Retinoblastoma (RB) is an inherited childhood ocular cancer caused by mutations in the tumor suppressor RB1 gene. Identification of RB1 mutations is essential to assess the risk of developing retinoblastoma in the patients´ relatives. Retinoblastoma is a potentially curable cancer and an early diagnosis is critical for survival and eye preservation. Unilateral retinoblastoma is mostly non-heritable and results from two somatic mutations whereas bilateral retinoblastoma is heritable and results from one germline and one somatic mutation, both have high penetrance, 90%. The purpose of this study was to identify causative RB1 mutations in RB patients with different clinical presentations. A comprehensive approach was used to study a cohort of 34 patients with unilateral, bilateral and trilateral retinoblastoma. Blood and tumor DNA was analyzed by sequencing and multiplex ligation-dependent probe amplification (MLPA) assay. Validation of an insertion mutation was performed by cloning the PCR product. Most of the patients in our cohort had unilateral RB, eight patients had bilateral RB and one patient had a trilateral tumor with ocular and suprasellar/sellar locations. Other tumors in addition to retinoblastoma were also found in the affected families. One patient had two syndromes, retinoblastoma and schwannomatosis, and another RB patient had a father with a retinoma. Five out of the 25 unilateral RB patients carried germinal mutations (20%), which were mostly missense mutations. The bilateral and trilateral patients carried splice-site, nonsense and frameshift mutations as well as a whole RB1 gene deletion. Missense mutations were associated with mild phenotype: unilateral retinoblastoma, retinoma or no tumor. In this study we identified causative RB1 mutations in most bilateral RB patients and in some unilateral RB patients, including five novel mutations. These data are crucial for genetic counseling and confirm the need to perform complete genetic screening for RB1 mutations in both constitutional and tumor tissues.

This study enabled us to obtain information about molecular and genetic features of patients with retinoblastoma in Argentina and correlate them to their phenotype.

Hereditary predisposition to retinoblastoma is caused by germline mutations in the RB1 gene. Most of these mutations occur de novo and differ from one patient to another. DNA samples from 10 families with a child presenting sporadic bilateral retinoblastoma have been analysed for the causative mutation. Using intragenic DNA polymorphisms we detected large deletions in two patients. Heteroduplex and DNA sequence analysis of PCR products from each exon and the promoter region showed small mutations in four patients: a C to T transition in exon 18; 1 bp and 2 bp deletion in exons

Thymidine incorporation into the DNA of the anterior pituitary gland is stimulated by estrogen. We studied the relationship between this effect and expression of the protooncogenes c-myc and c-fos. Within one hour after estrogen administration, the level of c-myc and c-fos mRNA increased in the anterior pituitary gland and remained high throughout the experimental period (16 to 22 hrs). Transcription of the prolactin gene, one of the targets of estrogen action, was stimulated at the same time intervals. There were no modifications in the growth hormone mRNA level. Thus, estrogen induced the expression of c-myc and c-fos in the anterior pituitary gland in an early period.

We have studied the expression of c-myc and c-fos proto-oncogenes in various areas of the central nervous system during postnatal development. c-myc mRNA levels increased during the first 5 days and then decreased over the next 15 days in all nervous regions studied. c-fos mRNA levels changed in a different way in four brain areas. While in cerebral cortex and cerebellum there was a sharp decrease during the first 10 days, in white matter and hypothalamus c-fos transcript levels remained high during the same period, decreasing at a later stage. Changes in oncogenes mRNA levels are related to various developmental events, such as neurite growth, myelination and cell proliferation. The dissimilar patterns of c-myc and c-fos expression suggests that they play different functions in CNS maturation. c-myc mRNA levels are temporally related to active neurite growth and to cell proliferation. Changes in c-fos mRNA correlate in time with early developmental processes and also with those occurring at later stages, such as myelination.