibpairs (SPLINK: P=0.02; ASPEX: P=0.00004) and positive association (P= 0.034) of NOS2A to essential hypertension. Hence these results indicate that chromosome 17 and, more specifically, the NOS2A gene may play a role in human essential hypertension.

The B subunit of coagulation factor XIII is linked to renin and the Duffy blood group to α-spectrin on human chromosome 1

Family linkage studies were used to detect two linkage relationships on human chromosome 1. The B subunit of coagulation factor XIII showed significant linkage to renin with a maximum lod score of 5.071 at a distance of 10 cM. Significant linkage was also shown between the Duffy blood group and α-spectrin with linkage results giving a combined lod score of 3.194 at 5 cM.

Chromosome I linkage studies in Charcot-Marie-Tooth neuropathy type I

Charcot-Marie-Tooth neuropathy type 1 (CMT1) is an autosomal dominant disorder of peripheral nerve. The gene for CMT1 was originally localized to chromosome 1 by linkage to the Duffy blood group, but it has since been shown that not all CMT1 pedigrees show this linkage. We report here the results of linkage studies using five chromosome 1 markers - Duffy (Fy), antithrombin III (AT3), renin (REN), β-nerve growth factor (NGFB), and salivary amylase (AMY1) - in 16 CMT1 pedigrees. The total lod scores exclude close linkage of CMT1 to any of these markers. However, individual families show probable linkage of CMT1 to Duffy, AT3, and/or AMY1. No linkage was indicated with REN or NGFB. These results indicate that possible location of a CMT1 gene between the AMY1 and AT3 loci at p21 and q23, respectively, on chromosome 1 and support the theory that there is at least one other CMT1 gene.

Isolation and use of chromosome 1 probes for linkage studies on Charcot-Marie-Tooth disease

Nine probes were isolated from a human chromosome 1 enriched library and mapped to regions of chromosome 1 using somatic cell hybrid lines. One clone, LR67, which mapped 1q12→q23 detected a BglI RFLP. This probe, as well as 4 other known chromosome 1 markers, α-spectrin, Factor XIIIB, DR10 and DR78, were used for linkage studies in 15 Charcot-Marie-Tooth disease (CMT1) families. Close linking of CMT1 to any of the 5 markers was not indicated. Total lod scores excluded linkage of CMT1 to LR67 and to DR10 at 5 cM or less, to DR78 and 10 cM or less, α-spectrin at 15 cM or less and Factor XIIIB at 20 cM or less. Possible linkage, however, was shown between LR67 and CMT1 at a distance of 30 cM. Also linkage at a distance of 5 cM was detected between this probe and α-spectrin.

A locus on the long arm of chromosome 1 as a possible cause of essential hypertension

None of the genes responsible for essential hypertension has been identified. Recent work in genetically hypertensive rats has shown linkage of blood pressure with alleles of the renin gene. Since the renin gene is a member of a conserved synteny group that in humans spans chromosome 1q21.3-32.3 and includes the gene for antithrombin III (AT3), we used linkage studies to examine the relationship between alleles of AT3 and hypertension in a family having 10 affected members. From the lod score obtained at a recombination fraction of zero the odds for linkage of AT3 and hypertension in this family were calculated as 6:1 in favour of linkage. This result provides grounds for further examination of the possible role of the 1q23 locus in the aetiology of essential hypertension.

Familial typical migraine: Linkage to chromosome 19p13 and evidence for genetic heterogeneity

Migraine is a frequent familial disorder that, in common with most multifactorial disorders, has an unknown etiology. The authors identified several families with multiple individuals affected by typical migraine using a single set of diagnostic criteria and studied these families for cosegregation between the disorder and markers on chromosome 19, the location of a mutation that causes a rare form of familial hemiplegic migraine (FHM). One large tested family showed both cosegregation and significant allele sharing for markers situated within or adjacent to the FHM locus. Multipoint GENEHUNTER results indicated significant excess allele sharing across a 12.6- cM region containing the FHM Ca2+ channel gene, CACNL1A4 (maximum nonparametric linkage Z score = 6.64, p = 0.0026), with a maximum parametric lod score of 1.92 obtained for a (CAG)(n) triplet repeat polymorphism situated in exon 47 of this gene. The CAG expansion did not, however, appear to be the cause of migraine in this pedigree. Other tested families showed neither cosegregation nor excess allele sharing to chromosome 19 markers. HOMOG analysis indicated heterogeneity, generating a maximum HLOD score of 3.6. It was concluded that Chr19 mutations either in the CACNL1A4 gene or a closely linked gene are implicated in some pedigrees with familial typical migraine, and that the disorder is genetically heterogeneous.

Sibpair studies implicate chromosome 18 in essential hypertension

Interest in chromosome 18 in essential hypertension comes from comparative mapping of rat blood pressure quantitative trait loci (QTL), familial orthostatic hypotensive syndrome studies, and essential hypertension pedigree linkage analyses indicating that a locus or loci on human chromosome 18 may play a role in hypertension development. To further investigate involvement of chromosome 18 in human essential hypertension, the present study utilized a linkage scan approach to genotype twelve microsatellite markers spanning human chromosome 18 in 177 Australian Caucasian hypertensive (HT) sibling pairs. Linkage analysis showed significant excess allele sharing of the D18S61 marker when analyzed with SPLINK (P=0.00012), ANALYZE (Sibpair) (P=0.0081), and also with MAPMAKER SIBS (P=0.0001). Similarly, the D18S59 marker also showed evidence for excess allele sharing when analyzed with SPLINK (P=0.016), ANALYZE (Sibpair) (P=0.0095), and with MAPMAKER SIBS (P = 0.014). The adenylate cyclase activating polypeptide 1 gene (ADCYAP1) is involved in vasodilation and has been co-localized to the D18S59 marker. Results testing a microsatellite marker in the 3′ untranslated region of ADCYAP1 in age and gender matched HT and normotensive (NT) individuals showed possible association with hypertension (P = 0.038; Monte Carlo P = 0.02), but not with obesity. The present study shows a chromosome 18 role in essential hypertension and indicates that the genomic region near the ADCYAP1 gene or perhaps the gene itself may be implicated. Further investigation is required to conclusively determine the extent to which ADCYAP1 polymorphisms are involved in essential hypertension. © 2003 Wiley-Liss, Inc.

Understanding chromosome disorders and their implications for special educators

More children are now being diagnosed with chromosome abnormalities. Some chromosome disorder syndromes are relatively well known; while others are so rare that there is only limited evidence about their likely impact on learning and development. For educators, a basic level of knowledge about chromosome abnormalities is important for understanding the literature and communicating with families and professionals. This paper describes chromosomes, and the numerical and structural anomalies that can occur, usually spontaneously during early cell division. Distinctive features of various chromosome syndromes are summarised before a discussion of the rare chromosome disorders that are labelled, not with a syndrome name, but simply by a description of the chromosome number, size and shape. Because of the potential within-group variability that characterises syndromes, and the scarcity of literature about the rare chromosome disorders, expectations for learning and development of individual students need to be based on the range of possible outcomes that may be achievable.

Deamplification of pfmdr1-Containing Amplicon on Chromosome 5 in Plasmodium falciparum Is Associated with Reduced Resistance to Artelinic Acid In Vitro

Amplification of the Plasmodium falciparum multidrug resistance 1 gene (pfmdr1) has been implicated in multidrug resistance, including in vitro resistance to artelinic acid (AL). The stability and fitness of having multiple copies of pfmdr1 are important factors due to their potential effects on the resistance phenotype of parasites. These factors were investigated by using an AL-resistant line of P. falciparum (W2AL80) and clones originating from W2AL80. A rapid reduction in pfmdr1 copy number (CN) was observed in the uncloned W2AL80 line; 63% of this population reverted to a CN of <3 without exposure to the drug. Deamplification of the pfmdr1 amplicon was then determined in three clones, each initially containing three copies of pfmdr1. Interestingly, two outcomes were observed during 3 months without drug pressure. In one clone, parasites with fewer than 3 copies of pfmdr1 emerged rapidly. In two other clones, the reversion was significantly delayed. In all subclones, the reduction in pfmdr1 CN involved the deamplification of the entire amplicon (19 genes). Importantly, deamplification of the pfmdr1 amplicon resulted in partial reversal of resistance to AL and increased susceptibility to mefloquine. These results demonstrate that multiple copies of the pfmdr1-containing amplicon in AL-resistant parasites are unstable when drug pressure is withdrawn and have practical implications for the maintenance and spread of parasites resistant to artemisinin derivatives.