Zihinsel özür ve öğrenme güçlüğünün olduğu populasyonlarda DNA ve sitogenetik analizler ile frajil X sendromluların taranması

Frajil X sendromu kalıtsal mental retardasyonun en yaygın formudur. Hastalık sitogenetik olarak görülebilen (FRAXA) Xq27.3'teki frajil bölge ile ilişkili olup FMR1 olarak adlandırılan genin içinde (CGG)n tekrarının artmasıyla oluşmaktadır. Bu çalışma, toplam 154 birey üzerinde yapılmış olup bunların 82'si frajil X şüpheli grup diğerleri ise normal kontrol grubudur. Şüpheli grup, Samsun'da Milli Eğitim Bakanlığı Rehberlik Araştırma Merkezine bağlı, İlk öğretim okullarının öğrenme güçlüğü çeken özel alt sınıf öğrencileri ve zihinsel özürlülerin eğitildiği merkezlerden seçildi. Çalışmada DNA ve Sitogenetik analiz olmak üzere iki analiz uygulandı. DNA analizi için periferik kandan elde edilen DNA ile PCR yapılarak normal ve küçük premutasyonlu (taşıyıcı) bireyler belirlendi. Daha sonra, Southern blot ve nonradyoaktif hibridizasyon uygulanarak, taşıyıcı (premutasyon) ve hasta (full mutasyon) kişiler belirlendi. PCR sonucunda, frajil X şüpheli grupta CGG tekrar sayısının 7 ile 60 arasında değiştiği, alellerin %94'ünün 40 tekrarın altında olduğu ve en sık gözlenen alelin (%15) 31 tekrarlı olduğu belirlendi. Ayrıca bu grupta bir erkek çocukta premutasyonlu (60 tekrar) bir alel gözlendi. Kontrol grubunda ise CGG tekrar sayısının 9 ile 55 arasında değiştiği ve alellerin %91'inde tekrar sayısının 40'ın altında olduğu gözlendi. En sık görülen alelin (%15) 30 CGG tekrarlı olduğu belirlendi. Bu gruptan bir erkekte premutasyonlu (55 tekrarlı) bir alel gözlendi. Southern blot ve non-radyoaktif hibridizasyon sonunda frajil X şüpheli gruptan bir erkek çocukta full mutasyon gözlendi. Bu çocuğun, iki erkek ve bir kız kardeşinin full mutasyonlu (hasta) olduğu, diğer kız kardeş ve annesinin ise premutasyonlu oldukları belirlendi. Sitogenetik analizde ise full mulasyonlu çocuğun, frajil X pozitif (%12) olduğu belirlendi. Frajil X şüpheli gruptan diğer bir erkek çocuk ve annesinde, 9 nolu kromozomda perisentrik inversiyon belirlendi. Bu çocukta ve annesinde frajil X negatifdi. Samsun'da yapılan bu çalışma ile halk sağlığı açısından önemli bir sorun olan frajil X sendromu sıklığının, şüpheli populasyonda yaklaşık%l olduğu bulundu.

Anahtar Kelimeler:

DNA, Frajil X sendromu, Öğrenme bozuklukları, Zeka geriliği, Mutasyon, Polimeraz zincir reaksiyonu, Nörodavranışsal belirtiler, Sitogenetik analiz

Screening of the fragile X syndromes with DNA and cytogenetic analysis in populations with learning difficulties and mental retardation

Fragile X syndrome is the most common inherited cause of mental retardation. The disorder is associated with a cytogenetically visible fragile site (FRAXA) at Xq27.3, caused by amplification of a (CGG)n repeat sequence within the gene at locus designated FMR1. This study was conducted on a total of 154 subjects, 82 of them are from fragile X suspected group, others from normal control group. The suspected group was selected from the special "subclasses" for students with learning difficulties, of primary schools under the auspice of the National Ministry of Education (of the Republic of Türkiye) in Samsun, and from the centers for special training, education and rehabilitation of mentally retarded individuals. In this study, DNA and cytogenetics analyses were used to screen individuals for CGG amplifications. For DNA analysis, DNAs were extracted from peripheral blood samples; normal and small premutation (carrier) individuals were identified by PCR amplification. The carriers (premutation) and affected (full mutation) were identified by Southern blot and non-radioactive hybridization. According to the PCR results, CGG repeat numbers of the fragile X suspected population ranged between 7 to 60; 94%alleles having fewer than 40 repeats. The most frequent allele (15%) had 31 repeats. Also, there was a male child with a premutation allele (60 repeats). In control group, the CGG alleles ranged from 9 to 55 repeats. The most frequent allele (15%) had 30 repeats. Also, in this group included was a male with a premutation allele (55 repeats). A male child with a full minalion was identified in the fragile X suspected group by Southern blot and non-radioactive hybridization. Both of the proband's two brothers and one of his two sisters had full mutations; his mother and his other sister had premutations. In cytogenetic analysis, the male child with full mutation was found fragile X positive (12%). In the fragile X suspected group, another male child and his mother were found to carry pericentric inversions on one of their chromosomes 9s. The incidence of the fragile X syndrome, which is an important public health concern, in our suspected study group was found to be approximately 1%, as determined by this study carried out in Samsun.

Keywords:

DNA, Fragile X Syndrome, Learning Disorders, Mental Retardation, Mutation, Polymerase Chain Reaction, Neurobehavioral Manifestations, Cytogenetic Analysis,

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