Linkage mapping in 29 Bardet-Biedl syndrome families confirms loci in chromosomal regions 11q13, 15q22.3-q23, and 16q21

Bardet-Biedl syndrome: Antenatal presentation of forty-five fetuses with biallelic pathogenic variants in known Bardet-Biedl syndrome genes

Bardet-Biedl syndrome (BBS) is an emblematic ciliopathy associated with retinal dystrophy, obesity, postaxial polydactyly, learning disabilities, hypogonadism and renal dysfunction. Before birth, enlarged/cystic kidneys as well as polydactyly are the hallmark signs of BBS to consider in absence of familial history. However, these findings are not specific to BBS, raising the problem of differential diagnoses and prognosis. Molecular diagnosis during pregnancies remains a timely challenge for this heterogeneous disease (22 known genes). We report here the largest cohort of BBS fetuses to better characterize the antenatal presentation. Prenatal ultrasound (US) and/or autopsy data from 74 fetuses with putative BBS diagnosis were collected out of which molecular diagnosis was established in 51 cases, mainly in BBS genes (45 cases) following the classical gene distribution, but also in other ciliopathy genes (6 cases). Based on this, an updated diagnostic decision tree is proposed. No genotype/phenotype correlation could be established but postaxial polydactyly (82%) and renal cysts (78%) were the most prevalent symptoms. However, autopsy revealed polydactyly that was missed by prenatal US in 55% of the cases. Polydactyly must be carefully looked for in pregnancies with apparently isolated renal anomalies in fetuses.

A rare case of obesity. Can it be Bardet-Biedl Syndrome?

Bardet-Biedl Syndrome (BBS) is a rare autosomal recessive disorder with a wide spectrum of clinical manifestations like retinal dystrophy, obesity, polydactyly, mental retardation, hypogonadism, and renal dysfunction. We report a case of 14-year-old obese boy with poor scholastic performances, hypothyroidism, and poor vision diagnosed as BBS.

Bardet-Biedl Syndrome with a Kidney Transplant, Esophageal Adenocarcinoma, and Postoperative Complications

The authors present a rare clinical case of a patient with Bardet-Biedl syndrome and chronic kidney disease, who reached end-stage renal disease (ESRD) and underwent a long-term hemodialysis treatment, during which infections with Hepatitis C Virus (HCV) infection and Cytomegalovirus (CMV) infection were established. Kidney transplantation from an alive unrelated donor was performed. Later, an adenocarcinoma of the esophagus was diagnosed at an early stage, treated surgically with resection of the esophagus and gastroesophagoplasty afterward. Seven months later, a rare complication of the immunosuppressive therapy with Cyclosporin A occurred, which consisted of spontaneous bilateral pleural hemorrhage. The same, as well as the postoperative ventral hernia, was successfully resolved. Concomitant HCV was also treated. Rare autosomal recessive syndrome with severe complications, adenocarcinoma of the esophagus, spontaneous bilateral pleural hemorrhage after the operation, and successful treatment were discussed.

Genetics of Obesity

Numerous classical genetic studies have proved that genes are contributory factors for obesity. Genes are directly responsible for obesity associated disorders such as Bardet-Biedl and Prader-Willi syndromes. However, both genes as well as environment are associated with obesity in the general population. Genetic epidemiological approaches, particularly genome-wide association studies, have unraveled many genes which play important roles in human obesity. Elucidation of their biological functions can be very useful for understanding pathobiology of obesity. In the near future, further exploration of obesity genetics may help to develop useful diagnostic and predictive tests for obesity treatment.

Spot14/Spot14R expression may be involved in MSC adipogenic differentiation in patients with adolescent idiopathic scoliosis

The aim of the present study was to evaluate the different expression levels of thyroid hormone responsive (THRSP; Spot14)/S14 related, Mig12 (S14R) during bone marrow mesenchymal stem cell (BM-MSC) adipogenesis in adolescent idiopathic scoliosis (AIS) patients. MSCs were retrospectively isolated from AIS patients and controls, and adipogenic differentiation was induced. Total RNA was extracted for Affymetrix 3′-IVT expression profiling microarrays and compared with the results from healthy controls. The results were confirmed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) validation and the protein expression levels of Spot14 and its paralogous gene S14R by western blotting and immunohistochemistry. A total of 300 significantly altered mRNAs were detected (111 upregulated and 189 downregulated) and confirmed by RT-qPCR. The mRNA expression levels of seven genes, including Spot14, were altered by >2-fold in AIS patients. Spot14/S14R was selected for further investigation. The results of the western blotting demonstrated that mRNA and protein expression levels of Spot14/S14R were significantly higher in AIS patients than the controls (P<0.05). Immunohistochemistry demonstrated Spot14 was expressed in 85% (17/20 cases) in adipose tissue samples from AIS patients and 23.1% (3/13 cases) of adipose tissue samples from controls. The positive ratio of Spot14 in adipose tissue samples from AIS was significantly higher than the controls (P<0.001). The results of the present study indicated that Spot14/S14R were differently expressed in MSC adipogenesis in AIS patients, and they may be important in the abnormal adipogenic differentiation in AIS.

Advances in understanding the expression and function of dipeptidyl peptidase 8 and 9

DPP8 and DPP9 are recently identified members of the dipeptidyl peptidase IV (DPPIV) enzyme family, which is characterized by the rare ability to cleave a post-proline bond two residues from the N-terminus of a substrate. DPP8 and DPP9 have unique cellular localization patterns, are ubiquitously expressed in tissues and cell lines, and evidence suggests important contributions to various biological processes including: cell behavior, cancer biology, disease pathogenesis, and immune responses. Importantly, functional differences between these two proteins have emerged, such as DPP8 may be more associated with gut inflammation whereas DPP9 is involved in antigen presentation and intracellular signaling. Similarly, the DPP9 connections with H-Ras and SUMO1, and its role in AKT1 pathway downregulation provide essential insights into the molecular mechanisms of DPP9 action. The recent discovery of novel natural substrates of DPP8 and DPP9 highlights the potential role of these proteases in energy metabolism and homeostasis. This review focuses on the recent progress made with these post-proline dipeptidyl peptidases and underscores their emerging importance.

Identification of the kinesin KifC3 as a new player for positioning of peroxisomes and other organelles in mammalian cells

The attachment of organelles to the cytoskeleton and directed organelle transport is essential for cellular morphology and function. In contrast to other cell organelles like the endoplasmic reticulum or the Golgi apparatus, peroxisomes are evenly distributed in the cytoplasm, which is achieved by binding of peroxisomes to microtubules and their bidirectional transport by the microtubule motor proteins kinesin-1 (Kif5) and cytoplasmic dynein. KifC3, belonging to the group of C-terminal kinesins, has been identified to interact with the human peroxin PEX1 in a yeast two-hybrid screen. We investigated the potential involvement of KifC3 in peroxisomal transport. Interaction of KifC3 and the AAA-protein (ATPase associated with various cellular activities) PEX1 was confirmed by in vivo colocalization and by coimmunoprecipitation from cell lysates. Furthermore, knockdown of KifC3 using RNAi resulted in an increase of cells with perinuclear-clustered peroxisomes, indicating enhanced minus-end directed motility of peroxisomes. The occurrence of this peroxisomal phenotype was cell cycle phase independent, while microtubules were essential for phenotype formation. We conclude that KifC3 may play a regulatory role in minus-end directed peroxisomal transport for example by blocking the motor function of dynein at peroxisomes. Knockdown of KifC3 would then lead to increased minus-end directed peroxisomal transport and cause the observed peroxisomal clustering at the microtubule-organizing center.

The genetics of human obesity

It has long been known that there is a genetic component to obesity, and that characterizing this underlying factor would likely offer the possibility of better intervention in the future. Monogenic obesity has proved to be relatively straightforward, with a combination of linkage analysis and mouse models facilitating the identification of multiple genes. In contrast, genome-wide association studies have successfully revealed a variety of genetic loci associated with the more common form of obesity, allowing for very strong consensus on the underlying genetic architecture of the phenotype for the first time. Although a number of significant findings have been made, it appears that very little of the apparent heritability of body mass index has actually been explained to date. New approaches for data analyses and advances in technology will be required to uncover the elusive missing heritability, and to aid in the identification of the key causative genetic underpinnings of obesity.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

McKusick-Kaufman or Bardet-Biedl syndrome? A new borderline case in an Italian nonconsanguineous healthy family

McKusick-Kaufman syndrome (MKS, OMIM #236700) is a rare syndrome inherited in an autosomal recessive pattern with a phenotypic triad comprising hydrometrocolpos (HMC), postaxial polydactyly (PAP), and congenital cardiac disease (CHD). The syndrome is caused by mutations in the MKKS gene mapped onto chromosome 20p12 between D20S162 and D20S894 markers. Mutations in the same gene causes Bardet-Biedl-6 syndrome (BBS-6, OMIM #209900) inherited in an autosomal recessive pattern. BBS-6 comprises retinitis pigmentosa, polydactyly, obesity, mental retardation, renal and genital anomalies. HMC, CHD, and PAP defects can also occur in BBS-6, and there is a significant clinical overlap between MKS and BBS-6 in childhood. We describe a new borderline case of MKS and BBS syndrome and suggest insights for understanding correlation between MKKS gene mutations and clinical phenotype. Here, we report the results of molecular analysis of MKKS in a female proband born in an Italian nonconsanguineous healthy family that presents HMC and PAP. The mutational screening revealed the presence of two different heterozygous missense variants (p.242A>S in exon 3, p.339 I>V in exon 4) in the MKKS gene, and a nucleotide variation in 5’UTR region in exon 2 (-417 A>C).

Genetics of childhood obesity

Obesity is a major health problem and an immense economic burden on the health care systems both in the United States and the rest of the world. The prevalence of obesity in children and adults in the United States has increased dramatically over the past decade. Besides environmental factors, genetic factors are known to play an important role in the pathogenesis of obesity. Genome-wide association studies (GWAS) have revealed strongly associated genomic variants associated with most common disorders; indeed there is general consensus on these findings from generally positive replication outcomes by independent groups. To date, there have been only a few GWAS-related reports for childhood obesity specifically, with studies primarily uncovering loci in the adult setting instead. It is clear that a number of loci previously reported from GWAS analyses of adult BMI and/or obesity also play a role in childhood obesity.

No association between LRP5 gene polymorphisms and bone and obesity phenotypes in Chinese male-offspring nuclear families

AIM

To investigate the effect of low-density lipoprotein receptor-related protein 5 (LRP5) gene polymorphisms on bone and obesity phenotypes in young Chinese men.

METHODS

A total of 1244 subjects from 411 Chinese nuclear families were genotyped by using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique at the Q89R, N740N, and A1330V sites in the LRP5 gene. Bone mineral density (BMD) in the lumbar spine and the hip, total fat mass and total lean mass were measured using dual-energy X-ray absorptiometry. The association between LRP5 gene polymorphisms and peak BMD, body mass index (BMI), total fat mass, total lean mass and percentage of fat mass was assessed using a quantitative transmission disequilibrium test (QTDT).

RESULTS

No significant within-family associations were found between genotypes or haplotypes of the LRP5 gene and peak BMD, BMI, total fat mass, total lean mass and percentage of fat mass. The 1000 permutations that were subsequently simulated were in agreement with these within-family association results.

CONCLUSION

Our results suggest that common polymorphic variations of the LRP5 gene do not influence peak bone mass acquisition and obesity phenotypes in young Chinese men.

A Novel Familial BBS12 Mutation Associated with a Mild Phenotype: Implications for Clinical and Molecular Diagnostic Strategies

Bardet-Biedl syndrome (BBS) is an autosomal recessively inherited ciliopathy mainly characterized by rod-cone dystrophy, postaxial polydactyly, obesity, renal tract anomalies, and hypogonadism. To date, 14 BBS genes, BBS1 to BBS14, have been identified, accounting for over 75% of mutations in BBS families. In this study, we present a consanguineous family from Pakistan with postaxial polydactyly and late-onset retinal dysfunction. Adult affected individuals did not show any renal or genital anomalies, obesity, mental retardation or learning difficulties and did thus not fulfill the proposed clinical diagnostic criteria for BBS. We mapped the disease in this family to the BBS12 locus on chromosome 4q27 and identified the novel homozygous p.S701X nonsense mutation in BBS12 in all three affected individuals of this family. We conclude that BBS12 mutations might cause a very mild phenotype, which is clinically not diagnosed by the current diagnostic criteria for BBS. Consequently, we suggest the use of less strict diagnostic criteria in familial BBS families with mild phenotypic expression.

Pitfalls of homozygosity mapping: an extended consanguineous Bardet-Biedl syndrome family with two mutant genes (BBS2, BBS10), three mutations, but no triallelism

The extensive genetic heterogeneity of Bardet-Biedl syndrome (BBS) is documented by the identification, by classical linkage analysis complemented recently by comparative genomic approaches, of nine genes (BBS1-9) that account cumulatively for about 50% of patients. The BBS genes appear implicated in cilia and basal body assembly or function. In order to find new BBS genes, we performed SNP homozygosity mapping analysis in an extended consanguineous family living in a small Lebanese village. This uncovered an unexpectedly complex pattern of mutations, and led us to identify a novel BBS gene (BBS10). In one sibship of the pedigree, a BBS2 homozygous mutation was identified, while in three other sibships, a homozygous missense mutation was identified in a gene encoding a vertebrate-specific chaperonine-like protein (BBS10). The single patient in the last sibship was a compound heterozygote for the above BBS10 mutation and another one in the same gene. Although triallelism (three deleterious alleles in the same patient) has been described in some BBS families, we have to date no evidence that this is the case in the present family. The analysis of this family challenged linkage analysis based on the expectation of a single locus and mutation. The very high informativeness of SNP arrays was instrumental in elucidating this case, which illustrates possible pitfalls of homozygosity mapping in extended families, and that can be explained by the rather high prevalence of heterozygous carriers of BBS mutations (estimated at one in 50 in Europeans).

Polymorphisms of the low-density lipoprotein receptor-related protein 5 (LRP5) gene are associated with obesity phenotypes in a large family-based association study

BACKGROUND

The low-density lipoprotein receptor-related protein 5 (LRP5) gene, essential for glucose and cholesterol metabolism, may have a role in the aetiology of obesity, an important risk factor for diabetes.

PARTICIPANTS AND METHODS

To investigate the association between LRP5 polymorphisms and obesity, 27 single-nucleotide polymorphisms (SNPs), spacing about 5 kb apart on average and covering the full transcript length of the LRP5 gene, were genotyped in 1873 Caucasian people from 405 nuclear families. Obesity (defined as body mass index (BMI) >30 kg/m(2)) and three obesity-related phenotypes (BMI, fat mass and percentage of fat mass (PFM)) were investigated.

RESULTS

Single markers (12 tagging SNPs and 4 untaggable SNPs) and haplotypes (5 blocks) were tested for associations, using family-based designs. SNP4 (rs4988300) and SNP6 (rs634008) located in block 2 (intron 1) showed significant associations with obesity and BMI after Bonferroni correction (SNP4: p<0.001 and p = 0.001, respectively; SNP6: p = 0.002 and 0.003, respectively). The common allele A for SNP4 and minor allele G for SNP6 were associated with an increased risk of obesity. Significant associations were also observed between common haplotype A-G-G-G of block 2 with obesity, BMI, fat mass and PFM with global empirical values p<0.001, p<0.001, p = 0.003 and p = 0.074, respectively. Subsequent sex-stratified analyses showed that the association in the total sample between block 2 and obesity may be mainly driven by female subjects.

CONCLUSION

Intronic variants of the LRP5 gene are markedly associated with obesity. We hypothesise that such an association may be due to the role of LRP5 in the WNT signalling pathway or lipid metabolism. Further functional studies are needed to elucidate the exact molecular mechanism underlying our finding.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

Cloning and characterization of a splice variant of human Bardet-Biedl syndrome 4 gene (BBS4)

Bardet-Biedl syndrome (BBS) is a heterogeneous multisystemic disorder characterized primarily by five cardinal features of retinal degeneration, obesity, polydactyly, hypogenitalism and mental retardation. To date, six distinct BBS loci that have been identified on different chromosomes. BBS4 gene is mapped to 15q22.2-23, which when mutated can cause BBS4. Its protein shows strong homology to O-linked N-acetylglucosamine (O-GlcNAc) transferase. Here we report a splice variant of BBS4, which is 2556 bp in length and has an open reading frame coding a predicted 527 amino-acids protein. RT-PCR shows that the cDNA is widely expressed while it has higher expression levels in pancreas, liver and prostate.

Linkage disequilibrium mapping in the Newfoundland population: a re-evaluation of the refinement of the Bardet?Biedl syndrome 1 critical interval

Genetically isolated populations, such as Newfoundland, have contributed greatly to the identification of disease-causing genes. A linkage disequilibrium (LD) study involving six Newfoundland families predicted a critical interval for Bardet-Biedl syndrome 1 (BBS1) (Young et al. in Am J Hum Genet 65:1680-1687, 1999), but the subsequent identification of BBS1 revealed that it lies outside this region. This suggested that either there is another gene responsible for BBS in these families or the Newfoundland population may not be ideal for LD studies. We screened these six Newfoundland families for mutations in BBS1 and found that affected individuals in five of them were homozygous for the same M390R mutation. There was no evidence for any BBS1 mutation in the affected individual in the sixth family. Therefore, one of the criteria for LD mapping was not met; namely, there should be a single disease-causing allele in the population. Haplotype analysis of unaffected individuals from south-west Newfoundland and English BBS1 patients homozygous for M390R, revealed that a second criterion for LD mapping was violated. The M390R mutation occurred in a common haplotype and both of these chromosomes, the ancestral wild-type and disease-causing haplotypes, were introduced to Newfoundland and spread by a founder effect. Moreover, it was found that disease-associated alleles occurred at relatively high frequencies in normal haplotypes and this probably accounted for the incorrect prediction in the previous LD study. Knowing the amount of genetic variation and its distribution in the Newfoundland population would be useful to maximize its potential for mapping hereditary disorders.

Comparative genomic analysis identifies an ADP-ribosylation factor-like gene as the cause of Bardet-Biedl syndrome (BBS3)

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous, pleiotropic human disorder characterized by obesity, retinopathy, polydactyly, renal and cardiac malformations, learning disabilities, and hypogenitalism. Eight BBS loci have been mapped, and seven genes have been identified. BBS3 was previously mapped to chromosome 3 by linkage analysis in a large Israeli Bedouin kindred. The rarity of other families mapping to the BBS3 locus has made it difficult to narrow the disease interval sufficiently to identify the gene by positional cloning. We hypothesized that the genomes of model organisms that contained the orthologues to known BBS genes would also likely contain a BBS3 orthologue. Therefore, comparative genomic analysis was performed to prioritize BBS candidate genes for mutation screening. Known BBS proteins were compared with the translated genomes of model organisms to identify a subset of organisms in which these proteins were conserved. By including multiple organisms that have relatively small genome sizes in the analysis, the number of candidate genes was reduced, and a few genes mapping to the BBS3 interval emerged as the best candidates for this disorder. One of these genes, ADP-ribosylation factor-like 6 (ARL6), contains a homozygous stop mutation that segregates completely with the disease in the Bedouin kindred originally used to map the BBS3 locus, identifying this gene as the BBS3 gene. These data illustrate the power of comparative genomic analysis for the study of human disease and identifies a novel BBS gene.

[Lymphangioma with epithelial hyperplasia included in a Bardet-Biedl syndrome]

INTRODUCTION

The Bardet-Biedl syndrome is a rare autosomal recessive disorder, which associates obesity, pigmentary retinopathy, hexadactyly, hypogenitalism, renal dysfunction and mental retardation. Other abnormalities can be observed in the Bardet-Biedl syndrome, but few cutaneous abnormalities have been described.

CASE REPORT

A 41 year-old woman, suffering from a Bardet-Biedl syndrome diagnosed when she was 7 Years old, presented with an atypical pseudo verruca-like, dark red lesion of the interbuttock area that had developed over fifteen Years and had become a handicap. The histological examination revealed a double component: epithelial, papillomatous and acanthosic on the one hand and vascular and lymphatic on the other, suggesting a lymphangioma with epidermal hyperplasia. Magnetic resonance imaging of the sacral area revealed a median subcutaneous lesion, extending deeply to the third coccygial vertebra.

DISCUSSION

Such a lymphangioma is unusual. Because it occurred during a rare polymalformative syndrome, we suggest that it may represent a new clinical sign that can be observed during the Bardet-Biedl syndrome.

Genetic interaction of BBS1 mutations with alleles at other BBS loci can result in non-Mendelian Bardet-Biedl syndrome

Bardet-Biedl syndrome is a genetically and clinically heterogeneous disorder caused by mutations in at least seven loci (BBS1-7), five of which are cloned (BBS1, BBS2, BBS4, BBS6, and BBS7). Genetic and mutational analyses have indicated that, in some families, a combination of three mutant alleles at two loci (triallelic inheritance) is necessary for pathogenesis. To date, four of the five known BBS loci have been implicated in this mode of oligogenic disease transmission. We present a comprehensive analysis of the spectrum, distribution, and involvement in non-Mendelian trait transmission of mutant alleles in BBS1, the most common BBS locus. Analyses of 259 independent families segregating a BBS phenotype indicate that BBS1 participates in complex inheritance and that, in different families, mutations in BBS1 can interact genetically with mutations at each of the other known BBS genes, as well as at unknown loci, to cause the phenotype. Consistent with this model, we identified homozygous M390R alleles, the most frequent BBS1 mutation, in asymptomatic individuals in two families. Moreover, our statistical analyses indicate that the prevalence of the M390R allele in the general population is consistent with an oligogenic rather than a recessive model of disease transmission. The distribution of BBS oligogenic alleles also indicates that all BBS loci might interact genetically with each other, but some genes, especially BBS2 and BBS6, are more likely to participate in triallelic inheritance, suggesting a variable ability of the BBS proteins to interact genetically with each other.

Identification of a novel Bardet-Biedl syndrome protein, BBS7, that shares structural features with BBS1 and BBS2

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder, the primary features of which include obesity, retinal dystrophy, polydactyly, hypogenitalism, learning difficulties, and renal malformations. Conventional linkage and positional cloning have led to the mapping of six BBS loci in the human genome, four of which (BBS1, BBS2, BBS4, and BBS6) have been cloned. Despite these advances, the protein sequences of the known BBS genes have provided little or no insight into their function. To delineate functionally important regions in BBS2, we performed phylogenetic and genomic studies in which we used the human and zebrafish BBS2 peptide sequences to search dbEST and the translation of the draft human genome. We identified two novel genes that we initially named "BBS2L1" and "BBS2L2" and that exhibit modest similarity with two discrete, overlapping regions of BBS2. In the present study, we demonstrate that BBS2L1 mutations cause BBS, thereby defining a novel locus for this syndrome, BBS7, whereas BBS2L2 has been shown independently to be BBS1. The motif-based identification of a novel BBS locus has enabled us to define a potential functional domain that is present in three of the five known BBS proteins and, therefore, is likely to be important in the pathogenesis of this complex syndrome.

The human obesity gene map: the 2002 update

This is the ninth update of the human obesity gene map, incorporating published results through October 2002 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and various animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. For the first time, transgenic and knockout murine models exhibiting obesity as a phenotype are incorporated (N = 38). As of October 2002, 33 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and the causal genes or strong candidates have been identified for 23 of these syndromes. QTLs reported from animal models currently number 168; there are 68 human QTLs for obesity phenotypes from genome-wide scans. Additionally, significant linkage peaks with candidate genes have been identified in targeted studies. Seven genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 222 studies reporting positive associations with 71 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. More than 300 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

Evaluation of complex inheritance involving the most common Bardet-Biedl syndrome locus (BBS1)

Bardet-Biedl syndrome (BBS) is a genetic disorder with the primary features of obesity, pigmentary retinopathy, polydactyly, renal malformations, mental retardation, and hypogenitalism. Patients with BBS are also at increased risk for diabetes mellitus, hypertension, and congenital heart disease. BBS is known to map to at least six loci: 11q13 (BBS1), 16q21 (BBS2), 3p13-p12 (BBS3), 15q22.3-q23 (BBS4), 2q31 (BBS5), and 20p12 (BBS6). Although these loci were all mapped on the basis of an autosomal recessive mode of inheritance, it has recently been suggested-on the basis of mutation analysis of the identified BBS2, BBS4, and BBS6 genes-that BBS displays a complex mode of inheritance in which, in some families, three mutations at two loci are necessary to manifest the disease phenotype. We recently identified BBS1, the gene most commonly involved in Bardet-Biedl syndrome. The identification of this gene allows for further evaluation of complex inheritance. In the present study we evaluate the involvement of the BBS1 gene in a cohort of 129 probands with BBS and report 10 novel BBS1 mutations. We demonstrate that a common BBS1 missense mutation accounts for approximately 80% of all BBS1 mutations and is found on a similar genetic background across populations. We show that the BBS1 gene is highly conserved between mice and humans. Finally, we demonstrate that BBS1 is inherited in an autosomal recessive manner and is rarely, if ever, involved in complex inheritance.

Barrier to autointegration factor interacts with the cone-rod homeobox and represses its transactivation function

Crx (cone-rod homeobox) is a homeodomain transcription factor implicated in regulating the expression of photoreceptor and pineal genes. To identify proteins that interact with Crx in the retina, we carried out a yeast two-hybrid screen of a retinal cDNA library. One of the identified clones encodes Baf (barrier to autointegration factor), which was previously shown to have a role in mitosis and retroviral integration. Additional biochemical assays provided supporting evidence for a Baf-Crx interaction. The Baf protein is detectable in all nuclear layers of the mouse retina, including the photoreceptors and the bipolar cells where Crx is expressed. Transient transfection assays with a rhodopsin-luciferase reporter in HEK293 cells demonstrate that overexpression of Baf represses Crx-mediated transactivation, suggesting that Baf acts as a negative regulator of Crx. Consistent with this role for Baf, an E80A mutation of CRX associated with cone-rod dystrophy has a higher than normal transactivation potency but a reduced interaction with Baf. Although our studies did not identify a causative Baf mutation in retinopathies, we suggest that Baf may contribute to the phenotype of a photoreceptor degenerative disease by modifying the activity of Crx. In view of the ubiquitous expression of Baf, we hypothesize that it may play a role in regulating tissue- or cell type-specific gene expression by interacting with homeodomain transcription factors.

Current and future genetic screening for male infertility

Although much of male infertility is currently unexplained, it is likely that underlying defects in critical genes or entire gene pathways are responsible. Because powerful technologies exist to bypass severe male-factor infertility, improving the diagnosis of genetic infertility is important for the infertile couple, not only to explain the problem but also to inform them of conditions potentially transmissible to offspring.

Cerebellar vermis hypoplasia in a patient with Bardet-Biedl syndrome

Laurence-Moon-Bardet-Biedl syndome is an autosomal recessive condition characterized by retinal dystrophy, obesity, mental retardation, distal limb anomaly, hypogonadism, and renal dysfunction. The symptoms vary among families and even among affected siblings. Certain clinical signs have been used to identify subgroups of patients with this complex condition. Laurence-Moon syndrome as a distinct entity is rare and features paraplegia in the absence of polydactyly or obesity. Bardet-Biedl syndrome is characterized by distal limb anomaly, obesity, and renal involvement, but neurologic symptoms are very unusual. We report a patient exhibiting characteristic features of Bardet-Biedl syndrome in addition to cerebellar vermis hypoplasia and mega cisterna magna.

A review of the literature of Bardet-Biedl disease and report of three cases associated with metabolic syndrome and diagnosed after the age of fifty

Bardet-Biedl syndrome (BBS) is a genetic autosomal-recessive disease (formerly grouped with Laurence-Moon-Biedl syndrome but considered today as a separate entity) characterized by abdominal obesity, mental retardation, dysphormic extremities (syndactyly, brachydactyly or polydactyly), retinal dystrophy or pigmentary retinopathy, hypogonadism or hypogenitalism (limited to male patients) and kidney structural abnormalities or functional impairment. The expression and severity of the various clinical BBS features show inter- and intrafamilial variability. This study focuses on three cases of familial BBS--two sisters and one brother (66, 64 and 51 years of age, respectively)--with the main cardinal findings of the disease plus a classic 'metabolic syndrome' (characterized by abdominal obesity, atherogenic dyslipidaemia, raised blood pressure, insulin resistance with or without glucose intolerance, and prothrombotic risk and proinflammatory states). One female patient (not affected by reproductive dysfunction) had three healthy offspring, while the other two patients were unmarried. Another severely affected brother died at 70 years of age; two other brothers are lean but affected by nephropathy, retinopathy, slight mental retardation, polydactyly, hypertension and thrombotic diseases, and had healthy offspring. BBS is a rather rare but severe syndrome that is often mis- or undiagnosed. Ophthalmologists, endocrinologists and nephrologists should be aware of BBS because of its adverse prognosis--early onset of blindness, associated findings of metabolic syndrome and increased vascular risk, and severe renal impairment (the most frequent cause of reduced survival and death early in life).

The human obesity gene map: the 2001 update

This report constitutes the eighth update of the human obesity gene map, incorporating published results up to the end of October 2001. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) uncovered in human genome-wide scans and in crossbreeding experiments in various animal models, association and linkage studies with candidate genes and other markers is reviewed. The human cases of obesity related in some way to single-gene mutations in six different genes are incorporated. Twenty-five Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models currently reaches 165. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 174 studies reporting positive associations with 58 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months, and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.

Triallelic inheritance in Bardet-Biedl syndrome, a Mendelian recessive disorder

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder characterized by multiple clinical features that include pigmentary retinal dystrophy, polydactyly, obesity, developmental delay, and renal defects. BBS is considered an autosomal recessive disorder, and recent positional cloning efforts have identified two BBS genes (BBS2 and BBS6). We screened our cohort of 163 BBS families for mutations in both BBS2 and BBS6 and report the presence of three mutant alleles in affected individuals in four pedigrees. In addition, we detected unaffected individuals in two pedigrees who carry two BBS2 mutations but not a BBS6 mutation. We therefore propose that BBS may not be a single-gene recessive disease but a complex trait requiring three mutant alleles to manifest the phenotype. This triallelic model of disease transmission may be important in the study of both Mendelian and multifactorial disorders.

Patient with Bardet-Biedl syndrome presenting with nystagmus at fifteen months of age

Bardet-Beidl syndrome (BBS) is an autosomal recessive disorder predominantly characterized by dysmorphic distal extremities, obesity, renal abnormalities, hypogenitalism, and varying degrees of mental retardation. Other less common abnormalities are cardiac and hepatic diseases, anal atresia, cerebellar dysfunction, and, in rare cases, nystagmus. This is a report of a child with Bardet-Biedl syndrome who presented at 15 months of age with a horizontal and rotary nystagmus as the initial sign of this disorder.

Identification of the gene that, when mutated, causes the human obesity syndrome BBS4

Bardet-Biedl syndrome (BBS, MIM 209900) is a heterogeneous autosomal recessive disorder characterized by obesity, pigmentary retinopathy, polydactyly, renal malformations, mental retardation, and hypogenitalism. The disorder is also associated with diabetes mellitus, hypertension, and congenital heart disease. Six distinct BBS loci map to 11q13 (BBS1), 16q21 (BBS2), 3p13-p12 (BBS3), 15q22.3-q23 (BBS4), 2q31 (BBS5), and 20p12 (BBS6). Although BBS is rare in the general population (<1/100,000), there is considerable interest in identifying the genes causing BBS because components of the phenotype, such as obesity and diabetes, are common. We and others have demonstrated that BBS6 is caused by mutations in the gene MKKS (refs. 12,13), mutation of which also causes McKusick-Kaufman syndrome (hydrometrocolpos, post-axial polydactyly, and congenital heart defects). MKKS has sequence homology to the alpha subunit of a prokaryotic chaperonin in the thermosome Thermoplasma acidophilum. We recently identified a novel gene that causes BBS2. The BBS2 protein has no significant similarity to other chaperonins or known proteins. Here we report the positional cloning and identification of mutations in BBS patients in a novel gene designated BBS4.

The molecular genetics of Bardet–Biedl syndrome

Bardet-Biedl syndrome (BBS) has been shown to be a genetically heterogeneous disorder involving genes mapping to at least six known loci. One BBS gene (MKKS) has been identified and the form of the disorder caused by this gene is allelic to McKusick-Kaufman syndrome. MKKS codes for a putative chaperonin, suggesting that other BBS genes may also code for components of chaperone complexes or be substrates of chaperone function.

09/15: Comparative genomics of a conserved chromosomal region associated with a complex human phenotype

Three genes that encode related immunoglobulin superfamily molecules have recently been mapped to human chromosome 15 in the region q22.3-q23 and to the syntenic region on mouse chromosome 9. These genes presumably derived from gene duplications, and they are highly similar to Deleted in Colorectal Cancer (DCC), which functions as an axon guidance molecule during development of the nervous system. To find out whether additional genes of this class were present in a chromosomal cluster, we produced a comparative physical map within the region of synteny between mouse chromosome 9 and human chromosome 15. This interval overlaps the critical region for the fourth genetic locus for Bardet-Biedl syndrome (BBS4) in humans. Bardet-Biedl syndrome (OMIM 600374) is characterized by poly/syn/brachydactyly, retinal degeneration, hypogonadism, mental retardation, obesity, diabetes, and kidney abnormalities. A detailed map of this locus will help to identify candidate genes for this disorder.

Prenatal diagnosis of Bardet-Biedl syndrome by targeted second-trimester sonography

Bardet-Biedl syndrome (BBS) is an autosomal recessive disorder characterized by mental retardation, obesity, retinal degeneration, polydactyly and syndactyly, diabetes mellitus, hypogenitalism, renal dysplasia and short stature. Definitive molecular diagnosis for BBS is not currently available and counseling of affected families is based on the 25% recurrence risk consistent with autosomal recessive inheritance. Our case presents the first successful use of second trimester targeted sonographic anatomy scanning to prospectively identify a fetus affected with BBS, and indicates that ultrasound can be of critical importance in providing precise as well as timely prenatal diagnosis for families at risk for this serious disorder.

Cloning and characterization of a human beta,beta-carotene-15,15'-dioxygenase that is highly expressed in the retinal pigment epithelium

Retinoids play a critical role in vision, as well as in development and cellular differentiation. beta,beta-Carotene-15,15'-dioxygenase (Bcdo), the enzyme that catalyzes the oxidative cleavage of beta,beta-carotene into two retinal molecules, plays an important role in retinoid synthesis. We report here the first cloning of a mammalian Bcdo. Human BCDO encodes a protein of 547 amino acid residues that demonstrates 68% identity with chicken Bcdo. It is expressed highly in the retinal pigment epithelium (RPE) and also in kidney, intestine, liver, brain, stomach, and testis. The gene spans approximately 20 kb, is composed of 11 exons and 10 introns, and maps to chromosome 16q21-q23. A mouse orthologue was also identified, and its predicted amino acid sequence is 83% identical with human BCDO. Biochemical analysis of baculovirus expressed human BCDO demonstrates the predicted beta,beta-carotene-15,15'-dioxygenase activity. The expression pattern of BCDO suggests that it may provide a local supplement to the retinoids available to photoreceptors, as well as a supplement to the retinoid pools utilized elsewhere in the body. In addition, the finding that many of the enzymes involved in retinoid metabolism are mutated in retinal degenerations suggests that BCDO may also be a candidate gene for retinal degenerative disease.

Genetic and mutational analyses of a large multiethnic Bardet-Biedl cohort reveal a minor involvement of BBS6 and delineate the critical intervals of other loci

Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder characterized primarily by obesity, polydactyly, retinal dystrophy, and renal disease. The significant genetic and clinical heterogeneity of this condition have substantially hindered efforts to positionally clone the numerous BBS genes, because the majority of available pedigrees are small and the disorder cannot be assigned to any of the six known BBS loci. Consequently, the delineation of critical BBS intervals, which would accelerate the discovery of the underlying genetic defect(s), becomes difficult, especially for loci with minor contributions to the syndrome. We have collected a cohort of 163 pedigrees from diverse ethnic backgrounds and have evaluated them for mutations in the recently discovered BBS6 gene (MKKS) on chromosome 20 and for potential assignment of the disorder to any of the other known BBS loci in the human genome. Using a combination of mutational and haplotype analysis, we describe the spectrum of BBS6 alterations that are likely to be pathogenic; propose substantially reduced critical intervals for BBS2, BBS3, and BBS5; and present evidence for the existence of at least one more BBS locus. Our data also suggest that BBS6 is a minor contributor to the syndrome and that some BBS6 alleles may act in conjunction with mutations at other BBS loci to cause or modify the BBS phenotype.

C-terminal elements control location, activation threshold, and p38 docking of ribosomal S6 kinase B (RSKB)

RSKB, a p90 ribosomal S6 protein kinase with two catalytic domains, is activated by p38- and extracellular signal-regulated kinase mitogen-activated protein kinase pathways. The sequences between the two catalytic domains and of the C-terminal extension contain elements that control RSKB activity. The C-terminal extension of RSKB presents a putative bipartite (713)KRX(14)KRRKQKLRS(737) nuclear location signal. The distinct cytoplasmic and nuclear locations of various C-terminal truncation mutants supported the hypothesis that the nuclear location signal was essential to direct RSKB to the nuclear compartment. The (725)APLAKRRKQKLRS(737) sequence also was essential for the intermolecular association of RSKB with p38. The activation of RSKB through p38 could be dissociated from p38 docking, because RSKB truncated at Ser(681) strongly responded to p38 pathway activity. Interestingly, Delta(725-772)-RSKB was nearly nonresponsive to p38. Sequence alignment with the autoinhibitory C-terminal extension of Ca+2/calmodulin-dependent protein kinase I predicted a conserved regulatory (708)AFN(710) motif. Alanine mutation of the key Phe709 residue resulted in strongly elevated basal level RSKB activity. A regulatory role also was assigned to Thr687, which is located in a mitogen-activated protein kinase phosphorylation consensus site. These findings support that the RSKB C-terminal extension contains elements that control activation threshold, subcellular location, and p38 docking.

The human obesity gene map: the 2000 update

This report constitutes the seventh update of the human obesity gene map incorporating published results up to the end of October 2000. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci uncovered in human genome-wide scans and in cross-breeding experiments in various animal models, and association and linkage studies with candidate genes and other markers are reviewed. Forty-seven human cases of obesity caused by single-gene mutations in six different genes have been reported in the literature to date. Twenty-four Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different quantitative trait loci reported from animal models currently reaches 115. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 130 studies reporting positive associations with 48 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.

Renal cancer and malformations in relatives of patients with Bardet-Biedl syndrome

BACKGROUND

Bardet-Biedl syndrome (BBS) is an autosomal recessive disorder with five loci identified thus far. The spectrum of disease includes diverse malformations of the kidney and lower urinary tract. The incidence of BBS is approximately 1/100,000 with a predicted heterozygote frequency of 1/160, and it has been suggested that heterozygotes are at increased risk of obesity and hypertension.

METHODS

We describe renal disease in relatives of 109 UK BBS patients. Using PCR with fluorescent microsatellite markers we amplified DNA derived from renal tumours of affected parents to determine whether there was loss of heterozygosity at any of four BBS loci and two other gene loci associated with clear cell renal cell carcinoma (CC-RCC).

RESULTS

CC-RCC was diagnosed in three of 180 BBS parents and there was loss of heterozygosity at BBS1 (11q13) in the tumour tissue of one of these subjects. In addition, there was a high incidence of renal agenesis in siblings of BBS patients and two BBS families were identified with apparently dominant inheritance of renal malformations. In one family we were able to demonstrate that renal malformations segregated with the BBS2 locus (16q21).

CONCLUSIONS

Since all parents and two-thirds of siblings of BBS patients must be heterozygous for BBS mutations, our observations may implicate BBS genes in the pathogenesis of both renal cancer and malformations, both disorders of precursor cell growth and differentiation. We suggest these observations may have important implications for screening potential BBS carriers for kidney disease and may lead to a greater understanding of the aetiology of renal disease in the general population.

Bardet-Biedl syndrome type 3 in an Iranian family: clinical study and confirmation of disease localization

Bardet-Biedl syndrome (BBS) is a group of autosomal recessive MCA/MR syndromes characterized by pigmentary retinopathy, postaxial polydactyly, hypogenitalism, obesity, and mental retardation. Five BBS loci have been identified; among them, BBS type 1 (BBS1) and type 3 (BBS3) are most common and most rare, respectively. We encountered an Iranian family that had seven affected members. All patients had a history of mild to severe obesity, but it was reversible in some patients by caloric restriction and exercise. All patients had pigmentary retinopathy, beginning as night blindness in early childhood and progressing toward severe impairment of vision by the end of the second decade. Polydactyly varied in limb distribution, ranging from four-limb involvement to random involvement or even to nonaffectedness. Six of the seven patients were not mentally retarded. Although kidney anomaly or an adrenal mass was pres- ent in two patients, the fact that one patient had seven children rules out reproductive dysfunction. Linkage analysis with microsatellite markers showed that the disease in the family was assigned to a region around marker loci at 3p13-p12 (maximum LOD score = 4.15 and recombination fraction straight theta = 0, at D3S1603 microsatellite marker), to which the BBS3 locus has been mapped. Haplotype analysis did not reduce the extent of the previously reported critical region of BBS3. A comparison of clinical manifestations of our patients with those of previously reported BBS3 patients did not support any type-specific phenotypes, though manifestations in our patients are similar to those in BBS3 patients of a family in Newfoundland.

Cloning, expression and chromosomal localization of a novel human dipeptidyl peptidase (DPP) IV homolog, DPP8

Dipeptidyl peptidase (DPP) IV has roles in T-cell costimulation, chemokine biology, type-II diabetes and tumor biology. Fibroblast activation protein (FAP) has been implicated in tumor growth and cirrhosis. Here we describe DPP8, a novel human postproline dipeptidyl aminopeptidase that is homologous to DPPIV and FAP. Northern-blot hybridization showed that the tissue expression of DPP8 mRNA is ubiquitous, similar to that of DPPIV. The DPP8 gene was localized to chromosome 15q22, distinct from a closely related gene at 19p13.3 which we named DPP9. The full-length DPP8 cDNA codes for an 882-amino-acid protein that has about 27% identity and 51% similarity to DPPIV and FAP, but no transmembrane domain and no N-linked or O-linked glycosylation. Western blots and confocal microscopy of transfected COS-7 cells showed DPP8 to be a 100-kDa monomeric protein expressed in the cytoplasm. Purified recombinant DPP8 hydrolyzed the DPPIV substrates Ala-Pro, Arg-Pro and Gly-Pro. Thus recombinant DPP8 shares a postproline dipeptidyl aminopeptidase activity with DPPIV and FAP. DPP8 enzyme activity had a neutral pH optimum consistent with it being nonlysosomal. The similarities between DPP8 and DPPIV in tissue expression pattern and substrates suggests a potential role for DPP8 in T-cell activation and immune function.

Mutations in MKKS cause Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is an autosomal recessive disorder with locus heterogeneity. None of the 'responsible' genes have previously been identified. Some BBS cases (approximately 10%) remain unassigned to the five previously mapped loci. McKusick-Kaufma syndrome (MKS) includes hydrometrocolpos, postaxial polydactyly and congenital heart disease, and is also inherited in an autosomal recessive manner. We ascertained 34 unrelated probands with classic features of BBS including retinitis pigmentosa (RP), obesity and polydactyly. The probands were from families unsuitable for linkage because of family size. We found MKKS mutations in four typical BBS probands (Table 1). The first is a 13-year-old Hispanic girl with severe RP, PAP, mental retardation and obesity (BMI >40). She was a compound heterozygote for a missense (1042GA, G52D) and a nonsense (1679TA, Y264stop) mutation in exon 3. Cloning and sequencing of the separate alleles confirmed that the mutations were present in trans. A second BBS proband (from Newfoundland), born to consanguineous parents, was homozygous for two deletions (1316delC and 1324-1326delGTA) in exon 3, predicting a frameshift. An affected brother was also homozygous for the deletions, whereas an unaffected sibling had two normal copies of MKKS. Both the proband and her affected brother had RP, PAP, mild mental retardation, morbid obesity (BMI >50 and 37, respectively), lobulated kidneys with prominent calyces and diabetes mellitus (diagnosed at ages 33 and 30, respectively). A deceased sister (DNA unavailable) had similar phenotypic features (RP with blindness by age 13, BMI >45, abnormal glucose tolerance test and IQ=64, vaginal atresia and syndactyly of both feet). Both parents and the maternal grandfather were heterozygous for the deletions. Genotyping with markers from the MKKS region confirmed homozygosity at 20p12 in both affected individuals.