Evidence that a dodecamer duplication in the gene HOPA in Xq13 is not associated with mental retardation

The association of the HOPA(12bp) polymorphism with schizophrenia in the NIMH Genetics Initiative for Schizophrenia sample

HOPA (MED12) is an X-chromosome gene that codes for a critical member of the Mediator Complex, a group of proteins that regulates transcription via the nuclear receptor, Wnt and Receptor Tyrosine Kinase pathways. In prior association and meta-analyses, we have shown that the presence of an evolutionarily conserved, 12 bp (4 amino acid) insertional polymorphism in exon 43 of this gene is associated with increased risk for an endophenotype of schizophrenia. In this communication, we describe the results of our work with subjects and data from the National Institutes of Mental Health (NIMH) Genetics Initiative for Schizophrenia. We report that the presence of the HOPA(12bp) polymorphism is associated with increased risk for schizophrenia in subjects of European ancestry. In the light of this new study and the prior wealth of clinical and basic science data, we conclude that the HOPA(12bp) allele is a risk factor for schizophrenia in subjects of European ancestry and suggest that further studies to define the endophenotype and mechanisms of illness associated with this polymorphism are indicated.

A recurrent mutation in MED12 leading to R961W causes Opitz-Kaveggia syndrome

Opitz-Kaveggia syndrome (also known as FG syndrome) is an X-linked disorder characterized by mental retardation, relative macrocephaly, hypotonia and constipation. We report here that the original family for whom the condition is named and five other families have a recurrent mutation (2881C>T, leading to R961W) in MED12 (also called TRAP230 or HOPA), a gene located at Xq13 that functions as a thyroid receptor-associated protein in the Mediator complex.

Association of the HOPA12bp allele with a large X-chromosome haplotype and positive symptom schizophrenia

HOPA is a X-chromosome gene that encodes an essential nuclear receptor co-activator. Previously, we have demonstrated that an exonic polymorphism, termed HOPA(12bp), in the Opa (Opposite Paired) domain of this gene that is critical for neuronal growth and differentiation is associated with a low risk for schizophrenia. But curiously, we have also noted that all HOPA(12bp) probands have the same haplotype immediately surrounding the HOPA(12bp), and other investigators have found evidence of population stratification with the HOPA(12bp) allele. Since deleterious alleles are weeded from the population, and the HOPA(12bp) allele is not rare, these prior findings suggest the possibility that positive selection may be occurring with respect to the HOPA(12bp) allele and that unique phenotypic features may be associated with this allele. To test these hypotheses, we analyzed symptom data collected from schizophrenic probands and conducted haplotyping studies around the HOPA(12bp) polymorphism. Consistent with our hypotheses, genotyping studies of 43 unrelated HOPA(12bp) males and 137 HOPA(wild) males demonstrated that the HOPA(12bp) allele is associated with a large conserved DNA haplotype that extends over several genes known to be critical for human survival. Furthermore, ANOVA analysis of symptom data demonstrated that HOPA(12bp) schizophrenic probands (n = 14) have significantly lower severity of negative symptoms (P < 0.002) and better attention (P < 0.002) than matched controls (n = 30). Taken together, these findings further refine the behavioral endophenotype associated with the HOPA(12bp) allele and suggest that the sequence surrounding HOPA may need to be considered to fully understand the molecular basis of the phenotype associated with the HOPA(12bp) allele.

Polymorphism analysis of HOPA: a candidate gene for schizophrenia

HOPA is a 25 kb Xq13 gene that codes for a member of the thyroid receptor co-activator protein (TRAP) family of nuclear receptor co-activators. In our prior research, polymorphisms in the opposite paired (Opa) domain of HOPA have been associated with a syndrome of aberrant behavior, most prominently psychosis, and hypothyroidism. These Opa domain polymorphisms are intriguing because subsequent research has demonstrated that changes in the Opa domain of the C. elegans orthologue of HOPA results in altered neurogenesis and release of transcriptional suppression. In an effort to determine whether other allelic polymorphisms in this gene exist and may potentially contribute to increased susceptibility to neuropsychiatric illness, we have performed single stranded conformational polymorphism (SSCP) analysis of all 45 exons and each of the two potential promoter regions of HOPA using DNA from a panel of patients with psychosis. We found a rare promoter polymorphism in an individual with schizoaffective disorder and extremely low thyroid stimulating hormone (TSH). The most common exonic polymorphism in HOPA is the previously demonstrated HOPA(12 bp) polymorphism. Transmission disequilibrium analysis of the HOPA(12 bp) polymorphism showed segregation with affected status in six of eight instances. We suggest that this evidence supports previous associations of HOPA(12 bp) with a broad range of neuropsychiatric illness and conclude that further studies of this uncommon polymorphism are merited.

No association of a dodecamer duplication in the human opposite paired (HOPA) gene with mental retardation and schizophrenia in Chinese patients from Taiwan

The human opposite paired-containing (HOPA) gene is believed to be a co-activator of the thyroid hormone receptor and involved in thyroid hormone signal transduction. The gene consists of 45 exons and includes a dodecamer duplication in exon 43, which has been reported to be associated with mental retardation, autism, psychiatric disorders and hypothyroidism. We were interested to know if the 12-bp duplication variant of the HOPA gene is a risk factor for mental retardation and schizophrenia in the Chinese population. We investigated the prevalence of the 12-bp variant in a sample of Chinese mental retardation and schizophrenic patients from Taiwan by PCR-based genotyping. None of the mentally retarded and schizophrenic patients were found to have this dodecamer duplication variant. Our results indicate that the HOPA polymorphism might be very rare in our population and is unlikely to be a major risk factor for mental retardation and schizophrenia in the Chinese population.

Association analysis of the HOPA12bp polymorphism in schizophrenia and manic depressive illness

Variations in exon 42 of the HOPA (human opposite paired) gene have been associated with mental retardation, hypothyroidism and psychiatric disorders. We attempted to replicate the association with schizophrenia using 309 parent-offspring trios from Bulgaria and 367 unrelated cases and 368 blood donors from the UK. We also tested 125 bipolar trios from Bulgaria, 112 bipolar trios from the UK and a sample of 178 unrelated bipolar cases and 188 blood donors from the UK. The frequency of HOPA(12bp) in the 556 UK blood donors was 2.6% and it was not significantly different in the UK patients groups, where it ranged from 1.2 to 3.8%. Sixteen mothers transmitted the HOPA(12bp) allele to schizophrenic offspring, while 12 did not transmit, a non-significant difference. There was a trend for under-transmission of the rare allele to bipolar patients (T/NT = 4/10) and they had a lower rate of that allele than schizophrenic patients in the Bulgarian population (1% vs. 4.2%, P = 0.043). However the two diagnostic groups had similar allele frequencies in the UK populations: 2% versus 2.6%, P = 0.6. We conclude that the HOPA polymorphism is unlikely to be a major risk factor in the pathogenesis of these major psychiatric disorders although there could be a small effect in schizophrenia.

Association studies of the HOPA dodecamer duplication variant in different subtypes of autism

The HOPA gene in Xq13 is coding for a protein involved in a nuclear thyroid receptor complex. Previous studies suggested association of the dodecamer duplication in the OPA-repeat region in exon 43 (according to the genomic database sequence) with autism, mental retardation, and schizophrenia/hypothyroidism. We determined the frequency of this 12 bp duplication variant in a sample of 155 patients divided in different subtypes of autism, 278 parents of those patients, and 157 control individuals. The allele frequency of the duplication variant was not significantly different between autistic patients, their parents, and the control group. Therefore, it is unlikely that this 12 bp duplication variant of the HOPA gene has major relevance to the susceptibility to different subtypes of autism at least in this German patient sample. In addition, we identified a third variant with a 15 bp deletion in the OPA-repeat region, recently described by another group, in one autistic patient. This third allele was also present in the patient's nonautistic mother and sister, who are heterozygous for this variant, but could not be detected in any other individual genotyped in this study. Expression analysis revealed transcription of all three allelic variants in lymphoblastoid cell lines. Furthermore, we identified a new splice variant that utilizes an additional 9 bp of the 3' intron subsequent to exon 39. Both alternative transcripts are coexpressed in all fetal and adult tissues examined.

The HOPA gene dodecamer duplication is not a significant etiological factor in autism

A recent study has suggested that a dodecamer duplication in the HOPA gene in Xq13 may occur in a significant portion of male patients with autism. We have determined the incidence of this duplication in 202 patients from the South Carolina Autism Study. The incidence of the duplication was not significantly different between patients and controls. Three of the female patients inherited the duplication from nonautistic fathers. In addition, there was no systematic skewing of X inactivation in the female patients with the duplication, or in nonautistic mothers and sisters with the duplication. These findings suggest that the dodecamer duplication in the HOPA gene does not play a significant role in the etiology of autism.