Susan, the third-born, volunteered to take care of Christy full time, and Jenny, the eighth, searched for a specialist (the family members asked to be identified by their first names to protect their privacy). Depression was the first suspected diagnosis, then schizophrenia, though neither seemed quite right. Christy wasn’t sad or delusional; she wasn’t even upset. It was more as if she were reverting to a childlike state, losing her knack for self-regulation. Her personality was diluting — on its way out, with seemingly nothing to replace it…That strange, reckless profligacy made Barb think of their mother, who in her final years sat at home, saying yes to every sales phone call. How heartbreaking but also interesting, Barb thought, that Christy shared the same peculiar tendencies — a family trait of sorts.

…

There is no bright side to any FTD diagnosis — no cure, no path forward. With very few exceptions, everyone who inherits the mutation will, like Christy and Mary, long before their old age, develop inappropriate social behavior and lose the ability to earn an income, look after their children, do household chores or take care of their hygiene. They will eventually be unable to speak, feed or dress themselves or use the bathroom on their own.

…

Her aunts, uncles and cousins all had to be wondering about the genetic implications of having children. But the mutation casts a shadow over every interaction: Those who have it are too preoccupied to question the choices of others, and those who don’t feel too guilty to second-guess those who do. Barb, for one, has never broached the subject with C. “This disease brings up so many moral and ethical questions,” Barb told me. “I think all of us have tried to refrain from judging.”

…

Of the nine brothers and sisters, five now have active signs of FTD: Christy, Mary, Jenny, Peggy and Oliver — the fourth-born, four years younger than Christy — who had been behaving strangely for many years until, in his 60s, he dropped out of sight during the pandemic, homeless and off the grid for more than a year. These were people who, decades ago, had come to care for Barb when she needed them the most, when their mother died. What will happen to them? Whose responsibility were they now?

“I had thought long and hard about what’s my job here? What’s my role in the family?” Barb said. “Maybe if there was one sibling for me to care for, I could do that. But now I’m looking at five, potentially. How could I possibly take in five FTD patients? And if I want to help one of them, how do I choose?” Barb wondered whether the family could chip in for a compound somewhere — a place where everyone could care for one another, pooling resources. It seemed too complicated to pull off, with so many siblings having to uproot themselves.

…

This will be Susan’s 27th consecutive year as Christy’s full-time caregiver. When Susan started, she was barely out of her 30s, single and between careers. She did not expect her life to take this turn, and in all this time, she has demonstrated a capacity for forbearance that others in the family freely admit they lack, a sort of secret reservoir of equanimity she can draw from in times of trouble.

Read more in the New York Times.