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A twin study of febrile convulsions in the general population.

Seven monozygotic (MZ) and six dizygotic (DZ) twin pairs with febrile convulsions (FC) in the general population were studied. The pairwise concordance rate for FC in MZ 85.7% (6/7) was higher than that in DZ 16.7% (1/6). In a discordant MZ pair, the unaffected co-twin was attacked by epileptic seizures later. Between the concordant DZ twins, the clinical symptoms and EEGs differed in quality. According to the ratio of concordance rate in MZ to that in DZ 5.1, a multifactorial mode of inheritance for FC was suspected.

Child↗

Genetic considerations in childhood epilepsy.

This report reviews various lines of evidence demonstrating important genetic influences in the epilepsies, with special emphasis on childhood epilepsy. Five pertinent topics are discussed: (a) examples of dominant, recessive, and X-linked single-gene disorders known to be associated with epilepsy, (b) examples of gross chromosomal aberrations associated with epilepsy, (c) discussion of multifactorial and polygenic inheritance and issues of genetic heterogeneity with specific reference to idiopathic generalized epilepsy, febrile seizures, and infantile spasms, (d) brief review of experimental clues to possible pathogenetic mechanisms underlying genetic forms of epilepsy, and (e) an overview of strategies for applying genetic linkage analysis to hereditary epileptic disorders.

Central Nervous System Diseases↗

William G. Lennox: a remembrance.

William G. Lennox, author of Epilepsy and Related Disorders, had a lasting effect on our understanding of this illness. He postulated that epilepsy was not a unitary condition and that neuronal chemistries differed from one form of the disease to another. A leader in the use of electroencephalography in epilepsy, he described the first nearly pathognomonic EEG pattern and demonstrated specific features for each of the three most common types of seizure. His pioneering investigations into the biochemical basis of epilepsy helped to identify pathological mechanisms in epileptic attacks. Lennox stood alone in his belief, now generally accepted, that the genetics of epilepsy could be understood only through a multifactorial mode of inheritance. The author presents an affectionate portrait of the physician, the teacher and the man, the founder of the Seizure Unit and the unifying force in the study of epilepsy by both professionals and lay persons.

Epilepsy↗

Challenging pancreatic cancer-prone pedigrees: a nosologic dilemma.

OBJECTIVES: Our objective is to describe 11 pancreatic cancer (PC)-prone families, none of which are consonant with known hereditary cancer syndromes, in an attempt to portray familial aggregations of this disease that might be encountered in a clinical practice setting. METHODS: We selected 11 families containing two or more first- and/or second-degree relatives affected with PC from a registry of 200 PC-prone kindreds. Each proband and/or key relative(s) was interviewed and completed a detailed family history questionnaire (after providing informed consent) that allowed us to extend the pedigree as far as possible with retrieval of primary medical and pathology documents, whenever available. RESULTS: All of the 11 families show PC features that merit clinical attention and raise questions as to whether this familial clustering could be due to "chance" alone, exposure to certain common environmental factors, such as cigarette smoking, and/or polygenic, multifactorial, or Mendelian inherited factors. CONCLUSIONS: It is estimated that about 5% of PC may have a primary hereditary etiology. Because of early death, reduced penetrance, and often profuse phenotypic and genotypic heterogeneity, particularly with respect to variable age of onset and association with diverse patterns of cancer at different anatomic sites, the pedigrees require extension for ultimate diagnosis. Physician knowledge about PC's natural history and syndrome delineation should ultimately foster earlier diagnoses and possibly prevention of this disease. These high-risk patients may provide a source of DNA for formal linkage analysis in the search for culprit cancer-prone susceptibility loci.

Adolescent↗

Infraocclusion of primary molars: an epidemiologic and familial study.

The prevalence of infraocclusion of primary molars was studied in 1059 Swedish children aged 3-12 years with an even distribution between the age groups. No extractions were performed due to infraocclusion. 94 children (8.9%) showed infraocclusion of primary molars. Infraocclusion was found from 3 years of age. The prevalence varied between age groups, with a maximum of 14.3% in 8- and 9-year-old children and a minimum of 1.9% in 12-year-old children. 49 children had a single tooth in infraocclusion. The primary mandibular molars were affected more than 10 times as often as the maxillary. The prevalence of infraocclusion of the primary mandibular second molar showed a similar pattern but with a 1-2-year delay, up to a maximum in 9-year-old children. After this age the mandibular second molar was the tooth most commonly found ion infraocclusion. In a study of 138 3-12-year-old siblings of 109 children with infraocclusion the prevalence of infraocclusion was found to be 18.1%. When compared with the frequency in the total material (8.9%), the difference proved to be significant, supporting the hypothesis that there is a familial tendency in infraocclusion of primary molars. The mode of inheritance is discussed and it is concluded that the most likely explanation is that the condition is inherited on a multifactorial basis.

Age Factors↗

Steiger on refraction: a reappraisal.

Seventy years ago Steiger, a Swiss ophthalmologist, found the distribution of corneal powers to follow a normal (binomial) curve. He noted a wide range of values among emmetropes, and he also knew that their axial lengths varied significantly. He expected that normal distributions would be found for other components of refraction and also for refraction as a whole, and in seeking a controlling mechanism he recalled the multifactorial pattern of inheritance of such characteristics as stature. The present study employs modern mathematical techniques to test the validity of 2 related hypotheses: that the components of refraction are correlated and that a polygenic mode of inheritance is responsible for determining the refractive power of the eye. In the light of this study and of other modern knowledge about refraction Steiger's work is reassessed. Most of his views are vindicated, although his assumption of a normal distribution for refraction as a whole could not be justified. His contribution to the understanding of refraction establishes him among the great names in ophthalmology.

Adult↗

Genetics of adolescent idiopathic scoliosis.

A genetic family study was undertaken by photofluorography of the first, second, and third degree relatives of 116 index patients with adolescent idiopathic scoliosis (AIS). The index patients were ascertained in the course of an epidemiological screening. The pattern of familial clusters and the recurrence risk related to the number of affected relatives and to the severity of the disorder in the index patients support the theory of polygenic inheritance, a multifactorial-threshold aetiological model. The recurrence risk table for first degree relative, prepared by computerised data processing and analysis, may contribute to the early diagnosis and prevention of the disorder.

Adolescent↗

Parental age and birth order in Chinese children with congenital heart disease.

Parental age and birth order were studied in 100 Chinese children with congenital heart disease (proven by cardiac catheterisation) and in 100 controls. A higher incidence of congenital heart disease was present in the children with higher birth orders. No relationship was found between the incidence and the paternal or maternal ages. Using the method of multiple regression analysis this birth order effect was significant (p less than 0.01) and independent of parental age. This finding provides indirect evidence of environmental influence in the causation of congenital heart disease, which is known to be inherited in a multifactorial manner. Family planning to limit the size of the family may possibly contribute to the reduction of the incidence of congenital heart disease.

Adult↗

Molecular approaches to dysmorphology.

The biochemical and physiological defects underlying human dysmorphic syndromes can now be approached using techniques of molecular biology. The genetic component of the causation of the dysmorphology can be studied in isolation from the environmental component by using large, rare families which exhibit the same phenotype as more complex multifactorial disorders, but inherit the mutation in a monogenic fashion. Such an analysis starts with the determination of linkage to a gene probe, followed by the use of newer techniques of molecular biology to enable cloning and sequencing of the mutated gene. Analysis of the gene product by amino acid sequence homology to other known proteins, and tissue specific expression, may place the defect within the cascade of events associated with development and differentiation. Once cloned, the gene can also be manipulated in transgenic laboratory animals and the effect of its mutation studied directly. The use of techniques of molecular biology to study the genetic aspects of dysmorphic syndromes will allow insight to be gained both into normal fetal development and into the causes of congenital malformations.

Animals↗

Clustering of malformations in the families of South American oral cleft neonates.

The relatives of 741 newborn children with non-syndromic cleft lip with or without cleft palate (CL +/- P), of 115 with isolated cleft palate (CP), and of equal numbers of appropriate controls were screened for the presence of the same or different malformations. The main findings were as follows. (1) The frequency of familial cases of CL +/- P (17.3%) was much higher than the prevalence of this malformation among the relatives of controls (0.5%). (2) The sibs of CL +/- P subjects showed a higher prevalence of this condition than their parents (2.9% v 1.6%). (3) The degree of genetic determination of this condition should be high (70 to 74%), and the data in general favour a multifactorial model of inheritance, with different thresholds between sexes. However, the action of dominant genes cannot be excluded since selection or dominant genes or both could be postulated to explain the parent/sib difference. (4) The frequency of other malformations was also significantly raised in the families of CL +/- P probands, as compared to controls (12.1% v 6.2%). (5) The prevalence of these other malformations was higher among sibs (1.6%) than parents (0.7%) of CL +/- P babies. (6) A general susceptibility to malformations and different exposure to selective agents may explain these latter findings. (7) None of the comparisons involving CP children yielded significant results.

Case-Control Studies↗

Recurrence risk figures for isolated tetralogy of Fallot after screening for 22q11 microdeletion.

Isolated tetralogy of Fallot (TF) has a multifactorial mode of inheritance in most cases, and recurrence risk rates of 2.5-3% have been attributed to first degree relatives of an affected child. In a subgroup of patients with a strong family history, the transmission of a monogenic trait has been suspected. Microdeletion 22q11 (del(22q11)) can cause TF in the setting of DiGeorge and velocardiofacial syndromes, and has also been related to familial conotruncal cardiac defects. Empirical risk figures in families after exclusion of del(22q11) have never been calculated. We have investigated the overall occurrence of congenital heart defect (CHD) in relatives of 102 patients with isolated non-syndromic TF previously screened for del(22q11). Our results show that the frequency of CHD is 3% in sibs, 0.5% in parents, 0.3% in grandparents, 0.2% in uncles or aunts, and 0.6% in first cousins. The recurrence risk rate for sibs in our series is the same as that previously estimated, indicating that after exclusion of patients with del(22q11) genetic counselling to patients with isolated TF should not be modified. A high concordance rate among our affected sibs has been documented. Gene(s) different from those located on chromosome 22q11 must be involved in causing familial aggregation of non-syndromic TF in these cases.

Adolescent↗

Sex-limited and sex-modified genetic defects in swine--cryptorchidism.

Review of published data suggests that cryptorchidism in Chester Whites and Yorkshires is caused by completely penetrant, recessive genes at two autosomal loci; in Lacombes, multifactorial modes of inheritance are more plausible. Different genetic systems control presence of the trait vs. number of sides affected; left testes are retained more often in almost all samples. Contrary to previous claims prenatal viability of homozygous males and females is normal. Genes causing cryptorchidism are unlikely to affect many other malformations in either sex, but pleiotropy is suggested to extend to economic traits such as conformation in females.

Animals↗

Evidence for the Carter effect in atopy.

In atopy, the sex ratio deviates markedly from unity when the specific organ manifestations are considered separately. In atopic asthma, the male to female ratio is about 2:1. In the children of patients affected with atopic asthma, we determined the incidence of atopic dermatitis, atopic asthma and atopic rhinitis. Among children of women affected with atopic asthma, we found more often atopic manifestations than among children of men affected with atopic asthma (44 vs. 25.5%). This phenomenon, called the Carter effect, can be explained by the multifactorial mode of inheritance. A certain number of genes is necessary for clinical signs of atopy to become manifest. Women with atopic asthma have a higher threshold and therefore transmit more predisposing genes to their children. This demonstration of the Carter effect is a further argument in favor of polygenic inheritance of atopy.

Adolescent↗

Evidence for linkage between essential hypertension and a putative locus on human chromosome 17.

Several clinical and animal studies indicate that essential hypertension is inherited as a multifactorial trait with a significant genetic and environmental component. In the stroke-prone spontaneously hypertensive rat model, investigators have found evidence for linkage to blood pressure regulatory genes (quantitative trait loci) on rat chromosomes 2, 10, and X. In 1 human study of French and UK sib pairs, evidence for linkage has been reported to human chromosome 17q, the syntenic region of the rat chromosome 10 quantitative trait loci (QTL). Our study confirms this linkage (P=0.0005) and refines the location of the blood pressure QTL.

Aged↗

A genetic contribution to intraocular pressure: the beaver dam eye study.

PURPOSE: To investigate a potential genetic contribution to intraocular pressure (IOP), we performed a complex segregation analysis on 2337 individuals in 620 extended pedigrees ascertained through a population-based cohort, the Beaver Dam Eye Study (BDES). IOP is a principal risk factor for primary open-angle glaucoma (POAG) a leading cause of blindness worldwide. METHODS: Segregation analysis is an analytical method that provides statistical evidence supporting the involvement of a major gene or polygenes in a particular phenotype. Detailed medical histories and eye examinations were performed on all participants. From the two eyes, the higher IOP measurement was used as a continuous trait after adjustment for covariates. A genome-wide scan (GWS) using affected sib pair linkage analysis was performed on 218 sibling pairs. RESULTS: In this segregation analysis the model that allowed for an unmeasured major environmental effect plus a polygenic/multifactorial effect provided the best fit and was the most parsimonious model. The lack of an adequate fit for the Mendelian single-gene models is consistent with a multifactorial model of inheritance that may include multiple genes and environmental factors that contribute to IOP. The results of the GWS yielded two novel loci as potential linkage regions for IOP on chromosomes 6 (P = 0.008) and 13 (P = 0.0007). Neither of these regions has previously been identified in GWS of POAG. CONCLUSIONS: The segregation and familial correlation analyses of IOP suggest a polygenetic component with environmental influences. The pilot linkage study further confirms the heterogeneity of IOP with the identification of two novel genetic loci.

Adult↗

Hereditary factors in sleepwalking and night terrors.

The families of 25 probands with sleepwalking and 27 probands with night terrors were studied. Eighty per cent of the sleepwalking pedigrees and 96 per cent of the night terror pedigrees included one or more individuals, other than the proband, who were affected by sleepwalking, night terrors, or both. Our data appear to fit a 'two threshold' multifactorial mode of inheritance. This finding supports the hypothesis that sleepwalking and night terrors share a common genetic predisposition, with sleepwalking being a more prevalent and less severe manifestation of the same substrate that underlies night terrors. Heritable factors predispose an individual to develop sleepwalking and/or night terrors, but expression of the trait may be influenced by environmental factors.

Female↗

Prevalence of primary monofixation syndrome in parents of children with congenital esotropia.

The prevalence of primary monofixation syndrome (MFS) in the general population is approximately 1%. This study was performed to determine the prevalence of primary monofixation in biological parents of children with congenital esotropia. Ninety children with congenital esotropia were seen between November 1991 and June 1992 by one ophthalmologist (M.M.P.). One hundred and twenty-nine biological parents of these children were screened for sensorimotor abnormalities. Twelve parents were found to have secondary MFS and were removed from the analysis. This left 78 apparently non-strabismic families consisting of a total of 117 parents. Seven parents were identified as having primary MFS. The prevalence of primary MFS in this population is 9% of families and 6% of parents. Congenital esotropia is believed to be inherited in a multifactorial fashion. We believe that this increase in the prevalence of primary MFS compared to the general population lends support to the hypothesis that primary MFS may be a mild (subthreshold) effect of the "gene(s)" that cause congenital esotropia.

Adult↗

Major gene segregation of actinic prurigo among North American Indians in Saskatchewan.

Actinic prurigo is an idiopathic, familial photodermatosis seen especially in American Indians. Segregation analysis was performed on 12 Saskatchewan pedigrees with American Indian ancestry, comprising a total of 1,148 individuals, ascertained via probands diagnosed with actinic prurigo. Although a high degree of familial aggregation has been noted in the past and dominant inheritance has been suggested, no formal segregation analysis has been attempted. Actinic prurigo has a variable age of onset and, therefore, age at the time of censoring must be taken into account in the analysis. However, as these ages of 57% of the unaffected individuals were missing, an algorithm was devised to impute the missing ages from known birth years in the family based on the age differences among relatives and spouses. Using these imputed ages, simple dominant inheritance with incomplete penetrance and a single age of onset distribution was found. The method for imputing the ages at examination was evaluated, as was the correction for ascertainment, by using alternative methods and comparing the results. Regardless of the method used, a dominant mode of inheritance without any multifactorial component remained the best hypothesis.

Adolescent↗