Tay-Sachs disease (TSD) is a recessively inherited neurodegenerative disorder 
caused by mutations in the HEXA gene resulting in β-hexosaminidase A (HEX A) 
deficiency and neuronal accumulation of GM2 ganglioside. We describe the first 
patient with Tay-Sachs disease in the Cypriot population, a juvenile case which 
presented with developmental regression at the age of five. The diagnosis was 
confirmed by measurement of HEXA activity in plasma, peripheral leucocytes and 
fibroblasts. Sequencing the HEXA gene resulted in the identification of two 
previously described mutations: the nonsense mutation c.78G>A (p.Trp26X) and the 
silent mutation c.1305C>T (p.=). The silent mutation was reported once before in 
a juvenile TSD patient of West Indian origin with an unusually mild phenotype. 
The presence of this mutation in another juvenile TSD patient provides further 
evidence that it is a disease-causing mutation. Successful preimplantation 
genetic diagnosis (PGD) and prenatal follow-up were provided to the couple.