Growing up in Minnesota, Helen Hoang suffered from crippling social anxiety and struggled to make friends. She found refuge in romance novels, frothy stories that allowed her to experience intense feelings that were clearly spelled out on the page, always with the promise of a happy ending. “It was like I found a pure, undiluted drug,” she said.

Many years later, as a mother of two in her 30s, Ms. Hoang began researching autism and realized that she’s on the spectrum, a condition that makes it difficult for her to hold casual conversations, read emotional cues, have an office job and meet new people. She once again turned to romance. But this time, she wrote the story herself.

So far, romance fans have swooned over Ms. Hoang’s debut novel, “The Kiss Quotient,” a multicultural love story centered on an autistic woman who has trouble navigating the nuances of dating and courtship. Readers have flooded the website Goodreads with more than 7,000 positive ratings, and the book, which was published in June, is already in its fourth printing.

The novel’s unexpected success is all the more astonishing given the striking lack of diversity within the romance genre. Romance novels released by big publishing houses tend to center on white characters, and rarely feature gay, lesbian, bisexual or transgender people in leading roles, or heroines with disabilities. Even as the genre has evolved to reflect readers’ varied tastes and fetishes — popular subcategories include vampire and werewolf romance, military romance, cowboy romance, time travel romance, pirate and Viking romance — the lead characters are often confined to a fairly narrow set of ethnic, cultural and aesthetic types.