Histopathology of lesions caused by Pseudocorynosoma constrictum (Acanthocephala: Polymorphidae) in the ileum of blue-winged teal.

Pseudocorynosoma constrictum (Van Cleave, 1918) is a polymorphid acanthocephalan that attaches to the digestive tract of waterfowl to complete its life cycle, causing severe histological damage to its definitive avian hosts. In the present study, we present a histopathological analysis of the lesions that P. constrictum induced in the layers of the ileum of the blue-winged teal Anas discors. The results revealed that worms insert the attachment structures into the inner gut muscular layer, which causes substantial swelling, haemorrhaging and necrosis in the tissue near the parasite's proboscis. We also observed that the number of parasites attached to the tissue can obstruct the intestinal lumen; in the most serious case, we observed more than 30 parasites penetrating completely the walls of the bird intestine.

Anestesia en paciente pediátrico con síndrome de Rohhad / Anesthesia in a pediatric patient with ROHADD syndrome

El síndrome obesidad de rápida progresión, hipoventilación alveolar, disfunción hipotalámica y disregulación autonómica (ROHHAD) es una entidad infrecuente caracterizada por un comienzo en niños sanos a los 2-4 años. Se trata de un síndrome complejo caracterizado por una rápida ganancia de peso con hiperfagia, disfunción hipotalámica, hipoventilación central y disregulación autonómica, entre otros síntomas. Presentamos el caso de un niño de 10 años con diagnóstico de síndrome de ROHHAD a quien se colocó un porth-a-cath bajo anestesia general y que desarrolló complicaciones durante el procedimiento anestésico relacionadas con su enfermedad. El manejo perioperatorio de estos pacientes supone todo un reto para el anestesista dada la afectación de múltiples sistemas y las frecuentes comorbilidades respiratorias que asocian. Se resumen algunas de las implicaciones y consideraciones anestésicas que hay que tener en cuenta en el manejo de estos pacientes

Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) syndrome is a rare entity that is characterised by its onset in healthy children at 2-4 years of age. It is a complex syndrome that includes, among other symptoms, rapid weight gain with hyperphagia, hypothalamic dysfunction, central hypoventilation, and autonomic dysregulation. The case is presented of a 10-year-old boy with a diagnosis of ROHHAD syndrome undergoing insertion of a port-a-cath under general anaesthesia, who developed complications during the anaesthetic procedure related to his illness. The peri-operative management of these patients represents a challenge for the anaesthetist, given the involvement of multiple systems and the frequent respiratory comorbidities associated with them. A summary is presented of some of the implications and anaesthetic considerations that must be taken into account in the management of these patients

Anesthesia in a pediatric patient with ROHADD syndrome. / Anestesia en paciente pediátrico con síndrome de Rohhad.

Rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation (ROHHAD) syndrome is a rare entity that is characterised by its onset in healthy children at 2-4 years of age. It is a complex syndrome that includes, among other symptoms, rapid weight gain with hyperphagia, hypothalamic dysfunction, central hypoventilation, and autonomic dysregulation. The case is presented of a 10-year-old boy with a diagnosis of ROHHAD syndrome undergoing insertion of a port-a-cath under general anaesthesia, who developed complications during the anaesthetic procedure related to his illness. The peri-operative management of these patients represents a challenge for the anaesthetist, given the involvement of multiple systems and the frequent respiratory comorbidities associated with them. A summary is presented of some of the implications and anaesthetic considerations that must be taken into account in the management of these patients.

Icosahedral boron clusters: a perfect tool for the enhancement of polymer features.

Boron clusters and organic molecules display manifestly different electronic, physical, chemical and geometrical characteristics. These differences highlight the complementarity of organic synthons and boron clusters, and therefore the feasibility of producing hybrid polymers incorporating both types of fragments. This review focuses on the development of hybrid organic-inorganic π conjugated, silane, siloxane and coordination polymers containing icosahedral boron clusters in the last few decades, which have received considerable academic and technological interest due to the combination of the electronic, optical and thermal properties of traditional inorganic materials with many of the desirable properties of organic plastics, including mechanical flexibility and low production costs.

Valoración pronóstica de mortalidad y hospitalizaciones en pacientes ambulatorios con EPOC avanzada. Utilidad del índice CODEX / Prognostic assessment of mortality and hospitalizations of outpatients with advanced chronic obstructive pulmonary disease. Usefulness of the CODEX index

Objetivos: Validar el índice CODEX en pacientes ambulatorios con EPOC avanzada. Pacientes y métodos: Se estudió a todos los pacientes con EPOC controlados en una unidad de pacientes crónicos respiratorios. Se calcularon los índices BODEX y CODEX y su relación con mortalidad, hospitalizaciones o ambas, y se realizó un análisis por número de eventos (mortalidad o reingresos), mediante el análisis de riesgos proporcionales de Cox. Resultados: Se incluyó a 80 pacientes (90% varones) con una edad media de 73,4 años. El seguimiento medio fue de 656 días con un rango intercuartílico (25-75%) de 417-642 días. Un total de 17 pacientes fallecieron (21%) y 57 (71,3%) requirieron hospitalización por EPOC. El índice CODEX se relacionó significativamente con la mortalidad (p<0,008; HR: 1,56; IC 95%: 1,1-2,15), el ingreso hospitalario (p<0,01; HR: 1,35; IC 95%: 1,13-1,62) y la variable combinada (p<0,03; HR: 1,27; IC 95%: 1,1-1,5). El BODEX no se asoció con la mortalidad (p=0,17), pero sí con los ingresos (p<0,001; HR: 1,4; IC 95%: 1,15-1,73) y la variable combinada (p<0,03; HR: 1,2; IC 95%: 1,02-1,34). Durante el seguimiento se produjeron 187 eventos. Tanto el índice CODEX (p<0,001; HR:1,17; IC 95%:1,1-1,27) como el BODEX (p<0,02; HR: 1,12; IC 95%: 1,02-1,23) se relacionaron con el número de eventos, aunque tras ajustar por la interacción entre ambos índices solo el CODEX conservó la significación estadística para la variable combinada por pacientes (p<0,03) y en el análisis por número de eventos (p<0,001). Conclusiones: Tanto el CODEX como el BODEX son útiles en la predicción de ingresos hospitalarios, aunque la capacidad pronóstica del CODEX es superior al BODEX tanto en mortalidad como en ingresos hospitalarios

Objectives: To validate the CODEX index in outpatients with advanced chronic obstructive pulmonary disease (COPD). Patients and methods: We studied all patients with COPD treated in a chronic respiratory disease unit. We calculated the BODEX and CODEX indices and their relationship with mortality, hospitalisations or both and performed an analysis by number of events (mortality and/or readmissions), using the Cox proportional hazards analysis. Results: We included 80 patients (90% men) with a mean age of 73.4 years. The mean follow-up was 656 days, with an interquartile range (25-75%) of 417-642 days. Seventeen patients died (21%) and 57 (71.3%) required hospitalisation for COPD. The CODEX index was significantly related to mortality (P<.008; HR: 1.56; 95% CI: 1.1-2.15), hospitalisations (P<.01; HR: 1.35; 95% CI: 1.13-1.62) and the combined variable (P<.03; HR: 1.27; 95% CI: 1.1-1.5). The BODEX index was not associated with mortality (P=.17) but was associated with hospitalisation (P<.001; HR: 1.4; 95% CI: 1.15-1.73) and the combined variable (P<.03; HR: 1.2; 95% CI: 1.02-1.34). There were 187 events during follow-up. Both the CODEX (P<.001; HR: 1.17; 95% CI: 1.1-1.27) and BODEX (P<.02; HR: 1.12; 95% CI: 1.02-1.23) indices were related to the number of events. However, after adjusting for the interaction between the 2 indices, only the CODEX index maintained statistical significance for the combined variable for patients (P<.03) and in the analysis by number of events (P<.001). Conclusions: Both the CODEX and BODEX indices are useful for predicting hospitalisations, although the prognostic ability of the CODEX index is greater than that of the BODEX index, both for mortality and hospitalisations

Prognostic assessment of mortality and hospitalizations of outpatients with advanced chronic obstructive pulmonary disease. Usefulness of the CODEX index. / Valoración pronóstica de mortalidad y hospitalizaciones en pacientes ambulatorios con EPOC avanzada. Utilidad del índice CODEX.

OBJECTIVES: To validate the CODEX index in outpatients with advanced chronic obstructive pulmonary disease (COPD). PATIENTS AND METHODS: We studied all patients with COPD treated in a chronic respiratory disease unit. We calculated the BODEX and CODEX indices and their relationship with mortality, hospitalisations or both and performed an analysis by number of events (mortality and/or readmissions), using the Cox proportional hazards analysis. RESULTS: We included 80 patients (90% men) with a mean age of 73.4 years. The mean follow-up was 656 days, with an interquartile range (25-75%) of 417-642 days. Seventeen patients died (21%) and 57 (71.3%) required hospitalisation for COPD. The CODEX index was significantly related to mortality (P<.008; HR: 1.56; 95% CI: 1.1-2.15), hospitalisations (P<.01; HR: 1.35; 95% CI: 1.13-1.62) and the combined variable (P<.03; HR: 1.27; 95% CI: 1.1-1.5). The BODEX index was not associated with mortality (P=.17) but was associated with hospitalisation (P<.001; HR: 1.4; 95% CI: 1.15-1.73) and the combined variable (P<.03; HR: 1.2; 95% CI: 1.02-1.34). There were 187 events during follow-up. Both the CODEX (P<.001; HR: 1.17; 95% CI: 1.1-1.27) and BODEX (P<.02; HR: 1.12; 95% CI: 1.02-1.23) indices were related to the number of events. However, after adjusting for the interaction between the 2 indices, only the CODEX index maintained statistical significance for the combined variable for patients (P<.03) and in the analysis by number of events (P<.001). CONCLUSIONS: Both the CODEX and BODEX indices are useful for predicting hospitalisations, although the prognostic ability of the CODEX index is greater than that of the BODEX index, both for mortality and hospitalisations.

Intramolecular Communication in Anionic Oxidized Phosphanes through a Chelated Proton.

Oxidation of the 1,2-(PR2 )2 -1,2-closo-C2 B10 H10 (R=Ph, iPr) platform with hydrogen peroxide in acetone is a two-step procedure in which partial deboronation of the closo cluster and oxidation of the phosphorus atoms occur. Based on NMR spectroscopic and kinetic data, we demonstrate that the phosphorus atoms are oxidized in the first step, followed by cluster deboronation. DFT calculations and natural-bond orbital (NBO) analysis were used to obtain insight into the electronic structures of diphosphane ortho-carborane derivatives.

Synthesis, reactivity and complexation studies of N,S exo-heterodisubstituted o-carborane ligands. Carborane as a platform to produce the uncommon bidentate chelating (pyridine)N-C-C-C-s(H) motif.

The synthesis of N,S-heterodisubstituted 1-(2'-pyridyl)-2-SR-1,2-closo-C2B10H10 compounds (R = Et, 2; R = (i)Pr, 3) has been accomplished starting from 1-(2'-pyridyl)-l,2-closo-C2B10H11 (1), and their partial deboronation reaction leading to the structurally chiral [7-(2'-pyridyl)-8-SR-7,8-nido-C2B9H10]-derivatives (R = Et, [4]-; R = (i)Pr, [5]-) has been studied. Capillary electrophoresis combined with the chiral selector alpha-cyclodextrin has permitted the separation of the electrophoretically pure racemic [7-(2'-pyridyl)-8-SR-7,8-nido-C2B9H11]- ions into two peaks each one corresponding to the interaction of one enantiomer with the alpha-cyclodextrin. The N,S-heterodisubstituted o-carborane containing a mercapto group, 1-(2'-pyridyl)-2-SH-1,2-closo-C2B10H10, 1, is one of the two examples of a rigid bidentate chelating (pyridine)N-C-C-C-S(H) motif having been structurally fully characterized. To study the potential of such a binding site, 1 has been tested as a ligand with metal ions requiring different coordination numbers, two (Au(+)) and four (Pd2+ and Rh+). The crystal structures of the Pd(II) and Au(I) complexes are reported. For the Pd(II) complex, 1 acts as a bidentate ligand whereas for Au(I), 1 acts as a monodentate ligand through the thiolate.

Synthesis, characterization, and dynamic studies of 12-vertex eta5-ruthenium(II) closo-phosphine complexes with monoanionic [10-L-nido-7-R-7,8-C2B9H9]- ligands.

Ruthenacarborane complexes of formula [3-H-3,3-(PPh3)2-8-L-closo-3,1,2-RuC2B9H10)] (L = SMe2 (2a), SEt2 (2b), S(CH2)4 (2c), SEtPh (2d)) and [1-Me-3-H-3,3-(PPh3)2-8-L-closo-3,1,2-RuC2B9H9)] (L = SMe2 (2e), SEt2 (2f)) were prepared by reaction of the respective monoanionic charge-compensated ligands [10-L-nido-7,8-C2B9H10]- and [7-Me-10-L-nido-7,8-C2B9H9]- with [RuCl2(PPh3)3]. Similary, complexes [3-H-3,3,8-(PPh3)3-closo-3,1,2-RuC2B9H10)] (4a) and [3-H-3,3-(PPh3)2-8-PPh2Me-closo-3,1,2-RuC2B9H10)] (4b) were prepared from the corresponding phosphonium ligands. The reaction is done in one pot by reacting the ligand with the Ru(II) complex in a 1.5:1 ratio. All compounds have been fully characterized by multinuclear NMR spectroscopy, and the molecular structures for 2a and 4a have been elucidated by single-crystal X-ray diffraction analysis. The Ru(II) atom in this complex is on the open face of the monoanionic charge-compensated ligand adopting a pseudooctahedral coordination. Formally, three positions are supplied by the C2B3 open face, two PPh3 groups occupy two other positions, and a hydride fulfills the remaining one. The hydride complexes were generated with no special reagent. They result from a dehalogenation in the presence of ethanol.

Simple PVC-PPy electrode for pH measurement and titrations.

Cobaltabis(dicarbollide) [3,3'-Co(1,2-C2B9H11)](-)-doped polypyrrole (PPy) films have been prepared galvanostatically on glassy carbon electrodes in acetonitrile solution. The potential response behavior of the film of this new material has been investigated in some common pH buffers and in acid-base titrations. The potentiometric characteristics of the resulting films are indicative of a quasi-Nernstian response (approximately 50 mV/pH unit), a linearity range from pH 12 to 3 and correlation coefficients (r2) of approximately 0.98. The electrode is suitable for pH measurements and for monoprotic titrations of strong alkalis with strong acids, and weak bases with strong acids, but the long response time hinders the use of this electrode for multiprotic titrations. The time response has been dramatically improved by reducing the film thickness by using the template effect of a non-conducting polymer (PVC) cast over the graphite surface before PPy deposition. PPy polymerization occurs in the free channels of PVC leading to the formation of PPy wires. The morphological change of PPy does not affect the slope or linearity range. The response of the PVC-PPy electrochemical sensor is rapid and the sensor is easy to prepare, at low cost, and its performance is comparable with that of commercial glass electrodes.

Are halocarboranes suitable for substitution reactions? The case for 3-I-1,2-closo-C(2)B(10)H(11): molecular orbital calculations, aryldehalogenation reactions, (11)B NMR interpretation of closo-carboranes, and molecular structures of 1-Ph-3-Br-1,2-closo-C(2)B(10)H(10) and 3-Ph-1,2-closo-C(2)B(10)H(11).

In this paper, the chemistry of 3-X-1,2-closo-C(2)B(10)H(11) (X = halogen) derivatives is extended. Molecular orbital and (11)B and (13)C NMR calculations on these species are presented. A qualitative interpretation of the (11)B NMR spectra of closo o-carborane derivatives is also provided. The synthesis of 3-X-1-R-o-carborane (X = I, Br and R = Me, Ph) derivatives is reported, and aryldehalogenation at the B3 position is reported for the first time. The molecular and crystal structures of 1-phenyl-3-bromo-1,2-dicarba-closo-dodecaborane and 3-phenyl-1,2-dicarba-closo-dodecaborane are described.

Eta5-(3)-1-methyl-1,2-dicarbollyl-eta5-2',5'-dimethylpyrrolylcobalt(III).

In the title compound, (eta(5)-2,5-dimethylpyrrolyl)[(7,8,9,10,11-eta)-7-methyl-7,8-dicarba-nido-undecaborato]cobalt(III), [3-Co[eta(5)-[2,5-(CH(3))(2)-NC(4)H(2)]]-1-CH(3)-1,2-C(2)B(9)H(10)] or [Co(C(3)H(13)B(9))(C(6)H(8)N)], the Co(III) atom is sandwiched between the pentagonal faces of the pyrrolyl and dicarbollide ligands, resulting in a neutral molecule. The C-C distance in the dicarbollide cage is 1.649 (3) A.

Comparative study of NS(2)(S-aryl) pyridine-based dithia-containing ligands with different substituent groups. Reactivity toward Cu(II) and Ru(II).

Ligands LX of the type NS(2) with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced. Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results from the reaction of these ligands with Cu(ClO(4))(2).6H(2)O and [RuCl(2)(PPh(3))(3)] have revealed that their coordination capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas [Cu(LX)][ClO(4)](2), except for L5, and [RuCl(2)(LX)(PPh(3))], have been obtained, respectively. The electronic characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-bis[(2'-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl(2)(L5)(PPh(3))].2CCl(4) have been characterized by single-crystal X-ray diffraction methods.

Contribution of the nido-[7,8-C2B9H10]- anion to the chemical stability, basicity, and 31P NMR chemical shift in nido-o-carboranylmonophosphines.

The icosahedral dicarboranes and their decapitated anion, 1-R'-1,2-C(2)B(10)H(10) (closo) and [7-R'-7,8-C(2)B(9)H(10)](-) (nido), exert a distict influence at the alpha position of substituents attached to the cage carbon atom. The closo fragment is electron-withdrawing while the nido anion is electron-releasing. These effects are studied by (31)P NMR, phosphorus oxidation, and phosphorus protonation in [7-PR(2)-8-R'-7,8-C(2)B(9)H(10)](-) species. The (31)P NMR chemical shift dependence is related to the R alkyl or aryl nature of [7-PR(2)-8-R'-7,8-C(2)B(9)H(10)](-). No direct relationship to the nature of the R substituent on the nido-carboranylmonphosphine toward oxidation has been found. The basicity of the nido-alkylcarboranylmonophosphines is the highest while the lowest corresponds to the nido-arylcarboranylmonophosphines. Interpretation can be carried out qualitatively by considering the electronic properties of the cluster and the nature of the R groups. The influence of R' is less relevant. Confirmation of the molecular structure of the oxidated and protonated nido-carboranylmonophosphine compounds was obtained by X-ray diffraction analysis of [NBu(4)][7-P(O)Ph(2)-8-Ph-7,8-C(2)B(9)H(10)] and [7-PH((i)Pr)(2)-8-Me-7,8-C(2)B(9)H(10)].

Unusual 9-->10 rearrangement of the substituted cage carbon in the ferratricarbollide series. Synthesis of the isomeric complexes [2-eta 5-(C5H5)-10-X-closo-2,1,7,10-FeC3B8H10] (where X = H2N, MeHN, Me2N, and ButHN).

Treatment of the zwitterionic amine tricarbollides of general formula 7-L-nido-7,8,9-C3B8H10 (1) (where L = Me2HN (1c) and ButH2N (1d)) with [(eta 5-C5H5)Fe(CO)2]2 in refluxing mesitylene resulted in the formation of a mixture of the known compounds [2-(eta 5-C5H5)-9-X-closo-2,1,7,9-FeC3B8H10] (2) (where X = H2N (2a), Me2N (2c), and ButHN (2d)) and a series of new, isomeric ferratricarbollylamines [2-(eta 5-C5H5)-10-X-closo-2,1,7,10-FeC3B8H10] (3) (where X = H2N (3a), Me2N (3c), and ButHN (3d)) in moderate yields. Complexes of type 3 (where X = H2N (3a), MeHN (3b), Me2N (3c), and ButHN (3d)) were also obtained readily by heating complexes of type 2 (where X = H2N (2a), MeHN (2b), Me2N (2c), ButHN (2d), and Bu(t)(Me)N (2e)) at ca. 300 degrees C for 10 min. All the complexes of type 3 contain reactive amine functions in meta positions with respect to the metal center. The observed 9-->10 rearrangement of the substituted cluster carbon is quite unexpected and is believed to result from higher thermodynamic stability of the 10-substituted isomers. The structures of all compounds of type 3 were established by high-field NMR spectroscopy and mass spectrometry, and that of 3d was determined by an X-ray diffraction study.

[Microsporidiasis in AIDS patients with chronic diarrhea. Expieriences at the National Institute of Nutrition "Salvador Zubrirán"]. / Microsporidiasis en pacientes con SIDA y diarrea crónica. Experiencia en el Instituto Nacional de la Nutrición "Salvador Zubirán".

BACKGROUND: Microsporidium sp. has been considered as a rare cause of diarrhea in AIDS patients. However, the improvement of some histochemical stains in the analysis of small bowel biopsies has shown an increase in its prevalence. In Mexico there are no series reporting intestinal microsporidiasis. DESIGN: Small bowel biopsies of 98 patients with AIDS and chronic diarrhea stained with HE and Giemsa were reviewed (January 1987-December 1994). The clinical, demographic and laboratory information was obtained from the clinical charts. RESULTS: In 50 patients an opportunistic microorganism was identified in the small bowel biopsy (51%). Microsporidium sp. was identified in 30 patients (31%). The clinical charts were reviewed in all but six cases. Of the 24 patients with microsporidiasis as the cause of diarrhea, 17 were male and seven female with a median age, of 33 years, old. Homosexuality was the main risk factor in males (11/17), and blood transfusion in females (4/7). A low socioeconomical classification was found in 75% cases. The initial manifestation of AIDS was diarrhea in 16/24 (67%), CD4 count cell below 200 mm3 was identified in 13/24 patients and more than 200 mm3 in 2/24. The stool examination and the original histologic interpretations were negative for Microsporidium sp. Lymphoplasmocytic inflammatory infiltrate with eosinophils in the lamina propia and atrophy was frequently seen. A pale red and gray color was observed in spore and merogonial phases of Microsporidium stained with Giemsa. CONCLUSION: Microsporidium sp. was present as the only pathogen in 31% of the small bowel biopsies reviewed by light microscopy. Diarrhea due to Microsporidium sp. is frequently seen in advanced stages of AIDS with CD4 count cell below 200 mm3 Giemsa stain in the evaluation of small biopsies is a cheap and useful method to, identify Microsporidium sp.

Contribution of ipratropium bromide to the bronchodilator test in patients with chronic obstructive pulmonary disease.

The aim of the study was to analyze the bronchodilator test (BDT) response to ipratropium bromide (IB) in patients with chronic obstructive pulmonary disease (COPD) who do not respond to inhaled terbutaline. Sixty patients with stable COPD who showed a negative response to BDT, defined as an increase of less than 160 ml in the forced expiratory volume in the first second (FEV1) after inhaling 1500 microg of terbutaline, were recruited. Each patients randomly received 200 microg of IB or placebo in a single blinded fashion, and a spirometric study was made at 30 and 60 min. The increase in absolute values of FEV1 at 30 and 60 min after IB was significantly higher than after placebo. The means +/- SD were 126 +/- 93 vs. 70 +/- 96 ml at 30 min and 148 +/- 120 vs. 74 +/- 132 ml at 60 min (P=0.01). The BDT was positive in 57% of patients who received IB, considering a positive response as an increase of FEV1 greater than 160 ml (P=0.01). We conclude that the BDT was positive with high doses of IB in more than half of COPD patients who did not respond to terbutaline alone.

Etiological characterization of 512 severely mentally retarded institutionalized patients in havana.

OBJECTIVE: To investigate etiological factors in severe mental retardation (SMR). METHODS: An etiological study is presented of 512 SMR patients in five specialized institutions in Havana. RESULTS: Prenatal, perinatal and postnatal causes were apparent in 58.0, 24.8 and 11.1% of the patients, respectively; infantile psychosis was determined in only 0.4%. The remaining 5.6% were classified as having SMR of undeterminable origin, i.e. patients with apparently normal pre-, peri- and postnatal histories who had neither dysmorphism nor affected first-degree relatives, and had a normal karyotype and metabolic screen. Among prenatal causes, genetic factors were the most frequent (82.8%), while environmental factors were apparent in only 5.3% of these cases. Of the cases with prenatal genetic etiology, chromosomal aberrations were present in 86.5% (Down syndrome 96.2% and 3.7% other chromosomal aberrations), monogenic disorders in 11.3% [neurocutaneous diseases (32.1%) and fragile X syndrome (25%) were the most frequent], and multifactorial disorders in 2.0%. Thirty-five patients (11.7%) presented multiple congenital anomalies of 'prenatal unknown' causes. The latter group may include unidentifiable chromosomal aberrations, uniparental disomy, de novo mutations and multifactorial or teratogenic factors. CONCLUSION: Accurate determination of the etiology of SMR is important not only for genetic counseling purposes, but also in identifying prenatal events which make infants more vulnerable to perinatal risk factors.