Saima Siddiqi

Patient HLA-DRB1 * and -DQB1 * allele and haplotype association with hepatitis C virus persistence and clearance

Hepatitis C virus (HCV) infection is prevalent throughout the world and interferon (IFN)-based treatments are currently the only therapeutic option. However, depending upon variations in their human leukocyte antigen (HLA), some patients do not respond well to IFN therapy. The current study evaluated the HLA allele and haplotype distribution of 204 HCV-seropositive individuals from Islamabad, Pakistan, who were receiving standard IFN therapy. In this cohort, 150 patients (74%) showed a sustained virological response to IFN therapy, whereas 54 (26%) did not. In addition to the HCV patients, 102 unrelated healthy volunteers were used as controls. DNA was isolated from the blood of the patients and controls for HLA-DRB1 and HLA-DQB1 allele typing, whilst plasma was used for HCV detection and genotyping. HLA-DRB1*04 was found to impart a significant protective advantage [Bonferroni-corrected P value (pc)=0.047] against HCV infection. In patients on IFN therapy, HLA-DRB1*11 and -DQB1*0301 (pc=0.044) were found to be associated with viral clearance. In contrast, HLA-DRB1*07 (pc=0.008) individually or in combination with HLA-DQB1*02 was found to be associated with viral persistence. These associations of HLA with HCV persistence or clearance will be beneficial in deciding the therapeutic regimen for Pakistani patients infected with HCV genotype 3a.

Genetic spectrum of autosomal recessive non-syndromic hearing loss in Pakistani families.

The frequency of inherited bilateral autosomal recessive non-syndromic hearing loss (ARNSHL) in Pakistan is 1.6/1000 individuals. More than 50% of the families carry mutations in GJB2 while mutations in MYO15A account for about 5% of recessive deafness. In the present study a cohort of 30 ARNSHL families was initially screened for mutations in GJB2 and MYO15A. Homozygosity mapping was performed by employing whole genome single nucleotide polymorphism (SNP) genotyping in the families that did not carry mutations in GJB2 or MYO15A. Mutation analysis was performed for the known ARNSHL genes present in the homozygous regions to determine the causative mutations. This allowed the identification of a causative mutation in all the 30 families including 9 novel mutations, which were identified in 9 different families (GJB2 (c.598G>A, p.Gly200Arg); MYO15A (c.9948G>A, p.Gln3316Gln; c.3866+1G>A; c.8767C>T, p.Arg2923* and c.8222T>C, p.Phe2741Ser), TMC1 (c.362+18A>G), BSND (c.97G>C, p.Val33Leu), TMPRSS3 (c.726C>G, p.Cys242Trp) and MSRB3 (c.20T>G, p.Leu7Arg)). Furthermore, 12 recurrent mutations were detected in 21 other families. The 21 identified mutations included 10 (48%) missense changes, 4 (19%) nonsense mutations, 3 (14%) intronic mutations, 2 (9%) splice site mutations and 2 (9%) frameshift mutations. GJB2 accounted for 53% of the families, while mutations in MYO15A were the second most frequent (13%) cause of ARNSHL in these 30 families. The identification of novel as well as recurrent mutations in the present study increases the spectrum of mutations in known deafness genes which could lead to the identification of novel founder mutations and population specific mutated deafness genes causative of ARNSHL. These results provide detailed genetic information that has potential diagnostic implication in the establishment of cost-efficient allele-specific analysis of frequently occurring variants in combination with other reported mutations in Pakistani populations.

Investigation of the Greek ancestry of populations from northern Pakistan

Three populations from northern Pakistan, the Burusho, Kalash, and Pathan, claim descent from soldiers left behind by Alexander the Great after his invasion of the Indo-Pak subcontinent. In order to investigate their genetic relationships, we analyzed nine Alu insertion polymorphisms and 113 autosomal microsatellites in the extant Pakistani and Greek populations. Principal component, phylogenetic, and structure analyses show that the Kalash are genetically distinct, and that the Burusho and Pathan populations are genetically close to each other and the Greek population. Admixture estimates suggest a small Greek contribution to the genetic pool of the Burusho and Pathan and demonstrate that these two northern Pakistani populations share a common Indo-European gene pool that probably predates Alexander’s invasion. The genetically isolated Kalash population may represent the genetic pool of ancestral Eurasian populations of Central Asia or early Indo-European nomadic pastoral tribes that became sequestered in the valleys of the Hindu Kush Mountains.

Genetics of vascular dementia – review from the ICVD working group

BackgroundVascular dementia is a common disorder resulting in considerable morbidity and mortality. Determining the extent to which genes play a role in disease susceptibility and their pathophysiological mechanisms could improve our understanding of vascular dementia, leading to a potential translation of this knowledge to clinical practice.DiscussionIn this review, we discuss what is currently known about the genetics of vascular dementia. The identification of causal genes remains limited to monogenic forms of the disease, with findings for sporadic vascular dementia being less robust. However, progress in genetic research on associated phenotypes, such as cerebral small vessel disease, Alzheimer’s disease, and stroke, have the potential to inform on the genetics of vascular dementia. We conclude by providing an overview of future developments in the field and how such work could impact patients and clinicians.ConclusionThe genetic background of vascular dementia is well established for monogenic disorders, but remains relatively obscure for the sporadic form. More work is needed for providing robust findings that might eventually lead to clinical translation.

Association of HLA-DRB1 and -DQB1alleles and haplotypes with rheumatoid arthritis in a Pakistani population.

IntroductionRheumatoid arthritis is an autoimmune disease with poorly understood pathophysiology. Genetic components of disease etiology, especially human leukocyte antigen (HLA) associations, are well known. Ethnic differences account for a number of variations in disease association with the HLA locus and there seem to be differences in various studies regarding its genetic predisposition. This study was aimed at determining the contribution of DRB1 and DQB1 components of HLA class II in rheumatoid arthritis in a Pakistani cohort.MethodFor this study, 110 patients and 120 healthy controls from the same geographical area and matched ethnicity were enrolled. Blood DNA was isolated from all the subjects and HLA alleles were typed following allele specific amplification. Subsequently, haplotypes were generated and allelic and haplotype distribution frequencies were compared among the patients and controls using χ2 and Arlequin software. The data obtained by this analysis were also compared with other reported associations found in the Pakistani population by meta-analysis.ResultsHLA allelic status was determined among the patients and controls from the same geographical area to account for differences in ethnicity and environmental factors. Significant associations were found for alleles as well as haplotypes among the patients of rheumatoid arthritis. DRB1*10, DQB1*05 and DQB1*602 were found to be associated with disease susceptibility, whereas DRB1*11 and DQB1*02 had protective effect against the disease. Similarly, haplotype DRB1*10-DQB1*05 was associated disease risk, whereas DRB1*07-DQB1*02 and DRB1*11-DQB1*0301 had a protective effect.ConclusionThere is a significant DRB1and DQB1 allele and haplotype association with rheumatoid arthritis susceptibility and protection.

Occult HCV or delayed viral clearance from lymphocytes of Chronic HCV genotype 3 patients after interferon therapy

BackgroundA recently discovered occult HCV entity reported by various investigators seems to be highly controversial. Especially, the clinical significance of these findings remains uncertain. For optimal outcome of antiviral therapy, investigation of occult HCV needs a broad-based probe in order to investigate the results of viral therapy and its host/viral interaction. The current study was aimed at determining the prevalence of occult HCV in peripheral blood lymphocytes of predominantly genotype 3 HCV-infected patients after completion of antiviral therapy and to investigate long term outcomes in the presence or absence of PBMC positivity.MethodA total of 151 chronic, antiHCV and serum RNA-positive patients were enrolled in the study. Patients with a complete virological response at the end of treatment were screened for the presence of viral RNA in their PBMCs and were followed for up to one year for the presence of serum and PBMC viral genomic RNA.ResultsOut of 151 patients, 104 (70%) responded to the prescribed interferon treatment and showed viral-clearance from serum. These were screened for the presence of genomic RNA in their PBMCs. Sixteen samples were PBMC-positive for viral RNA at the end of treatment (EOT). All these patients had also cleared the virus from peripheral blood cells after the 6-12 month follow-up study.ConclusionTrue occult hepatitis C virus does not exist in our cohort. Residual viremia at the EOT stage merely reflects a difference in viral kinetics in various compartments that remains a target of immune response even after the end of antiviral therapy and is eventually cleared out at the sustained viral response (SVR).

Prevalence of the C677T single-nucleotide polymorphism in the methylenetetrahydrofolate reductase gene among Pakistani ethnic groups.

Methylenetetrahydrofolate reductase is an important enzyme in metabolism of homocysteine, and a mutation in the gene predisposes individuals to several disorders related to homocysteine levels. Polymorphism at C677T shows marked heterogeneity based upon ethnicity and geographical location. Pakistani population consists of various ethnic groups confined to different regions of the country where congenital and genetic defects are a major health concern. We have analyzed the distribution of C677T alleles in different Pakistani ethnic groups. A cross-sectional study was conducted from all the four provinces of the country with samples representing the 14 different ethnic clans. A questionnaire with details of their ethnic origin was used, and informed consent was obtained. Blood samples from 701 individuals were collected for DNA isolation and subsequent C677T single-nucleotide polymorphism determination. The data were statistically analyzed. The study revealed that genotypic frequency for CC varied from 0.89 (Mohanna) to 0.38 (Hazara), CT from 0.56 (Hazara) to 0.11 (Mohanna), and TT from 0.06 to 0. Our data revealed a varied distribution of C677T mutation. This information could be helpful for designing future public health strategies, as it can be used to predict the prevalence of several disorders associated with genetic predisposition due to methylenetetrahydrofolate reductase C677T alleles.

A Novel Splice-Site Mutation in ALS2 Establishes the Diagnosis of Juvenile Amyotrophic Lateral Sclerosis in a Family with Early Onset Anarthria and Generalized Dystonias

The diagnosis of childhood neurological disorders remains challenging given the overlapping clinical presentation across subgroups and heterogeneous presentation within subgroups. To determine the underlying genetic cause of a severe neurological disorder in a large consanguineous Pakistani family presenting with severe scoliosis, anarthria and progressive neuromuscular degeneration, we performed genome-wide homozygosity mapping accompanied by whole-exome sequencing in two affected first cousins and their unaffected parents to find the causative mutation. We identified a novel homozygous splice-site mutation (c.3512+1G>A) in the ALS2 gene (NM_020919.3) encoding alsin that segregated with the disease in this family. Homozygous loss-of-function mutations in ALS2 are known to cause juvenile-onset amyotrophic lateral sclerosis (ALS), one of the many neurological conditions having overlapping symptoms with many neurological phenotypes. RT-PCR validation revealed that the mutation resulted in exon-skipping as well as the use of an alternative donor splice, both of which are predicted to cause loss-of-function of the resulting proteins. By examining 216 known neurological disease genes in our exome sequencing data, we also identified 9 other rare nonsynonymous mutations in these genes, some of which lie in highly conserved regions. Sequencing of a single proband might have led to mis-identification of some of these as the causative variant. Our findings established a firm diagnosis of juvenile ALS in this family, thus demonstrating the use of whole exome sequencing combined with linkage analysis in families as a powerful tool for establishing a quick and precise genetic diagnosis of complex neurological phenotypes.

Novel mutation in AAA domain of BCS1L causing Bjornstad syndrome

Bjørnstad syndrome is an extremely rare condition characterized by pilitorti and nerve deafness. Only few large families have been reported worldwide. Here we describe a large Pakistani family with five affected individuals. The hair fibers of all the patients were twisted around their axis and devoid of any pigment. In addition the patients had a moderate-to-severe degree of hearing impairment. Genotyping with high-density single-nucleotide polymorphism arrays showed homozygosity in two intervals on chromosome 2. Linkage with one of these regions (genomic position 218745685–221025443, hg19) was confirmed. This region encompasses the BCS1L gene. Mutations in this gene have previously been associated with Bjørnstad’s syndrome. We sequenced the BCS1L gene for identification of the causative mutation in the family. A novel homozygous missense mutation c.901T>A was identified, which segregated with the disease in the family. This mutation results in the amino acid change p.Tyr301Asn and was predicted to be pathogenic by bioinformatics tools.

A canonical splice site mutation in GIPC3 causes sensorineural hearing loss in a large Pakistani family

With homozygosity mapping we have identified two large homozygous regions on chromosome 3q13.11–q13.31 and chromosome 19p13.3–q31.32 in a large Pakistani family suffering from autosomal recessive nonsyndromic hearing impairment (arNSHI). The region on chromosome 19 overlaps with the previously described deafness loci DFNB15, DFNB72 and DFNB95. Mutations in GIPC3 have been shown to underlie the nonsyndromic hearing impairment linked to these loci. Sequence analysis of all exons and exon–intron boundaries of GIPC3 revealed a homozygous canonical splice site mutation, c.226-1G>T, in GIPC3. This is the first mutation described in GIPC3 that affects splicing. The c.226-1G>T mutation is located in the acceptor splice site of intron 1 and is predicted to affect the normal splicing of exon 2. With a minigene assay it was shown to result in the use of an alternative acceptor site in exon 2, resulting in a frameshift and a premature stop codon. This study expands the mutational spectrum of GIPC3 in arNSHI.