Maria Mercado, 38, walks with son Jackson, who was diagnosed with autism. Even though she has never been diagnosed herself, she says she can relate to her son’s experiences. “It’s not that I know him too well, it is that I know myself.” (Elias Williams/For The Washington Post)

Maria Mercado always knew she was different. Growing up in a boisterous Puerto Rican family in the Bronx, Mercado rarely spoke unless challenged or angry. To the outside world, she came across as a smart but shy girl, who learned to read at age 4 and couldn’t keep eye contact. For most of her school years, she had little trouble with academics — despite a severe stutter and constant daydreaming — but struggled in social settings.

Even into adulthood, Mercado sometimes had a hard time verbalizing her thoughts. “Can I say this?” she asked herself. Yet only she appeared to be aware of the problem. She just didn’t understand why.

The answer came in 2009 when Mercado was 28. Her son, Jackson, who was then 13 months old, began to regress in his development.

Abruptly, Jackson no longer seemed attuned to his surroundings. He stopped saying “mama” and “dada” and responding to his name when called. Five months later, following a 40-minute home interview with a psychologist and a speech therapist, Jackson was diagnosed with pervasive developmental disorders, now known as autism spectrum disorder.

At first, Mercado felt overwhelmed. But when she laid out flashcards and watched Jackson successfully match the words with the corresponding pictures, she knew “he was in there,” as she puts it, just the same as she had always been.

It isn’t uncommon for women with autism to receive a late diagnosis, or none at all. In the United States, autism is about four times more prevalent in boys than in girls — so much that, for decades, doctors didn’t even look for it in the latter.

Researchers now believe, however, that many girls have gone overlooked. Sometimes, they went on to be mothers of children with autism and, only then, did they find both the tools to navigate their own lives better and to care for their children in ways that perhaps no one else could.

After almost three decades without an explanation for her challenges growing up, Mercado didn’t need an official diagnosis to know that she was also on the spectrum. “It made me feel so much better that I can help him because I understand exactly who he is,” she said. “It’s not that I know him too well, it is that I know myself.”

When Jackson was young and couldn’t sleep, she turned him horizontally on the bed in the same way she had done herself on many restless nights. In a heartbreaking effort to get him to speak, Mercado would take away his toys and they sat together, crying, until Jackson made a sound.

“I knew that to get him to communicate I had to push him because that’s how I was able to break out of it,” she said. And because, like Jackson, Mercado is extremely sensitive to loud noises, she keeps headphones handy at all times for him to shut the world outside when it becomes too overwhelming.

The reason Mercado is so mindful of Jackson’s special needs is because hers were never addressed.

Gender differences in autism are little understood. But, in recent years, a growing body of research suggests that males and females exhibit their symptoms in different ways.

Girls tend to be better at masking their challenges with social interactions, for instance. And that they are obsessed with the color pink or collecting stuffed animals might not raise a flag about their development because these are expected from girls. Like Mercado, they are often labeled as introverted and their symptoms attributed to anxiety or attention-deficit/hyperactivity disorder.

“The way our culture thinks of autism is a 4-year-old boy who can’t talk,” said Julia Bascom, the executive director of the Autistic Self Advocacy Network. “So whoever doesn’t fit that picture is swept under the rug.”

When Jennifer Malia took her 2-year-old daughter to the family practitioner and to a developmental pediatrician for consultation, they wrote off the child’s communication issues as a language disorder. Her daughter wasn’t on the autism spectrum because she was able to keep eye contact, Malia was told.

But Malia wasn’t convinced. She had witnessed the 45-minute emotional meltdowns during which her daughter would go from angry to nonverbal. She knew it because she had experienced such episodes herself.

So after hours of research, Malia, an author and associate professor of English at Norfolk State University, concluded that she was also on the autism spectrum and, at 39, received a diagnosis on the same day as her daughter. A year later, her son was also diagnosed, following an evaluation with a clinical psychologist and formal testing.

“It was really frustrating because my daughter didn’t have the stereotypical autism traits,” Malia said. “If I hadn’t pushed for that, we would have never been diagnosed.”

That early detection allowed her daughter to undergo 35 to 40 hours of speech, occupational and behavioral therapy per week and, eventually, overcome her language delay.

“She’s still on the spectrum, but she has manageable challenges,” Malia said.

Missing that critical intervention may have lasting effects on women, including depression and anxiety caused by a persistent feeling of failure. But a diagnosis, even later in life, means being part of a community and having access to a much-needed support network. For some, it even means finding a mission.

Dena Gassner, 60, used to blame herself for forgetting to buy tickets for her daughter’s Halloween party or for her inability to manage daily chores, such as being on time for church every week or doing laundry. (“The way I describe it is: I can do what you’re doing but I’m wearing an 80 pound backpack,” Gassner said.)

Everything changed when her 4-year-old son, Patrick, was diagnosed — and that prompted her own discovery at 38. Gassner immersed herself in the autism community and started attending conferences and reading biographies by other women on the spectrum, such as Valerie Paradiz’s “Elijah’s Cup” and Liane Holliday Willey’s “Pretending to Be Normal.”

Following three decades of self-doubt and 15 different medications for clinical depression and bipolar disorder, she found her own way both as a parent and a professional — Gassner is a PhD candidate in social work at Adelphi University and a board member of The Arc, an organization serving people with intellectual and developmental disabilities.

“Getting my own diagnosis has helped me liberate from the social pressures and enabled me to help my son become his own personal best,” Gassner said. “The journey was necessary, and now I can look back and say ‘thank God,’ because his autism has resulted in me finding out my identity.”

Maria Mercado said she was terrified when she became a public advocate appointee to the Citywide Council on Special Education in February 2018. At school meetings, Jackson’s father, from whom she has separated, always introduced the family because she couldn’t bring herself to speak in public. So Mercado didn’t know how to address dozens of parents who had been advocating for years, some of whom were even in charge of their own nonprofit groups.

But confronting her fear, Mercado faced a crowd to say: “This is who I am. I didn’t just parent, I lived this life. I live in my head just like our children.”

When it was over, she went to the bathroom and cried.

“If I expect Jackson to push himself, then I have to do the same thing,” she said recently. “I can’t expect him to be the best if I’m not pushing myself to be the best.”

Because of Jackson, Mercado has learned a lot about herself and what she can do.

Today, besides being a full-time mother and an advocate, she’s also a filmmaker. Her first short documentary is called “Apple of My Tree,” about her relationship with Jackson and being on the spectrum together.

Even without an official diagnosis, Mercado finds comfort in the special connection she has with her son. In her living room, surrounded by portraits of Jackson and “Breakfast at Tiffany’s” and “I Love Lucy” books and vintage dolls, Mercado dwells on the same uncertainties as any other parent. She wishes she could guarantee Jackson’s future after she is gone. She wishes she could ensure his happiness and safety.

But it all goes away when she lies in bed with him at night and he looks at her and says: “Don’t worry, mommy.”