26 Journal of Prenatal Diagnosis and Therapy | January-June 2010 | Vol 1 | Issue 1 A PCR-based screening method for rapid detection and genetic counseling in Fragile-X syndrome Usha Dave 1 , Dhanlaxmi Shetty Post-Doc. Research Fellow, 1 Principal Scientist-R &D, Super Religare Labs, Mumbai, India Address for correspondence: Dr. Usha Dave, Super Religare Labs. (SRL), Plot No. 1, Prime Building, S. V. Road, Goregaon (W), Mumbai-400 062, India. E-mail: usha.dave@srl.in Introduction Genetic research is rapidly progressing with completion of Human Genome Project, and search for disease-associated genes are presently targeted for cure and management of genetic disorders. Neurogenetic disorders are on top of this list as one third of human genes are expressed in the brain. Identifying the relevant genetic test for diagnosis of several neurological conditions is thus a challenge, especially for those dealing with mental and behavioral dysfunction. Fragile-X Syndrome (MIM 309550) also referred as Martin- Bell syndrome is the most common inherited cause of X-linked mental retardation. [1] It is recognized as the second common cause of mental retardation after Down syndrome, and occurs in both males and females causing intellectual and cognitive deficits. A spectrum of deficits ranges from mental retardation (hereafter referred to as intellectual disability) to dull normal, learning difficulties, autistic features/autism, anxiety and emotional problems. The prevalence in general population is one in 3600 for FXS associated MR. The milder phenotypes like mathematics and language deficits, attention-deficit/ hyperactivity disorder (ADHD), social phobia are known to be more common. [2] The incidence is estimated to be 1 in 4000 males and 1 in 8000 females worldwide. It varies from learning disabilities and normal intelligence in females to mild to severe mental retardation and autistic behaviors in males due to mutational differences. FXS is characterized by a group of clinical symptoms, which includes specific physical features such as large head and ears, long triangular face, macroorchdism, defective speech and language. The behavioral phenotype includes anxiety, hyper-arousal, attention and executive function problems and symptoms of pervasive developmental disorders. [1,2] ABSTRACT The Fragile-X syndrome (FXS), an X-linked disorder, is recognized as the second common cause of mental retardation after Down syndrome. It is associated with a variety of neurobehavioral deficits, including cognitive dysfunction, attention-deficit /hyperactivity, autism spectrum disorders, and other emotional problems. FXS is caused by full mutation (> 200 CGG repeats) in FMR1 (fragile X mental retardation 1 gene). This dynamic mutation of FMR1 is due to progressive expansion of polymorphic (CGG)n trinucleotide repeats located in the promoter region of the FMR1 at Xq27.3 causing decreased or absent levels of fragile X mental retardation protein (FMRP). The smaller expansion (55-200 CGG) of FMR1 is termed a premutation, often found in mothers of FXS and also in premutation carriers with varying degrees of physical phenotypes and intellectual impairment correlated with the magnitude of FMRP deficit. Both full mutation and premutation makes FXS a family concern as an array of disabilities are seen throughout multiple generations. The aim of the study was thus to establish the polymerase chain reaction (PCR)-based method as a routine screening method for rapid detection of FXS. In view of this, total 720 MR children were selected for cytogenetic and further molecular investigation to check the reliability of the PCR method. The chromosomal analysis conducted in 443 children revealed 20 (4.5%) subjects with fragile site on X-chromosome, characteristic of FXS. Molecular study conducted on 12/65 cases showed (18.46%) to be positive by PCR technique and was confirmed by Southern Blotting. The clinical and dysmorphic features though well-described, are often mild and subtle; as a result go unnoticed by the clinicians. It is therefore important for a clinician who is not so equipped with genetic knowledge in India, to address the issues of transmission and genetic counseling to family members emphasizing the genetic testing in mental retardation (MR), associated learning and behavioral problems. This relatively simple and accurate molecular test was used to screen all patients with unexplained mental retardation/ learning impairment for FXS. The detection of FMR1 mutation was found helpful in informed genetic counseling for medical management, prenatal diagnosis and follow-up. Key words: Fragile X Syndrome, FMR1 gene, genetic counseling, prenatal diagnosis BRIEF REPORT DOI: 10.4103/0976-1756.62140