Let’s talk numbers: Epidemiology of intellectual and developmental disabilities research at the Waisman Center

By Charlene N. Rivera-Bonet, Waisman Science Writer

Maureen S. Durkin, PhD
Maureen S. Durkin, PhD

In 2001, newborn screening of Hmong babies had an alarming number of positive results for an enzyme deficiency called MBADD. But it turned out the screening results were not clinically important, according to Maureen Durkin, PhD, DrPH, an epidemiologist, Waisman investigator, and professor of population health sciences and pediatrics, who used epidemiology to better understand this trend. For more than 20 years, Durkin’s epidemiology research has helped advance the knowledge on intellectual and developmental disabilities at the Waisman Center and throughout the nation and globally.

Epidemiology is the study of the frequency and distribution of a disease, disability, or other health outcomes in populations. “Just by describing those frequencies, and the distributions, the differences and the trends over time, we get clues to what’s going on. It can give clues to the causes, and point to health disparities and service needs,” Durkin says.

The Hmong population is the largest Asian American ethnic group in the state of Wisconsin. Changes to newborn screening in 2001 meant there were now 40 metabolic conditions that could be detected. “But the technology had gotten ahead of the knowledge, so they started picking up something called MBADD in the Hmong population in Wisconsin,” says Durkin. MBADD, short for 2-Methylbutyryl-CoA Dehydrogenase Deficiency, is a rare enzyme deficiency associated with severe developmental delays, seizures, muscular atrophy, decreased muscle tone, and cerebral palsy. When positive newborn screening results for this deficiency started popping up for Hmong babies, the public health system assumed it was a pathological condition and started referring the infants to the Waisman Center. “It turns out it’s probably a benign mutation in this population, but we didn’t know that,” Durkin says.

In order to arrive at the conclusion that this deficiency wasn’t a threat to the Hmong population, Durkin and her team did a prospective cohort study. They identified children from the Hmong population who screened positive for MBADD, and a control group from the Hmong population that screened negative. After five years of following this cohort, Durkin and other researchers didn’t find any significant disability associated with the deficiency in this population.

The first epidemiologist and the first epidemiology project

Durkin was the first epidemiologist at the Waisman Center, which meant the center was a fertile ground for epidemiology research when she first started in 2002. She was recruited by former Waisman Center directors Terry Dolan, PhD, and Marsha Mailick, PhD. Even though Durkin was the pioneer, it didn’t mean she had to start from scratch. “Epidemiologists never work alone. You have to work with experts in whatever it is you’re studying,” Durkin says. “I’m sure that the reason we have been successful in getting funding was because we have the Waisman Center environment with all the knowledge of developmental disabilities.”

Map of the 11 states that form part of the ADDM Network
Map of the 11 states that form part of the ADDM Network

Just as Durkin was setting up at Waisman, an opportunity arose to apply for a grant from the Centers for Disease Control and Prevention (CDC) to monitor the prevalence of autism spectrum disorder (ASD) and other developmental disabilities, including cerebral palsy. The Waisman Center then became part of the network of 11 sites across the United States working on this project called ADDM – Autism and Developmental Disabilities Monitoring.

ADDM is the largest ongoing ASD tracking system in the United States. Every two years, each site publishes its estimates of the prevalence of autism. “Public health surveillance is the most basic form of epidemiology. It is simply to get a handle on how common something is, what the trends are, is it increasing or decreasing? Who is most affected? Are there disparities or gaps in access to services? And then once you have that information, you can start planning to meet service needs,” Durkin says.

The local network of the ADDM project, the Wisconsin Surveillance of Autism and Other Developmental Disabilities System (WISADDS) monitors the prevalence of ASD, cerebral palsy, and co-occurring intellectual disability in more than 58,000 four- and eight-year-old children within an eight-county area in southeast Wisconsin. WISADDS also monitors outcomes at age 16.

In addition to providing estimates of autism and cerebral palsy, WISADDS provides trainings and dissemination of information on developmental disabilities to professionals.

Each type of epidemiological study – local, nationwide, and global – has similar but separate goals. “I think the local is really important. Because you can use the information to identify your own community needs. But in order to get the numbers of cases for relatively rare conditions you need a large sample,” Durkin explains. Being part of a national network of sites allows them to have the numbers they need, the intellectual exchange with researchers across the country, and more generalizability of the condition to the nation.

Part of something big

Maureen Durkin delivering a talk during a Day with the Experts: Autism.
Maureen Durkin delivering a talk during a Day with the Experts: Autism.

In addition to tracking the prevalence of autism through ADDM and WISADDS, Durkin is part of the Study to Explore Early Development (SEED), designed to compare children with autism and other developmental delays to typically developing kids. This type of study is known as a case control study and intends to help researchers better understand the health and behavior of kids with ASD, and identify factors that contribute to autism. “You’ll do [a case control study] for something where you really don’t understand what causes it. Looking back to say, was there anything different about the pregnancy of kids who have autism compared to the control group?” Durkin says.

SEED is funded by the Centers for Disease Control and Prevention (CDC), and considered the largest case control study of autism in the country. Wisconsin SEED is one of the five sites that make up this network and has been very successful in enrolling children with autism and other developmental disabilities.

“One thing with epidemiology is we don’t just describe [a condition] for its own sake. It’s to stimulate action, and often further research. Once you see it, you can’t just ignore it anymore, then it’s a problem that we have to address,” Durkin says.

Moving the field forward

Part of the recommendations based on findings from autism surveillance is a universal screening for autism. Now, the American Academy of Pediatrics recommends that all children, regardless of a suspicion of autism or not, get screened for autism at their 18- and 24-month visit. “It was in part the data from epidemiologic studies demonstrating rising trends in autism prevalence and disparities in early identification that led to this policy recommendation,” Durkin says.

Susan Ellis Weismer, PhD
Susan Ellis Weismer, PhD

Other Waisman investigators have also utilized epidemiological data from Durkin’s studies to go into more specific aspects of disabilities. For example, Susan Ellis Weismer, PhD, professor emeritus of communication sciences and disorders, uses SEED’s very well documented and large sample of data from children to see if she can identify those who meet criteria for social communication disorders.

An area of growth for epidemiology as it continues to evolve is lifespan coverage. For Durkin’s work at Waisman this means looking at cohorts over time to see how symptoms evolve, what services are needed, and what is required to ensure that children with autism and cerebral palsy reach their full potential in education, employment, and self. This is something, Durkin says, Leann Smith DaWalt, PhD, a Waisman investigator with the Lifespan Family Research Program and director of the University Center for Excellence in Developmental Disabilities (UCEDD), is doing well. Her research focuses on understanding the behavioral continuum and change for individuals with intellectual disabilities and their families across the life course.

As the field of epidemiology has advanced, many changes have been made to ensure just outcomes for everyone. Some have required a shift in how we think, view and talk about disabilities. “Thinking about how we can study developmental disabilities without contributing to the stigma and embracing more of an inclusive, diverse world. It’s part of the human diversity,” Durkin says.

Leann Smith DaWalt, PhD
Leann Smith DaWalt, PhD

Along those lines is also working to remove disparities in access based on socioeconomic status, race, ethnicity, and disability. “What history has shown is that if the treatment isn’t accessible, if it’s very expensive, and only some people can get it, it’s going to lead to huge disparity. Advancing equitable access to autism services to improve outcomes is essential” Durkin says.

A way epidemiology can promote inclusion is engaging with different communities. The UCEDD, Durkin says, plays a major role in making these types of local epidemiology studies successful through community outreach and education. With the Hmong community, for example, part of the research process focused on creating materials that explained the screening process in ways that resonated with the Hmong community. “Another really important part of epidemiologic studies is the realization that you can’t just study people in the population,” Durkin says. “You have to engage with communities, communicate well, and involve members of the community, including those with disabilities.”

Related Story: From brain stimulation to speech and language interventions, Waisman researchers are making strides to better understand and treat individuals with cerebral palsy

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