No evidence for a preferential transmission of the methylenetetrahydrofolate reductase 677T allele in families with schizophrenia offspring.

The methylenetetrahydrofolate reductase (MTHFR) 677C > T polymorphism has been associated with an increased risk of schizophrenia in various case-control studies. However, case-control studies are sensitive to population stratification, which is not an issue in family-based studies. We conducted a family-based study comprising 120 families with a schizophrenic family member to explore the association between the parental MTHFR 677C > T polymorphism and schizophrenia risk in offspring. In addition, a meta-analysis was performed using the available studies with data on this subject. Transmission Disequilibrium Test (TDT) analysis showed no preferential transmission of the 677T allele from parents heterozygous for the MTHFR 677C > T polymorphism to schizophrenia offspring (P = 0.27). The genotype relative risks were 1.43 (95% CI: 0.83-2.47) for the 677TT and 1.42 (95% CI: 0.54-3.78) for the 677CT genotype, relative to the 677CC genotype. A meta-analysis using data from family-based studies comprising a total of 416 parent-child triads yielded no evidence implicating the 677T allele in schizophrenia risk (P = 0.58). By applying a log-linear model, we found no asymmetry within parental mating type. Our data provided no evidence that transmission of the MTHFR 677T allele is associated with schizophrenia risk. In addition, we found no evidence that the maternal genotype influences the risk of having schizophrenia offspring substantially.     

Sequence variation within the RPGR gene: evidence for a founder complex allele

In our study of sequence variation within the RPGR gene associated with X-linked retinitis pigmentosa, we and others have observed a high rate of new mutation within this gene, as all reported mutations are unique or uncommon. In this article we report the identification in a single family of a complex allele of 7 sequence variants in linkage disequilibrium, of which four result in amino-acid alterations (Arg425Lys, DGlu, Thr533Met and Gly566Glu). This complex allele was initially found in a family with XLRP. However, further study revealed an estimated prevalence of 4.3% (15/344 chromosomes) with this complex allele in the European population indicating the non-pathogenic nature of this allele and, along with previously reported polymorphisms, further supporting a high level of human protein diversity for RPGR. This common complex allele may have been established in the population as a founder effect. Complete gene sequencing identified a potential pathogenic sequence variant in the family described (IVS6+5G>A). This study emphasises the need to create a more complete picture of the allelic variation within a gene, suggests cautious interpretation of a phenotypic association with variant sequences, and highlights the potential problems associated with interpreting genetic studies for diagnostic purposes.     

DAT1 3'-UTR 9R allele: preferential transmission in Indian children with attention deficit hyperactivity disorder.

Genetic alterations in the dopaminergic system are frequently observed in association with attention deficit hyperactivity disorder (ADHD) and a 40 bp variable number of tandem repeats (VNTR) in the 3'-untranslated region (3'-UTR) of the dopamine transporter gene (DAT1) has been investigated in different populations. Both significant association and lack of association with the10 repeat allele (10R) of DAT1 VNTR have been reported. Objective of the present investigation was to examine association of this polymorphism with ADHD in Indian children. Genotypic data obtained from ADHD probands (n = 79), their parents (n = 148) and control individuals (n = 153) were analyzed for haplotype-based haplotype relative risk analysis (HHRR), transmission disequilibrium test (TDT), and family-based association test (FBAT). HHRR analysis revealed significant (P = 0.009) transmission of shorter alleles (< or =9R). TDT analysis of informative ADHD families (n = 32) also exhibited highly significant transmission of the shorter alleles (P = 0.002). Further analysis by FBAT showed preferential transmission (P = 0.019) of the 9R allele from parents to ADHD probands. It can be inferred from the data obtained that the DAT1 3'-UTR 9R allele may confer risk of ADHD in the Indian population.     

Atelosteogenesis type III: long term survival, prenatal diagnosis, and evidence for dominant transmission

We describe two additional instances of atelosteogenesis, type III, in a woman and her son. Clinical and radiographic information concerning these individuals allows further definition of this rare skeletal dysplasia. This is the first documentation of survival to adulthood of an individual with this disorder, of prenatal diagnostic assessment of an affected individual, and of vertical transmission suggestive of autosomal dominant inheritance. The clinical and radiologic phenotype of atelosteogenesis, type III overlaps with that of another skeletal dysplasia, autosomal dominant Larsen syndrome; these most likely represent allelic conditions.     

Dopaminergic transmission in the rat retina: evidence for volume transmission

The study was designed to determine whether dopaminergic neurotransmission in the retina can operate via volume transmission. In double immunolabelling experiments, a mismatch as well as a match was demonstrated in the rat retina between tyrosine hydroxylase (TH) and dopamine (DA) immunoreactive (ir) terminals and cell bodies and dopamine D2 receptor-like ir cell bodies and processes. The match regions were located in the inner nuclear and plexiform layers (D2 ir cell bodies plus processes). The mismatch regions were located in the ganglion cell layer, the outer plexiform layer, and the outer segment of the photoreceptor layer, where very few TH ir terminals can be found in relation to the D2 like ir processes. In similar experiments analyzing D1 receptor like ir processes versus TH ir nerve terminals, mainly a mismatch in their distribution could be demonstrated, with the D1 like ir processes present in the outer plexiform layer and the outer segment where a mismatch in D2 like receptors also exists. The demonstration of a mismatch between the localization of the TH terminal plexus and the dopamine D2 and D1 receptor subtypes in the outer plexiform layer, the outer segment and the ganglion cell layer (only D2 immunoreactivity (IR)) suggests that dopamine, mainly from the inner plexiform layer, may reach the D2 and D1 mismatch receptors via diffusion in the extracellular space. After injecting dopamine into the corpus vitreum, dopamine diffuses through the retina, and strong catecholamine (CA) fluorescence appears in the entire inner plexiform layer and the entire outer plexiform layer, representing the match and mismatch DA receptor areas, respectively. The DA is probably bound to D1 and D2 receptors in both plexiform layers, since the DA receptor antagonist chlorpromazine fully blocks the appearance of the DA fluorescence, while only a partial blockade is found after haloperidol treatment which mainly blocks D2 receptors. These results indicate that the amacrine and/or interplexiform DA cells, with sparse branches in the outer plexiform layer, can operate via volume transmission in the rat retina to influence the outer plexiform layer and the outer segment, as well as other layers of the rat retina such as the ganglion cell layer.     

Serotonin genes and attention deficit/hyperactivity disorder in a Brazilian sample: preferential transmission of the HTR2A 452His allele to affected boys.

Attention-deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood. The role of genetic factors in its etiology is strongly supported by family, adoption, and twin studies. Low serotonin activity has been associated in both animal and human studies with measures of impulsivity, aggression, and disinhibited behaviors, which make genes from the serotonin system reasonable candidates for ADHD susceptibility. In the present study, we investigated a polymorphism in the promoter region of the serotonin transporter (SLC6A4) and two polymorphisms (-1438 A > G and His452Tyr) in the serotonin 5-HTR2A receptor gene using family based association analyses in a sample of 243 Brazilian ADHD children and adolescents and their parents. No linkage disequilibrium between the two HTR2A polymorphisms was detected in this sample (P = 0.76). Considering several evidences from animal models for sexual dimorphism in serotonin genes expression, analyses were performed separately for the whole sample and for male probands. No evidences for biased transmissions of both HTR2A -1438 A > G and SLC6A4 polymorphisms to ADHD youths were observed. Preferential transmission of the HTR2A His452 allele was observed only in families with affected boys (P = 0.04). Our results suggest that findings from ADHD association studies for serotonin genes might be understood in the context of a gender effect, which may help to explain conflicting results in these association studies.     

Distribution of the mutated delta 32 allele of the CCR5 gene in a Sicilian population

The CCR5 gene encodes a cell-surface chemokine receptor molecule that serves as a co-receptor for macrophage-tropic strains of human immunodeficiency virus type 1 (HIV-1). A mutation in this gene may alter the expression or the function of the protein product, thereby altering chemokine binding and/or signalling or HIV-1 infection of cells that normally express CCR5 protein. Individuals homozygous for a 32-bp deletion allele of CCR5 (CCR5 delta32), heritable as a Mendelian trait, are relatively resistant to HIV-1 infection. The CCR5 delta32 mutation is present in the Caucasian population at different frequencies. The aim of this study was to investigate the frequency of truncated alleles of the CCR5 delta32 gene in a Sicilian population, as the interpopulation variation in CCR5 delta32 frequency may be a significant factor in the prediction of AIDS endemicity in future studies. We examined 901 healthy individuals from several Sicilian provinces. We found a mean (+/- standard deviation) delta32 allele frequency (fr) of 0.04 +/- 0.012. The highest value was observed in the province of Messina, with a mean delta32 allele frequency of 0.06 +/- 0.024, where we collected samples from a cohort of 114 HIV-1-infected individuals. The observed frequency amongst these patients was quite low (fr = 0.03 +/- 0.031) compared to the healthy population, although the difference was not statistically significant.     

Molecular aspects of a novel HLA-A*02 allele (A*0297): the first HLA class I allele mutated at codon 232

We describe a new HLA-A*02 allele, identified in a cord blood unit and in her mother. Nucleotide sequence analysis showed the presence of a new HLA-A*02 allele identical to HLA-A*02010101 except for a non-synonymous nucleotide exchange in exon 4 modifying codon 232 from GAG (Glu) to GAC (Asp). No other human leucocyte antigen class I allele sequenced so far shows this triplet at codon 232. The amino acid exchange affects a position that is part of the membrane proximal domain of class I major histocompatibility complex (MHC), designated alpha 3, and involved in the interaction with CD8 molecule. Using molecular modelling approach, the interactions between different subunits of the native and mutated forms of MHC-I resulted in relevant changes.     

Structural evidence for a new IgG1 antibody sequence allele of cattle

Analysis of the heavy-chain gene (pTGHC9907) encoding a bovine IgG1 antibody against bovine herpes virus type 1 (BHV-1) isolated from a Holstein cow has led to the identification of a new IgG1 sequence allele. A comparison of nucleotide sequence of pTGHC9907 with the IgG1(a) (clone 2) and IgG1(b) (clone 8.10) sequence variants and unclassified IgG1 cDNA sequence (clone 8.75) has revealed significant differences in the hinge region spanning codons 216-230. The Thr224 and Thr226 of IgG1(a) were replaced with Arg224 and Pro226, while both Thr218 and Pro224 of IgG1(b) were substituted with Arg with deletion of Ser225 in HB9907 antibody. Additional amino acid substitutions were noted in the CH1 (positions 190, 192), CH2 (position 281) and CH3 (position 402) exons. Thus, the polymorphic sites occurred in all constant domains, but were clustered in the hinge region of IgG1. Examination of a three-dimensional model of the HB9907 heavy chain revealed that all sequence variations were on the surface of the IgG and are possible targets for recognition by antisera and effector molecules such as cellular adhesion molecules. The presence in the CH1 domain of a repeating motif of Pro-Ala-Ser-Ser indicated a potential structure-enhancing function and a role in cellular adhesion and migration. Replacement of Thr with Arg residues within the hinge was predicted to have a dual effect of reducing the number of O-linked glycosylation sites and increasing the susceptibility to degradation by protease-secreting bacteria of the hinge region. As unclassified IgG1 cDNA sequence (clone 8.75) is structurally distinct from other variants, it is also classified as IgG1(d). Collectively, these observations support the identification of a new allotypic variant of bovine IgG1, designated as IgG1(c) that is distinct in both sequence and structure from the known sequence variants.     

Dw subtypes of DR4 in rheumatoid arthritis: evidence for a preferential association with Dw4

We have determined the frequency of the DR4-associated Dw subtypes, defined by homozygous typing cells, in a group of rheumatoid arthritis (RA) patients on second-line drug therapy. The frequency of DR4 in these patients was 86%. Among Caucasians, the frequency of Dw4 in the DR4-positive patients was significantly increased (68%) as compared to DR4-positive normal individuals (46%; p less than 0.025). Dw4, as compared to the other DR4 subtypes tested, may also be associated with more severe disease as judged by indices of functional impairment and joint damage. In a small subgroup of non-Caucasian (black and Native American) patients, the Dw13 (DB3) subtype of DR4 was often seen, suggesting that RA may have different Dw associations in different ethnic groups.     

Preferential transmission of the MTHFR 677 T allele to infants with Down syndrome: implications for a survival advantage

We have examined the transmission frequencies of the methylenetetrahydrofolate reductase (MTHFR) 677 T and C alleles from heterozygous parents to children with Down syndrome (trisomy 21) in 202 Caucasian families. Our results indicated that the MTHFR 677T allele was transmitted to children with Down syndrome at a significantly higher rate than would be expected based on Mendelian inheritance patterns, and the C allele was transmitted at a significantly lower rate (P < 0.009). Transmission frequencies were also examined independently for maternally and paternally transmitted alleles to assess potential parent-of-origin effects. Because the vast majority of conceptions with trisomy 21 end in pregnancy loss, we questioned whether the observed preferential transmission of the T allele to this population of liveborn infants with Down syndrome could reflect a survival advantage. A plausible biochemical interpretation of these results is presented based on a maternal-fetal MTHFR 677T allele interaction in the context of the constitutive overexpression of three copies of the cystathionine beta synthase gene in the trisomy 21 fetus. Published 2002 Wiley-Liss, Inc.     

A mutated HLA-A*0101 allele in the colorectal cell line HCA-7

The colorectal cell line HCA-7 expresses surface human leucocyte antigen-A*0201 (HLA-A*0201), but lacks expression of HLA-A*0101 whilst the normal B-cell line (EVA-1224), derived from the same individual, expresses both surface HLA-A1 and HLA-A2. Amplification refractory mutation system-polymerase chain reaction analysis, using sequence-specific primers, suggested that HCA-7 has a mutation in a 7 base pair (bp) cytosine repeat sequence located at the beginning of Exon 4 (bp 621-627). Cloning and sequencing revealed HCA-7 to have eight cytosine residues in this repeat sequence. In contrast, EVA-1224 contained only 7 cytosines. Analysis of the mRNA for HLA-A*010 using reverse trancriptase-polymerase chain reaction (RT-PCR), with an allele-specific 5' primer in exon 2 (bp 253-271) and a series of 3' primers in exons 3, 4 and 7 and in the 3'untranslated region, revealed that HCA-7 contained a shortened message terminating in the region of the exon 3/4 boundary. The insertion of an extra cytosine in this region, which is only two bases from the exon 3/4 splice site, is presumed to lead to a splicing defect between exons 3 and 4 resulting in the lack of expression of a functional HLA-A*0101 product. HCA-7 is mismatch repair (MMR) defective due to lack of expression of hMLH1 resulting from hypermethylation of the promoter region. The consequential increase in errors in single-nucleotide repeat stretches of DNA can account for the HLA-A*0101 mutation. This has probably then been selected for in the tumour to enable escape from immune attack against an HLA-A*0101-restricted tumour-specific determinant that has also arisen as a result of the tumour being MMR defective.     

Direct evidence for preferential multiplication ofBabesia gibsoni in young erythrocytes

To clarify the effect of the age of host erythrocytes on the multiplication ofBabesia parasites,B. gibsoni was cultured together with reticulocytes, immature erythrocytes, or mature erythrocytes from dogs. Parasitemia reached peak levels (34.1%±15.8%) at cultivation day 8 in immature-erythrocyte culture, whereas the highest parasitemia attained in mature-cell culture was only 3.6%±2.2% at day 5. These results clearly demonstrate thatB. gibsoni parasites preferentially invade and multiply in young erythrocytes rather than in mature cells.     

Association analysis of the monoamine oxidase A and B genes with attention deficit hyperactivity disorder (ADHD) in an Irish sample: preferential transmission of the MAO-A 941G allele to affected children.

Pharmacological and genetic studies suggest the importance of the dopaminergic, serotonergic, and noradrenergic systems in the pathogenesis of attention deficit hyperactivity disorder (ADHD). Monoamine oxidases A and B (MAO-A and MAO-B) degrade biogenic amines such as dopamine and serotonin and thereby control the levels of these neurotransmitters in the central nervous system. We examined four polymorphisms in the MAO-A gene (30 bp promoter VNTR, CA microsatellite in intron 2, 941G/T SNP in exon 8, and A/G SNP in intron 12) as well as two markers in the MAO-B gene (CA microsatellite in intron 2 and T/C SNP in intron 13) for association with ADHD in an Irish sample of 179 nuclear families. TDT analysis of the examined MAO-A markers revealed a significant association of the more active MAO-A 941G allele with the disorder (chi2 = 5.1, P = 0.03, OR = 1.7). In addition, haplotype analysis revealed a significantly increased transmission of a haplotype consisting of the shorter allele of the promoter VNTR (allele 1), the 6-repeat allele of the CA microsatellite and the G-allele of the 941G/T SNP (famhap global statistic 34.54, P = 0.01) to ADHD cases. No significant distortion in the number of transmitted alleles was observed between the two examined MAO-B polymorphisms and ADHD. These findings suggest the importance of the 941G/T MAO-A polymorphism in the development of ADHD at least in the Irish population.     

Testicular persistence of Parvovirus B19: evidence for preferential infection of germ cell tumors

Human Parvovirus B19 has previously been implicated in the pathogenesis of testicular germ cell tumors, but this could not have been confirmed. This study was designed to investigate the testicular persistence of Parvovirus B19 and possible associations with germ cell tumors. Paraffin-embedded or fresh tissues from 36 germ cell tumors, 20 germ cell aplasias, 26 normal testicular tissues, 20 liver tissues, and 20 spleen tissues were evaluated by two different molecular assays: a nested PCR for Parvovirus B19 capsid genes and a commercial quantitative real-time PCR. Positive results were further confirmed by another commercial real-time PCR assay. Viral DNA was detected in 3 of 36 (8.3%) germ cell tumors, but not in other groups. Viral loads observed in all positive samples were less than 20 IU/reaction, suggesting very low levels of viral replication or latency. These results either directly or indirectly imply the involvement of Parvovirus B19 with testicular germ cell tumors. Viral persistence in normal testis, germ cell aplasia tissues, or hepatic/splenic tissues was not observed in this study.     

Genetic segregation analysis of recurrent, early-onset major depression: evidence for single major locus transmission

Coordinated efforts are now underway to identify susceptibility genes for unipolar major depressive disorder (MDD) and related disorders. These studies have focused on recurrent, early-onset MDD (RE-MDD), thought to be the most familial form of this disorder. The goal of this study was to conduct a complex segregation analysis of recurrent MDD and other major mood disorders aggregating in families identified by probands with RE-MDD. Eighty-one families were identified through probands over the age of 18 who met criteria for recurrent (> or =2 episodes), early-onset (< or =25 years), nonpsychotic, unipolar MDD (RE-MDD) and included 407 first-degree relatives and 835 extended relatives. Psychiatric diagnoses for probands and their family members who provided blood samples were formulated from structured personal interviews, structured family history assessments, and available medical records. The remaining family members who participated and those who were deceased were evaluated through the family history method augmented by available medical records. Best-estimate diagnoses were made during a consensus conference according to established diagnostic criteria. Segregation analyses were performed using the REGD routine in S.A.G.E. release 4.0. The segregation analysis of recurrent MDD supported a sex-independent Mendelian codominant model. Analysis of major mood disorders supported a sex-independent Mendelian dominant model. Interestingly, inclusion of spousal residual correlations provided better fitting models for recurrent MDD but not the broader phenotype of major mood disorders. Unlike unipolar MDD, the lifetime prevalence of bipolar I disorder in this sample of families did not exceed the reported population prevalence [Zubenko et al., 2001]. Our results suggest that a major locus contributes to the expression of recurrent MDD and possibly other major mood disorders within families identified by probands with RE-MDD. Due to the limitations of the segregation analysis model, our results cannot address whether the same major locus is segregating across families in our sample or whether multiple major loci are involved (genetic heterogeneity). The absence of aggregation of bipolar I disorder in these families strongly suggests that while the genetic determinants of unipolar and bipolar disorders may overlap, they are not identical. Our findings illustrate the advantage of employing families identified by probands with RE-MDD in studies designed to detect susceptibility loci for unipolar MDD and related disorders.