But Avery didn't do what Helena liked to call "baby tai chi," in which infants wave their arms around. She was content to sit wherever she was placed, without moving. With three other daughters, Helena and her husband, Brennan, were aware that things seemed a little different with Avery.
At Avery's 4-month checkup, she wasn't holding up her head like a child her age should. Her pediatrician recommended a neurologist.
The Houston couple didn't realize that their first visit with a neurologist would be the beginning of a lifetime of doctor's visits for Avery, trying to understand why their youngest daughter would never develop like her sisters or other children.
Her neurologist, Dr. Timothy Lotze of Texas Children's Hospital, found that Avery had poor muscle tone. It meant milestones were delayed. Indeed, she wasn't able to sit up until age 3 or crawl until age 5.
Now 10, she cannot speak or walk, although she's still engaged with everything around her and has a positive, supportive network to help her grow and enjoy life.
Until recently, the reason behind her condition was a complete mystery to most doctors. But research shed light on a new mutation in her body.
"A doctor told us that science just hasn't caught up with Avery," Helena said. "It's shocking when you leave the doctor's office and they really don't know. You think, 'we can't solve this. Will we ever?' The way he put that gave us hope.
"We were really proactive in telling all of the doctors we would be happy to enroll in any research-based studies, hopeful to learn something for Avery, or even if it helps the next Avery down the line."
Defining a mystery
Avery started physical therapy at 5 months old under Lotze's recommendation, and she's still doing physical therapy at 10, her mother said. It took her years to roll over.
The appointments when she was just months old led to a process of "innumerable tests," Brennan said. Blood tests for metabolic markers, MRIs, spinal taps, nerve conduction studies: Doctors performed every test they could think over the next two years.
It enabled them to rule out serious conditions like cerebral palsy, multiple sclerosis and other genetic disorders that result in degenerative movement or low muscle tone.
"For the most part, that was good news," Brennan said. "Most of those disorders they can diagnose don't have a good prognosis. It wasn't bad news to hear they don't know what you have."
General tests were followed by incredibly specific ones. Doctors would bring in peers and specialists to discuss symptoms.
In 2014, a friend told Helena about the National Institute of Health's initiative called the Undiagnosed Diseases Network, a research study to bring experts together to solve medical mysteries. They learned that Texas Children's Hospital and the Baylor College of Medicine, both in Houston, would be participating in the network.
A glimmer of hope appeared in 2015, when the Reillys' geneticist at Texas Children's, Dr. Seema Lalani, presented Avery's case to the network. After testing and vetting, her case was accepted.
Because of her significant testing, Avery had had DNA sequencing of her "exome," the part of her genome that makes proteins in the body, said Dr. Michael Wangler, a researcher at the Jan and Dan Duncan Neurological Research Institute at Texas Children's Hospital.
In the Undiagnosed Diseases Network, the doctors and researchers reviewed her symptoms and previous studies, including her DNA sequencing.
"It was found that she had a variant in a gene called CACNA1A," Wangler said. "CACNA1A is a gene that encodes a crucial calcium channel in our bodies that is involved in the function of our brain and nerves. The change seen in Avery is not one we had seen before."
They studied this mutation in a fruit fly, used as a model organism, to see how genes are affected by the changes.
"In the fly, we found that Avery's mutation causes a gain of function of the calcium channel," Wangler said. "We think calcium moves through her channels more easily and leads to long-term damage of her nerves."
It even led Lotze to change her medications. She now takes a calcium channel blocker, with a goal of helping her avoid further nerve damage and even improve, if possible.
"Our hope is that we can understand more how her mutation and others alter the function of the calcium channel, and this might help us identify patients who are going to benefit from certain drugs like calcium blockers," Wangler said. "We also want to see if providing these drugs earlier in life can help avoid the nerve damage. This is an idea we are testing in flies."
The Reillys finally had a diagnosis. And the discovery enabled doctors to find other patients who carry this mutation. It's just the beginning, but Avery's condition is no longer a mystery.
"The reason why anybody searches for a diagnosis is because you need to define the problem so that then you can come up with a solution," Helena said. "It's wonderful we have that diagnosis. Any future research based on this calcium channel gene will be useful for us and future Averys."
Genetic testing is becoming cheaper and more accessible, which the Reillys hope will enable more children to be diagnosed. And as new research becomes available, the Undiagnosed Diseases Network will reach out to see what might be helpful for Avery and other children like her.
Striving for a normal childhood
Avery has been going to physical, occupational and speech therapy sessions weekly for most of her life, as well as doctors appointments. But her parents felt that public schools, even those with special needs departments, wouldn't work for her.
When she was 2½, Avery began attending the Arbor School, near the Reilly family home in Houston. The year-round school provides targeted programs for children with developmental disabilities from birth to age 12. In addition to academics, it helps children learn how to eat, use the bathroom, brush their teeth, crawl, stand and walk.
The school was understanding and accepting of Avery, even before she had a diagnosis, because other students were also "medical mysteries." Workers tailored a curriculum just for Avery and her needs, and she was thrived, Helena said. Finding the school was life-changing. And the Reillys have been able to connect with parents they can relate to, forming a large support network.
Every child at the Arbor School is evaluated and given a large set of goals, including social, academic, fine motor, gross motor and self care. Students work on their goals every day, and as they check them off, more are added. Avery is always working on at least 20. Teachers will also call her physical therapist to learn what they can work on at school.
When she was younger, it was holding a spoon and learning to feed herself. Now, the goals include pre-reading skills like determining which image doesn't fit with the others. For someone who can't read, phonics is incredibly tough, but Avery is learning to sight-read words. She points, makes noises and shakes her head yes or no to communicate.
Avery can also sign some words. When she gets home from school every day, she signs "outside" and "friends" to let her parents know she wants to play with her friends, they said. Her perceptive language is excellent, and she communicates in her own way. And she uses assistive communication devices like iPad apps with which she can use an image keyboard to communicate her wants and needs.
Her calendar is full of activities, like Girl Scouts, Sunday School and play dates.
Avery can't walk independently, but she can use a gait-trainer, a wheeled walking-assistance device, thanks to her mother and her physical therapist. For so long, the focus had been on eventually walking.
"Getting her wheelchair was a big moment," Brennan said. "Being in a wheelchair is allowing her to control where she goes. It was awesome, and it changes the way she interacts. She really can engage, and it's a blessing, despite her limitations, to do what she wants to do."
Her sisters have been a big part of helping Avery to be so engaged.
"I think it was great that Avery had these older sisters she could model after even though she couldn't do these things," Helena said. "I think she is very socially motivated, and partly that's because of her sisters, who has always interacted with her. She has always been a normal part of our family, even though she wasn't walking or talking, but people were still talking to her.
"When you have a baby, you know what they say even without words -- that was just extended out for Avery. We always have tried really hard for everybody to have a really normal life and not to treat her differently than our other kids."
Still, an MRI of her brain revealed that most of her cerebellum, the part that coordinates and regulates muscular activity, has atrophied and essentially disappeared.
"When new doctors see her, they're amazed at how well she can move given that she doesn't really have a cerebellum," Brennan said. "Her brain compensated for that."
Avery's parents have tried to maintain a normal life for her, as well as their older daughters, Presley, Emory and Trinity.
"My other children will grow up, go to college and live on their own, but Avery won't," Helena said. "She won't ever live independently. That's hard to accept that your child's future isn't going to be as you imagined, or not going to be like her sisters'. That took me a few years to really come to terms with all of that."
But the Reillys wouldn't want their family any other way.
"Her sisters have learned a lot of patience, tolerance, unconditional love and acceptance," Helena said. "I think they are better people because they have Avery for a sister. For Avery, it's been wonderful to have all these sisters to interact with. She's a sweetheart. She works hard every single day, and she has the most positive outlook of any of us."