Familial vesicoureteral reflux: testing replication of linkage in seven new multigenerational kindreds

Vesicoureteral reflux (VUR) (OMIM %193000), a common cause of childhood renal failure, is strongly influenced by hereditary factors. Familial VUR most closely conforms to autosomal-dominant inheritance, but because of variable penetrance and expressivity, large multigenerational pedigrees tractable to linkage analysis have been difficult to ascertain. A single genome-wide study of familial VUR has demonstrated linkage to chromosome 1p13, with 78% locus heterogeneity. Previous studies in humans have also suggested loci on chromosomes 6p21, 10q26, and 19q13, whereas mutations in ROBO2 were recently reported in some patients with VUR. Replication of these studies was attempted in seven previously undescribed families from Italy and the United States. Simulation studies, assuming 50% locus heterogeneity, showed that these kindreds had 85% power to replicate linkage and 53% power to achieve genome-wide significance at candidate intervals. Thirty-five markers on chromosomes 1p13, 3p12, 6p21, 10q26, and 19q13 were genotyped and analysis of linkage under a variety of models was performed. Parametric analysis excluded linkage to all candidate loci under genetic homogeneity; moreover, the data did not support statistically significant linkage under models of locus heterogeneity. Similarly, nonparametric, allele-sharing analysis did not reveal any evidence of linkage at any of the loci tested. Thus, despite sufficient power, linkage of familial VUR to previously reported candidate intervals could not be replicated. These data demonstrate substantial genetic heterogeneity of VUR and suggest that mapping strategies relying on a large number of kindreds or single "loaded" pedigrees will be most effective to achieve replication or detection of linkage.     

Identification of a major locus for Paget's disease on chromosome 10p13 in families of British descent.

Mutations of SQSTM1 are an important cause of PDB, but other genes remain to be discovered. A major susceptibility locus for PDB was identified on chromosome 10p13 by a genome-wide linkage scan in families of British descent, which accounted for the vast majority of cases not caused by SQSTM1 mutations. INTRODUCTION: Paget's disease of bone (PDB) has a strong genetic component, and several susceptibility loci have been identified by genome-wide linkage scans. We previously identified three susceptibility loci for PDB using this approach on chromosomes 5q35, 2q36, and 10p13 in 62 families of mainly British descent, but subsequently, mutations in the SQSTM1 gene were found to be the cause of PDB in 23 families from this cohort. Here we reanalyzed the results of our genome-wide search in families from this cohort who did not have SQSTM1 mutations. MATERIALS AND METHODS: The study population consisted of 210 individuals from 39 families of predominantly British descent with autosomal dominant inheritance of PDB in whom SQSTM1 mutations had been excluded by mutation screening. The average family size was 5.44 +/- 3.98 (SD) individuals (range, 2-24 individuals). Genotyping was performed using standard techniques with 382 microsatellite markers spaced at an average distance of 9.06 cM throughout the autosomes. Multipoint linkage analysis was performed using the GENEHUNTER program under models of homogeneity and heterogeneity. RESULTS: Multipoint parametric linkage analysis under a model of homogeneity and nonparametric linkage analysis under a model of heterogeneity both showed strong evidence of linkage to a single locus on chromosome 10p13 (LOD score, +4.08) close to the marker D10S1653 at 41.43cM. No evidence of linkage was detected at the chromosome 2q36 locus previously identified in this population, and linkage to other candidate loci previously implicated in the pathogenesis of PDB was excluded. CONCLUSIONS: We conclude that there is an important susceptibility gene for PDB on chromosome 10p13 in families of British descent and find no evidence to support the existence of a susceptibility locus on chromosome 2q36 or other previously identified candidate loci for PDB in this population. The gene that lies within the 10p13 locus seems to account for the development of PDB in the vast majority of families of British descent who do not carry SQSTM1 mutations.     

Genome-wide linkage in three Dutch families maps a locus for abdominal aortic aneurysms to chromosome 19q13.3.

OBJECTIVES: Elucidation of the genetic background of familial abdominal aortic aneurysm (AAA) suggests a genetic etiology. METHODS AND RESULTS: We carried out a genome-wide scan in three Dutch families with four or five affected siblings. Suggestive loci were further studied by subsequent fine mapping of the locus performed in 101 affected sib-pairs. The genome-wide scan was performed with 400 DNA markers and results were given as non-parametric, multipoint linkage scores (NPL). We observed a suggestive linkage for AAA (NPL score 3.25 at D19S902, 72.72 cM) on chromosome 19q in the three families. After fine mapping on chromosome 19, the NPL score became nominal in the 101 affected sib-pairs. A separate analysis of the three families with fine mapping revealed a peak with significant evidence for linkage (NPL score 3.95 at D19S904, 78.08 cM) on chromosome 19q. This peak was situated to the right compared to the region found in a previously published article for familial AAA on chromosome 19q. CONCLUSIONS: Our results identified a candidate locus in three Dutch families with AAA at chromosome 19q13.3. Separate analysis of these three families provides evidence for genetic heterogeneity.     

Autosomal dominant medullary cystic kidney disease: evidence of gene locus heterogeneity

Autosomal dominant medullary cystic kidney disease (ADMCKD; synonym: medullary cystic disease, MCD) is an autosomal dominant kidney disorder, sharing morphological and clinical features with recessive juvenile nephronophthisis (NPH), such as reduced urinary concentration ability and multiple renal cysts at the corticomedullary junction. While in NPH end-stage renal disease (ESRD) occurs in adolescence, ADMCKD leads to ESRD in adulthood. Recently a gene locus for ADMCKD has been localized to chromosome 1q21 in two large Cypriot families. This prompted us to examine linkage in three ADMCKD-families, using the same set of polymorphic microsatellite markers spanning the critical region on chromosome 1q21. Haplotype analysis revealed that none of the three families showed linkage to this locus, thus demonstrating evidence for genetic locus heterogeneity. Additional linkage analysis studies need to be performed in order to identify further gene loci cosegregating with this autosomal dominant kidney disorder.     

Gene for susceptibility to diabetic nephropathy in type 2 diabetes maps to 18q22.3-23

BACKGROUND: Diabetic nephropathy is the major cause of end-stage renal failure in patients with diabetes mellitus types 1 and 2. Epidemiological studies have suggested a genetic susceptibility to diabetic nephropathy. The aim of this study was to localize the gene(s) responsible for susceptibility to diabetic nephropathy. METHODS: A genetic linkage analysis was performed in 18 large Turkish families with type 2 diabetes mellitus and diabetic nephropathy. The result was checked in 101 affected sibling pairs of Pima Indians. RESULTS: A highly significant LOD score of 6.1 on chromosome 18q22.3-23 between the markers D18S469 and D18S58 was obtained in multipoint analysis. There was no indication for locus heterogeneity. In Pima Indians, linkage to the markers D18S469 and D18S58 was confirmed (P = 0.033), using the affected sib-pair method. The genetic model that fit best was a dominant mode of inheritance with an almost complete penetration in the Turkish population. CONCLUSIONS: There is strong evidence for the localization of a gene responsible for diabetic nephropathy in Turkish type 2 diabetes mellitus patients. This locus maps to chromosome 18q22.3-23, between D18S43 and D18S50, an interval of 8.5 cM.     

Mapping of a new candidate locus for uromodulin-associated kidney disease (UAKD) to chromosome 1q41

BACKGROUND: Autosomal-dominant juvenile hyperuricemia, gouty arthritis, medullary cysts, and progressive renal insufficiency are features associated with familial juvenile hyperuricemic nephropathy (FJHN), medullary cystic kidney disease type 1 (MCKD1) and type 2 (MCKD2). MCKD1 has been mapped to chromosome 1q21. FJHN and MCKD2 have been mapped to chromosome 16p11.2. FJHN and MCKD2 are allelic, result from uromodulin (UMOD) mutations and the term uromodulin-associated kidney disease (UAKD) has been proposed for them. Linkage studies also reveal families that do not show linkage to any of the identified loci. To identify additional UAKD loci, we analyzed one of these families, with features suggestive of FJHN. METHODS: Clinical, biochemical, and immunohistochemical investigations were used for phenotype characterization. Genotyping, linkage and haplotype analyses were employed to identify the candidate disease region. Bioinformatics and sequencing were used for candidate gene selection and analyses. RESULTS: We identified a new candidate UAKD locus on chromosome 1q41, bounded by markers D1S3470 and D1S1644. We analyzed and found no linkage to this region in eight additional families, who did not map to the previously established loci. We noted that affected individuals showed, in addition to the characteristic urate hypoexcretion, significant reductions in urinary excretion of calcium and UMOD. Immunohistochemical analysis showed that low UMOD excretion resulted from its reduced expression, which is a different mechanism to intracellular UMOD accumulation observed in cases with UMOD mutations. CONCLUSION: We have mapped a new candidate UAKD locus and shown that UAKD may be a consequence of various defects affecting uromodulin biology.     

Quantitative trait linkage analysis of lipid-related traits in familial type 2 diabetes: evidence for linkage of triglyceride levels to chromosome 19q.

Macrovascular disease is a major complication of type 2 diabetes. Epidemiological data suggest that the risk of macrovascular complications may predate the onset of hyperglycemia. Hypertriglyceridemia, low levels of HDL cholesterol, and an atherogenic profile characterize the insulin resistance/metabolic syndrome that is also prevalent among nondiabetic members of familial type 2 diabetic kindreds. To identify the genes for lipid-related traits, we first performed a 10-cM genome scan using 440 markers in 379 members of 19 multiplex families ascertained for two diabetic siblings (screening study). We then extended findings for three regions with initial logarithm of odds (LOD) scores >1.5 to an additional 23 families, for a total of 576 genotyped individuals (extended study). We found heritabilities for all lipid measures in the range of 0.31 to 0.52, similar to those reported by others in unselected families. However, we found the strongest evidence for linkage of triglyceride levels to chromosome 19q13.2, very close to the ApoC2/ApoE/ApoC1/ApoC4 gene cluster (LOD 2.56) in the screening study; the LOD increased to 3.16 in the extended study. Triglyceride-to-HDL cholesterol ratios showed slightly lower LOD scores (2.73, extended family) in this same location. Other regions with LOD scores >2.0 included HDL linkage to chromosome 1q21-q23, where susceptibility loci for both familial type 2 diabetes and familial combined hyperlipidemia have been mapped, and to chromosome 2q in the region of the NIDDM1 locus. Neither region showed stronger evidence for linkage in the extended studies, however. Our results suggest that genes in or near the ApoE/ApoC2/ApoC1/ApoC4 cluster on 19q13.2 may contribute to the commonly observed hypertriglyceridemia and low HDL seen in diabetic family members and their offspring, and thus may be a candidate locus for the insulin resistance syndrome.     

Candidate locus analysis of familial ascending aortic aneurysms and dissections confirms the linkage to the chromosome 5q13-14 in Finnish families

OBJECTIVE: The purpose of the study was to carry out a candidate gene analysis in families with familial thoracic aortic aneurysms and dissections. METHODS: The study material consisted of 11 Finnish families (with 115 members genotyped) who underwent echocardiographic examination for measurement of the aortic root diameter. Selected candidate genes included the loci for Marfan and Ehlers-Danlos syndromes, the genes of matrix metalloproteinases 3 and 9 and tissue inhibitor of metalloproteinase 2 as well two loci on the chromosomes 5q13-14 and 11q23.2-q24, previously found to be linked to the disease. RESULTS: The chromosomal locus 5q13-14 was linked to the disease risk (nonparametric linkage score 3.0, P =.005) confirming the previous linkage. Other candidate genes and loci were excluded as major loci in these families. CONCLUSIONS: The identification of the gene at chromosomal location 5q13-14 causing the development of such diseases would give us important knowledge on the pathogenesis of the disease and enable the identification of subjects at risk. This in turn would lead to appropriate treatment before the occurrence of fatal complications and, likely, to the development of new treatment methods.     

Suggestive evidence for association of human chromosome 18q12-q21 and its orthologue on rat and mouse chromosome 18 with several autoimmune diseases

Some immune system disorders, such as type 1 diabetes, multiple sclerosis (MS), and rheumatoid arthritis (RA), share common features: the presence of autoantibodies and self-reactive T-cells, and a genetic association with the major histocompatibility complex. We have previously published evidence, from 1,708 families, for linkage and association of a haplotype of three markers in the D18S487 region of chromosome 18q21 with type 1 diabetes. Here, the three markers were typed in an independent set of 627 families and, although there was evidence for linkage (maximum logarithm of odds score [MLS] = 1.2; P = 0.02), no association was detected. Further linkage analysis revealed suggestive evidence for linkage of chromosome 18q21 to type 1 diabetes in 882 multiplex families (MLS = 2.2; lambdas = 1.2; P = 0.001), and by meta-analysis the orthologous region (also on chromosome 18) is linked to diabetes in rodents (P = 9 x 10(-4)). By meta-analysis, both human chromosome 18q12-q21 and the rodent orthologous region show positive evidence for linkage to an autoimmune phenotype (P = 0.004 and 2 x 10(-8), respectively, empirical P = 0.01 and 2 x 10(-4), respectively). In the diabetes-linked region of chromosome 18q12-q21, a candidate gene, deleted in colorectal carcinoma (DCC), was tested for association with human autoimmunity in 3,380 families with type 1 diabetes, MS, and RA. A haplotype ("2-10") of two newly characterized microsatellite markers within DCC showed evidence for association with autoimmunity (P = 5 x 10(-6)). Collectively, these data suggest that a locus (or loci) exists on human chromosome 18q12-q21 that influences multiple autoimmune diseases and that this association might be conserved between species.     

Identification of a locus for maturity-onset diabetes of the young on chromosome 8p23

Maturity-onset diabetes of the young (MODY) is a subtype of diabetes defined by an autosomal dominant inheritance and a young onset. Six MODY genes have been discovered to date. To identify additional MODY loci, we conducted a genome scan in 21 extended U.S. families (15 white and 6 from minorities, for a total of 237 individuals) in which MODY was not caused by known MODY genes. Seven chromosomal regions (1q42, 2q24, 2q37, 4p13, 8p23, 11p15, and 19q12) had a parametric heterogeneity logarithm of odds (HLOD) > or =1.00 or a nonparametric logarithm of odds (LOD) > or =0.59 (P < or = 0.05) in the initial screen. After typing additional markers at these loci to reduce the spacing to 2-3 cM, significant linkage was detected on 8p23 (HLOD = 3.37 at D8S1130 and nonparametric LOD = 3.66; P = 2 x 10(-5) at D8S265), where a 4.7-Mb inversion polymorphism is located. Thirty percent of the families (6 of 21) were linked with this region. Another linkage peak on chromosome 2q37 with an HLOD of 1.96 at D2S345/D2S2968 accounted for diabetes in an additional 25% of families (5 of 21). All 6 minority families were among the 11 families linked to these loci. None of the other loci followed up had an HLOD exceeding 1.50. In summary, we have identified a MODY locus on 8p23 that accounts for diabetes in a substantial proportion of MODY cases unlinked to known MODY genes. Another novel MODY locus may be present on 2q37. Cloning these new MODY genes may offer insights to disease pathways that are relevant to the cause of common type 2 diabetes.     

Genome-wide linkage scan of a large family with IgA nephropathy localizes a novel susceptibility locus to chromosome 2q36

IgA nephropathy (IgAN) is the most common glomerulonephritis worldwide and an important cause of ESRD. Familial clustering of cases suggests genetic predisposition to this disease. Two recent genome-wide studies in IgAN have identified a major susceptibility locus on chromosome 6q22 (IGAN1) and two additional loci with suggestive linkage signals on chromosomes 4q26-31 and 17q12-22. A large four-generation family with 14 affected individuals has been clinically ascertained and excluded from linkage to these loci. A genome-wide linkage scan was performed on this family with GeneChip Mapping 10K 2.0 Arrays using an "affected-only" strategy. By nonparametric analysis, two regions of suggestive linkage (multipoint logarithm of odds [LOD] scores >2) were identified on chromosomes 2q36 and 13p12.3. By parametric analysis (assuming an autosomal dominant inheritance, a disease allele frequency of 0.001, phenocopy rate of 0.01, and penetrance of 75%), a significant linkage to chromosome 2q36 (maximum multipoint LOD score 3.47) was found. Nine simple sequence repeat markers then were genotyped in 21 members (included all of the affected individuals), and significant linkage to chromosome 2q36 over a region of 12.2 cM (maximum multipoint LOD score 3.46) was confirmed. Recombination events in two affected individuals, as detected by haplotype analysis, delineated a critical interval of approximately 9 cM (equivalent to approximately 7 Mb) between D2S1323 and D2S362. Taken together, these data provide strong evidence for a novel disease susceptibility locus for familial IgAN.     

Exclusion of the candidate genes ACE and Bcl-2 for six families with nephronophthisis not linked to the NPH1 locus.

BACKGROUND: Nephronophthisis (NPH) is an autosomal recessively transmitted kidney disease, characterized by cyst formation at the cortico-medullary junction, and a sclerosing tubulointerstitial nephropathy. Juvenile nephronophthisis (NPH1) is the most common genetic cause of renal failure in children and maps to chromosome 2q12-q13. The responsible gene NPHP1 has been identified and encodes for nephrocystin. Not all families with NPH demonstrate linkage to that locus. METHODS: We studied six families with NPH without linkage to the NPH1 locus. In order to attempt identification of a new causative gene, the candidate genes ACE (angiotensin converting enzyme) and Bcl-2 (B cell leukaemia/lymphoma 2 gene) originating from mouse models, were examined. For the six families highly polymorphic microsatellites covering the whole candidate gene regions were haplotyped and linkage analysis was performed. RESULTS: Haplotype analyses of all families examined were incompatible with linkage of the disease status to ACE or Bcl-2. Linkage analysis excluded both candidate gene regions with a LOD-score of < -2. CONCLUSIONS: This study excluded the candidate genes ACE and Bcl-2 for NPH. Additional linkage studies need to be performed in order to identify further genes responsible for nephronophthisis.     

Further evidence for linkage of autosomal-dominant medullary cystic kidney disease on chromosome 1q21

BACKGROUND: Autosomal-dominant medullary cystic kidney disease (ADMCKD) is characterized by the development of cysts at the corticomedullary border of the kidneys. It resembles nephronophthisis (NPH) with an autosomal-recessive mode of inheritance. Genetic linkage has been shown either on chromosome 1q21 (ADMCKD1) or 16p12 (ADMCKD2), and families exist who are not linked to the aforementioned loci. No disease-causing gene underlying this disorder has been reported. METHODS: The Finnish Transplantation Register and hospital records were searched to identify all of the ADMCKD families in the Finnish population. Detailed clinical information of the patients was collected. Linkage analysis was used to study whether the Finnish families originating from a homogeneous population showed genetic linkage to the ADMCKD1 or ADMCKD2 loci. Also, the coding region of a strong candidate gene, natriuretic peptide receptor A (NPRA), located on the chromosome 1q21 critical region, was sequenced using polymerase chain reaction sequencing with an ABI 377XL Automated DNA sequencer (Applera Corp., Norwalk, CT, USA). RESULTS: Five of the six families showed linkage to the previously identified region of chromosome 1q21. Family 6 with hyperuricemia as a prominent clinical feature was linked to neither of the ADMCKD loci. Wide interfamiliar and intrafamiliar variability in the clinical picture of the patients was detected. The NPRA gene mutation was excluded as a causative gene by sequencing. CONCLUSION: This study locates the gene for ADMCKD1 close to a marker D1S1595 in a region <5 cM, and further confirms the existence of at least three loci for the medullary cystic kidney disease. Heterogeneity of the symptoms complicates the clinical diagnosis and classification of the patients. Further studies are needed to identify the disease-causing gene.     

Otosclerosis: a genetically heterogeneous disease involving at least three different genes

Otosclerosis is caused by abnormal bone homeostasis of the otic capsule, resulting in hearing impairment in 0.3%-0.4% of the white population. The etiology of the disease remains unclear and environmental as well as genetic factors have been implicated. We localized the first autosomal-dominant locus to chromosome 15 in 1998 (OTSC1) in an Indian family and, recently, we reported the localization of a second gene for otosclerosis to a 16 cM interval on chromosome 7q (OTSC2). In this study, we recruited and analyzed nine additional families (seven Belgian and two Dutch families with 53 affected and 20 unaffected subjects) to investigate the importance of these loci in autosomal-dominant otosclerosis. We completed linkage analysis with three microsatellite markers of chromosome 15 (D15S652, D15S1004, D15S657) and five microsatellite markers of chromosome 7 (D7S495, D7S2560, D7S684, D7S2513, D7S2426). In two families, results compatible with linkage to OTSC2 were found, but in the seven remaining families OTSC1 and OTSC2 were excluded. Heterogeneity testing provided significant evidence for genetic heterogeneity, with an estimated 25% of families linked to OTSC2. These results indicate that, besides OTSC1 and OTSC2, there must be at least one additional otosclerosis locus.     

A genome-wide search for type 2 diabetes susceptibility genes in Utah Caucasians.

Considerable evidence supports a major inherited component of type 2 diabetes. We initially conducted a genome-wide scan with 440 microsatellite markers at 10-cM intervals in 19 multigenerational families of Northern European ancestry with at least two diabetic siblings. Initial two-point analyses of these families directed marker typing of 23 additional families. Subsequently, all available marker data on the total of 42 families were analyzed using both parametric and nonparametric multipoint methods to test for linkage to type 2 diabetes. One locus on chromosome 1q21-1q23 met genome-wide criteria for significant linkage under a model of recessive inheritance with a common diabetes allele (logarithm of odds [LOD] = 4.295). Both pedigree-based nonparametric linkage (NPL) analysis and affected sib pair (MAPMAKER/SIBS) nonparametric methods also showed the highest genome-wide scores at this region, near markers CRP and APOA2, but failed to meet levels of genome-wide significance. The risk of type 2 diabetes to siblings of a diabetic person when compared with the population (lambdaS) was estimated from MAPMAKER/SIBS to be 2.8 in these 42 families. Simulation studies using study data confirmed a genome-wide significance level of P<0.05 (95% CI 0.005-0.0466). However, analysis of 20 similarly ascertained but smaller families failed to confirm this linkage. The LOD score with 50% heterogeneity for all 62 families considered together was only 2.25, with an estimated lambdaS of 1.87. Our data suggest a novel diabetes susceptibility locus near APOA2 on chromosome 1 in a region with many transcribed genes.     

Autosomal recessive Alport syndrome: linkage analysis and clinical features in two families.

BACKGROUND: Genetic heterogeneity is a well-known feature of Alport syndrome (AS). Most families with AS show an X-linked dominant pattern of inheritance but about 15% of families show an autosomal inheritance of the disease. Autosomal recessive AS may account for 10% of the total number of cases and is caused by mutations in the COL4A3 and COL4A4 genes. The clinical spectrum of this rare disorder has not been well clarified. METHODS: We present two families with AS. Two affected members of these families have entered end-stage renal disease (ESRD) in their 30s, and the other three are older than 15 years and have normal serum creatinine. Four of the five patients have deafness but none have ocular abnormalities. Two have been transplanted and have not suffered from anti-GBM antibody nephritis. Men and women are equally affected. We have performed linkage analysis for chromosome 2 with the following markers: D2S279, COL4A3/4 DNTR, COL4A4 RFLP Hae III. RESULTS: We demonstrate that both families, one of them consanguineous, are linked to the COL4A3/4 locus. CONCLUSIONS: We can conclude that the only significant difference between the X-linked and the autosomal recessive forms of AS lies in the fact that in the latter females are as affected as males; thus the idea that autosomal recessive AS causes ESRD during childhood must be discarded. Other clinical features such as age of deafness or the presence of post-transplant anti-GBM antibody nephritis show no differences between the entities. Thus an accurate familial study is mandatory in patients with AS, as the identification of the different patterns of inheritance may cause a great difference in genetic counselling. Linkage analysis is the only effective molecular diagnosis that can be performed nowadays.     

Evidence for further genetic heterogeneity in nephronophthisis.

BACKGROUND: A new type of nephronophthisis (NPH) has been recently identified in a large Venezuelan kindred: adolescent nephronophthisis (NPH3) causes end-stage renal disease (ESRD) at a median age of 19 years. The responsible gene (NPHP3) maps to 3q21-q22. NPH3 shares with juvenile nephronophthisis (NPH1) the same disease manifestations such as polyuria, polydipsia, and secondary enuresis. Histopathological findings consist of tubular basement membrane changes, cysts at the corticomedullary junction, and a chronic sclerosing tubulointerstitial nephropathy. The only difference is a younger age at ESRD in NPH1 (median age of 13 years) when compared with NPH3. METHODS: In order to evaluate whether there might be a fourth locus of isolated nephronophthisis, we studied eight NPH families without extrarenal disease manifestations and without linkage to the NPH1 locus (NPHP1) on chromosome 2q12-q13. ESRD was reached at ages ranging from 7 to 33 years. Individuals were haplotyped with microsatellites covering the genetic locus of NPHP3. Infantile NPH (NPH2) was excluded in all families by the clinical history and histological findings. RESULTS: In four of the examined families haplotype analysis was compatible with linkage to the NPHP3 locus. In one of these families identity by descent was observed. In contrast, in another four families linkage was excluded for NPHP3. CONCLUSION: Four NPH-families were neither linked to NPHP1 nor to NPHP3, indicating further genetic heterogeneity within the group of nephronophthisis. The finding of further genetic heterogeneity in NPH has important implications for genetic counselling.     

Autosomal dominant gnathodiaphyseal dysplasia maps to chromosome 11p14.3-15.1.

Gnathodiaphyseal dysplasia (GDD) is a syndrome characterized by bone fragility, sclerosis of tubular bones, and cemento-osseous lesions of jawbones. Although some cases of this syndrome exist in families with autosomal dominant inheritance, the underlying gene has never been identified. We analyzed a large four-generation family with GDD by linkage analysis using genomic DNA from nine affected and six nonaffected family members. A genome-wide search using a set of highly polymorphic microsatellite markers showed evidence for linkage to chromosome 11p14.3-15.1. Two-point linkage analysis of microsatellite markers spanning this locus resulted in a maximum logarithm of odds (LOD) score of 2.70 with a recombination fraction (theta) of 0 at D11S1755, D11S1759, and D11S915, and a maximum LOD score of 3.01 at D11S4114 was obtained in multipoint linkage analysis. Haplotype analysis detected no recombination between GDD and six closely linked markers (D11S928, D11S1755, D11S4114, D11S1759, D11S915, and D11S929) and established the candidate interval of 8.7 cM on chromosome 11p for GDD. Although GDD has been considered to be a variation of osteogenesis imperfecta (MIM 166260), our results indicate that this syndrome is a new and distinct disease entity from other systemic bone diseases. Furthermore, these genetic markers are useful for presymptomatic diagnosis of GDD in some families and for identification of the GDD gene.     

Mutation Screening of the TNFRSF11A Gene Encoding Receptor Activator of NFkB (RANK) in Familial and Sporadic Paget's Disease of Bone and Osteosarcoma

Paget's disease of bone (PDB) is a common disorder characterized by focal areas of increased and disorganized osteoclastic bone resorption, leading to bone pain, deformity, pathological fracture, and an increased risk of osteosarcoma. Genetic factors play an important role in the pathogenesis of Paget's disease. In some families, the disease has been found to be linked to a susceptibility locus on chromosome 18q21-22, which also contains the gene responsible for familial expansile osteolysis (FEO)--a rare bone dysplasia with many similarities to Paget's disease. Insertion mutations of the TNFRSF11A gene encoding Receptor Activator of NF kappa B (RANK) have recently been found to be responsible for FEO and rare cases of early onset familial Paget's disease. Loss of heterozygosity (LOH) affecting the PDB/FEO critical region has also been described in osteosarcomas suggesting that TNFRSF11A might also be involved in the development of osteosarcoma. In order to investigate the possible role of TNFRSF11A in the pathogenesis of Paget's disease and osteosarcoma, we conducted mutation screening of the TNFRSF11A gene in patients with familial and sporadic Paget's disease as well as DNA extracted from Pagetic bone lesions, an osteosarcoma arising in Pagetic bone and six osteosarcoma cell lines. No specific abnormalities of the TNFRSF11A gene were identified in a Pagetic osteosarcoma, the osteosarcoma cell lines, DNA extracted from Pagetic bone lesions, or DNA extracted from peripheral blood in patients with familial or sporadic Paget's disease including several individuals with early onset Paget's disease. These data indicate that TNFRSF11A mutations contribute neither to the vast majority of cases of sporadic or familial PDB, nor to the development of osteosarcoma.     

A genome scan for diabetic nephropathy in African Americans

BACKGROUND: There is substantial evidence for a genetic contribution to diabetic nephropathy susceptibility in the African American population, but little is known about location or identity of susceptibility genes. METHODS: DNA samples were collected from 206 type 2 diabetes (T2DM) and end-stage renal disease (ESRD)/nephropathy-affected sib pairs from 166 African American families (355 affected individuals). A genome scan was performed and data analyzed using nonparametric linkage regression (NPLR) analysis and ordered subsets analysis (OSA) methods. RESULTS: In initial NPLR analyses no logarithm of odds (LOD) scores >2.0 were observed. Four loci had LOD scores > or =1.0, with LOD = 1.43 at 29 cM on chromosome 7p the highest. NPLR analyses of multilocus interactions detected 6 loci (7p, 12p, 14q, 16p, 18q, and 21q) with LOD scores 1.15 to 1.63. NPLR analyses evaluating phenotypic interactions revealed multiple locations with evidence (P < 0.05) for interactions with age-at-onset of ESRD (9 loci), duration of diabetes before onset of ESRD (19 loci), and age-at-onset of diabetes (14 loci). Several loci identified by NPLR analyses were also identified using OSA. OSA revealed evidence for a nephropathy locus at 135 cM on chromosome 3 in an estimated 29% of the families (LOD = 4.55 in the optimal subset). Additional linkage evidence, LOD = 3.59, was observed on chromosome 7p (37% of the families, longer duration of diabetes prior to diagnosis of ESRD), and 18q (max. LOD = 3.72; 64% of the families, early diabetes diagnosis). The 7p linkage has been observed in a recent genome scan of African American type 2 diabetes. CONCLUSION: This first genome scan of diabetic nephropathy in African Americans reveals evidence for susceptibility loci on chromosomes 3q, 7p, and 18q. The 7p locus may represent a type 2 diabetes susceptibility locus.