In a moving piece in the the New York Times’s Sunday Review this week, author Emily Rapp describes what it is like to have a son with Tay-Sachs, a rare and untreatable genetic disorder that means he will probably die before he turns 4.

Ronan and Emily Rapp. (Image via Facebook. )

Rapp explains that because of the way Tay-Sachs strikes its victims, she will have to watch her son Ronan slowly regress into a “vegetative state,” become paralyzed, have seizures and, one day, lose all of his senses.

Only one in 5,000 people have Tay-Sachs, most of them infants. But for the parents of the children who do, it is a horribly traumatic disease. There is no cure or treatment.

The National Institute of Neurological Disorders and Stroke paints this picture:

Infants with Tay-Sachs disease appear to develop normally for the first few months of life. Then, as nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. The child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in. Other neurological symptoms include dementia, seizures, and an increased startle reflex to noise

The disorder also affects a tiny number of people in their 20s and early 30s, also causing progressive neurological deterioration.

Tay-Sachs has the highest incidence in people of Eastern European and Askhenazi Jewish descent.

Carriers of the disease can be identified by a simple blood test, and both parents must carry the mutated gene for a child to have Tay-Sachs.

The only thing Rapp can do, she writes, “is protect my son from as much pain as possible, and then finally do the hardest thing of all, a thing most parents will thankfully never have to do: I will love him to the end of his life, and then I will let him go.”

Read more about Ronan here.