Winnie Thomas¹, Sireesha Divyakolu¹, Vemula Ramana Sreekanth², Vallomkonda Ramesh Om Sai³, Vallomkonda Nagaratna³, Qurratulain Hasan^{1, 4}, Yog Raj Ahuja^1,

Non-synonymous mutations/ polymorphism in amyloid precursor protein (APP) gene cause overproduction of Aβ proteins or affect its split into Aβ40 and Aβ42 peptides. Aβ42 has been considered to be a toxic peptide playing a major role in the pathogenesis of Alzheimers (AD). Similar APP plaques were observed in the brains of Down syndrome (DS) patients and high level of plasma APP was observed in patients with severe Autism spectrum Disorder (ASD). The aim of this study was to evaluate exon 16 and 17, the hotspot regions of APP gene in patients with neurobehavioral disorders like AD, DS and ASD. A total of 75 cases were recruited in the study which included AD (n=25), DS (n=25), and ASD (n=25). Polymerase chain reaction (PCR) analysis and sequencing was carried out using exon-intron encompassing primers for the selected APP gene regions. In-silico analysis was also carried out to identify the impact of sequence variants on the protein structure. Three exonic variants, two in exon 16: V683V, H684Y and one in exon 17, H733Q were identified in sporadic AD cases. Apart from these, two intronic variants were also observed. In-silico analysis showed that H733Q mutation may affect the structure and function of APP, whereas H684Y mutation is neutral. In an ASD case, our analysis showed an intronic variation ie. An A insertion at c.1964-13_1964-12insA. In-silico analysis predicted that this variation affects the elongation feature of the protein. None of the DS cases had any variation in this hotspot region. Our data indicate that variations in the selected hotspot region of APP may play an important role in the aetiology of neurobehavioral disorders.

Alzheimer Disease, exon 16 and 17 of APP gene, Amyloid precursor protein (APP), Polymorphism, mutations