A novel leucine to valine mutation in residue 7 of the helix initiation motif of keratin10 leads to bullous congenital ichthyosiform erythroderma

Population genomics of Wolbachia and mtDNA in Drosophila simulans from California

Wolbachia pipientis is an intracellular endosymbiont infecting many arthropods and filarial nematodes. Little is known about the short-term evolution of Wolbachia or its interaction with its host. Wolbachia is maternally inherited, resulting in co-inheritance of mitochondrial organelles such as mtDNA. Here I explore the evolution of Wolbachia, and the relationship between Wolbachia and mtDNA, using a large inbred panel of Drosophila simulans. I compare this to the only other large population genomic Wolbachia dataset from D. melanogaster. I find reduced diversity relative to expectation in both Wolbachia and mtDNA, but only mtDNA shows evidence of a recent selective sweep or population bottleneck. I estimate Wolbachia and mtDNA titre in each genotype, and I find considerable variation in both phenotypes, despite low genetic diversity in Wolbachia and mtDNA. A phylogeny of Wolbachia and of mtDNA suggest a recent origin of the infection derived from a single origin. Using Wolbachia and mtDNA titre as a phenotype, I perform the first association analysis using this phenotype with the nuclear genome and find several implicated regions, including one which contains four CAAX-box protein processing genes. CAAX-box protein processing can be an important part of host-pathogen interactions in other systems, suggesting interesting directions for future research.

Novel genes as primary triggers for polygenic hypertension

OBJECTIVES

The discovery of causative genes leading to hypertension in animal models can reveal new mechanistic insights into blood pressure (BP) regulations. Previously, we isolated segments that harbor BP quantitative trait loci (QTLs) on rat chromosome 10 as defined by congenic strains made from crosses of inbred hypertensive Dahl salt-sensitive (DSS) and normotensive Lewis rats. The aim of the current study was to identify hypertension-causing genes for each QTL.

METHODS

Molecular analysis was performed.

RESULTS

A systematic and comprehensive molecular analysis divulged particular genes that carry nonconserved mutations. Specifically, the proline rich 11 gene is likely responsible for C10QTL5. C10QTL1 is one of five genes, namely Benzodiazepine receptor associated protein 1, Loc689764, myotubularin related protein 4, protein phosphatase 1E, PP2C domain containing and ring finger protein 43. Loc100363423 with no known function is a candidate for C10QTL3. The ATP-binding cassette, subfamily A (ABC1), member 8a gene is probably responsible for C10QTL2.

CONCLUSIONS

Primary genes initiating polygenic hypertension are those not known to be involved in BP modulation. Novel pathways towards BP homeostasis appear to underlie the functionality of C10QTL5, C10QTL1 and C10QTL3 and C10QTL2. Moreover, these genes may become innovative targets for the diagnosis and therapeutics of essential hypertension.

A recurrent intragenic genomic duplication, other novel mutations in NLRP7 and imprinting defects in recurrent biparental hydatidiform moles

A complete hydatidiform mole (CHM) is an abnormal pregnancy with hyperproliferative vesicular trophoblast and no fetal development. Most CHM are sporadic and androgenetic, but recurrent HM have biparental inheritance (BiHM) with disrupted DNA methylation at differentially methylated regions (DMRs) of imprinted loci. Some women with recurrent BiHM have mutations in the NLRP7 gene on chromosome 19q13.42. Using bisulfite genomic sequencing at eight imprinted DMRs on DNA from two BiHMs, we found a pattern of failure to acquire or maintain DNA methylation at DMRs (PEG3, SNRPN, KCNQ1OT1, GNAS exon 1A) that normally acquire CpG methylation during oogenesis, but not at H19, which acquires CpG methylation during spermatogenesis. Secondary imprints at the GNAS locus showed variable abnormal patterns with both gain and loss of CpG methylation. We found novel missense and splice-site mutations in NLRP7 in women with non-familial recurrent BiHM. We identified and characterized a homozygous intragenic tandem duplication including exons 2 through 5 of NLRP7 that results in a predicted truncated protein in affected women of three unrelated Egyptian kindreds, suggesting a founder effect. Our findings firmly establish that NLRP7 mutations are a major cause of BiHM and confirm presence of a complex pattern of imprinting abnormalities in BiHM tissues.

Farber lipogranulomatosis: clinical and molecular genetic analysis reveals a novel mutation in an Indian family

Farber disease is a rare lysosomal storage disorder caused by a deficiency of the acid ceramidase enzyme, leading to the accumulation of ceramide in various tissues. It usually manifests within a few months after birth with a unique triad of symptoms, including painful and progressive deformed joints, progressive hoarseness and subcutaneous nodules. The disease is inherited as an autosomal recessive trait, and mutations in the N-acylsphingosine amidohydrolase (ASAH1) gene, which codes for the acid ceramidase enzyme, have been shown to cause the disease. In the current study, we report the identification of a novel disease-causing mutation in the ASAH1 gene that results in Farber disease in an Indian family. The mutation was identified in the eighth exon and is a missense mutation resulting in replacement of Valine by Leucine at codon 182. Two affected siblings harboured the identical mutation. The possible mechanism(s) of disease caused by this mutation are discussed.

Glial fibrillary acidic protein mutations in infantile, juvenile, and adult forms of Alexander disease

Alexander disease is a progressive, usually fatal neurological disorder defined by the widespread and abundant presence in astrocytes of protein aggregates called Rosenthal fibers. The disease most often occurs in infants younger than 2 years and has been labeled a leukodystrophy because of an accompanying severe myelin deficit in the frontal lobes. Later onset forms have also been recognized based on the presence of abundant Rosenthal fibers. In these cases, clinical signs and pathology can be quite different from the infantile form, raising the question whether they share the same underlying cause. Recently, we and others have found pathogenic, de novo missense mutations in the glial fibrillary acidic protein gene in most infantile patients examined and in a few later onset patients. To obtain further information about the role of glial fibrillary acidic protein mutations in Alexander disease, we analyzed 41 new patients and another 3 previously described clinically, including 18 later onset patients. Our results show that dominant missense glial fibrillary acidic protein mutations account for nearly all forms of this disorder. They also significantly expand the catalog of responsible mutations, verify the value of magnetic resonance imaging diagnosis, indicate an unexpected male predominance for the juvenile form, and provide insights into phenotype-genotype relations.

GFAP mutations in Alexander disease

Alexander disease is a rare but often fatal disease of the central nervous system. Infantile, juvenile and adult forms have been described that present with different clinical signs, but are unified by the characteristic presence in astrocytes of Rosenthal fibers-protein aggregates that contain glial fibrillary acidic protein (GFAP) and small stress proteins. The chance discovery that mice expressing a human GFAP transgene formed abundant Rosenthal fibers suggested that mutations in the GFAP gene are a cause of Alexander disease. Sequencing results from several laboratories have indeed now identified GFAP coding mutations in most cases of the disease, including both the infantile and juvenile forms. These mutations have been found in the 1A, 2A and 2B segments of the conserved central rod domain of GFAP, and also in the variable tail region. All changes detected are heterozygous missense mutations, and none has been found in any parent of a patient that has been tested. This indicates that most cases of Alexander disease arise through de novo, dominant, GFAP mutations. Many of these mutations are homologous to ones described in other intermediate filament diseases. These other diseases have been attributed to a dominant loss of function, as the intermediate filament network is usually disrupted and a similar phenotype is observed in mice in which the corresponding intermediate filament gene has been inactivated. However, astrocytes of Alexander disease patients have normal appearing intermediate filaments, and GFAP null mice do not display the symptoms or pathology of Alexander disease. Thus, Alexander disease likely results from a dominant gain of function. Drawing upon the homology of many of the Alexander disease mutations to those found in other intermediate filament diseases, it is suggested that the gain of function is due to a partial block of filament assembly that leads to accumulation of an intermediate that participates in toxic interactions.