As bases genéticas da dificuldade de aprendizagem da Matemática

Abstract

Mathematical learning disability (MLD) is a common cognitive condition affecting approximately 3 to 6% of the school aged population.Although social and economical factors, cognitive disability and low educational Standards may contribute to MLD,those are not the primary cause in most of the cases, and a genetic etiology has been put forward several times. Impacts of MDL are lowscholarachievement, low self-esteem, low employability, and low income. Familial aggregation has been reported for MLD in some populations. This is the first study aiming to ascertain the genetic basis of MLD among Brazilian families. This project was approved by the Ethics in Research Committee of the Universidade Federal de Minas Gerais. This is part of a population based case-control study, in which arandom, representative sample of the school aged population of Belo Horizonte city, Brazil, was collected. In order to ascertain individuals with MLD, a two steps strategy was adopted. The first one was a collective screening Math achievement test and the second an individual, diagnostic battery. Students with results below the P25 in the Math achievement test were further evaluated with a battery of tests covering intelligence, mental state, memory, working memory, fine motor coordination, language,somato-sensorial function.Students with QI<85 were excludedbecause of below-average mental abilities. A family history was collected with an specifically developed, structured questionary composed by simple questions such as “can he/she add?”, “can he/she subtract?”, “can he/she multiply?”, “can he/she divide?”, “can he/she exchange money”, “can he/she discriminate left and right”, “can he/she tell the time on the clock?”, “can he/she go around by him/herself”, “can he/she write?”, “can he/she read?”.Besides, data were collected on health conditions, consanguinity, scholarship, profession, and familial income. Fifty-eight families were ascertained. In 22 of them the index case was affected with MLD, 12 with MSLD plus spelling, and 24 normal controls, summing up 1778 relatives, 981 biological ones. Frequency of Math learning disability (with or without spelling difficulties) was estimated in 7% for this sample. No significative differences in sexual proportion were observed among MLD or MSLD index cases or among their relatives. No significative differences in the parameters ascertained by the structured questionary for family history collection of there were found between MLD and MSLD. Moreover, there were MLD cases in MSLD families and viceversa, suggesting that they represent two different clinical manifestations of a single nosological condition. Frequency of MLD/MSLD affected persons was significantly higher among relatives of affected index cases than among relatives of the controls. In the same way, relative risks (lambda) estimated ranged from 1.77 to 9.57.Taken together, these last two findings point to the existence of familial aggregation for MLD/MSLD in this sample.