Tay-Sachs: Boy dies from rare genetic disorder just FOUR DAYS before baby sister he longed to meet is born Archie Watson, 2, had a Tay-Sachs, a disorder that causes nerve cells to die Died last Monday in children's hospice after singing his favourite songs His sister Matilda Rose arrived on Friday, weighing 7lb 8oz Parents Bradley and Lauren believe he is now Matilda's guardian angel A two-year-old boy who longed to be alive for the birth of his sister has lost his battle to a rare genetic disorder just four days before her arrival. Archie Watson died last Monday after suffering from Tay-Sachs, which causes deterioration of nerve cells, mental and physical abilities and a maximum life expectancy of four years. Now his parents, Bradley, 34 and Lauren, 27, believe he is watching over their newborn, Matilda Rose, as her guardian angel. A life cut short: Two-year-old Archie Watson suffered from a rare genetic disorder and died four days before his longed-for baby sister was born Archie was suffering from Tay-Sachs, a rare but fatal genetic condition that causes derioration of nerve cells and a maximum life expectancy of four years Mr Watson, from South Wales, said: 'Matilda has a guardian angel now in Archie, who will be there for her. I know it sounds strange, but we honestly believe it - that she will carry on where he left off. We wanted him to be here when she was born, but he was poorly and hung on for as long as possible. He is not suffering any more. Archie, who was diagnosed in December 2011, died at Ty Hafan Children's Hospice, after singing his favourite Sesame Street songs and watching a starlight projector. His death resulted in Lauren, who was due to give birth on April 7, deciding to be induced. Four days after Archie died, his sister Matilda Rose was born (pictured with parents Lauren and Bradley and bother Jack). Mr and Mrs Watson believe Archie is watching over his sister as her guardian angel She didn't want to miss the celebration of his life, which they are having instead of a funeral. Matilda Rose arrived on Friday afternoon, weighing 7lbs 8oz. At nine months, Archie stopped developing properly, had trouble walking and began having seizures. He was then diagnosed with Tay-Sachs. Mr Watson said: 'We could have wallowed in despair, closed the curtains and counted down the days. But, we threw the curtains open and got much good out of something so bad. After he was diagnosed, we had a "no tears at Christmas" policy. We didn't want regrets and to look back having wasted two years we had with Archie.' The little boy's life was crammed with as much fun as possible from trips to Euro Disney and Wembley, as well as being a mascot for the Cardiff Blues rugby team. Archie, who was diagnosed in December 2011, died at Ty Hafan Children's Hospice, after singing his favourite Sesame Street songs Mr Watson, who works for an insurance broker in Cardiff, told his local paper that the couple had first realised there was something wrong with Archie when he started having fits at the age of nine months. He told the said: 'Archie suddenly started having a lot of seizures. Then, just before Christmas, he had some blood tests and brain scans and it was found that he had a deficiency of a protein which helps the nervous system. Unfortunately both my wife and I are carriers of the gene, so Archie inherited that gene. We knew something was wrong as his development was changing and he was having the seizures. Archie's death resulted in Mrs Watson, was due to give birth on April 7, deciding to be induced, so as not to miss the celebration of Archie's life being held instead of a funeral We thought is might be cerebral palsy or something similar, but we did not realise it would be terminal. Then, after Archie developed pneumonia, the family feared he wouldn't make it to Christmas. His parents and brother Jack, 10, said goodbye every day of the final four weeks they spent at Ty Hafan and had a birthday for each of the 30 months Archie lived. Mr Watson said: 'He fought until there was nothing left in him. He was hoping to meet his sister, but it wasn't meant to be. His legacy will live on and he will keep inspiring people. His story has touched the hearts of thousands of people through postings on social networking sites as he bravely fought the terminal illness. Through sky dives, marathons and other fundraisers, family and friends have already raised £23,000 for Caerphilly Children's Centre, Ty Hafan and Cure and Action for Tay-Sachs. For more information: www.amazingarchie.com/index.html Tay-Sachs disease is a rare and usually fatal genetic disorder that causes progressive damage to the nervous system. In the most common form of the condition, symptoms usually begin at around five months of age, when a previously normal child's development begins to slow and they gradually lose their ability to move. Other symptoms can include muscle stiffness and fits. The first noticeable symptom is usually that a baby is excessively surprised and startled by noises, such as people clapping their hands or a telephone ringing. A red spot may also appear near the centre of each of their eyes. Babies with the condition will also be much slower in reaching developmental milestones, such as gripping objects and learning to crawl. Tay-Sachs disease is caused by a genetic mutation. This happens when the instructions that are found in all living cells become 'scrambled' in some way, causing one or more processes of the body not to work properly. In Tay-Sachs disease, a genetic mutation known as the HEXA mutation results in the body not producing an enzyme called Hexosaminidase-A (Hex-A). Without this enzyme, a fatty substance called ganglioside builds up in the cells of the nervous system, causing them to stop working normally, eventually killing them.