He had already gone through puberty as a girl, an experience that made him conclude he had been born into the wrong gender. "I was always uncomfortable calling myself 'she' or 'her,' " he explained. "It made my skin crawl."
At 13, Jacob — then called Samantha — had informed his mother, sending her the news in a Facebook message after being dropped off at school one morning in Ukiah, one of Northern California's iconic hippie towns.
Now, the two sat in an examination room at the University of California at San Francisco, or UCSF, as Jennifer Bilstein signed her name to a seemingly endless succession of medical forms. Bilstein acknowledged that she initially had trouble accepting the news.
"I didn't understand the words coming out of my child's mouth," she said. "To raise a beautiful daughter to 13 and then have her tell me she's a boy . . . "
As she spoke, her child studied his hands, legs swinging back and forth under the examining table. "But the reality is that Jacob's my child, and regardless of gender or whatever, my child always comes first in my life," she said. "And realistically, it's not about me. It's about Jake."
As they navigate the rough shoals of the trans life, the Bilsteins are putting their hopes in the Child and Adolescent Gender Center at UCSF. Founded in 2012, it is one of 40 or so such clinics around the country, seeing patients as young as 3 and as old as 25.
It is also one of the busiest, encompassing four disciplines: medical, mental health, patient advocacy and legal services. Although surgery is not available at the center, its clinicians maintain close ties with local surgeons to whom they refer patients upon request. On the day that Jacob arrived for his appointment, the examining rooms were filled with 15 elementary schoolchildren, adolescents and teenagers who had traveled from as far away as Hawaii and Sweden and as nearby as the Bay Area. All were seeking a change in their physical sex characteristics to align with their gender identity.
Since opening, the center has seen close to 700 patients. The demand for its services has grown so much that UCSF over the past two years opened two satellite clinics.
The type of services being requested has also changed. Clinicians say they are no longer taken aback by youths seeking some kind of boutique treatment — often "just a touch of testosterone" for an androgynous, nonbinary identity.
'I'm a rainbow kid, I'm boy-girl'
"It's the children who are now leading us," said Diane Ehrensaft, the director of mental health for the clinic. "They're coming in and telling us, 'I'm no gender.' Or they're saying, 'I identify as gender nonbinary.' Or 'I'm a little bit of this and a little bit of that. I'm a unique gender, I'm transgender. I'm a rainbow kid, I'm boy-girl, I'm everything.' "
In fact, the entire medical field is playing catch-up. Last summer, the Mount Sinai Health System in New York awarded two medical fellowships — the first of their kind in the United States — in transgender surgery and transgender psychiatry.
The National Institutes of Health last year awarded $5.7 million for a five-year, multicenter study — also the first of its kind — to evaluate long-term outcomes of medical treatment for transgender youth. The UCSF clinic is one of the study's four sites.
Nationally, the transgender adult population is estimated at 1.4 million, according to the Williams Institute at the UCLA School of Law. That is twice as many as previously estimated. The rate among U.S. youths is even greater. At 0.7 percent of the population, 150,000 Americans between 13 and 17 years old reportedly identify as transgender.
"The question I'm most often asked is whether the transgender population is actually growing or whether more people are coming out," said Stephen Rosenthal, the clinic's medical director and founder. "I'm convinced it's the latter. It seems there's almost a critical mass that's emerged because of increased public awareness and increasing acceptance of diversity."
A pediatric endocrinologist, Rosenthal is not only the central figure of UCSF's gender clinic; as immediate past president of the Pediatric Endocrine Society (PES), he is one of the most influential authorities in the field.
Early hormone therapy
His views are helping to shape a new generation of medical providers. A longtime advocate of early hormone therapy for transgender youth, he was instrumental in helping rewrite the international guidelines for medical treatment for transgender youth.
While the previous guidelines cited 16 as the cutoff age to begin hormone therapy, the new ones, published in November in the Journal of Clinical Endocrinology & Metabolism, make no reference to age and cite "compelling reasons" to start earlier.
Medical treatment for younger children will continue unchanged. As before, they will receive puberty blockers, which work by decreasing secretion of pituitary and sex hormones.
Puberty blockers have long been the gold standard for treatment of precocious puberty. They work by preventing the growth of breasts and onset of menstruation, or the sprouting of facial hair and swelling of the penis. In the case of transgender youth, endocrinologists say that blockers can buy teenagers some precious time, allowing them to put off a final decision and prevent future and unnecessary surgeries such as breast removal.
And if they change their minds and become what are called "desisters" — kids who return to their assigned gender at birth — no harm done; their puberty has simply been delayed a year or two. The effects are largely reversible.
"We recognized that there's no biological logic to a cutoff of 16," explained Joshua Safer, an endocrinologist at Boston University School of Medicine who was also instrumental in revising the guidelines. "There are kids with a clear gender identity out there and there is no reason to make them wait for some legal line when we can already be helping them with their biological reality."
But puberty blockers do come with a shelf life, according to Rosenthal.
"One of the things that happens during puberty is that the rate of calcium development increases markedly," he said. A puberty blocker slows down the rate of bone mineral acquisition, potentially lowering bone density. "This uptick is important in minimizing risks of osteoporosis later in life. So there's a theoretical harm if you put puberty on hold a long time."
The average age for puberty in girls is 10 or 11. In boys, it's generally between 10 and 12.
"As an endocrinologist, I decided years ago that if you waited until 16, which is way beyond the normal age of puberty, that would be taking an unnecessary risk,' Rosenthal continued. "We made the decision we wouldn't do that. A person needs to determine by 14 what their gender is. If they aren't sure, they have to come off the blocker."
In other words, the decision to transition — often irreversibly — is increasingly made by age 14.
Some psychologists have pushed back on this idea, arguing that a child should be required to go through puberty before making such an enormous decision.
Gender dysphoria — the feeling that the body one is born into doesn't conform to one's sense of gender identity — may dissipate as kids get older. A 2011 study is often cited as an argument against medical and social transitioning. It found that 84 percent of kids with gender dysphoria eventually desisted, or came to feel comfortable with their birth-assigned gender. But the study has been widely criticized for its lack of follow-up and other problems.
The controversy — whether gender dysphoria is permanent or ephemeral — has occasionally made its way into the UCSF clinic, with clinical psychologist Erica Anderson — herself a transgender woman — sometimes playing devil's advocate.
"I think a fair number of kids are getting into it because it's trendy," said Anderson, who was married for 30 years and fathered two children before transitioning seven years ago.
"I'm often the naysayer at our meetings. I'm not sure it's always really trans. I think in our haste to be supportive, we're missing that element. Kids are all about being accepted by their peers. It's trendy for professionals, too."
Rosenthal is of the opinion that the vast amount of interest is real. In his experience, people — especially young people — rarely seek medical intervention unless they're deeply committed. Young patients are required to undergo a mental-health screening and evaluation in tandem with medical treatment "to help achieve clarity for the best path forward," as Rosenthal put it.
Transgender youth are inordinately susceptible to acute depression, according to studies published by the Williams Institute. More than anything, Rosenthal said, it's this understanding that brings families to the UCSF clinic.
Every parent here is familiar with the statistic, the one that says 41 percent of transgender people have attempted suicide at least once. Most of the kids who come through the doors at UCSF have experienced at least one episode of acute depression, according to Rosenthal.
'It's just a label'
For years, Muir, a self-possessed 12-year-old from the East Bay, told his parents that he was a "birl": part boy, part girl.
He knows how to tie his own bow tie and loves to read. And while he's not positive what he wants to be when he grows up, he's pretty sure it's either an actor, a writer, a doctor or a park ranger.
"I don't think of [being born female] as a particularly important detail," he said during a recent visit to the UCSF clinic. "If you start out life with a female body and you're like me, you're labeled straight. It's just a label."
Muir (to protect his privacy, he and his parents asked that only his middle name be used in this article and that the family's last name not be used) was 10 years old when he came out to his fourth-grade classmates at circle time. "Some of you have known I haven't been an average girl," he began. His parents stood by in support, videotaping the conversation. They needn't have worried. "Everyone I've told is, like, 'Oh, what's for lunch?' " he said with a shrug.
At the UCSF clinic, young patients such as Muir are closely followed and frequently checked for signs of puberty such as breast budding or testes enlargement. As soon as any are spotted, they are given the option of hormone blockers to delay puberty for a few years.
Muir's initial treatment was a momentous occasion. The date is burned in his memory: May 5, 2017. So is the setting: "The room had puppies on the wall," he said. Muir loves dogs.
His parents have changed the birth name and gender on his passport and birth certificate. "It's not something we feel there's any possibility he would change his mind," said his mother, who uses the pen name Elle White on the blog justmyboy.com, about the journey that she has embarked on with her child.
"He's living as the boy he's always been," she said. "There's still a lot ahead: hormone therapy when he's an adolescent, possibly gender affirmation surgery when he's an adult, navigating relationships and making choices about parenthood.
"But he'll make his way along his journey as a person, as we all do, regardless of the body we're in or who we love. He'll discover who he is in the world, just like any other kid."
'Everything is changing so fast'
Clinicians at UCSF anticipate a future in which trans women will be able carry their own babies to term, thanks to medical breakthroughs such as uterine transplantation.
They now routinely counsel young patients on their future fertility options, encouraging them to bank their sperm or eggs in case they ever want to have a genetically related baby.
"Everything is changing so fast," said Ehrensaft, a supportive presence who oversees fertility counseling at the clinic. "One of the reasons we have a clinic today is because we have puberty blockers and cross-sex hormones. Most transgenders who are 50, 60 years old — they never imagined that would be possible."