Mónica Acuña

Probability of Exclusion in Paternity Testing: Time to Reassess*

ABSTRACT: The average exclusion probability is a measure of efficiency in paternity testing; it refers to the a priori ability of a battery of tests to detect paternity inconsistencies. This parameter measures the capacity of the system to detect a false accusation of paternity. Traditionally, this average exclusion probability has been estimated as the probability of excluding a man who is not the father by an inconsistency in at least one of the studied loci. We suggest that this criterion should be corrected, as currently the presumed father is excluded when at least three genetic inconsistencies are found with the child being tested, not just one. This change of criterion has occurred because of the use of microsatellite loci, whose mutation rates are much greater than those of the coding genes used previously in paternity studies. We propose the use of the average probability of exclusion for at least three loci (not only one), as an honest measure of the combined probability of exclusion of several loci, and we propose an algebraic expression to calculate it.

DNA extraction from formalin-fixed laryngeal biopsies: Comparison of techniques

Abstract Conclusion: PCR-quality DNA could be extracted from formalin-fixed paraffin-embedded (FFPE) samples with amplicons of at least 390 bp. Paraffin removal was not a necessary step. Proteinase K digestion was as efficient as the commercial kit for DNA extraction with a lower cost. Objectives: To compare different DNA extraction protocols for FFPE samples and to describe the suitability of the extracted DNA for PCR reactions. Methods: For deparaffinization the following techniques were compared: alkaline heat, xylene, and no removal. For DNA extraction, proteinase K digestion and organic extraction were compared. A commercial extraction kit was included as standard. DNA quality was assessed by PCR amplification of the HFE gene, for amplicons of 208 and 390 bp. Results: Extraction with the commercial kit and proteinase K digestion were more efficient than other techniques, with no statistical difference between them for both amplicons. The proteinase K digestion buffer had a cost of U

Prevalence of the 35delG mutation in the GJB2 gene in two samples of non-syndromic deaf subjects from Chile

0.2 per sample and the commercial kit of U

Allele frequencies for six STR in a Chilean population.

7 per sample.

CTG repeats at the myotonic protein kinase gene in a healthy Chilean population sample

Hearing loss is the most common inherited sensorial deficiency in humans; about 1 in 1000 children suffer from severe or profound hearing loss at birth. Mutations in the GJB2 gene are the most common cause of prelingual, non-syndromic autosomal recessive deafness in many populations; the c.35delG mutation is the most common in Caucasian populations. The frequency of the c.35delG mutation was estimated in two samples of deaf patients from Santiago, Chile. Unrelated non-syndromic sensorioneural deaf patients were examined: Group 1 consisted of 47 unrelated individuals with neurosensory deafness referred to the Chilean Cochlear Implant Program; Group 2 included 66 school children with prelingual deafness attending special education institutions for deaf people. Individuals with profound to moderate isolated neurosensory hearing loss with unknown etiology were included. The presence of the c.35delG mutation was evaluated by the allele-specific polymerase chain reaction method (PCR), and in some cases it was confirmed by direct DNA sequencing of the coding region of the GJB2 gene. Deaf relatives were present in 20.3% of the cases. We found 19.5% (22/113) patients with the c.35delG mutation, 6 of them homozygous; these rates are similar to frequencies found in other Latin American countries.

Gene Frequencies for Three Hypervariable DNA Loci in a Chilean Population of Mixed Ancestry

A sample of Chilean individuals from the northern area of Santiago, the capital of Chile, was studied. The current Chilean population was sprung from the admixture between aborigine populations of mongoloid origin (Amerindians) and Spanish conquerors of Caucasian origin. Blood samples from unrelated blood donors were randomly collected in the Hospital San Jose. An appropriate informed consent was obtained from all of them according to the Ethical Board of the Medicine School of the University of Chile.

Is chagasic cardiopathy associated with HLA haplotype

Objectives –  To study the variability at the myotonic dystrophy protein kinase (DMPK) gene in a Chilean sample of healthy people. DM1 is an autosomal dominant disorder caused by an expansion of a (CTG) repeat at the 3′‐UTR of the gene DMPK. Healthy individuals have alleles under 35 repeats and diseased individuals have over 50.

Muir-Torre Syndrome: case report and molecular characterization

Blood samples were collected in tubes containing ACD from 121 unrelated individuals who asked paternity analysis in The Clinical Hospital of the University of Chile during the years 2000 and 2001. The method presented by Comey (1) was used to remove DNA from the samples. The three STR were amplified using 1 ng of DNA for each PCR reaction, and the fragments electrophoresed through 6% acrylamide gels and silver stained, according to the manufacturers recommendations (2).

Genetic Variants of Cytochrome CYP2D6 in Two Mixed Chilean Populations

Sir-On the basis of paleopathological evidence obtained in 2500 year old mummies exhumed in northern Chile, we suggested that Chagas disease is much older in this area than previously realize@. Consequently, the milder symptoms of Chagas disease in Chile, as compared for example to Brazil, could, in theory, be explained as the result of a genetic adapta-tion of Chilean natives to Trypanosoma cruzi. In order to test this hypothesis, we employed a battery of marker gene systems (ABO, Rh, Dully and HLA) to analyse the genetic composition of a sample of Chagas serologically positive individuals, residents of the towns of Combarbal~ and lllapel, located in Chiles most endemic area 2. Indian admixture of this population was estimated to be 62 --- 17% 3 . The sample of 94 people was subdivided in two groups according to the presence or absence of chagasic cardiopathy 4. With few exceptions (cDe, cdE, HLA B 15 and HLA B40) marker gene frequencies did not exhibit significant differences between the two groups. HLA haplotype B40Cw3 however, was absent among subjects with cardiopathy and present at a frequency of 9% among the non-cardiopathic serologically positive controls. This difference is statistically significant. Genes B40 and Cw3 are frequent among Chilean aborigines, but exhibit low frequencies in Europeans. In Spain for example, the frequency of haplotype B40 Cw3 is 1.2% s, compared to 3% in Chilean indians in non-endemic areas 6. Assuming that our studied population had an indian admixture of 60%, the expected frequency of B40 Cw3 would be only 2%. Furthermore, among serologically positive subjects not affected by cardiopathy, genes [340 and Cw3 are in highly significant linkage disequilibrium, suggesting strongly that they are kept together on the ~me chromosome more often than expected, by natural selection. If our preliminary results turn outto be correct, we may conclude that haplotype B40 Cw3 confers some protection against

HLA antigens in cardiomyopathic Chilean chagasics.

CONTEXT Muir-Torre syndrome is a rare autosomal dominant genodermatosis caused by mutations in the mismatch repair genes. It is characterized by the presence of sebaceous skin tumors and internal malignancies, affecting mainly the colon, rectum and urogenital tract. Awareness of this syndrome among physicians can lead to early diagnosis of these malignancies and a better prognosis. CASE REPORT We report the case of a Chilean patient who, over the course of several years, had multiple skin lesions, endometrial cancer and colon cancer. The syndrome was diagnosed using molecular techniques such as microsatellite instability analysis, immunohistochemistry and DNA sequencing, which allowed us to find the causative mutation. CONCLUSION Molecular diagnostics is a highly useful tool, since it allows clinicians to confirm the presence of mutations causing Muir-Torre syndrome. It is complementary to the analysis of the clinical data, such as dermatological presentation, presence of visceral malignancies and family history of colorectal tumors, and it provides important knowledge to help physicians and patients choose between treatment options.