Clinical Cytogenetic, and Molecular Testing of Argentme Patients With Retinoblastoma Alejandra Arbetman, Biochemist,- a Mirta Abdala, MD' b- Adriana Fandifio, MD, b lorge Herrera, Biolo#st.h Sergio Baranzini, PhD,- a Daniel Borelina, Biochemist,aDiana Parma, PhD,a Julio Manzitti, MD, b Cristina Barreiro, MD,h Florencia Giliberto, Biochemist, a and Irene Szijan, PhD a Purpose: The purpose of this study is to determine the clinical, chromosomal, and molecular characteristics of Argentine patients with unilateral and bilateral retinoblastoma. Study Design: Eighty-six patients belonging to 82 families were studied; 59% of them were examined during the first year of life. Leukocoria was the most common reason for consultation. Other presenting signs were strabismus and glaucoma. Enucleation of the affected eye was performed in 85% of the cases and the complication rate was 13%. Results:An appropriate therapy allowed the sur- vival of 84 of the 86 patients. Two children with malformations and growth retardation had an abnormal karyotype with a deletion in 13q14. Segregation analysis of polymorphic sites within the retinoblastoma gene and the parental origin of the allele lost in the tumor were analyzed in 30 of the 82 families. Five mutant alleles transmitted through the germline and six de novo germline mutant alleles were identified in 12 patients with hereditary retinoblastoma. Most de novo germline mutant alleles were paternally derived. Molecular analysis of nonhereditary retinoblastoma showed loss of heterozygosity in three of eight cases. From these, two maternal alleles and one paternal allele were lost, thus not indicating a significant difference in the parental origin for the lost allele. Conclusions:These data are useful for deoxyribonucleic acid diagnosis of susceptibility to retinoblastoma in relatives of hereditary patients, even if mutations have not been identified. (J AAPOS 1998;2:102-7) R etinoblastoma is the most common intraocular malignancy in children.1 There is a dominant pre- disposition to this cancer, as in other solid child- hood neoplasms, e, 3 It originates from immature retinal cells committed to cone differentiation 4 and develops at an early age (birth to 3 years), before full differentiation of the cells. The tumor might appear during fetal life, 5 demon- strafing its tendency to affect undifferentiated cells. Compared with other malignancies, retinoblastoma is a rare tumor occurring with an incidence of 1 in 15,000 to 34,000 live births in developed countries and perhaps more frequently in developing nations, especially in Latin America. 6 The time of diagnosis is important for the prog- nosis of both vision and survival. In developed nations most patients with intraocular retinoblastoma resorting to the ophthalmologist are cured by means of several therapeutic treatments 7, 8 not involving enucleation. Extraocular retinoblastoma occurs more frequently in Latin America From the Gen(tica y Bioloffa Molecular, Facultad de Farmacia y Bioquimica, University of Buenos Aires, a and the Hospital de Pediatrfa "Profesor Juan Garraban, "b Buenos Aires, Argentina. Supported by BID-CON1CET 2 grant No. 0430 and PID-CONICET grant No. 3174 and by grant No. FA 129-UBA. Submitted J'ane 25, 1997. Revision acceptedNovember 6, 199Z Reprint requeyts: Irene Szijan, PbD, Gendtica y Biologfa Molecular, Facultad de Farmacia y Bioqufmica UBA, ~:un£n 9Y6, I 113 BuenosAires, Argentina. Copyright © 1998 by the American Associationfor Pediatric Ophthalmology and Strabismus. 1091-8531/98 SY.O0 + 0 75/1/88080 because of delayed diagnosis 9 and the survival rates are lower than for intraocular retinoblastoma. The tumor can be detected at a relatively early developmental stage because it can be identified by some presenting signs, such as leukocoria. 10 A genetic component of retinoblastoma was proposed several decades ago. 11 The retinoblastoma susceptibility gene, RB1, was located in the subband 13q14.212 and sub- sequently cloned. 13-15 Later studies demonstrated that it encodes a protein with a regulatory function in the cellu- lar growth cycle. 16 Clinical examination of patients with unilateral or bilat- eral tumor normally does not show other dysmorphic fea- tures. However, some patients with a microscopic deletion in chromosome 13q (less than 5%) have growth and men- tal retardation and other dysmorphic features, thus sug- gesting that such deletions include genetic material in addition to the retinoblastoma gene. 16 The inactivation of both alleles of the retinoblastoma gene is essential for the development of the tumor, and it was described by Knudson 17 as the "two-hit" mechanism. The first mutation predisposes to retinoblastoma and can occur in the germline cells or in somatic cells, leading to hereditary retinoblastoma (40%) or nonhereditary retinoblastoma (60%), respectively. TM The second mutation occurs only in somatic cells. According to this mechanism, patients with retinoblastoma can be divided into three types: (1) patients with a transmitted germline mutation in the retinoblastoma gene (familial retinoblastoma, 10%), (2) 102 Aprit 1998 Journal of AAPOS