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An additive genetic gamma frailty model for linkage analysis of diseases with variable age of onset using nuclear families.

Many late-onset complex diseases exhibit variable age of onset. Efficiently incorporating age of onset information into linkage analysis can potentially increase the power of dissecting complex diseases. In this paper, we treat age of onset as a genetic trait with censored observations. We use multiple markers to infer the inheritance vector at the disease susceptibility (DS) locus in order to extract information about the inheritance pattern of the disease allele in a pedigree. Given the inheritance distribution at the DS locus, we define the genetic frailty for each individual within a nuclear family as the sum of frailties due to a putative major disease gene and a polygenic effect due to any remaining DS loci. Conditioning on these frailties we use the proportional hazards model for the risk of developing disease. We show that a test of linkage can be formulated as a test of zero variance due to a specific locus of the additive gamma frailties. Maximum likelihood estimation, using the EM algorithm, and likelihood ratio tests are employed for parameter estimation and tests of linkage. A simulation study presented indicates that the proposed method is well behaved and can be more powerful than the currently available allele-sharing based linkage methods. A breast cancer data example is used for illustration.

Adult↗

Familial abdominal aortic aneurysms: collection of 233 multiplex families.

OBJECTIVE: This study investigated a large number of families in which at least two individuals were diagnosed with abdominal aortic aneurysms to identify the relationship of the affected relatives to the proband. SUBJECTS AND METHODS: Families for the study were recruited through various vascular surgery centers in the United States, Finland, Belgium, Canada, the Netherlands, Sweden, and the United Kingdom and through our patient recruitment website (www.genetics.wayne.edu/ags). RESULTS: We identified 233 families with at least two individuals diagnosed with abdominal aortic aneurysms. The families originated from nine different nationalities, but all were white. There were 653 aneurysm patients in these families, with an average of 2.8 cases per family. Most of the families were small, with only two affected individuals. There were, however, six families with six, three with seven, and one with eight affected individuals. Most of the probands (82%) and the affected relatives (77%) were male, and the most common relationship to the proband was brother. Most of the families (72%) appeared to show autosomal recessive inheritance pattern, whereas in 58 families (25%), abdominal aortic aneurysms were inherited in autosomal dominant manner, and in eight families, the familial aggregation could be explained by autosomal dominant inheritance with incomplete penetrance. In the 66 families where abdominal aortic aneurysms were inherited in a dominant manner, 141 transmissions of the disease from one generation to another were identified, and the male-to-male, male-to-female, female-to-male, and female-to-female transmissions occurred in 46%, 11%, 32%, and 11%, respectively. CONCLUSION: Our study supports previous studies about familial aggregation of abdominal aortic aneurysms and suggests that first-degree family members, male relatives, in particular, are at increased risk. No single inheritance mode could explain the occurrence of abdominal aortic aneurysms in the 233 families studied here, suggesting that abdominal aortic aneursyms are a multifactorial disorder with multiple genetic and environmental risk factors.

Aortic Aneurysm, Abdominal↗

Genome fragment of Wolbachia endosymbiont transferred to X chromosome of host insect.

The adzuki bean beetle, Callosobruchus chinensis, is triple-infected with distinct lineages of Wolbachia endosymbiont, wBruCon, wBruOri, and wBruAus, which were identified by their wsp (Wolbachia surface protein) gene sequences. Whereas wBruCon and wBruOri caused cytoplasmic incompatibility of the host insect, wBruAus did not. Although wBruCon and wBruOri were easily eliminated by antibiotic treatments, wBruAus persisted over five treated generations and could not be eliminated. The inheritance pattern of wBruAus was, surprisingly, explained by sex-linked inheritance in male-heterozygotic organisms, which agreed with the karyotype of C. chinensis (2n = 20, XY). Quantitative PCR analysis demonstrated that females contain around twice as much wsp titer as males, which is concordant with an X chromosome linkage. Specific PCR and Southern blot analyses indicated that the wBruAus-bearing strain of C. chinensis contains only a fraction of the Wolbachia gene repertoire. Several genome fragments of wBruAus were isolated using an inverse PCR technique. The fragments exhibited a bacterial genome structure containing a number of ORFs typical of the alpha-proteobacteria, although some of the ORFs contained disruptive mutations. In the flanking region of ftsZ gene, a non-long terminal repeat (non-LTR) retrotransposon sequence, which is typical of insects but not found from bacteria, was present. These results strongly suggest that wBruAus has no microbial entity but is a genome fragment of Wolbachia endosymbiont transferred to the X chromosome of the host insect.

Animals↗

Genetics of lattice degeneration of the retina.

First-degree relatives of proband patients with lattice degeneration of the retina revealed a significantly higher prevalence of the disease than the prevalence in the general population: the former had the disease about three times as frequently as the latter. The observed data were analyzed in terms of their accordance with recognized genetic models. The inheritance pattern did not fit well to a monogenic mode of inheritance, and it was hypothesized that a polygenic or multifactorial mode of inheritance is the most likely for lattice degeneration of the retina.

Adolescent↗

Mitochondrial DNA and disease.

Mitochondrial diseases are a group of disorders characterized by morphological or functional defects of the mitochondria, the organelles producing most of our cellular energy. As the only extranuclear site carrying genetic information, the mitochondria add an important chapter into the inheritance patterns of genetic diseases. Mitochondrial DNA (mtDNA) is exclusively maternally inherited in humans, but a mitochondrial disorder may follow either maternal or Mendelian inheritance, depending on the site of the primary gene defect. After the initial finding of mtDNA mutations in rare ocular myopathies in 1988, an explosion in the amount of information on mitochondrial diseases has occurred. Because the mitochondria produce energy in all the tissues, symptoms resulting from mtDNA mutations may originate from any organ system, and the clinical spectrum of mitochondrial diseases has expanded to virtually all branches of medicine. Subgroups of several common diseases, such as diabetes, deafness and inherited cardiomyopathies, have been found to be caused by mtDNA mutations, and some mtDNA defects have been suggested to modify the outcome of diseases primarily caused by other factors, such as Parkinson's or Alzheimer's disease. Although no breakthroughs in the therapeutic trials on the devastating mitochondrial diseases have so far been achieved, detection of mtDNA mutations offers an accurate diagnosis and is a prerequisite for genetic counselling, being now accessible to most clinicians.

Cardiomyopathies↗

Genetic study on ossification of posterior longitudinal ligament.

Family studies and blood grouping tests were conducted in an attempt to elucidate the etiology and genetic mechanism of ossification of posterior longitudinal ligament of the spine (OPLL). Analysis of the collected date revealed the following results: Testing of inheritance pattern Fitness of OPLL to the hypotheses of simple recessive inheritance, simple dominant inheritance and multifactorial inheritance was tested, but fitness to any one of these hypotheses was statistically denied. Analyses of OPLL and genetic markers A comparative study was made between the OPLL patients and healthy donors residing in Tokyo on the phenotype frequency of the blood groups (eight systems), serum groups (six systems) and red cell enzyme groups (three systems). A significant association of OPLL with MN blood groups, Hp types and PGM1 types was observed. Examination of the correlation after combining MN and Hp showed the coefficient of contingency to be C = 0.6739 and that after the multiple combination of MN, Hp and PGM1 revealed the coefficient of contingency to be C = 0.8923, indicating a remarkably high correlation.

Adult↗

Stargazer: a new neurological mutant on chromosome 15 in the mouse with prolonged cortical seizures.

We report here the initial description of the inheritance pattern, linkage mapping, and electroclinical phenotype of a recessive mutation on mouse Chromosome 15, stargazer (stg), that produces epilepsy. The salient epileptic phenotype is a syndrome of spontaneous, prolonged, generalized spike-wave cortical discharges with behavioral arrest. A second, complex, seizure pattern featuring movements during the discharge can also appear. The stg/stg mutant phenotype confirms the general principal that inherited epilepsies sharing similar cortical excitability patterns can be transmitted by single gene loci residing on different chromosomes and provides new evidence that the severity of seizure expression depends on the specific mutant gene affected.

Animals↗

Sparse hair, short stature, hypoplastic thumbs, single upper central incisor and abnormal skin pigmentation: a possible "new" form of ectodermal dysplasia.

A family is described where a mother and three sons have an unusual form of ectodermal dysplasia that may have been described in the medical literature only once before. The unusual manifestations in this family are mild short stature, sparse scalp hair, skin pigmentation and a transient urticarial-like reaction on the hands and arms. The mother and one son demonstrated a single, upper central incisor and the mother and another son had hypoplastic thumbs. The mother alone had hyperkeratosis of the palms and soles. The inheritance pattern is most likely autosomal dominant, although X-linked dominant inheritance cannot be excluded.

Adult↗

Semiparametric linkage analysis using pseudolikelihoods on neighbouring sets.

For many complex diseases, study has suggested that the disease genes influence not only the occurrence of the disease, but also the age of onset. Current methods in linkage analysis are mainly concentrated on affected relative pairs or affected family members, and age of onset information is either ignored or is taken into account by specifying age-dependent penetrances for liability classes. In fact, affected relatives with different ages of onset may be the result of different genetic aetiologies and unaffected relatives are censored at the study time. Therefore, incorporation of age of onset and including contrasts between affected and unaffected pedigree members are important components of effective analysis for the detection of linkage with genetic markers. We use multiple markers to infer the inheritance vector in order to extract information about the inheritance pattern of the disease allele in a pedigree. For a given inheritance vector, we define two neighbour sets for each individual based on allele identical by descent (IBD). We then use the within-set and between-sets conditional hazard ratios to characterize the dependence of age of onset among relatives. A pseudolikelihood ratio test is proposed for testing linkage. Simulated and real data sets are used to illustrate these new statistical methods.

Age of Onset↗

Isozymes in androgenetic and gynogenetic white amur, gynogenetic carp, and carp-amur hybrids.

Gynogentic and androgenetic progeny appeared in crosses between white amur, Ctenopharyngodon idella, and carp, Cyprinus carpio. Hemoglobin, plasma general proteins, and plasma isoenzymes were studied by electrophoresis to determine inheritance patterns. Electrophoretic bands indicated that gynogenetic white amur had no paternal inheritance from carp and that adrogenetic white amur also were pure white amur. Gynogeneiss in carp was confirmed by the absence of paternal inheritance. Hemoglobins, general proteins, and esterases distinguished the two species. Within a species there were no differences in proteins between gynogenetic, adrogenetic and normal fish. Lactate dehydrogenase (LDH) differed between carp and white amur and was a good marker for detecting heterologous inheritance in adrogenesis or gynogenesis because expression of LDH alleles from white amur was inhibited by the carp genome. Alkaline phosphatase and malate dehydrogenase had similar electrophoretic mobility in the two species.

Alkaline Phosphatase↗

Polar overdominance at the ovine callipyge locus.

An inheritable muscular hypertrophy was recently described in sheep and shown to be determined by the callipyge gene mapped to ovine chromosome 18. Here, the callipyge phenotype was found to be characterized by a nonmendelian inheritance pattern, referred to as polar overdominance, where only heterozygous individuals having inherited the callipyge mutation from their sire express the phenotype. The possible role of parental imprinting in the determinism of polar overdominance is envisaged.

Animals↗

Familial koilonychia.

Koilonychia is a well-recognized clinical sign of iron deficiency occurring either with or without anemia. A case of familial koilonychia with an inheritance pattern consistent with an autosomal dominant trait is presented. Comments on inherited koilonychia and other causes of koilonychia are also included. The possible causes of the nail disorder are discussed.

Anemia, Hypochromic↗

Diagnosis and classification of severe combined immunodeficiency disease.

The failure to demonstrate normal humoral and cell-mediated immunity (CMI) in patients diagnosed as SCID is seen to reflect the varied pathogenesis of this syndrome. Two major groups of patients have been described, those with or without an associated absence of the enzyme ADA. The heterogeneity of the syndrome is expressed in variable inheritance patterns (particularly defined X-linked or autosomal recessive modes of inheritance), differing clinical presentations, and significant variability in laboratory findings. Some of this heterogeneity of laboratory findings may in fact be contributed to by the high incidence of infection or engraftment of maternal cells in utero. Common to all, however, is the profound deficiency of functional attributes of humoral and cell-mediated immunity. Insight into the biology of this immunodeficiency has advanced steadily in the last decade. Although initially hypothesized to represent a primary lymphoid stem-cell defect, newer technologies to identify and enumerate lymphocyte subpopulations and precursor lymphocytes have revealed the complexity of the disorder. This complexity may now be attributable to a number of abnormalities in the quantitative and qualitative differentiation of these lymphoid stem cells. Functional differentiation of lymphocytes is the result of a progressive and orderly sequence of events. In SCID, lymphocytes of both lineages may be arrested at specific and identifiable stages of maturation, leading to a deficiency of cell-mediated and humoral immunity. In many patients with SCID, the combined immune deficiency may be linked solely to a failure in the stepwise progression of T-cell differentiation.

Acute Disease↗

Pattern dystrophy of the retinal pigment epithelium.

We describe six related patients presenting with an autosomal dominantly inherited pattern dystrophy of the retinal pigment epithelium, significantly abnormal electro-oculogram and minor colour vision abnormalities. There is a continuum of variable phenotypic expression within the pattern dystrophies of the retinal pigment epithelium.

Adolescent↗

Problems of genetic model testing in early onset periodontitis.

Familial aggregation of early onset or juvenile periodontitis (JP), a disorder that varies in expression and age of onset, has been recognized for some time. Autosomal recessive and X-linked inheritance patterns have been suggested, and one large pedigree has demonstrated autosomal dominant inheritance. The variability and age limitations in clinical phenotypic diagnosis present several problems to genetic analysis, because information on members of the youngest and older generations may be lost to the analysis. The purpose of the present study was to elucidate the genetic basis of JP by formal pedigree analysis and comparison of competing genetic models. Twenty-eight families were included, with general and specific autosomal models, and an X-linked model being compared. The autosomal recessive model provided the most parsimonious explanation of the data, and its likelihood was not significantly different from the more general model. Likelihoods for the sporadic (nongenetic) and X-linked models were considerably lower than the autosomal models. While comparison of genetic models suggests recessive inheritance of JP, the serious complications to pedigree analysis posed by limitations warns against acceptance of this conclusion, without more exhaustive evaluation of: (1) a more extensive collection of family data, (2) more complete investigation of the effects of age limitations on comparisons among competing models, and (3) elucidation of the importance of diagnosis and phenotype assignment of adults through past dental records.

Adult↗

The ovine callipyge locus: a paradigm illustrating the importance of non-Mendelian genetics in livestock.

An inheritable muscular hypertrophy was recently described in sheep and shown to be determined by the callipyge (CLPG) gene mapped to ovine chromosome 18. We demonstrate in this work that the callipyge phenotype is characterized by a non-Mendelian inheritance pattern, referred to as polar overdominance, in which only heterozygous individuals having inherited the CLPG mutation from their sire express the phenotype. The possible role of parental imprinting in the determinism of polar overdominance is envisaged.

Animals↗

Exclusion of uniparental inheritance of chromosome 15 in a fetus with a familial dicentric (Y;15) translocation.

We present a prenatal case with a 45,X,dic(Y;15) (q11.23;p11.1) karyotype and describe the inheritance pattern of the chromosome 15s. Chromosome 15 has an imprinted region and inheritance of both chromosome 15 from one parent results in either Angelman syndrome (AS) (paternal inheritance) or Prader Willi syndrome (PWS) (maternal inheritance). Parental chromosome studies revealed that the father carried the same dicentric (Y;15) translocation. Since familial chromosome rearrangements can result in aberrant chromosomal segregation during meiosis, we wanted to exclude paternal uniparental inheritance of chromosome 15. By using DNA microsatellite markers at several 15q11q13 loci, we determined that the fetus had inherited his normal non-translocated chromosome 15 from his mother.

Adult↗

The genetics of vitiligo in Korean patients.

BACKGROUND: Vitiligo is a common disorder whose exact cause is unknown, but genetic factors are thought to be involved. We analyzed 120 Korean proband families to clarify which genetic factors are involved in the pathogenesis of vitiligo in Korean patients. METHODS: The genetics of vitiligo were analyzed in 120 Korean proband families out of 1030 vitiligo patients. Each family was analyzed through a proband afflicted with vitiligo. RESULTS: In 51 (42.5%) of 120 proband families, at least one first-degree relative of the proband had vitiligo. The incidence of those affected among 1755 relatives (first-, second-, and third-degree) was found to be 8.0+/-0.6%. There was a statistically significant departure for segregation analysis which was inconsistent with inheritance as an autosomal or X-linked locus model. On the basis of our results, the inheritance pattern of vitiligo is more likely to tend toward the model of multifactorial inheritance. The threshold trait among first-degree relatives (7.2%) appeared to tend more toward the square root of the frequency in the general population (10%) than towards those of dominant (50%) or recessive (25%) models. CONCLUSIONS: These results indicate that there are certain genetic factors involved in the etiology of vitiligo, and that vitiligo seems to have a polygenic nature.

Female↗