Balkan Journal of Medical Genetics

CLINICAL AND MOLECULAR DATA ON MENTAL RETARDATION IN BULGARIA
Todorov T1#, Todorova A1#, Avdjieva D2, Dimova P3, Angelova L4, Tincheva R2 and Mitev V1
*Corresponding Author: Tihomir Todorov, Department of Medical Chemistry and Biochemistry, Sofia Medical University, 2 “Zdrave” str., Sofia 1431, Bulgaria; Tel./Fax: +359 29530715; tisho.todorov@abv.bg
page: 11

INTRODUCTION

Mental retardation (MR) is clinically and genetically highly heterogeneous. Mental retardation and absent speech may be the only clinical finding, or may be associated with progressive neurodevelopmental deficits, seizures, autism and ataxia. A variety of genes, X-linked or autosomal, have been found to be involved in pathogenesis. The most common form of X-linked MR (XLMR) is the fragile X syndrome MR (FXS, OMIM #300624), which is due to an expansion of an unstable CGG repeat in the 5’UTR (5’ untranslated region) of the FMR1 (fragile X MR 1) gene. The polymorphic CGG repeat numbers 6 to 54 ± 2 copies in normal individuals, 55 ± 2 to 200 copies in healthy carriers of premutation, and >200 copies in FXS patients [1,2]. One of the most common forms of severe MR in females is Rett syndrome (RTT, OMIM#312750), which is mostly due to point mutations or large deletions in MECP2 (methyl-CpG binding protein 2) gene, and rarely in CDKL5 (cyclin dependent kinase-like 5) gene [3,4]. On the other hand, retarded females with infantile spasms and other early onset seizures could be caused by mutations in the CDKL5 gene [5]. It has been expected that a number of mentally retarded males with epilepsy will be explained by the common mutation dup24 or other mutations in the Aristaless X (ARX) gene [6,7]. An autosomal gene mutation that gives rise to common clinical symptoms include Prader-Willi/Angelman syndromes (PWS/AS, OMIM#176270; 105830), due to a deletion of 15q11-q13 or uniparental disomy (UPD) 15. The CpG islands around exon 1 of the small nuclear ribonucleoprotein polypeptide N (SNRPN) gene are methylated on the maternal chromosome and completely devoid of methylation on the paternal chromosome [8]. This finding is used in developing diagnostic methods for PWS/AS. In case of male patients, PWS can have some clinical aspects of FXS, and in female patients, some clinical aspects of RTT. Here we report clinical/molecular data in a group of 85 Bulgarian patients, out of whom 32 were clinically diagnosed as FXS, 23 as classical RTT, 13 as atypical RTT, 14 as PWS, and three as Angelman syndrome (AS). Some of these patients were discussed elsewhere [9].

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