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Dominantly inherited cardioskeletal myopathy with lysosomal glycogen storage and normal acid maltase levels.

A family is presented in which 7 members over 3 generations were affected by cardioskeletal myopathy. A vacuolar myopathy with excessive free and intralysosomal glycogen storage in skeletal and cardiac striated muscle was identified in biopsy studies. Post-mortem studies in several patients revealed changes of a congestive cardiomyopathy with myocardial fibrosis. Acid maltase, phosphorylase, debrancher and lysosomal enzyme screens, and glycolytic enzyme levels in skeletal muscle, were normal in 1 case. This is the third report of non-acid maltase deficient lysosomal glycogen storage disease and adds to previous reports with the presentation of detailed family studies, examined of ante- and post-mortem cardiac histology and reports of detailed glycolytic and lysosomal enzyme analysis. This syndrome is unusual among glycogenoses in having a dominant inheritance pattern.

Adult↗

Chromosome X-wide association study in multiple system atrophy identifies sex-differential risk loci.

The human X chromosome accounts for ∼5% of the genome. Despite its size, the role of X-chromosomal variants in human diseases is not well understood, mainly due to its distinct inheritance pattern and the frequent omission of sex chromosomes from genome-wide association studies. This study used whole-genome sequencing data from 888 multiple system atrophy (MSA) cases and 7128 controls to perform an X-chromosome-wide common variant association study. Our analyses revealed two sex-differential risk loci: one located at Xq28, associated with increased risk for MSA in females [index variant: rs4898389, odds ratio (OR) = 1.69, 95% confidence interval (CI) = 1.40-2.03, P-value = 2.43 × 10⁻⁸], and another at Xp22.2 within the TBL1X gene, identified in males (index variant: rs6638956, OR = 1.48, 95%CI = 1.26-1.73, P-value = 9.92 × 10⁻⁷). In the Xq28 locus, colocalization analyses pointed to FAM3A and PLXNA3 as genes of interest. These findings emphasize the vital role of sex-differential genetic factors in the pathogenesis of MSA.

Humans↗

A multigenerational family with multiple sclerosis.

We report a family with 15 individuals affected with multiple sclerosis present in three and possibly four generations. The segregation of multiple sclerosis within this pedigree is consistent with an autosomal dominant mode of inheritance with reduced penetrance. The clinical characteristics of the affected individuals are indistinguishable from those seen in sporadic multiple sclerosis with respect to sex ratio, age at onset, onset symptom, MRI and clinical course. Eleven of 14 cases (78.6%) were positive for the known multiple sclerosis-associated major histocompatibility complex (MHC) Class II HLA DRB1*15 allele. Parametric linkage analysis gave a non-significant LOD score of 0.31 (theta; = 0.33) for the DRB1 gene. However, among 11 affected children with at least one DRB1*15 bearing parent, all 11 out of 11 received at least one copy of this known susceptibility allele. A transmission disequilibrium test analysis was significant for the DRB1*15 allele within this single family; P = 0.0054. The inheritance pattern in this family suggests the presence of a single major locus responsible for multiple sclerosis susceptibility, with DRB1 acting as an important modifier. This family could be an important resource for the identification of a multiple sclerosis susceptibility gene.

Adolescent↗

Autosomal dominant restless legs syndrome maps on chromosome 14q.

Restless legs syndrome (RLS) is a common neurological disorder characterized by an irresistible desire to move the extremities associated with paraesthesia/dysaesthesia. These symptoms occur predominantly at rest and worsen at night, resulting in nocturnal insomnia and chronic sleep deprivation. In this paper, we show significant evidence of linkage to a new locus for RLS on chromosome 14q13-21 region in a 30-member, three-generation Italian family affected by RLS and periodic leg movements in sleep (PLMS). This is the second RLS locus identified so far and the first consistent with an autosomal dominant inheritance pattern. The new RLS critical region spans 9.1 cM, between markers D14S70 and D14S1068. The maximum two-point log of odds ratio score value, of 3.23 at theta = 0.0, was obtained for marker D14S288. The accurate clinical evaluation of RLS-affected, as well as unaffected, family members allowed for the configuring of RLS as a phenotypic spectrum ranging from PLMS to RLS. Motor component, both while awake and during sleep, was an important aspect of the phenotype in the family analysed. The complementary clinical and genetic studies on multiplex families are likely to be of the utmost importance in unfolding the complete expressivity of RLS phenotype spectrum.

Adolescent↗

Striosomes and mood dysfunction in Huntington's disease.

Variable phenotype is common in neurological disorders with single-gene inheritance patterns. In Huntington's disease, mood and cognitive symptoms are variably co-expressed with motor symptoms. There is also variable degeneration of neurons in the two major neurochemical compartments of the striatum, the striosomes and the extrastriosomal matrix. To determine whether the phenotypic variability in Huntington's disease is related to this compartmental organization, we carried out a double-blind study in which we used GABA(A) receptor immunohistochemistry to analyse the status of striosomes and matrix in the brains of 35 Huntington's disease cases and 13 control cases, and collected detailed data on the clinical symptomatology expressed by the patients from family members and records. We report here a significant association between pronounced mood dysfunction in Huntington's disease patients and differential loss of the GABA(A) receptor marker in striosomes of the striatum. This association held for both clinical onset and end-stage assessments of symptoms. The cases with accentuated striosome abnormality further exhibited later onset age, lower disease grade and lower CAG repeat length in the HD gene. We found no independent association, however, between CAG repeat length or age of onset and mood dysfunction. We suggest that variation in clinical symptomatology in Huntington's disease is associated with variation in the relative abnormality of GABA(A) receptor expression in the striosome and matrix compartments of the striatum, and that striosome-related circuits may modulate mood functioning.

Adult↗

Diploids derived from polyploids: genetic characteristics of four novel interspecific Sorghum populations.

Polyploidy has repeatedly shaped grass evolution, yet direct observations of how polyploid-derived chromosomes behave when returned to diploidy remain rare. Interspecific crosses between diploid Sorghum bicolor and tetraploid hybrids derived from Sorghum halepense generate mixed-ploidy progeny, providing an opportunity to examine chromosome transmission during the early stages of diploidization. Using genome-wide SNP markers, we characterized chromosomal inheritance patterns in 2 diploid and 2 tetraploid families derived from these crosses. Genotype-dosage profiles alone distinguished diploids from tetraploids with complete accuracy, reflecting strong ploidy-dependent differences in dosage-class distributions. Although diploid progeny retained much of the halepense-derived genomic background, several genomic intervals exhibited extended, nonrandom runs of S. bicolor homozygosity that remained polymorphic in corresponding tetraploid populations. These patterns, together with recurrent segregation distortion across independent families, suggest that the transition from tetraploidy to diploidy can expose allelic combinations that differ in transmission or viability. Analyses of flowering time further indicated that diploid and tetraploid derivatives possess distinct genomic architectures, with major association peaks occurring in different chromosomal regions across ploidy levels. Collectively, these results indicate that early diploidization involves nonrandom retention and loss of parental haplotypes shaped by both selective and structural constraints. The diploid extractions characterized here provide a rare empirical system for investigating the early stages of diploidization and a practical framework for studying and eventually mobilizing polyploid-derived variation for sorghum germplasm development. However, broader integration into elite breeding programs will require additional evaluation of cross-fertility, meiotic behavior, and chromosomal stability across diverse breeding backgrounds.

Sorghum↗

Linkage of the steroid sulfatase gene to the sex-reversed mutation in the mouse.

Dosage studies and the inheritance pattern of the gene for steroid sulfatase (Sts) in the mouse have previously provided indirect evidence for a functional Y-linked allele which recombines obligatorily with its X-linked allele in male meiosis. In this study, we have investigated the linkage relationship of Sts and the sex-reversed mutation (Sxr), a gene which is known to reside in the pairing region of the Y chromosome. The results clearly demonstrate that Sxr and Sts are linked in a region of obligatory recombination and Sts maps proximal to Sxr with most recombinants occurring proximal to the two genes.

Alleles↗

The unusual sexual preferences of a chlamydomonas mutant may provide insight into mating-type evolution.

Chlamydomonas monoica undergoes intraclonal mating-type differentiation (homothallism). Although the species differs in this regard from the more commonly studied heterothallic C. reinhardtii, cell-cell interactions and progression of the sexual cycle are similar for many homothallic and heterothallic species of the genus. Regulation of chloroplast gene transmission by the nuclear mating-type alleles (mt+ and mt-) is another common denominator for Chlamydomonas species studied thus far. We have previously reported the use of chloroplast inheritance patterns to identify mutants of C. monoica that have lost the potential to function as the mt+ mating-type. A similar screening procedure led to the isolation of an unusual mutant, mtl-3 whose phenotype is less readily explained. Chloroplast gene transmission patterns in crosses involving mtl-3 suggest that the mtl-3 strain mates preferentially as mt+. However, normal mating efficiencies and high zygospore viability are observed in clonal culture, indicating the unbiased production of functional opposite mating-types. By construction of appropriately marked strains we have been able to show that mtl-3 mt- gametes prefer the mt+ gametes of their own strain. A model is presented which invokes unequal crossing over between highly homologous flagellar agglutinin genes to account for the unusual properties of the mtl-3 strain and for the evolution of mating barriers within the genus.

Alleles↗

Mendelian factors underlying quantitative traits in tomato: comparison across species, generations, and environments.

As part of ongoing studies regarding the genetic basis of quantitative variation in phenotype, we have determined the chromosomal locations of quantitative trait loci (QTLs) affecting fruit size, soluble solids concentration, and pH, in a cross between the domestic tomato (Lycopersicon esculentum Mill.) and a closely-related wild species, L. cheesmanii. Using a RFLP map of the tomato genome, we compared the inheritance patterns of polymorphisms in 350 F2 individuals with phenotypes scored in three different ways: (1) from the F2 progeny themselves, grown near Davis, California; (2) from F3 families obtained by selfing each F2 individual, grown near Gilroy, California (F3-CA); and (3) from equivalent F3 families grown near Rehovot, Israel (F3-IS). Maximum likelihood methods were used to estimate the approximate chromosomal locations, phenotypic effects (both additive effects and dominance deviations), and gene action of QTLs underlying phenotypic variation in each of these three environments. A total of 29 putative QTLs were detected in the three environments. These QTLs were distributed over 11 of the 12 chromosomes, accounted for 4.7-42.0% of the phenotypic variance in a trait, and showed different types of gene action. Among these 29 QTLs, 4 were detected in all three environments, 10 in two environments, and 15 in only a single environment. The two California environments were most similar, sharing 11/25 (44%) QTLs, while the Israel environment was quite different, sharing 7/20 (35%) and 5/26 (19%) QTLs with the respective California environments. One major goal of QTL mapping is to predict, with maximum accuracy, which individuals will produce progeny showing particular phenotypes. Traditionally, the phenotype of an individual alone has been used to predict the phenotype of its progeny. Our results suggested that, for a trait with low heritability (soluble solids), the phenotype of F3 progeny could be predicted more accurately from the genotype of the F2 parent at QTLs than from the phenotype of the F2 individual. For a trait with intermediate heritability (fruit pH), QTL genotype and observed phenotype were about equally effective at predicting progeny phenotype. For a trait with high heritability (mass per fruit), knowing the QTL genotype of an individual added little if any predictive value, to simply knowing the phenotype. The QTLs mapped in the L. esculentum X L. cheesmanii F2 appear to be at similar locations to many of those mapped in a previous cross with a different wild tomato (L. chmielewskii).(ABSTRACT TRUNCATED AT 400 WORDS)

Biological Evolution↗

Generation of a restriction fragment length polymorphism linkage map for Toxoplasma gondii.

We have constructed a genetic linkage map for the parasitic protozoan, Toxoplasma gondii, using randomly selected low copy number DNA markers that define restriction fragment length polymorphisms (RFLPs). The inheritance patterns of 64 RFLP markers and two phenotypic markers were analyzed among 19 recombinant haploid progeny selected from two parallel genetic crosses between PLK and CEP strains. In these first successful interstrain crosses, these RFLP markers segregated into 11 distinct genetic linkage groups that showed close correlation with physical linkage groups previously defined by molecular karyotype. Separate linkage maps, constructed for each of the 11 chromosomes, indicated recombination frequencies range from approximately 100 to 300 kb per centimorgan. Preliminary linkage assignments were made for the loci regulating sinefungin resistance (snf-1) on chromosome IX and adenine arabinoside (ara-1) on chromosome V by linkage to RFLP markers. Despite random segregation of separate chromosomes, the majority of chromosomes failed to demonstrate internal recombination events and in 3/19 recombinant progeny no intramolecular recombination events were detected. The relatively low rate of intrachromosomal recombination predicts that tight linkage for unknown genes can be established with a relatively small set of markers. This genetic linkage map should prove useful in mapping genes that regulate drug resistance and other biological phenotypes in this important opportunistic pathogen.

Animals↗

Statistical modeling of interlocus interactions in a complex disease: rejection of the multiplicative model of epistasis in type 1 diabetes.

In general, common diseases do not follow a Mendelian inheritance pattern. To identify disease mechanisms and etiology, their genetic dissection may be assisted by evaluation of linkage in mouse models of human disease. Statistical modeling of multiple-locus linkage data from the nonobese diabetic (NOD) mouse model of type 1 diabetes has previously provided evidence for epistasis between alleles of several Idd (insulin-dependent diabetes) loci. The construction of NOD congenic strains containing selected segments of the diabetes-resistant strain genome allows analysis of the joint effects of alleles of different loci in isolation, without the complication of other segregating Idd loci. In this article, we analyze data from congenic strains carrying two chromosome intervals (a double congenic strain) for two pairs of loci: Idd3 and Idd10 and Idd3 and Idd5. The joint action of both pairs is consistent with models of additivity on either the log odds of the penetrance, or the liability scale, rather than with the previously proposed multiplicative model of epistasis. For Idd3 and Idd5 we would also not reject a model of additivity on the penetrance scale, which might indicate a disease model mediated by more than one pathway leading to beta-cell destruction and development of diabetes. However, there has been confusion between different definitions of interaction or epistasis as used in the biological, statistical, epidemiological, and quantitative and human genetics fields. The degree to which statistical analyses can elucidate underlying biologic mechanisms may be limited and may require prior knowledge of the underlying etiology.

Animals↗

Pedigree data analysis with crossover interference.

We propose a new method for calculating probabilities for pedigree genetic data that incorporates crossover interference using the chi-square models. Applications include relationship inference, genetic map construction, and linkage analysis. The method is based on importance sampling of unobserved inheritance patterns conditional on the observed genotype data and takes advantage of fast algorithms for no-interference models while using reweighting to allow for interference. We show that the method is effective for arbitrarily many markers with small pedigrees.

Algorithms↗

Tetrazolium oxidase polymorphism in rainbow trout.

Tetrazolium oxidase from the blood and liver of rainbow trout was found to be genetically polymorphic. The inheritance pattern of the liver enzyme was compatible only with a one locus-two allele hypothesis. The enzymes in the blood while having an electrophoretically identical polymorphism could differ genotypically from that of the liver in a given fish. The significance of these findings to the understanding of the evolution of the salmonid genome is discussed.

Alleles↗

Linkage analysis conditional on HLA status in a large North American pedigree supports the presence of a multiple sclerosis susceptibility locus on chromosome 12p12.

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system with a probable immune-mediated pathogenesis. Strong evidence supports the hypothesis that MS is determined by genetic and environmental factors, but these factors remain largely undefined. The genetic component is suggested by a higher concordance rate in monozygotic (28%) versus dizygotic (5%) twins as well as familial recurrence risk. Several studies have shown association of MS with the histocompatibility leukocyte antigen (HLA) class II region, specifically DR15, DQ6. However, there is no convincing evidence of a common susceptibility locus. We have identified a pedigree of Pennsylvania Dutch extraction, in which MS segregates with an autosomal dominant inheritance pattern. We have collected blood samples from 18 family members, seven of whom show typical signs of MS lesions by magnetic resonance imaging. The 18 individuals were serotyped for HLA class I and II and analyzed by a genome-wide screen for linkage analysis. We have found evidence for suggestive linkage to markers on 12p12 with a maximum multipoint LOD score of 2.71, conditional on the presence of DR15, DQ6. Contingency table analysis showed that all MS affected individuals have both the DR15, DQ6 allele and the 12p12 haplotype whereas the unaffected individuals have either one or neither of these markers (P = 0.00011). Our data suggests that both HLA DR15, DQ6 and a novel locus on chromosome 12p12 may be necessary for development of MS in this family.

Chromosome Mapping↗

Crouzon syndrome: mutations in two spliceoforms of FGFR2 and a common point mutation shared with Jackson-Weiss syndrome.

Dominant mutations in the fibroblast growth factor receptor 2 (FGFR2) gene have been recently identified as causes of four phenotypically distinct craniosynostosis syndromes, including Crouzon, Jackson-Weiss, Pfeiffer, and Apert syndromes. These data suggest that the genetics of the craniosynostosis syndromes is more complex than would be expected from their simple autosomal-dominant inheritance pattern. Identical mutations in the FGFR2 gene have been reported to cause both Pfeiffer and Crouzon syndrome phenotypes. We now report the finding of a mutation in exon IIIc of the FGFR2 gene in a kindred affected with Crouzon syndrome (C1043 to G; Ala344Gly) that is identical to the mutation previously associated with Jackson-Weiss syndrome. We also report finding in a Crouzon kindred a mutation in the 3' end of exon IIIu (formerly referred to as exon 5, exon 7, or exon U) (A878 to C; Gln289Pro) which encodes the amino terminal portion of the Ig-like III domain of the FGFR2 protein. This exon is common to both the FGFR2 and the KGFR spliceoforms of the FGFR2 gene, unlike all previously reported Crouzon mutations, which have been found only in the FGFR2 spliceoform. These findings reveal further unexpected complexity in the molecular genetics of these craniosynostosis syndromes. The data implies that second-site mutations in FGFR2 itself (outside of exon IIIc) or in other genes may determine specific aspects of the phenotypes of craniosynostosis syndromes.

Base Sequence↗

Unravelling the genetics of vesicoureteric reflux: a common familial disorder.

Primary vesicoureteric reflux (VUR) is one of the more common genetic disorders. Little is yet known about the genetics of this potentially manageable childhood condition, which is characterised by regurgitation of urine from the bladder to the kidney. The VUR phenotype is associated with shortness of the submucosal segment of the ureter due to congenital lateral ectopia of the ureteric orifice. VUR is found in 30-50% of infants and young children with a urinary tract infection. A serious concern in families with an affected patient is that approximately one half of siblings or offspring will be affected, but up to a half of these affected siblings and offspring may be asymptomatic in childhood. If left untreated, these patients may present later in life with proteinuria, hypertension or renal failure. VUR is the commonest cause of end-stage renal failure in children, and an important cause in adults. As the kidney damage resulting from severe VUR is preventable, early detection is desirable. The techniques for clinical diagnosis are invasive and costly, reinforcing the importance of identification of a gene for VUR to facilitate genetic screening. Although family studies suggest a major dominant gene, the inheritance pattern is still a matter of debate. In rare instances, VUR occurs in association with other diseases, such as the coloboma-ureteric-renal syndrome, which is caused by a PAX2 gene mutation. In this review, we present evidence that this common disorder may be caused by mutations in the developmental pathway of which the PAX2 gene forms a part.

DNA-Binding Proteins↗

A catalogue of imprinted genes and parent-of-origin effects in humans and animals.

Parent-of-origin effects were first recorded >3000 years ago by mule breeders in Asia Minor. There are now several different types of evidence suggesting the presence of a large number of imprinted genes, many of which have not yet been identified. Here, we catalogue a wide range of evidence and phenomena which indicate or suggest the presence of genomic imprinting in animals. This evidence includes: the direct documentation of parent-of-origin-specific gene transcription; human disease inheritance patterns which suggest the involvement of imprinted genes; and older, less well studied animal models which may show parent-of-origin effects.

Animals↗

ClC-1 chloride channel mutations in myotonia congenita: variable penetrance of mutations shifting the voltage dependence.

Mutations in the ClC-1 muscle chloride channel cause either recessive or dominant myotonia congenita. Using a systematic screening procedure, we have now identified four novel missense mutations in dominant (V286A, F307S) and recessive myotonia (V236L, G285E), and have analysed the effect of these and other recently described mutations (A313T, I556N) on channel properties in the Xenopus oocyte expression system. Mutations V286A, F307S and A313T displayed a 'classical' dominant phenotype: their voltage dependence was shifted towards positive potentials and displayed a dominant-negative effect by significantly imparting a voltage shift on mutant-wild-type heteromeric channels as found in heterozygous patients. In contrast, the recessive mutation V236L also shifted the voltage dependence to positive values, but co-expression with wild-type ClC-1 gave almost wild-type currents. I556N, a mutation found in patients with benign dominant myotonia, drastically shifts the voltage dependence, but only a slight shift is seen when co-expressed with wild-type ClC-1. Thus, the voltage dependence of mutant heteromeric channels is not always intermediate between those of the constituent homomeric channel subunits, a conclusion further supported by mixing different ClC-1 mutants. These complex interactions correlate clinically with various inheritance patterns, ranging from autosomal dominant with various degrees of penetrance to autosomal recessive.

Amino Acid Sequence↗