Analysis of the Association Between Apolipoprotein E Polymorphism and Cardiovascular Risk Factors in an Elderly Population with Longevity

OBJECTIVE: To establish the allelic and genotypic frequencies related to apolipoprotein E (ApoE) polymorphism and association of the genotypes with risk factors and cardiovascular morbidity in an elderly population with longevity. METHODS: We analyzed 70 elderly patients aged 80 years or more who were part of the Projeto Veranópolis. We used the gene amplification technique through the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and cleavage with the restriction enzyme Hha I to identify the ApoE genotypes. The most frequent genotypes were compared considering biological variables and cardiovascular risks and morbidity. RESULTS: The frequencies of the E2, E3, and E4 alleles were 0.05, 0.84, and 0.11, respectively, and of the genotypes were as follows: E3E3 (0.70), E3E4 (0.22), E2E3 (0.06), and E2E2 (0.02). Individuals with the E3E4 had a mean age greater than those with the E3E3. No association was observed between the genotypes and the variables analyzed, except for obesity, which was associated with the E3E3 genotype. Individuals with the E3E4 genotype had high levels of LDL-cholesterol and fibrinogen as compared with those with the E3E3 genotype. CONCLUSION: The results suggest that the E4E4 genotype may be associated with early mortality. A balance between the protective or neutral factors and the cardiovascular risk factors may occur among the individuals with different genotypes, attenuating the negative effects of the E4 allele.

Estudios genético-poblacionales en especies de interés sanitario

Se reúnen en esta presentación tres proyectos relacionados que vienen desarrollándose desde hace varios años con subsidios independientes de ese Consejo. Los tres refieren a estudios genético poblacionales de especies de interés sanitario. Los temas son los siguientes: Tema I. Estudios de poblaciones de roedores Cricétidos. Tema II. Estudios de variabilidad genética en Aedes albifasciatus (Diptera, Culicidae). Tema III. Estudios de polimorfismo enzimático en aislamientos de Trypanosoma cruzi. En todos los casos se obtendrán muestras de poblaciones en distintas regiones del país y en ellas se realizará: a) análisis de polimorfismo enzimático detectable mediante técnicas de electroforesis en geles. b) Determinación de frecuencias alélicas, proporción de loci polimórficos y heterocigosis media por locus. c) Cálculo de Nm, estimador del grado de intercambio génico entre poblaciones de una especie. d) Cálculo de distancia genética y similitud entre poblaciones. e) Amplificación de DNA mitocondrial (tema II) y DNA quinetoplástico de minicírculos (tema III) y posterior caracterización por RFLP y sondas de DNAc.

CONOCIMIENTO SOBRE EL VIRUS PAPILOMA HUMANO (VPH): SU IMPLICANCIA EN LA PREVENCIÓN DEL CÁNCER ORAL.

El virus del papiloma humano (VPH) es una de las de infecciones de transmisión sexual (ITS) más frecuentes [1]. Varios genotipos de VPH pueden generar verrugas genitales, y otros están fuertemente asociados a displasia cervical, cáncer de cuello uterino, de vulva, ano, pene y de orofaringe. La alta prevalencia de la infección por este virus en caso de lesiones bucal premalignas indica que la infección podría ser un evento temprano en el proceso de transformación maligna de las c. Epitelial de la cavidad bucal. La asociación epidemiológica del VPH con Carcinoma de Células escamosa, así como la evidencia biológica dado por la transformación de las células epitelial por oncogenes del virus sugiere que los VPH específicos son importantes para el proceso de malignización, sin que este determine el tamaño ni el estado del tumor. Objetivos 1) Analizar el grado de conocimiento de la población incluida en una encuesta, respecto de las vías de transmisión del VPH, los métodos de prevención, los factores de riesgo y su asociación con las verrugas genitales y el cáncer de cuello de útero, ano, pene y de orofaringe. 2) Determinar la prevalencia y genotipos del VPH en lesiones preneoplásicas y neoplásicas de las vías aerodigestivas superiores de pacientes adultos que acuden a la Fac de Odontología y evaluar los factores de riesgo asociados (sexuales, hhábito de fumar, etc) 3) Determinar la prevalencia y genotipos del VPH en mucosa sana y que presenten lesiones de pacientes pediátricos que acuden a la Facultad de Odontología de la U.N.C.; Servicio del Hospital de Niños de la Pcia de Córdoba y evaluar los factores de riesgo asociados (sexuales, otras ITS por ej: C.trachomatis, M.genital) MATERIALES Y METODOS: Objetivo 1: Se entregará un cuestionario de 28 ítems, con carácter anónimo no vinculante, a estudiantes (mayores de 18 años de edad) universitarios de primer año de las carreras de Medicina, Odontología, FAMAF, Psicopedagogía del Inst Sup Dr. D.Cabred, de la catedra Bacteriologia y Virologia de la F.C.M., pacientes que asisten a los servicios de: Infectología y Ginecología del H.N.C., Ginecología e Infectología del Hospital Italiano, Urología del Hospital San Roque, Ginecología del H.M.N., Lab de Andrología y Reproducción y Lab de Chlamydias y HPV del Instituto de Virología y a empleados y afiliados que asisten a APROSS. Objetivo 2/3: Las muestras con PAP, serán receptadas en 500µl de PBS, luego se extraerá ADN, utilizando un equipo comercial (Bioneer). Se amplificará por PCR, un segmento (450 pb), correspondientes a la región L1 del genoma viral, utilizando los llamados “primer” degenerados MY09 y MY11. La amplificación del gen de la beta-globina se utilizará para comprobar la presencia de un templado; a partir de los productos VPH positivos se realizará digestión enzimática (BamHI, HaeIII, HinfI, PstI, RsaI, DdeI y Sau3A1) lo que permitirá la identificación del genotipo a por RFLP en gel de agarosa al 2%. Se utilizará para el análisis estadístico el programa Epi Info versión 3.5.1 2008 (http://www.cdc.gov/epiinfo/). Se alinearán las secuencias de ADN empleando el programa Clustal X (23). Las secuencias serán utilizadas para genotipificación por métodos filogenético [o utilizando la herramienta de genotipificación viral del NCBI (http://www.ncbi.nlm.nih.gov/projects/genotyping/formpage.cgi)] El análisis filogenético se realizará empleando el Programa MEGA 3 (11) empleando la metodología de Neighbor Joining y se evaluarán por Bootstrap. Resultados esperados:La encuesta brindará datos que se podrán aprovechar para los programas de prevención de la infección con VPH. Se podrá determinar cuáles son los genotipos circulantes en nuestra población y cuáles son los factores de riesgo asociados. Se podrá establecer cuáles son los genotipos asociados a las lesiones preneoplásicas y neoplásicas de la mucosa oral, y determinar la probabilidad de que la vacunación contra los VPH 6, 11, 16 y 18 pueda prevenir la aparición de estas lesiones.

VARIABILIDAD CLÍNICA DE LA MIOCARDIOPATÍA CHAGÁSICA: INFLUENCIA DE LA COMPOSICIÓN GENÉTICA DEL TRYPANOSOMA CRUZI

El descubrimiento de técnicas más sensibles para la detección del T. cruzi en el enfermo chagásico rescató el rol primordial del parásito en la patogenia y actualmente se considera a la enfermedad como el producto de la interacción de los genomas del parásito y el humano. Sin embargo aún queda por responder por qué el 30% de las personas infectadas evolucionan hacia una enfermedad cardíaca y el 70% permanece asintomático aunque con serología persistente; así como también la amplia variabilidad clínica, que puede resultar desde una cardiopatía sin consecuencias hasta producir muerte súbita. En este sentido, se ha descripto que la variabilidad genética del parásito debe estar relacionada con el tropismo del mismo a los diferentes órganos del huésped y, por lo tanto, con la forma clínica de la enfermedad y con las diferencias observadas luego del tratamiento específico de la enfermedad. Es por ello que proponemos determinar la importancia que tiene la composición genética del aislamiento de T. cruzi que infectó al huésped y/o la de los clones diferentes que pueden aparecer en sangre para explicar la amplia variabilidad de síntomas y signos que manifiestan los pacientes con cardiopatía chagásica crónica. Estos resultados contribuirán al entendimiento de la fisiopatogenia de la miocardiopatía chagásica y sus variabilidades clínicas y facilitarán establecer el pronóstico y tratamiento de la enfermedad. Pacientes que concurran al Hospital Materno Infantil de la Provincia de Córdoba, al Hospital Nacional de Clínicas y a la Clínica Sucre serán tratados de acuerdo con la declaración de Helsinki y firmarán consentimiento informado. Se seguirá la evolución clínico-cardiológica por radiografía, electrocardiografía y ecocardiografía. La serología para Chagas se determinará por HAI-ELISA. Se obtendrán muestras de sangre de estos pacientes que se clasificarán con serología positiva para Chagas sin cardiopatía, con cardiopatía leve y con cardiopatía severa. Extracción del ADN: las muestras de sangre periférica de cada paciente se mezclarán con igual volumen de guanidina 6M/EDTA 0,5M. El ADN se extraerá por técnicas convencionales con fenol:cloroformo:alcohol isoamílico y luego se precipitará con etanol. Finalmente la solución se resuspenderá en agua estéril libre de nucleasas. Se conservará a -4º C hasta su uso para la amplificación del contenido de ADN del parásito por la reacción en cadena de la polimerasa (PCR). PCR: la detección de los parásitos en cada muestra se determinará mediante la amplificación por PCR de un fragmento de la región variable correspondiente al minicírculo del ADN del kinetoplasto (kADN), utilizando primers específicos para dicha región. Análisis de la región variable del kADN por enzimas de restricción: la caracterización de los parásitos de cada muestra se realizará además mediante el análisis de los fragmentos producidos luego de la digestión con enzimas de restricción (RFLP). El amplificado producto de la PCR se utilizará para la digestión con las enzimas de restricción y los fragmentos obtenidos serán separados por electroforesis en geles de agarosa 2% teñidos con bromuro de etidio. Análisis de los resultados: Los perfiles de bandas obtenidos luego de la digestión con las enzimas de restricción de las muestras de sangre de los pacientes se correlacionarán con la sintomatología clínica de cada uno de ellos para determinar si existe relación entre la variabilidad genética del parásito infectante y la variedad clínica presentada. Los perfiles de bandas obtenidos luego de la RFLP de las muestras de sangre se analizarán cualitativamente por observación de los geles.

Homocisteína e polimorfismos dos genes MTHFR e VEGF: impacto na doença arterial coronariana

FUNDAMENTO: Polimorfismos em genes relacionados ao desenvolvimento da aterosclerose, angiogênese e metabolismo da homocisteína (Hcy) podem ser fatores de risco para a doença arterial coronariana (DAC). OBJETIVO: Avaliar o efeito dos polimorfismos VEGF C-2578A e MTHFR C677T na DAC e a associação desses polimorfismos com a gravidade e a extensão das lesões ateroscleróticas e concentrações de Hcy. MÉTODOS: 244 indivíduos foram avaliados através de angiografia coronariana e incluídos no estudo (145 com DAC e 99 indivíduos-controle). Os polimorfismos VEGF C-2578A e MTHFR C677T foram investigados através das técnicas de PCR-SSCP e PCR-RFLP, respectivamente. Os níveis de homocisteína plasmática foram mensurados através de cromatografia líquida/espectrometria de massa seqüencial (CL/EMS). RESULTADOS: Não houve diferença significante em relação à distribuição de alelos e genótipos entre os grupos, para ambos os polimorfismos. A análise univariada mostrou uma freqüência maior do genótipo VEGF -2578AA no grupo com doença em três vasos (p=0,044). Além disso, o genótipo VEGF -2578CA foi observado mais freqüentemente entre indivíduos com <95% de estenose (p=0,010). Após ajuste para outros fatores de risco para DAC em um modelo multivariado, observou-se que o polimorfismo VEGF C-2578A não era um correlato independente da DAC (p=0,688). O polimorfismo MTHFR não mostrou qualquer relação com a extensão e/ou gravidade da DAC. O polimorfismo MTHFR C677T não mostrou uma associação direta com hiperhomocisteinemia ou aumento das concentrações médias de Hcy no plasma. CONCLUSÃO: Embora haja uma aparente associação entre o polimorfismo VEGF C-2578A e o desenvolvimento de aterosclerose coronariana, essa associação não é independente dos fatores de risco cardiovasculares convencionais.

Gravidade da lesão angiográfica coronariana e polimorfismo da APOE nas síndromes coronarianas agudas

FUNDAMENTO: Existem evidências de associação entre o polimorfismo da apolipoproteína E (APOE) e a doença coronariana, entretanto há controvérsias. OBJETIVO: Avaliar a associação entre o número de vasos coronarianos acometidos por obstrução significativa definida por angiografia, o polimorfismo da APOE e as variáveis clínicas. MÉTODOS: Estudo transversal multicêntrico que envolveu 207 pacientes (138 homens) com síndrome coronariana aguda (SCA) em Niterói (RJ - Brasil), os quais realizaram angiografia coronariana e determinação do genótipo para o polimorfismo APOE *2*3*4, pelo método de Restriction Fragment Length Polymorphism (RFLP). RESULTADOS: A frequência dos alelos APOE *2 foi de 6,8%, *3 foi de 82,5%, e *4 foi de 10,7%. Quanto ao número de vasos lesados, 27% dos pacientes apresentavam obstrução uniarterial, 33,8%, biarterial, e 39,1%, triarterial ou de tronco da coronária esquerda. O grau de lesão multivascular não se relacionou com a presença do alelo *4 (p = 0,78), mas com a idade > 55 anos (p = 0,025), o ex-tabagismo (p = 0,004) e a dislipidemia (p = 0,05) na análise multivariada e com doença arterial coronariana prévia (p = 0,05), diabete (p = 0,038) e síndrome metabólica (p = 0,021) na análise univariada. A prevalência de dislipidemia, diabete e hipertensão arterial sistêmica (HAS) foi elevada em relação a estudos semelhantes, com aumento progressivo da prevalência de HAS (p = 0,59) e de diabete (p = 0,06), de acordo com o número de vasos lesados. CONCLUSÃO: O polimorfismo da APOE não se associou ao número de vasos coronarianos com obstrução significativa em qualquer faixa etária. Por outro lado, a idade > 55 anos, o ex-tabagismo e a dislipidemia associaram-se à lesão multivascular.

Polimorfismos beta1-adrenérgico associados com Fibrilação Atrial na Insuficiência Cardíaca Sistólica

FUNDAMENTO: O sistema nervoso simpático apresenta grande importância na patogênese da fibrilação atrial na insuficiência cardíaca sistólica. A identificação de polimorfismos no gene ADBR1 do receptor beta1-adrenérgico representa um importante passo no conhecimento dessa patogênese. OBJETIVO: Este estudo analisou a associação entre os dois polimorfismos funcionais do gene ADBR1 do receptor beta1-adrenérgico, Ser49Gly e Arg389Gly, e a presença da fibrilação atrial em pacientes com insuficiência cardíaca sistólica. MÉTODOS: Estudo caso-controle com 144 pacientes portadores de insuficiência cardíaca sistólica, dos quais 24 com fibrilação atrial (casos) e 120 sem fibrilação atrial (controles). O DNA genômico foi extraído de leucócitos do sangue periférico e os genótipos dos polimorfismos Ser49Gly e Arg389Gly foram identificados em todos os indivíduos por PCR/RFLP (polymerase chain reaction / restriction fragment length polymorphism). RESULTADOS: A média etária foi 59 ± 13 anos, 70% dos pacientes eram do sexo masculino, 42% apresentavam causa isquêmica e 74% apresentavam hipertensão arterial sistêmica. Os genótipos Ser49Ser e Arg389Arg apresentaram associação significativa com fibrilação atrial (p = 0,005 e p = 0,01; respectivamente). Por meio de regressão logística, ambos ajustados para o tamanho do átrio esquerdo e idade, mantiveram associação significativa (Arg389Arg - odds ratios: 2,78; intervalo de confiança de 95% = 1,02 - 7,56 e Ser49Ser - odds ratios: 8,02; intervalo de confiança de 95% = 1,02 - 63,82). CONCLUSÃO: Ambos os genótipos associaram-se com fibrilação atrial nos pacientes estudados, porém apenas o polimorfismo Ser49Gly apresentava-se em equilíbrio de Hardy-Weinberg.

APOE and LDLR Gene Polymorphisms and Dyslipidemia Tracking. Rio de Janeiro Study

Background:Studies show an association between changes in apolipoprotein E (ApoE) and LDLR receptor with the occurrence of dyslipidemia.Objectives:To investigate the association between polymorphisms of the APOE (ε2, ε3, ε4) and LDLR (A370T) genes with the persistence of abnormal serum lipid levels in young individuals followed up for 17 years in the Rio de Janeiro Study.Methods:The study included 56 individuals (35 males) who underwent three assessments at different ages: A1 (mean age 13.30 ± 1.53 years), A2 (22.09 ± 1.91 years) and A3 (31.23 ± 1.99 years). Clinical evaluation with measurement of blood pressure (BP) and body mass index (BMI) was conducted at all three assessments. Measurement of waist circumference (WC) and serum lipids, and analysis of genetic polymorphisms by PCR-RFLP were performed at A2 and A3. Based on dyslipidemia tracking, three groups were established: 0 (no abnormal lipid value at A2 and A3), 1 (up to one abnormal lipid value at A2 or A3) and 2 (one or more abnormal lipid values at A2 and A3).Results:Compared with groups 0 and 1, group 2 presented higher mean values of BP, BMI, WC, LDL-c and TG (p < 0.01) and lower mean values of HDL-c (p = 0.001). Across the assessments, all individuals with APOE genotypes ε2/ε4 and ε4/ε4 maintained at least one abnormal lipid variable, whereas those with genotype ε2/ε3 did not show abnormal values (χ2 = 16.848, p = 0.032). For the LDLR genotypes, there was no significant difference among the groups.Conclusions:APOE gene polymorphisms were associated with dyslipidemia in young individuals followed up longitudinally from childhood.

Characterisation of microbial communities colonising the hyphal surfaces of arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal fungi (AMF) are symbiotic soil fungi that are intimately associated with the roots of the majority of land plants. They colonise the interior of the roots and the hyphae extend into the soil. It is well known that bacterial colonisation of the rhizosphere can be crucial for many pathogenic as well as symbiotic plant-microbe interactions. However, although bacteria colonising the extraradical AMF hyphae (the hyphosphere) might be equally important for AMF symbiosis, little is known regarding which bacterial species would colonise AMF hyphae. In this study, we investigated which bacterial communities might be associated with AMF hyphae. As bacterial-hyphal attachment is extremely difficult to study in situ, we designed a system to grow AMF hyphae of Glomus intraradices and Glomus proliferum and studied which bacteria separated from an agricultural soil specifically attach to the hyphae. Characterisation of attached and non-attached bacterial communities was performed using terminal restriction fragment length polymorphism and clone library sequencing of 16S ribosomal RNA (rRNA) gene fragments. For all experiments, the composition of hyphal attached bacterial communities was different from the non-attached communities, and was also different from bacterial communities that had attached to glass wool (a non-living substratum). Analysis of amplified 16S rRNA genes indicated that in particular bacteria from the family of Oxalobacteraceae were highly abundant on AMF hyphae, suggesting that they may have developed specific interactions with the fungi.

A Laboratory-based Approach to Biological Control of Snails

Development of Schistosoma mansoni in the intermediate host Biomphalaria glabrata is influenced by a number of parasite and snail genes. Understanding the genetics involved in this complex host/parasite relationship may lead to an often discussed approach of introducing resistant B. glabrata into the field as a means of biological control for the parasite. For the snail, juvenile susceptibility to the parasite is controlled by at least four genes, whereas one gene seems to be responsible for adult nonsusceptibility. Obtaining DNA from F2 progeny snails from crosses between parasite-resistant and-susceptible snails, we have searched for molecular markers that show linkage to either the resistant or susceptible phenotype. Both restriction fragment length polymorphism (RFLP) and random amplified polymorphic DNA (RAPD) approaches have been used. To date, using a variety of snail and heterologous species probes, no RFLP marker has been found that segregates with either the resistant or susceptible phenotype in F2 progeny snails. More promising results however have been found with the RAPD approach, where a 1.3 kb marker appears in nearly all resistant progeny, and a 1.1 kb marker appears in all susceptible progeny

Molecular Epidemiologic Typing Systems of Bacterial Pathogens: Current Issues and Perpectives

The epidemiologic typing of bacterial pathogens can be applied to answer a number of different questions: in case of outbreak, what is the extent and mode of transmission of epidemic clone(s )? In case of long-term surveillance, what is the prevalence over time and the geographic spread of epidemic and endemic clones in the population? A number of molecular typing methods can be used to classify bacteria based on genomic diversity into groups of closely-related isolates (presumed to arise from a common ancestor in the same chain of transmission) and divergent, epidemiologically-unrelated isolates (arising from independent sources of infection). Ribotyping, IS-RFLP fingerprinting, macrorestriction analysis of chromosomal DNA and PCR-fingerprinting using arbitrary sequence or repeat element primers are useful methods for outbreak investigations and regional surveillance. Library typing systems based on multilocus sequence-based analysis and strain-specific probe hybridization schemes are in development for the international surveillance of major pathogens like Mycobacterium tuberculosis. Accurate epidemiological interpretation of data obtained with molecular typing systems still requires additional research on the evolution rate of polymorphic loci in bacterial pathogens.

Comparative Analysis by Polymerase Chain Reaction Amplified Minicircles of Kinetoplast DNA of a Stable Strain of Trypanosoma cruzi from São Felipe, Bahia, its Clones and Subclones: Possibility of Predominance of a Principal Clone in this Area

Molecular characterization of one stable strain of Trypanosoma cruzi, the 21 SF, representative of the pattern of strains isolated from the endemic area of São Felipe, State of Bahia, Brazil, maintained for 15 years in laboratory by serial passages in mice and classified as biodeme Type II and zymodeme 2 has been investigated. The kinetoplast DNA (kDNA) of parental strain, 5 clones and 14 subclones were analyzed. Schizodeme was established by comparative study of the fragments obtained from digestion of the 330-bp fragments amplified by polymerase chain reaction (PCR) from the variable regions of the minicicles, and digested by restriction endonucleases Rsa I and Hinf I. Our results show a high percentual of similarity between the restriction fragment lenght polymorphism (RFLP) for the parental strain and its clones and among these individual clones and their subclones at a level of 80 to 100%.This homology indicates a predominance of the same "principal clone" in the 21SF strain and confirms the homogeneity previously observed at biological and isozymic analysis. These results suggest the possibility that the T. cruzi strains with similar biological and isoenzymic patterns, circulating in this endemic area, are representative of one dominant clone. The presence of "principal clones" could be responsible for a predominant tropism of the parasites for specific organs and tissues and this could contribute to the pattern of clinico-pathological manifestations of Chagas's disease in one geographical area.

Further studies on the molecular systematics of Biomphalaria snails from Brazil

The polymerase chain reaction and restriction fragment length polymorphism (RFLP) of the internal transcribed spacer (ITS) region of the rRNA gene, using the enzyme DdeI were used for the molecular identification of ten species and one subspecies of Brazilian Biomphalaria. Emphasis is given to the analysis of B. oligoza, B. schrammi and B. amazonica. The RFLP profiles obtained using this enzyme were highly distinctive for the majority of the species and exhibited low levels of intraspecific polymorphism among specimens from different regions of Brazil. However, B. peregrina and B. oligoza presented very similar profiles that complicated their identification at the molecular level and suggested a very close genetic similarity between the two species. Others enzymes including HaeIII, HpaII, AluI and MnlI were tested for their ability to differentiate these species. For B. amazonica three variant profiles produced with DdeI were observed. The study demonstrated that the ITS contains useful genetic markers for the identification of these snails

Identification of planorbids from Venezuela by polymerase chain reaction amplification and restriction fragment length polymorphism of internal transcriber spacer of the RNA ribosomal gene

Snails of the genus Biomphalaria from Venezuela were subjected to morphological assessment as well as polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis. Morphological identification was carried out by comparison of characters of the shell and the male and female reproductive apparatus. The PCR-RFLP involved amplification of the internal spacer region ITS1 and ITS2 of the RNA ribosomal gene and subsequent digestion of this fragment by the restriction enzymes DdeI, MnlI, HaeIII and MspI. The planorbids were compared with snails of the same species and others reported from Venezuela and present in Brazil, Cuba and Mexico. All the enzymes showed a specific profile for each species, that of DdeI being the clearest. The snails were identified as B. glabrata, B. prona and B. kuhniana.

Analysis of genetic diversity of Trypanosoma cruzi: an application of riboprinting and gradient gel electrophoresis methods

Analysis of restriction fragment length polymorphism (RFLP) profiles derived from digestion of polymerase chain reaction (PCR) products of the ribosomal 18S from Trypanosoma cruzi yields a typical `riboprint' profile that can vary intraspecifically. A selection of 21 stocks of T. cruzi and three outgroup taxa: T. rangeli, T. conorhini and Leishmania braziliensis were analysed by riboprinting to assess divergence within and between taxa. T. rangeli, T. conorhini and L. braziliensis could be easily differentiated from each other and from T. cruzi. Phenetic analysis of PCR-RFLP profiles indicated that, with one or two exceptions, stocks of T. cruzi could be broadly partitioned into two groups that formally corresponded to T. cruzi I and T. cruzi II respectively. To test if ribosomal 18S sequences were homogeneous within each taxon, gradient gel electrophoresis methods were employed utilising either chemical or temperature gradients. Upon interpretation of the melting profiles of riboprints and a section of the 18S independently amplified by PCR, there would appear to be at least two divergent 18S types present within T. cruzi. Heterogeneity within copies of the ribosomal 18S within a single genome has therefore been demonstrated and interestingly, this dimorphic arrangement was also present in the outgroup taxa. Presumably the ancestral duplicative event that led to the divergent 18S types preceded that of speciation within this group. These divergent 18S paralogues may have, or had, different functional pressures or rates of molecular evolution. Whether or not these divergent types are equally transcriptionally active throughout the life cycle, remain to be assessed.