Sudha Srinivasan

Loss of p53 Sensitizes Mice with a Mutation in Ccm1 (KRIT1) to Development of Cerebral Vascular Malformations

Cerebral cavernous malformations (CCM) consist of clusters of abnormally dilated blood vessels. Hemorrhaging of these lesions can cause seizures and lethal stroke. Three loci are associated with autosomal dominant CCM, and the causative genes have been identified for CCM1 and CCM2. We have generated mice with a targeted mutation of the Ccm1 gene, but an initial survey of 20 heterozygous mice failed to detect any cavernous malformations. To test the hypothesis that growth of cavernous malformations depends on somatic loss of heterozygosity at the Ccm1 locus, we bred animals that were heterozygous for the Ccm1 mutation and homozygous for loss of the tumor suppressor Trp53 (p53), which has been shown to increase the rate of somatic mutation. We observed vascular lesions in the brains of 55% of the double-mutant animals but none in littermates with other genotypes. Although the genetic evidence suggested somatic mutation of the wild-type Ccm1 allele, we were unable to demonstrate loss of heterozygosity by molecular methods. An alternative explanation is that p53 plays a direct role in formation of the vascular malformations. The striking similarity of the human and mouse lesions indicates that the Ccm1(+/-) Trp53(-/-) mice are an appropriate animal model of CCM.

Neuronal expression of the Ccm2 gene in a new mouse model of cerebral cavernous malformations

Cerebral cavernous malformations are vascular defects of the central nervous system consisting of clusters of dilated vessels that are subject to frequent hemorrhaging. The genes mutated in three forms of autosomal dominant cerebral cavernous malformations have been cloned, but it remains unclear which cell type is ultimately responsible for the lesion. In this article we describe mice with a gene trap insertion in the Ccm2 gene. Consistent with the human phenotype, heterozygous animals develop cerebral vascular malformations, although penetrance is low. β-galactosidase activity in heterozygous brain and in situ hybridization in wild-type brain revealed Ccm2 expression in neurons and choroid plexus but not in vascular endothelium of small vessels in the brain. The expression pattern of Ccm2 is similar to that of the Ccm1 gene and its interacting protein ICAP1 (Itgb1bp1). These data suggest that cerebral cavernous malformations arise as a result of defects in the neural parenchyma surrounding the vascular endothelial cells in the brain.

Neonatal Co‐Infection with Helicobacter Species Markedly Accelerates the Development of Inflammation‐Associated Colonic Neoplasia in IL‐10−/–Mice

Background:  Inflammatory bowel disease (IBD) is hypothesized to represent an aberrant immune response against enteric bacteria that occurs in a genetically susceptible host. Humans and mice with IBD are at markedly increased risk for colonic neoplasia. However, the long lead time required before development of inflammation‐associated colon neoplasia in commonly used murine models of IBD slows the development of effective chemopreventative therapies.

Pro-GnRH processing

Publisher Summary An inspection of the deduced amino acid sequences from the nine complementary pro-GnRH forms demonstrates several points. All pro-gonadotropin-releasing hormone (GnRH) proteins contain GnRH at their N-termini and the peptide is separated by a putative processing site from GnRH-associated peptide (GAP). The organization and spatial arrangement of these sequences suggest that the enzymes that process the pro-GnRH in a given cell are similar across all species. In addition, excision of the GnRH peptide from the precursor is performed by an endopeptidase. Because most peptide precursors appear to be processed at monobasic or dibasic residues, the endopeptidase could cleave the pro-GnRH after the Lys or Arg residues. The regulation of peptide bioactivity is a complex process. Cells have devised ingenious mechanisms to control the amounts of peptides available for release. Some of these processes include gene transcription, pre-RNA splicing, protein biosynthesis, trafficking of the precursor to the regulated secretory pathway, conversion of the pro-peptide to fully processed product, secretion, and degradation. There is considerable controversy regarding the regulation of GnRH transcription in vivo , and in many cases, control appears to occur posttranscriptionally.

The promise of discovering population-specific disease-associated genes in South Asia

The more than 1.5 billion people who live in South Asia are correctly viewed not as a single large population, but as many small endogamous groups. We assembled genome-wide data from over 2,800 individuals from over 260 distinct South Asian groups. We identify 81 unique groups, of which 14 have estimated census sizes of more than a million, that descend from founder events more extreme than those in Ashkenazi Jews and Finns, both of which have high rates of recessive disease due to founder events. We identify multiple examples of recessive diseases in South Asia that are the result of such founder events. This study highlights an under-appreciated opportunity for reducing disease burden among South Asians through the discovery of and testing for recessive disease genes.The more than 1.5 billion people who live in South Asia are correctly viewed not as a single large population but as many small endogamous groups. We assembled genome-wide data from over 2,800 individuals from over 260 distinct South Asian groups. We identified 81 unique groups, 14 of which had estimated census sizes of more than 1 million, that descend from founder events more extreme than those in Ashkenazi Jews and Finns, both of which have high rates of recessive disease due to founder events. We identified multiple examples of recessive diseases in South Asia that are the result of such founder events. This study highlights an underappreciated opportunity for decreasing disease burden among South Asians through discovery of and testing for recessive disease-associated genes.

Organization for rare diseases India (ORDI) - addressing the challenges and opportunities for the Indian rare diseases' community.

In order to address the unmet needs and create opportunities that benefit patients with rare disease in India, a group of volunteers created a not-for-profit organization named Organization for Rare Diseases India (ORDI; www.ordindia.org). ORDI plans to represent the collective voice and advocate the needs of patients with rare diseases and other stakeholders in India. The ORDI team members come from diverse backgrounds such as genetics, molecular diagnostics, drug development, bioinformatics, communications, information technology, patient advocacy and public service. ORDI builds on the lessons learned from numerous similar organizations in the USA, European Union and disease-specific rare disease foundations in India. In this review, we provide a background on the landscape of rare diseases and the organizations that are active in this area globally and in India. We discuss the unique challenges in tackling rare diseases in India, and highlight the unmet needs of the key stakeholders of rare diseases. Finally, we define the vision, mission, goals and objectives of ORDI, identify the key developments in the health care context in India and welcome community feedback and comments on our approach.

Mutations in ARSB in MPS VI patients in India

Mucopolysaccharidosis VI (MPS VI) is an autosomal recessive inborn error of metabolism caused by mutations in the arylsulfatase B gene (ARSB) and consequent deficient activity of ARSB, a lysosomal enzyme. We present here the results of a study undertaken to identify the mutations in ARSB in MPS VI patients in India. Around 160 ARSB mutations, of which just 4 are from India, have been reported in the literature. Our study covered nine MPS VI patients from eight families. Both familial mutations were found in seven families, and only one mutation was found in one family. Seven mutations were found — four novel (p.G38_G40del3, p.C91R, p.L98R and p.R315P), two previously reported from India (p.D53N and p.W450C), and one reported from outside India (p.R160Q). One mutation, p.W450C, was present in two families, and the other six mutations were present in one family each. Analysis of the molecular structure of the enzyme revealed that most of these mutations either cause loss of an active site residue or destabilize the structure of the enzyme. The only previous study on mutations in ARSB in Indian MPS VI patients, by Kantaputra et al. 2014 [1], reported four novel mutations of which two (p.D53N and p.W450C) were found in our study as well. Till date, nine mutations have been reported from India, through our study and the Kantaputra study. Eight out of these nine mutations have been found only in India. This suggests that the population studied by us might have its own typical set of mutations, with other populations equally likely to have their own set of mutations.

The promise of disease gene discovery in South Asia

The more than 1.5 billion people who live in South Asia are correctly viewed not as a single large ethnic group, but as many small endogamous groups. We assembled genome-wide data from over 2,800 individuals from over 275 distinct South Asian groups. We document shared ancestry across groups that correlates with geography, language, and religious affiliation. We characterize the strength of the founder events that gave rise to many of the groups, and identify 14 groups with census sizes of more than a million that descend from founder events significantly stronger than those in Ashkenazi Jews and Finns, both of which have high rates of recessive disease due to founder events. These results highlight a major and under-appreciated opportunity for reducing disease burden among South Asians through the discovery of and testing for recessive disease genes. As a proof-of-principle, we show that it is possible to localize genes for progressive pseudorheumatoid dysplasia and mucopolysaccharidosis type IVA, two recessive diseases prevalent in South India, using the founder event disease gene mapping approach introduced here.