Genome scan for linkage to Gilles de la Tourette syndrome

Gilles de la Tourette Syndrome (TS) is a neuropsychiatric disorder characterized by both motor and vocal tics. Despite clear evidence for a genetic predisposition to TS from family, twin, and adoption studies, there have been no confirmed linkage findings. In this article we test for linkage to TS in multigenerational families segregating TS using a panel of 386 markers with the largest interval between any two markers being 28 cM and an average distance between markers of 10 cM. We tested for linkage using an autosomal dominant model with reduced penetrance and using nonparametric methods. No significant evidence for linkage was found with parametric analysis. A logarithm of the odds (LOD) score of greater or equal to one under the autosomal dominant model was observed in 24 of these markers in at least one of the families tested. No LOD scores greater than two were observed with any of the markers. For the nonparametric analysis, eight markers were observed with a P-value less than 0.00005 for significance evidence of linkage in at least one family. However caution should be used in the interpretation of the nonparametric analyses as this statistic (the affected-pedigree-member method) is know to have a high false-positive rate. Further support for linkage in these regions is required before linkage can be assumed. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:437–445, 1999. © 1999 Wiley-Liss, Inc.     

Fine mapping of a schizophrenia susceptibility locus at chromosome 6q23: increased evidence for linkage and reduced linkage interval

We previously reported an autosomal scan for schizophrenia susceptibility loci in a systematically recruited sample of Arab Israeli families. The scan detected significant evidence for linkage at chromosome 6q23 with a nonparametric LOD score (NPL) of 4.60 (P=0.000004) and a multipoint parametric LOD score of 4.16. In order to refine this finding we typed 42 additional microsatellite markers on chromosome 6q between D6S1570 (99.01 cM from the pter) and D6S281 (190.14 from the pter) in the same sample (average intermarker distance approximately 1.7 cM). In the 23 cM region between D6S1715 and D6S311, markers were more closely spaced ( approximately 1.1 cM). Multipoint nonparametric and parametric and single point linkage analyses were performed. The peak NPL rose to 4.98 (P=0.00000058) at D6S1626 (136.97 cM), immediately adjacent to D6S292 (NPL 4.98, P=0.00000068), the marker that gave the highest NPL in the original genome scan, under the broad diagnostic category. The putative susceptibility region (NPL-1) was reduced from 12.0 to 4.96 cM. The peak multipoint parametric LOD score was 4.63 at D6S1626 under a dominant genetic model, core diagnostic category and the LOD-1 interval was 2.10 cM. The maximum single point LOD score (3.55, theta=0.01) was also at D6S1626 (dominant model, core diagnostic category). Increased evidence for linkage in the same sample as in the original genome scan and consistent localization of the linkage peak add further support for the presence of a schizophrenia susceptibility locus at chromosome 6q23. Moreover, the markedly reduced linkage interval greatly improves prospects for identifying a schizophrenia susceptibility gene within the implicated region.     

Genome-wide linkage scan for spontaneous DZ twinning

In humans, spontaneous DZ twinning is known to have a genetic basis. A prior investigation in the Flemish and Dutch population showed that the phenotype of 'having DZ twins' was consistent with an autosomal monogenic dominant model, with a gene frequency of 3.5% and a female-specific lifetime penetrance of 10%. Recessive, X-linked, polygenic and sporadic models were rejected. This study reports on a genome-wide scan of 14 Flemish families containing 57 mothers of spontaneous DZ twins. Two-point linkage analysis using the autosomal dominant model showed nine chromosomal regions with a LOD score around 1. After multipoint linkage analysis, including heterogeneity, three chromosomes continued to give high LOD scores. These regions were further haplotyped with additional markers at 1 cM distance. The multipoint analysis was not in favour of linkage of the DZ twinning trait in most candidate genes and other regions (LOD score < -2) under the genetic model of autosomal dominance. To further evaluate the evidence for linkage given some uncertainty about the correct mode of inheritance of twinning susceptibility other models of inheritance were tested. Results of this analysis showed all models gave highest LOD scores under dominant models. If heterogeneity among the families is taken into account, the peaks that were observed on chromosome 2, 7 and 18 could well contain a potential gene contributing to DZ twinning. These results give suggestive evidence that the mode of inheritance of DZ twinning is probably more complex than was originally expected.     

Genome-wide linkage analysis of families with obsessive-compulsive disorder ascertained through pediatric probands

The goal of this study was to identify chromosomal regions likely to contain susceptibility alleles for early-onset obsessive-compulsive disorder (OCD). A genome scan was done in 56 individuals from seven families ascertained through pediatric OCD probands; 27 of the 56 subjects had a lifetime diagnosis of definite OCD. Denser mapping of regions on chromosomes 2, 9, and 16 was subsequently done with those subjects and ten additional subjects from the largest family in the study. Direct interviews were completed with 65 of the 66 genotyped individuals. Relatives were interviewed blind to proband status. Of the 65 interviewed individuals, 32 had a lifetime diagnosis of definite OCD. Three of the seven probands had a history of Tourette disorder. Two of the 25 relatives with OCD had a tic history, whereas none of the 33 relatives without OCD had tics. The genome scan consisted of 349 microsatellite markers with an average between-marker distance of 11.3 centiMorgan (cM). Fine mapping was done with 24 additional markers at an average spacing of 1.6 cM. Parametric and nonparametric linkage analyses were conducted using GENEHUNTER(+). The maximum multipoint LOD score with a dominant model was 2.25 on 9p. However, with fine mapping and additional subjects, that LOD score decreased to 1.97. The maximum multipoint nonparametric LOD* score was 1.73 on 19q. The maximum multipoint LOD score with a recessive model was 1.40 on 6p. The results provide suggestive evidence for linkage on 9p and identify regions requiring further study with much larger samples.     

Genome‐wide linkage analysis of families with obsessive‐compulsive disorder ascertained through pediatric probands

The goal of this study was to identify chromosomal regions likely to contain susceptibility alleles for early‐onset obsessive‐compulsive disorder (OCD). A genome scan was done in 56 individuals from seven families ascertained through pediatric OCD probands; 27 of the 56 subjects had a lifetime diagnosis of definite OCD. Denser mapping of regions on chromosomes 2, 9, and 16 was subsequently done with those subjects and ten additional subjects from the largest family in the study. Direct interviews were completed with 65 of the 66 genotyped individuals. Relatives were interviewed blind to proband status. Of the 65 interviewed individuals, 32 had a lifetime diagnosis of definite OCD. Three of the seven probands had a history of Tourette disorder. Two of the 25 relatives with OCD had a tic history, whereas none of the 33 relatives without OCD had tics. The genome scan consisted of 349 microsatellite markers with an average between‐marker distance of 11.3 centiMorgan (cM). Fine mapping was done with 24 additional markers at an average spacing of 1.6 cM. Parametric and nonparametric linkage analyses were conducted using GENEHUNTER⁺. The maximum multipoint LOD score with a dominant model was 2.25 on 9p. However, with fine mapping and additional subjects, that LOD score decreased to 1.97. The maximum multipoint nonparametric LOD* score was 1.73 on 19q. The maximum multipoint LOD score with a recessive model was 1.40 on 6p. The results provide suggestive evidence for linkage on 9p and identify regions requiring further study with much larger samples. © 2002 Wiley‐Liss, Inc.     

Hereditary lymphedema: evidence for linkage and genetic heterogeneity

Hereditary or primary lymphedema is a developmental disorder of the lymphatic system which leads to a disabling and disfiguring swelling of the extremities. Hereditary lymphedema generally shows an autosomal dominant pattern of inheritance with reduced penetrance, variable expression and variable age at onset. Three multigeneration families demonstrating the phenotype of hereditary lymphedema segregating as an autosomal dominant trait with incomplete penetrance were genotyped for 366 autosomal markers. Linkage analysis yielded a two-point LOD score of 6.1 at straight theta = 0. 0 for marker D5S1354 and a maximum multipoint LOD score of 8.8 at marker D5S1354 located at chromosome 5q34-q35. Linkage analysis in two additional families using markers from the linked region showed one family consistent for linkage to distal chromosome 5. In the second family, linkage to 5q was excluded for all markers in the region with LOD scores Z < -2.0. The vascular endothelial growth factor C receptor ( FLT4 ) was mapped to the linked region, and partial sequence analysis identified a G-->A transition at nucleotide position 3360 of the FLT4 cDNA, predicting a leucine for proline substitution at residue 1126 of the mature receptor in one nuclear family. This study localizes a gene for primary lymphedema to distal chromosome 5q, identifies a plausible candidate gene in the linked region, and provides evidence for a second, unlinked locus for primary lymphedema.      

Fine mapping of a multiple sclerosis locus to 2.5 Mb on chromosome 17q22-q24

Genome-wide linkage analyses performed in a Finnish study sample have identified four potential predisposing loci for multiple sclerosis (MS). Here we made an effort to restrict the wide linkage region on chromosome 17 with a dense set of 31 markers using multipoint linkage analyses and monitoring for shared marker alleles in MS chromosomes. We carried out the linkage analyses in 22 Finnish multiplex MS families originating from a regional subisolate that shows an exceptionally high prevalence of MS in order to minimize the genetic and environmental heterogeneity of the study sample. Thirty markers on the 23 cM initial interval gave positive pairwise LOD scores. We monitored for shared haplotypes among affected family members within a family, and identified an approximately 4 cM region flanked by the markers D17S1792 and ATA43A10 in 17 out of the 22 families (77.3%). The multipoint linkage analyses using Genehunter and SIMWALK 2.40 provided further evidence for the same 4 cM region, for example a maximal multipoint NPL score of 5.98 (P<0.0002). We observed nominal evidence for association to MS, with one marker flanking the shared region, and this association was replicated in the additional set of families. Using the combined power of linkage, association and shared haplotype analyses, we were thus able to restrict the MS locus on chromosome 17q from 23 cM to a 4 cM region covering a physical interval of approximately 2.5 Mb. Thus, this study describes the restriction of an MS locus outside the HLA region into a segment approachable by molecular tools.     

Dyschromatosis universalis hereditaria: evidence for autosomal recessive inheritance and identification of a new locus on chromosome 12q21-q23

Dyschromatosis universalis hereditaria (DUH) and dyschromatosis symmetrica hereditaria (DSH) are pigmentary dermatoses most commonly seen in Japan. Both disorders usually show autosomal dominant inheritance, although in some cases autosomal recessive inheritance was reported. DSH was mapped to chromosome 1q21.3, and mutations in the gene ADAR ( DSRAD ) were identified in Japanese, Chinese and Taiwanese families with autosomal dominant DSH. A second locus for dyschromatosis was mapped on chromosome 6q24.2-q25.2 in two Chinese families initially reported to be affected with DSH, but later suggested to have autosomal dominant DUH. The aim of this study was to investigate whether one of these two loci is involved in the development of DUH in a consanguineous Bedouin family from Saudi Arabia with four affected and three unaffected sibs, clearly pointing to autosomal recessive inheritance. After excluding mutations in ADAR and linkage to the candidate regions on chromosomes 1 and 6, we performed an single nucleotide polymorphism-based genome-wide scan for linkage with other loci. Under the assumption of autosomal recessive inheritance, we have identified a new locus for dyschromatosis on chromosome 12q21-q23 in this Arab family with a maximum logarithm of the odds (LOD) score of 3.4, spanning a distance of 18.9 cM. Our study revealed the first locus for autosomal recessive DUH and supports recent evidence that DSH and DUH are genetically distinct disorders.     

Assignment of a gene locus involved in craniosynostosis to chromosome 5qter

Craniosynostosis, the abnormal development of the calvarialsutures, occurs as an autosomal dominant trait in many clinicallydistinct syndromes. We performed linkage analysis of a provisionallynovel type of autosomal dominant craniosynostosis in a largethree generational family. Linkage was established between thecraniosynostotic locus and D5S211, a locus defined by the shorttandem repeat polymorphism (STRP) marker Mfd 154 in distal 5q.The maximum LOD score, Z_max, was 4.8 at a recombination fractionof zero. No significant linkage was found with markers located30 cM and more proximal to D5S211. The findings assign the craniosynostoticlocus in this family to a telomeric region in the long arm ofchromosome 5. Linkage analysis with Mfd 154 in other autosomaldominant craniosynostotic syndromes should reveal whether thesedisorders are caused by mutations of genes at the same or atdifferent loci.     

A genome-wide linkage scan for iron phenotype quantitative trait loci: the HEIRS Family Study

Iron overload phenotypes in persons with and without hemochromatosis are variable. To investigate this further, probands with hemochromatosis or evidence of elevated iron stores and their family members were recruited for a genome-wide linkage scan to identify potential quantitative trait loci (QTL) that contribute to variation in transferrin saturation (TS), unsaturated iron-binding capacity (UIBC), and serum ferritin (SF). Genotyping utilized 402 microsatellite markers with average spacing of 9 cM. A total of 943 individuals, 64% Caucasian, were evaluated from 174 families. After adjusting for age, gender, and race/ethnicity, there was evidence for linkage of UIBC to chromosome 4q logarithm of the odds (LOD) = 2.08, p = 0.001) and of UIBC (LOD = 9.52), TS (LOD = 4.78), and SF (LOD = 2.75) to the chromosome 6p region containing HFE (each p < 0.0001). After adjustments for HFE genotype and other covariates, there was evidence of linkage of SF to chromosome 16p (LOD = 2.63, p = 0.0007) and of UIBC to chromosome 5q (LOD = 2.12, p = 0.002) and to chromosome 17q (LOD = 2.19, p = 0.002). We conclude that these regions should be considered for fine mapping studies to identify QTL that contribute to variation in SF and UIBC.     

Genomewide linkage scan in a multigeneration Caucasian pedigree identifies a novel locus for keratoconus on chromosome 5q14.3-q21.1.

PURPOSE: Keratoconus is a corneal dystrophy with an incidence of 1 in 2000 and a leading cause for cornea transplantation in Western developed countries. Both clinical observations and segregation analyses suggest a major role for genes in its pathogenesis. It is genetically heterogeneous, most commonly sporadic, but inherited patterns with recessive or dominant modes have also been reported. We studied a four-generation autosomal-dominant pedigree to identify disease loci for keratoconus. METHODS: A two-stage genome-wide scan was applied to 27 family members. First linkage analysis was performed with 343 microsatellite markers along the 22 autosomal chromosomes at approximately 10 cM density. This was followed by fine mapping at approximately 2 cM density, in regions suggestive of linkage. Multipoint linkage analysis was performed using GeneHunter2. RESULTS: Evidence of suggestive linkage from the initial scan was observed at the 82 to 112 cM region of chromosome 5q14.1-q21.3 with a maximum lod score (LOD) of 3.48 (penetrance = 0.5). Fine mapping by testing an additional 11 microsatellite markers at 1 to 3 cM intervals revealed a narrower and higher peak (99-119 cM) with LOD 3.53. By analysis of the recombination of haplotypes, the putative locus of keratoconus was further narrowed to a 6 cM region (8.2 Mbp physical distance) between markers D5S2499 and D5S495. CONCLUSION: These results indicate a promising new locus for keratoconus in this pedigree. Because of the heterogeneous nature of keratoconus, this locus may be specific to familial autosomal-dominant keratoconus. Nevertheless, the identification of this locus may provide new insights into the pathogenesis of keratoconus.     

A genome-wide scan for coronary heart disease suggests in Indo-Mauritians a susceptibility locus on chromosome 16p13 and replicates linkage with the metabolic syndrome on 3q27.

Prevalence of coronary heart disease (CHD), of type 2 diabetes (T2DM) and of the metabolic syndrome are in Mauritius amongst the highest in the world. As T2DM and CHD are closely associated and have both a polygenic basis, we conducted a 10 cM genome scan with 403 microsatellite markers in 99 independent families of North-Eastern Indian origin including 535 individuals. Families were ascertained through a proband with CHD before 52 years of age and additional sibs with myocardial infarction (MI) or T2DM. Model-free two-point and multipoint linkage analysis were performed using the Mapmarker-Sibs (MLS) and maximum-likelihood-binomial (MLB) programs for autosomal markers and the Aspex program for chromosome X markers. In a second step, additional markers were studied to increase the genetic map density in three regions on chromosomes 3, 8 and 16 where initial indication for linkage was found. Our data show suggestive linkage with CHD on chromosome 16p13-pter with the MLS statistics at 8.69 cM (LOD = 3.06, P = 0.00017) which partially overlaps with a high pressure (HBP) peak. At the same locus, a nominal indication for linkage with T2DM was found in 35 large T2DM Pondicherian families also having Indian origin. With respect to region 8q23, we found suggestive linkage with T2DM (LOD = 2.55, P = 0.00058) as well as with HBP. On 3q27, we replicated previous indication for linkage found in Caucasians (for the metabolic syndrome and for diabetes) according to the categorized trait for CHD and MI with the MLB statistics (LOD = 2.13, P = 0.0009). The genome scan also revealed nominal evidence of linkage with CHD on 10q23 (LOD = 2.06, P = 0.00188). Interestingly, we detected in the same region overlapping linkages with three QTLs: age of onset of CHD (LOD = 2.03), HDL cholesterol (LOD = 1.48) and LDL/HDL ratio (LOD = 1.34). Ordered-subset analysis based on family body mass index ranking replicated finding on 2q37 for T2DM (at Calpain 10 locus). These results show the first evidence for susceptibility loci that predispose to CHD, T2DM and HBP in the context of the metabolic syndrome.     

Nonparametric simulation-based statistical analyses for bipolar affective disorder locus on chromosome 21q22.3

Straub et al. [1994: Nat Genet 8:291-296] reported a candidate bipolar affective disorder (BAD) locus on chromosome 21q22.3. As a replication study, we analyzed 12 Australian BAD pedigrees for the presence of excess allele sharing and cosegregation with the putative chromosome 21q22.3 BAD locus, using six microsatellite markers. The nonparametric simulation-based statistic SimAPM produced positive results for the marker PFKL (P < 0.001) and D21S198 (P = 0.007). PFKL also demonstrated linkage (P < 0.001) when analyzed using the more conservative statistic, SimIBD. Comparable results were obtained when using the original APM statistic (P = 0.02 for D21S198). However, other nonparametric analyses such as GENEHUNTER and model-free linkage (MFLINK) analysis did not yield significant results. Combined LOD scores for the 12 families were strongly negative for all six markers under six genetic models. Two-point and multipoint analyses of individual families revealed one family, family 17, with maximal LOD scores greater than 1.41 for the 10.5-cM region between PFKL and D21S198. This report provides additional support for the suggestive linkage of a susceptibility locus for BAD on chromosome 21q22.3.     

Linkage to chromosome 11p12 in two Maltese families with a highly penetrant form of osteoporosis

Osteoporosis is a metabolic bone disease with a strong genetic component. Family-based linkage studies were performed by a number of investigators to try to identify loci that might contain genes responsible for an increased susceptibility to osteoporosis. A whole-genome linkage scan using 400 microsatellite markers was performed in 27 members from two Maltese families with a highly penetrant form of osteoporosis. The phenotype was defined by lumbar and femoral z-scores calculated after measurement of bone mineral density by DEXA. Both males and females were among the affected individuals. Multipoint parametric and non-parametric linkage analyses were performed by EasyLinkage v4.01 using GENEHUNTER v2.1, assuming dominant and recessive modes of inheritance with variable penetrance. Evidence of linkage was observed to a marker at 11p12 where a non-parametric LOD score of 5.77 (P=0.0006) was obtained. A maximum heterogeneity LOD score of 2.55 for this region was obtained for the dominant mode of inheritance with 90% penetrance and a phenocopy rate of 1%. Following fine mapping, the critical interval was narrowed to a region that is 52.94 cM from 11p-telomere. In this region, the gene for tumour necrosis factor receptor-associated factor 6 (TRAF6) is located approximately 1 cM away from the indicated marker. Sequencing of the promoter region and exons of the TRAF6 gene revealed three sequence variants, one of which was found in three affected members within one family.     

Follow-up study on a susceptibility locus for schizophrenia on chromosome 6q.

Evidence for suggestive linkage to schizophrenia with chromosome 6q markers was previously reported from a two-stage approach. Using nonparametric affected sib pairs (ASP) methods, nominal p-values of 0.00018 and 0.00095 were obtained in the screening (81 ASPs; 63 independent) and the replication (109 ASPs; 87 independent) data sets, respectively. Here, we report a follow-up study of this 50cM 6q region using 12 microsatellite markers to test for linkage to schizophrenia. We increased the replication sample size by adding an independent sample of 43 multiplex pedigrees (66 ASPs; 54 independent). Pairwise and multipoint nonparametric linkage analyses conducted in this third data set showed evidence consistent with excess sharing in this 6q region, though the statistical level is weaker (p=0.013). When combining both replication data sets (total of 141 independent ASPs), an overall nominal p-value=0.000014 (LOD=3. 82) was obtained. The sibling recurrence risk (lambdas) attributed to this putative 6q susceptibility locus is estimated to be 1.92. The linkage region could not be narrowed down since LOD score values greater than three were observed within a 13cM region. The length of this region was only slightly reduced (12cM) when using the total sample of independent ASPs (204) obtained from all three data sets. This suggests that very large sample sizes may be needed to narrow down this region by ASP linkage methods. Study of the etiological candidate genes in this region is ongoing.     

A genome wide linkage search for breast cancer susceptibility genes

Mutations in known breast cancer susceptibility genes account for a minority of the familial aggregation of the disease. To search for further breast cancer susceptibility genes, we performed a combined analysis of four genome-wide linkage screens, which included a total of 149 multiple case breast cancer families. All families included at least three cases of breast cancer diagnosed below age 60 years, at least one of whom had been tested and found not to carry a BRCA1 or BRCA2 mutation. Evidence for linkage was assessed using parametric linkage analysis, assuming both a dominant and a recessive mode of inheritance, and using nonparametric methods. The highest LOD score obtained in any analysis of the combined data was 1.80 under the dominant model, in a region on chromosome 4 close to marker D4S392. Three further LOD scores over 1 were identified in the parametric analyses and two in the nonparametric analyses. A maximum LOD score of 2.40 was found on chromosome arm 2p in families with four or more cases of breast cancer diagnosed below age 50 years. The number of linkage peaks did not differ from the number expected by chance. These results suggest regions that may harbor novel breast cancer susceptibility genes. They also indicate that no single gene is likely to account for a large fraction of the familial aggregation of breast cancer that is not due to mutations in BRCA1 or BRCA2.     

Genome-wide scanning for linkage in Finnish breast cancer families

Only a proportion of breast cancer families has germline mutations in the BRCA1 or BRCA2 genes, suggesting the presence of additional susceptibility genes. Finding such genes by linkage analysis has turned out to be difficult due to the genetic heterogeneity of the disease, phenocopies and incomplete penetrance of the mutations. Isolated populations may be helpful in reducing the level of genetic heterogeneity and in providing useful starting points for further genetic analyses. Here, we report results from a genome-wide linkage analysis of 14 high-risk breast cancer families from Finland. These families tested negative for BRCA1 and BRCA2 germline mutations and showed no linkage to the 13q21 region, recently proposed as an additional susceptibility locus. Suggestive linkage was seen at marker D2S364 (2q32) with a parametric two-point LOD score of 1.61 (theta=0), and an LOD score of 2.49 in nonparametric analyses. Additional genotyping of a 40 cM chromosomal region surrounding the region of interest yielded a maximum parametric two-point LOD score of 1.80 (theta=0) at D2S2262 and a nonparametric LOD score of 3.11 at an adjacent novel marker 11291M1 in BAC RP11-67G7. A nonparametric multipoint LOD score of 3.20 was seen at 11291M1 under the assumption of dominant inheritance. While not providing proof of linkage considering the small number of families and large number of laboratory and statistical analyses performed, these results warrant further studies of the 2q32 chromosomal region as a candidate breast cancer susceptibility locus. Both linkage and association studies are likely to be useful, particularly in other isolated populations.     

Evidence for a susceptibility locus on chromosome 6q influencing phonological coding dyslexia

A linkage study of 96 dyslexia families containing at least two affected siblings (totaling 877 individuals) has found evidence for a dyslexia susceptibility gene on chromosome 6q11.2-q12 (assigned the name DYX4). Using a qualitative phonological coding dyslexia (PCD) phenotype (affected, unaffected, or uncertain diagnoses), two-point parametric analyses found highly suggestive evidence for linkage between PCD and markers D6S254, D6S965, D6S280, and D6S251 (LOD(max) scores = 2.4 to 2.8) across an 11 cM region. Multipoint parametric analysis supported linkage of PCD to this region (peak HLOD = 1.6), as did multipoint nonparametric linkage analysis (P = 0.012). Quantitative trait linkage analyses of four reading measures (phonological awareness, phonological coding, spelling, and rapid automatized naming speed) also provided evidence for a dyslexia susceptibility locus on chromosome 6q. Using a variance-component approach, analysis of phonological coding and spelling measures resulted in peak LOD scores at D6S965 of 2.1 and 3.3, respectively, under 2 degrees of freedom. Furthermore, multipoint nonparametric quantitative trait sibpair analyses suggested linkage between the 6q region and phonological awareness, phonological coding, and spelling (P = 0.018, 0.017, 0.0005, respectively, for unweighted sibpairs < 18 years of age). Although conventional significance thresholds were not reached in the linkage analyses, the chromosome 6q11.2-q12 region clearly warrants investigation in other dyslexia family samples to attempt replication and confirmation of a dyslexia susceptibility gene in this region.     

Full genome screen for Alzheimer disease: Stage II analysis*

We performed a two‐stage genome screen to search for novel risk factors for late‐onset Alzheimer disease (AD). The first stage involved genotyping 292 affected sibling pairs using 237 markers spaced at approximately 20 cM intervals throughout the genome. In the second stage, we genotyped 451 affected sibling pairs (ASPs) with an additional 91 markers, in the 16 regions where the multipoint LOD score was greater than 1 in stage I. Ten regions maintained LOD scores in excess of 1 in stage II, on chromosomes 1 (peak B), 5, 6, 9 (peaks A and B), 10, 12, 19, 21, and X. Our strongest evidence for linkage was on chromosome 10, where we obtained a peak multipoint LOD score (MLS) of 3.9. The linked region on chromosome 10 spans approximately 44 cM from D10S1426 (59 cM) to D10S2327 (103 cM). To narrow this region, we tested for linkage disequilibrium with several of the stage II microsatellite markers. Of the seven markers we tested in family‐based and case control samples, the only nominally positive association we found was with the 167 bp allele of marker D10S1217 (chi‐square = 7.11, P = 0.045, df = 1). © 2002 Wiley‐Liss, Inc.     

Blepharophimosis syndrome is linked to chromosome 3q

Blepharophimosis syndrome (BPES, blepharophimosis eyelid syndrome)is a distinctive congenital eyelid malformation which can occursporadically or be inherited in an autosomal dominant fashion.Previous reports have described associated cytogenetic abnormalitieson chromosome 3q. We have ascertained and sampled two BPES familieswith apparent autosomal dominant inheritance and have testedfor linkage with 17 polymorphic markers on 3q. Multipoint analysisgenerated a maximum LOD score of 3.23 using the markers RHO,ACPP and D3S1238. No evidence of genetic heterogeneity was observed.These studies provide the first non—cytogenetic evidencethat a defective gene responsible for BPES is located on 3q22.