Síndrome de Holt-Oram: caracterización de una nueva mutación / Holt-Oram syndrome: characterization of a novel mutation

Introducción Los síndromes cardiomiélicos comprenden cardiopatías congénitas y malformaciones esqueléticas de los miembros superiores, y están relacionados con mutaciones deletéreas de factores de transcripción con dominios del tipo T-Box. El síndrome de Holt-Oram se debe a una mutación dominante en el gen TBX5 que altera la estructura tridimensional de la proteína impidiendo su correcta unión al ADN. Se han descrito varias mutaciones puntuales y deleciones de TBX5 en pacientes con fenotipo de síndrome de Holt-Oram. Pacientes y métodos El paciente es un niño con una comunicación interauricular (CIA) del tipo ostium secundum grande y una comunicación interventricular (CIV) diagnosticados por clínica (soplo) y ecocardiografía. Presenta además unos dedos pulgares algo hipoplásicos y con un emplazamiento distal bilateral, con un índice de implantación de 0,19 frente a una media normal de 0,50 para su edad gestacional al nacer. Es remitido a la consulta de Genética para descartar microdeleción 22q11.2. Resultados El cariotipo y la hibridación in situ de fluorescencia (FISH) con sonda D22S75 resultaron normales y debido a los hallazgos clínicos se realizó un estudio molecular para el síndrome de Holt-Oram. Se encontró una mutación en el intrón 7 de TBX5 que produce una probable alteración del splicing del gen que da lugar a una proteína truncada en su extremo C-terminal. Los padres del propósito presentan una secuencia normal para el gen, lo que indica que la mutación se produjo de novo, sin que pueda descartarse un mosaicismo germinal en los padres. Conclusiones El síndrome de Holt-Oram es la causa más frecuente de síndrome cardiomiélico. Debería ser objeto de estudio molecular todo niño con malformaciones cardíacas y alteraciones de las extremidades superiores como pulgares ausentes, hipoplásicos, distalmente emplazados o trifalángicos

Introduction Cardiomyelic syndromes encompass congenital heart disease and skeletal malformations of the upper limbs and are related to mutations in transcription factors with T-Box domains. Holt-Oram syndrome is caused by a dominant mutation in the TBX5 gene that alters the three-dimensional structure of the protein and its DNA binding function. Several point mutations and deletions in TBX5 have been reported in patients with the Holt-Oram syndrome phenotype. Patients and methods The proband was a boy with a large atrial septal defect ostium secundum type and a ventricular septal defect, diagnosed by clinical findings (heart murmur) and echocardiography. He also presented slightly hypoplastic thumbs with distal bilateral placement and an implantation index of 0.19 (compared with an average of 0.50 for his gestational age at birth). The boy was referred to the department of medical genetics to rule out 22q11.2 microdeletion syndrome. Results Karyotype and fluorescence in situ hybridization at locus D22S75 were both normal. Because of his clinical findings, molecular study for Holt-Oram syndrome was indicated, leading to the finding of a mutation at intron 7 of TBX5, probably producing a splicing alteration of the gene and resulting in a protein truncated at its C-terminal end. The proband's parents presented the wild type sequence of the gene, thus indicating that the mutation was produced de novo, although a possible germinal mosaicism in the parents could not be ruled out. Conclusions Holt-Oram syndrome is the most frequent cause of cardiomyelic syndrome. All children with heart malformations and abnormalities of the upper limbs such as absent, hypoplastic, distally placed or triphalangic thumbs should undergo molecular studies for this syndrome

[Familial reciprocal translocations: estimation of the most probable imbalance in the offspring]. / Translocaciones recíprocas familiares: estimación del desbalance más probable en la descendencia.

Four familial reciprocal translocations detected in a chromosomic study made to a population of newborn babies with two or more congenital defects following the methodology of ECEMC is analyzed. We followed the criteria of pachytene-dyagrem model of Jalbert et al (1980) to predict the most probable mode of imbalance for reciprocal translocations is followed. On the four translocations it was observed the type of segregation which was most probable following that model: three of them produced imbalance by a 3:1 segregation and the other one be adjacent 1. According to these results and regarding that a given translocation produces imbalances almost always by the same mechanism, we can provide a useful information for genetic counselling for these families.