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Parent-of-origin effect and evidence for differential transmission in periodic catatonia.

In a family study involving 83 probands with periodic catatonia a subtype of DSM IIIR schizophrenia, we reported an age-specific morbidity risk of 26.9% in first-degree relatives with homotypical psychoses and genetic anticipation indicating a possible major gene effect. Paternal transmission was associated with a trend for a younger age at onset in probands compared to that observed in the case of maternal transmission (P = 0.099). If this can be confirmed in a larger sample and then replicated, there would be evidence for the occurrence of a parent-of-origin effect. Such an observation may indicate that a paternally imprinted locus acts on periodic catatonia. Among the non-genetic mechanisms that may modify the penetrance of the disease, paternal affection did lead to a decrease in male offspring (P = 0.007) and maternal affection showed an increased frequency of non-affected male offspring (P = 0.021). We therefore propose that parent-of-origin effects as well as prenatal mortality and psychosocial factors need further investigation in the periodic catatonia subtype of schizophrenia.

Adolescent↗

Mutations in the FIE and MEA genes that encode interacting polycomb proteins cause parent-of-origin effects on seed development by distinct mechanisms.

In flowering plants, two cells are fertilized in the haploid female gametophyte. Egg and sperm nuclei fuse to form the embryo. A second sperm nucleus fuses with the central cell nucleus, which replicates to generate the endosperm, a tissue that supports embryo development. The FERTILIZATION-INDEPENDENT ENDOSPERM (FIE) and MEDEA (MEA) genes encode WD and SET domain polycomb proteins, respectively. In the absence of fertilization, a female gametophyte with a loss-of-function fie or mea allele initiates endosperm development without fertilization. fie and mea mutations also cause parent-of-origin effects, in which the wild-type maternal allele is essential and the paternal allele is dispensable for seed viability. Here, we show that FIE and MEA polycomb proteins interact physically, suggesting that the molecular partnership of WD and SET domain polycomb proteins has been conserved during the evolution of flowering plants. The overlapping expression patterns of FIE and MEA are consistent with their suppression of gene transcription and endosperm development in the central cell as well as their control of seed development after fertilization. Although FIE and MEA interact, differences in maternal versus paternal patterns of expression, as well as the effect of a recessive mutation in the DECREASE IN DNA METHYLATION1 (DDM1) gene on mutant allele transmission, indicate that fie and mea mutations cause parent-of-origin effects on seed development by distinct mechanisms.

Arabidopsis↗

Parent-of-origin effects on allelic expression bias in interspecific poplar hybrids.

In hybrid plants, phenotypic outcomes are governed by interactions between the two parental genomes. However, the mechanisms underlying the interplay of divergent regulatory networks from these genomes remain poorly understood. In this study, we compared gene-level and allele-specific expression patterns, as well as differentially enriched pathways between F₁ and complex backcross (CBC) lines derived from a natural interspecific hybrid population of Populus fremontii (Pf) and P. angustifolia (Pa). Metabolic differences between Pf and Pa which exhibit low and high levels respectively of phenylpropanoid-derived condensed tannins were leveraged. Using individualized transcriptome references, differential expression and clustering analyses revealed CBC-biased and F₁-biased expression for genes involved in phenylpropanoid metabolism and photosynthesis, respectively. Biased expression of these genes at the allele level was also observed in F1. At the whole-transcriptome level, Pa-biased genes predominated in F₁ hybrids, and Pa alleles displayed more conserved expression patterns than Pf alleles across examined samples. Further analyses indicated that allelic expression bias was significantly associated with parental origin, which could be driven by sequence variations in cis-regulatory elements and differences in CpG island length. Our findings demonstrate strong parent-of-origin effects on divergent regulatory networks governing gene expression in poplar hybrids and provide clues for strategic parental selection tailored to specific metabolic pathways of interest.

cis-regulation↗

Sensitive flow cytometric analysis reveals a novel type of parent-of-origin effect in the mouse genome.

The discovery of classic parental imprinting came, at least in part, from the analysis of transgene expression in mice. It was noticed that some transgenes were only expressed following paternal transmission and that others sometimes showed differential patterns of methylation depending on the parent of origin. Here, we present evidence of a novel and more subtle form of parental imprinting by taking advantage of the highly sensitive detection of murine transgene expression afforded by flow cytometry. We have produced nine lines of transgenic mice carrying a GFP reporter linked to the human alpha-globin promoter and enhancer elements, which direct expression to erythroid cells. A high proportion of transgenic lines, four of the nine, display significantly lower levels of expression following maternal transmission. Both the percentage of expressing cells and the mean fluorescence in expressing cells are between 10% and 30% lower following maternal transmission. These effects are reversible upon passage through the opposite germline. This finding raises the possibility that differences in the epigenetic state of the maternal and paternal chromosomes in adult somatic cells are more widespread than was previously thought.

Animals↗

X-linked hypophosphatemia: a search for gender, race, anticipation, or parent of origin effects on disease expression in children.

X-Linked hypophosphatemia (XLH) is a sex-linked dominant disorder. It is possible that females are more mildly affected than males. No information is available regarding other potential genetic influences on XLH expression in patients, such as race, anticipation, parent of origin, or molecular heterogeneity. We investigated the above potential genetic influences on XLH expressivity using data from 116 pediatric patients. To compare biochemical parameters, we used data from the 30 prepubertal children (23 girls and 7 boys) selected because they had been without medical therapy for at least 3 months (25 of 30 never treated). To compare height z-scores, we used data from the 27 patients (pre- or postpubertal) selected because they had never received medical or surgical treatment. Ascertainment bias (i.e. referral of girls who were severely affected) was not apparent (observed female/male ratio, 1.64; expected, 2.00; P = 0.29). Parameters of mineral homeostasis did not show statistically significant differences between girls vs. boys, sporadic vs. multigenerational cases (except lower fasting serum phosphate levels in sporadic cases; mean +/- SEM, 2.68 +/- 0.10 vs. 3.02 +/- 0.04 mg/dL; P = 0.049), blacks vs. whites, or for the girls for whom affected fathers vs. mothers transmitted the disorder. Height z-scores correlated with renal phosphate reclamation (i.e. tubular maximum of phosphorus/glomerular filtration rate; r = 0.68; P = 0.014), but were not different for the groupings above. Furthermore, we found no evidence for meiotic drive or for a parental age effect to explain the 18.3% of patients that were new mutations for XLH. Our data fail to show any evidence for genetic heterogeneity or for gender, race, anticipation, or parent of origin effects on XLH expression in children. Despite the recent discovery of a gene (PEX) that is mutated in XLH, the sex-linked dominant phenotype and apparent absence of a gene dose effect in XLH expression in children require explanation.

Black People↗

The parent-of-origin effect of 10q22 in pre-eclamptic females coincides with two regions clustered for genes with down-regulated expression in androgenetic placentas.

By affected sib-pair linkage analysis of 24 families with pre-eclampsia, we confirm a susceptibility locus on chromosome 10q22.1 in Dutch females: a multipoint non-parametric linkage score of 3.6 near marker D10S1432 was obtained. Haplotype analysis showed a parent-of-origin effect: maximal allele sharing in the affected sibs was found for maternally derived alleles in all families, but not for the paternally derived alleles. As matrilineal inheritance suggests the presence of maternally expressed imprinted genes, while imprinting operates predominantly in (extra)embryonic tissues, all genes (n=132) known on 10q22 between GATA121A08 and D10S580 were screened for seven sequence-related features associated with imprinting and subsequently tested for expression in first trimester placenta. Placental expression of genes selected in this way (n=55) was compared with expression in androgenetic placentas of identical gestational age. Two regions on 10q22 were identified with developmentally co-repressed genes with non-random chromosomal distribution. Interestingly, these two clusters, near CTNNA3 and KCNMA1 and each containing five genes with down-regulated expression in androgenetic placentas, coincided with the regions with maximal maternal allele sharing seen in the pre-eclamptic sisters. Our linkage and expression data are compatible with the concept that pre-eclampsia involves maternally expressed imprinted genes that operate in the first trimester placenta.

Alleles↗

Detection of parent-of-origin effects in nuclear families using haplotype analysis.

Despite the potential pitfalls of stratification, population-based association studies nowadays are being conducted more often than family-based association studies. However, the mechanism of genomic imprinting has lately been implicated in the etiology of genetic complex diseases and can be detected using statistics only in family-based designs. Powerful tests for association and imprinting have been proposed previously for case-parent trios and single markers. Since the power of association studies can be improved if multiple affected children and haplotypes are considered, we extended the parental asymmetry test (PAT) for imprinting to a test that is suited for both general nuclear families and haplotypes, called HAP-PAT. Significance of the HAP-PAT is determined via a Monte-Carlo simulation procedure. In addition to the HAP-PAT, we modified a haplotype-based association test, proposed by us before, in such a way that either only paternal or maternal transmissions contribute to the test statistic. The approaches were implemented in FAMHAP and we evaluated their performance under a variety of disease models. We were able to demonstrate the usefulness of our haplotype-based approaches to detect parent-of-origin effects. Furthermore, we showed that also in the presence of imprinting it is more reasonable to consider all affected children of a nuclear family, than to randomly select one affected child from each family and to conduct a trio study using the selected individuals.

Computer Simulation↗

Age at diagnosis of isolated unilateral retinoblastoma does not distinguish patients with and without a constitutional RB1 gene mutation but is influenced by a parent-of-origin effect.

Patients with hereditary cancer are usually diagnosed earlier than patients with non-hereditary tumours. In children with isolated unilateral retinoblastoma, some of whom have a hereditary predisposition, this rule has been subject to debate. We have analysed the clinical manifestation of disease in 188 children with completely resolved mutational status. In 24 (13%) of these patients, testing of blood DNA showed a constitutional RB1 mutation. The distribution of age at diagnosis was not different between patients with and without a constitutional mutation. However, patients with loss of the maternally inherited RB1 allele had an earlier age at diagnosis than patients with loss of the paternally inherited RB1 allele. Our data show that early age at diagnosis does not identify patients with isolated unilateral retinoblastoma that have a higher risk of being carriers of a RB1 gene mutation. Our findings suggest that, at least in some patients, age at diagnosis is modified by a parent-of-origin effect.

Age of Onset↗

Genome-wide linkage analysis assessing parent-of-origin effects in the inheritance of birth weight.

Family studies suggest that genetic variation may influence birth weight. We have assessed linkage of birth weight in a genome-wide scan in 269 Pima Indian siblings (334 sibling pairs, 92 families). As imprinting (expression of only a single copy of a gene depending on parent-of-origin), is commonly found in genes that affect fetal growth, we used a recently described modification of standard multipoint variance-component methods of linkage analysis of quantitative traits. This technique allows for comparison of linkage models that incorporate imprinting effects (in which the strength of linkage is expressed as LOD(IMP)) and models where parent-of-origin effects are not included (LOD(EQ)). Where significant evidence of linkage was present, separate contributions of alleles derived from father (LOD(FA)) or mother (LOD(MO)) to the imprinting model were estimated. Significant evidence of linkage was found on chromosome 11 (at map position 88 cM, LOD(IMP)=3.4) with evidence for imprinting (imprinting model superior, P<0.001). In this region, birth weight was linked predominantly to paternally derived alleles (LOD(FA)=4.1, LOD(MO)=0.0). An imprinted gene on chromosome 11 may influence birth weight in the Pima population. This chromosome contains one of the two major known clusters of imprinted genes in the human genome, lending biological plausibility to our findings.

Birth Weight↗

Pulmonary atresia associated with maternal 22q11.2 deletion: possible parent of origin effect in the conotruncal anomaly face syndrome.

A blind study was designed to test the hypothesis that some persons with a relatively rare cardiac malformation, pulmonary atresia with ventriculoseptal defect (PA/VSD), have a recognisable phenotype. Fourteen patients with cyanotic congenital heart lesions were examined by dysmorphologists blinded to the type of cardiac malformation. Six children were judged to have a similar craniofacial appearance; all had PA/VSD. These children were not originally considered to fall within the classic phenotypes of the DiGeorge sequence or the velocardiofacial syndrome, both of which have been shown to be associated with deletions of 22q11. More recently, 22q11 deletions have been documented in the conotruncal anomaly face syndrome and apparently isolated conotruncal heart defects. A new acronym, CATCH 22 syndrome (Cardiac defects, Abnormal facies, Thymic hypoplasia, Cleft palate, and Hypocalcaemia) has been suggested to encompass this very broad phenotypic spectrum. A preliminary molecular study was conducted using the dinucleotide repeat D22S264 located on chromosome 22q11.2. All cases tested with the subtle but recognisable phenotype had deletions, all lacking the maternal contribution at this locus, suggesting there may be a parent of origin effect.

Base Sequence↗

Molecular definition of the chromosome 7 deletion in Williams syndrome and parent-of-origin effects on growth.

Williams syndrome (WS) is a developmental disorder with variable phenotypic expression associated, in most cases, with a hemizygous deletion of part of chromosomal band 7q11.23 that includes the elastin gene (ELN). We have investigated the frequency and size of the deletions, determined the parental origin, and correlated the molecular results with the clinical findings in 65 WS patients. Hemizygosity at the ELN locus was established by typing of two intragenic polymorphisms, quantitative Southern analysis, and/or FISH. Polymorphic markers covering the deletion and flanking regions were ordered by a combination of genetic and physical mapping. Genotyping of WS patients and available parents for 13 polymorphisms revealed that of 65 clinically defined WS patients, 61 (94%) had a deletion of the ELN locus and were also hemizygous (or noninformative) at loci D7S489B, D7S2476, D7S613, D7S2472, and D7S1870. None of the four patients without ELN deletion was hemizygous at any of the polymorphic loci studied. All patients were heterozygous (or noninformative) for centromeric (D7S1816, D7S1483, and D7S653) and telomeric (D7S489A, D7S675, and D7S669) flanking loci. The genetic distance between the most-centromeric deleted locus, D7S489B, and the most-telomeric one, D7S1870, is 2 cM. The breakpoints cluster at approximately 1 cM to either side of ELN. In 39 families informative for parental origin, all deletions were de novo, and 18 were paternally and 21 maternally derived. Comparison of clinical data, collected in a standardized quantifiable format, revealed significantly more severe growth retardation and microcephaly in the maternal deletion group. An imprinted locus, silent on the paternal chromosome and contributing to statural growth, may be affected by the deletion.

Adult↗

Parent-of-origin effects in multiple endocrine neoplasia type 2B.

Multiple endocrine neoplasia type 2B (MEN 2B) is characterized by medullary thyroid carcinoma, pheochromocytomas, mucosal neuromas, ganglioneuromas, and skeletal and ophthalmic abnormalities. It is observed as both inherited and sporadic disease, with an estimated 50% of cases arising de novo. A single point mutation in the catalytic core region of the receptor tyrosine kinase, RET, has been observed in germ-line DNA of MEN 2B patients. We have analyzed 25 cases of de novo disease in order to determine the parental origin of the mutated RET allele. In all cases the new mutation was of paternal origin. We observe a distortion of the sex ratio in both de novo MEN 2B patients and the affected offspring of MEN 2B transmitting males. These results suggests a differential susceptibility of RET to mutation in paternally and maternally derived DNA and a possible role for imprinting of RET during development.

Chromosomes, Human, Pair 10↗

Parent-of-origin effects on handedness and schizophrenia susceptibility on chromosome 2p12-q11.

Schizophrenia and non-right-handedness are moderately associated, and both traits are often accompanied by abnormalities of asymmetrical brain morphology or function. We have found linkage previously of chromosome 2p12-q11 to a quantitative measure of handedness, and we have also found linkage of schizophrenia/schizoaffective disorder to this same chromosomal region in a separate study. Now, we have found that in one of our samples (191 reading-disabled sibling pairs), the relative hand skill of siblings was correlated more strongly with paternal than maternal relative hand skill. This led us to re-analyse 2p12-q11 under parent-of-origin linkage models. We found linkage of relative hand skill in the RD siblings to 2p12-q11 with P=0.0000037 for paternal identity-by-descent sharing, whereas the maternally inherited locus was not linked to the trait (P>0.2). Similarly, in affected-sib-pair analysis of our schizophrenia dataset (241 sibling pairs), we found linkage to schizophrenia for paternal sharing with LOD=4.72, P=0.0000016, within 3 cM of the peak linkage to relative hand skill. Maternal linkage across the region was weak or non-significant. These similar paternal-specific linkages suggest that the causative genetic effects on 2p12-q11 are related. The linkages may be due to a single maternally imprinted influence on lateralized brain development that contains common functional polymorphisms.

Chromosome Mapping↗

Differential expression and parent-of-origin effect of the 5-HT2A receptor gene C102T polymorphism: analysis of suicidality in schizophrenia and bipolar disorder.

The serotonin 2A (5-HT2A) receptor gene has been implicated in the pathogenesis of suicidal behavior by a genetic association between the 5-HT2A C102T silent polymorphism and suicidality in patients with major depression. However, a recent meta-analysis failed to confirm this association. We developed an improved quantitative assay for the measurement of allele-specific expression of the 5-HT2A gene, and find that the ratio of C/T allele expression in the pre-frontal cortex of heterozygous suicide victims (n = 10) was significantly decreased in comparison with the non-suicide group (n = 10) (P = 0.049). Because the 5-HT2A gene is subject to imprinting, the parent-of-origin may affect the inheritance of suicidal behavior. Thus we examined the parental origin of specific alleles for genetic association in a genetic family-based sample of major psychoses in which information on suicidal behavior was available. No association between the 5-HT2A C102T polymorphism and suicidal behavior in major psychoses was detected with the transmission/disequilibrium test (TDT).

Adult↗