Balkan Journal of Medical Genetics

INTELLECTUAL ABILITY IN THE DUCHENNE MUSCULAR DYSTROPHY AND DYSTROPHIN GENE MUTATION LOCATION
Milic Rasic V1,2,*, Vojinovic D1, Pesovic J3, Mijalkovic G1, Lukic V1, Mladenovic J1, Kosac A1, Novakovic I4, Maksimovic N4, Romac S3, Todorovic S1, Savic Pavicevic D3
*Corresponding Author: Vedrana Milic Rasic, M.D., Ph.D., Clinic for Neurology and Psychiatry for Children and Youth, Dr. Subotica 6A, 11000 Belgrade, Serbia. Tel: +381-11-265-8355. Fax: +381-11-264-5064. E-mail: vedrana.milic.npk@gmail.com
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INTRODUCTION

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy during childhood, affecting 1 in 3500 live born males [1]. This fatal, X linked disease, leads to progressive muscular weakness and less well described non progressive central nervous system manifestations. The consistent finding in patients with DMD is reduction in a full-scale intelligence quotient (FSIQ) by one standard deviation (SD) from the population mean [1,2]. Although most affected boys are not intellectually disabled, the risk of cognitive impairment is increased in DMD patients. Therefore, up to 30.0% of patients have intellectual disability with a FSIQ of less than 70, including around 3.0% of them with severe impairment and FSIQ of less than 50 [2,3]. Duchenne muscular dystrophy is caused by various types of mutations within the dystrophin gene (DMD) [4], which changes the reading frame of coding transcripts affecting the production of protein dystrophin [5]. Expression of the dystrophin is controlled by three upstream promoters, which produce full-length dystrophin isoform (Dp427) and four internal promoters that regulate production of shorter dystrophin isoforms (Dp260, Dp140, Dp116 and Dp71) [6-9]. Dp427 is expressed in skeletal and cardiac muscle, brain and Purkinje cells, Dp260 is expressed in retina [10], Dp140 in brain, retina and kidney [11], while Dp116 is present in peripheral nerves [12]. Dp71 is the most abundant isoform in non muscular tissues and represents the major product in the adult brain [13]. The dystrophin is a part of dystrophinassociated glycoprotein complex, and in the brain, it is involved in the clustering of ion channels and post synaptic membrane receptors during synaptogenesis [9], suggesting that loss of its function may be responsible for intellectual impairment and cognitive deficits in DMD patients. Cognitive deficit is likely the result of cumulative loss of Dp427, Dp140 and Dp71 [9,14], whereas loss of Dp71 contributes to the severity of cognitive impairment [14,15]. Recently, one more dystrophin isoform (Dp40), produced from the same promoter as Dp71 but by the use of an alternative polyadenylation site, has been implicated in pre synaptic function [16]. Although cognitive impairment has frequently been reported, systematized data on the cognitive profile of patients with DMD in Serbia is lacking. Therefore, the aim of this study was to determine frequency of intellectual impairment and to examine association of intelligence level with mutation location and affected dystrophin isoforms among our patients with DMD.

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