ABSTRACT INTRODUCTION The consequences of de novo balanced structural chromosome aberrations diagnosed antenatally are unpredictable, and, as a result, they introduce uncertainty into genetic counseling decisions. OBJECTIVE Describe de novo balanced structural aberrations present at antenatal diagnosis in samples from pregnant women in five Latin American countries and determine their effect on carrier individuals. METHODS This was a retrospective observational study based on analysis of 109,011 antenatal tests conducted from January 1981 to December 2016 in Cuba, Uruguay, Costa Rica, Mexico, and Colombia. Thirteen cytogenetic laboratories provided information that included the cases analyzed during the study period; number of de novo balanced structural aberrations diagnosed antenatally; number of diagnoses with de novo balanced structural aberrations that resulted in termination of pregnancy; detailed descriptions of the karyotypes of de novo balanced structural aberration carriers, and descriptions of the form of diagnosis, including types of samples used (amniotic fluid, chorionic villus or fetal blood). Each laboratory also provided pathology reports and genetic counseling at time of diagnosis. Postnatal followup for pregnancies carried to term continued for at least two years. RESULTS Of the 109,011 antenatal tests studied, 72 (0.07%) showed de novo balanced structural aberrations. These events primarily involved chromosomes 1, 2, 7, 14, 18, and 20. Of the 79 breakpoints identified, the most common were 5p15.3, 7q11.2, 7q22, and 14q24. We identified three breakpoints corresponding to 3.8% (3q13.1, 3q13.2, and 9p12) that were not reported in other studies of de novo balanced structural aberrations diagnosed antenatally in patients from other geographic regions or in studies of chromosomal fragile sites. Two of these breakpoints (3q13.1 and 3q13.2) were associated with high risk of phenotypic abnormalities. Information on antenatal or postnatal followup was available for 62 (86%) of de novo balanced structural aberration carriers; of the 44 carriers with postnatal followup, 10 had phenotypic abnormalities. CONCLUSIONS Three new de novo breakpoints were identified, presumably related to genetic admixture characteristics in Latin America. Since some diseases associated with de novo balanced structural aberrations detected antenatally have a late onset, followup for at least two years is recommended for carriers of these aberrations. The information in this study is useful in genetic counseling for pregnant women in Latin America.

Pallister-Killian syndrome is caused by a tetrasomy 12p mosaicism and is characterized by facial dysmorphism, pigmentary skin anomalies, congenital heart defects, diaphragmatic hernia, epilepsy and mental retardation. The diagnosis is complex as the cytogenetic analysis in blood is usually normal, requiring karyotyping in other tissues, therefore the clinical suspicion is critical to guide the diagnostic tests and the patient requires an interdisciplinary clinical evaluation regarding the several manifestation of the syndrome. W e present the case of a Mexican mestizo female patient of 4 years of age referred by psychomotor delay and cleft palate; the clinical multidisciplinary evaluation demonstrated characteristics corresponding to the Pallister-Killian syndrome. The GTG banding karyotype analysis was normal, the skin fibroblast was mos47,XX,i(12)(p10)|-#91;85|-#93;/46,XX|-#91;21|-#93;. This case is an example of the importance of the clinical evaluation in order to establish a diagnosis that is a challenge for the clinical multidisciplinary team to offer medical management and genetic counseling.

El síndrome de Pallister-Killian es una entidad poco frecuente causada por tetrasomía 12p en mosaico. Presenta facies tosca, alopecia frontotemporal, frente prominente, fisuras palpebrales oblicuas ascendentes, hipertelorismo ocular, ptosis palpebral, estrabismo, epicanto, puente nasal ancho, nariz corta, narinas antevertidas, filtrum largo, labio superior delgado e inferior prominente, pabellones auriculares con lóbulos gruesos y protruidos, cuello corto, pezones supernumerarios, manos anchas, braquidactilia, alteraciones en la pigmentación de la piel, cardiopatía congénita, discapacidad intelectual y crisis convulsivas. Su diagnóstico es complejo, ya que, en sangre periférica, el cariotipo suele ser normal. Se presenta el caso de una paciente mestiza mexicana de 4 años de edad con retraso en el desarrollo psicomotor y características fenotípicas que correspondieron a síndrome de Pallister-Killian. El cariotipo en fibroblastos de la biopsia de piel demostró mos47,XX,i(12)(p10)|-#91;85|-#93;/46,XX|-#91;21|-#93;. Un equipo multidisciplinario realiza el seguimiento con controles regulares por los departamentos de Neurología, Pediatría General y Genética Médica.