Redefining the Spectrum: How Changing Diagnostics and Hidden Genetics Shape Our Understanding of Neurodiversity

Welcome to the jFunk42 Science Brief. Today, we are exploring one of the most significant, complex, and rapidly evolving frontiers in modern medicine and public health: how we define, diagnose, and understand neurodiversity. Over the last few decades, we have witnessed a massive, undeniable surge in the number of individuals diagnosed with neurodevelopmental conditions, particularly Attention-Deficit/Hyperactivity Disorder, or ADHD, and autism. If you look around your schools, your workplaces, or your own families, it seems almost certain that you know someone who has received one of these diagnoses. This dramatic rise has sparked intense debate among scientists, clinicians, educators, and the public. It raises a profound, fundamental question: Is there a true, biological increase in the underlying prevalence of these conditions? In other words, is something in our modern environment, our genetics, or our lifestyles causing more children to be born with autism or ADHD? Or, alternatively, is the surge a reflection of a changing scientific lens? Are we simply casting a wider net, changing our criteria, and identifying individuals who in previous generations would have gone unnoticed or been categorized differently? Two groundbreaking studies have recently been released that shed crucial new light on this debate. What makes these studies so fascinating is that they approach the question from opposite directions. One looks at the macro level—analyzing massive, population-wide diagnostic patterns over time to see how the demographic profile of diagnosed individuals is shifting. The other zoom in to the micro level—using advanced genetic analysis to reveal that a specific, highly significant genetic disorder linked to autism is far more common than we ever realized, yet remains hidden because we are failing to perform the necessary testing. Together, these discoveries are forcing us to rethink the very nature of the neurodivergent spectrum, balancing a broader, more inclusive behavioral definition of these conditions with a critical need for genetic precision. Let us begin at the macro level, with a massive new epidemiological study out of Denmark that helps explain why ADHD and autism diagnoses have experienced such a dramatic surge. To understand the significance of this research, we first have to understand how clinical diagnoses are made. Unlike conditions like diabetes or high blood pressure, which can be diagnosed with a simple, objective blood test or physical measurement, conditions like autism and ADHD are diagnosed based on behavioral observations. Clinicians use established diagnostic patterns—sets of behavioral criteria, developmental milestones, and clinical observations—to determine whether an individual meets the threshold for a diagnosis. Historically, these diagnostic patterns were highly restrictive. When autism was first defined as a clinical category, it was reserved for individuals with the most severe, classic, and highly visible presentations. These individuals often had profound challenges with verbal communication, highly repetitive behaviors, and significant intellectual disabilities. Because the diagnostic criteria were so narrow, the group of individuals diagnosed with autism looked incredibly different from the general, undiagnosed population. They represented the extreme outer edge of a spectrum of human behavior. But over the last few decades, our clinical criteria and societal awareness have undergone a profound evolution. We began to recognize that autism and ADHD are not binary conditions—you do not either have them or not in a simple black-and-white fashion. Instead, the traits associated with these conditions exist on a continuous spectrum that runs throughout the entire human population. Traits like social communication styles, sensory sensitivities, focus, hyperactivity, and executive functioning vary widely from person to person. As clinicians, researchers, and society grew to understand this spectrum, the criteria for what constitutes a diagnosis began to broaden. We realized that individuals with milder, more subtle variations of these traits also face real, significant challenges and can benefit immensely from clinical support, educational accommodations, and therapeutic interventions. Consequently, the guidelines used by healthcare professionals were updated, awareness among parents and teachers skyrocketed, and the stigma surrounding these diagnoses began to dissolve. This brings us directly to the findings of the massive Danish study. The researchers behind this study conducted an epidemiological cohort comparison, a powerful statistical method where scientists analyze large groups of people diagnosed with a condition at different points in time to see how the characteristics of those groups change. Specifically, the study compared children diagnosed with ADHD or autism today to children who received those same diagnoses ten years ago. What they discovered is both simple and profoundly revealing: children diagnosed with ADHD or autism today more closely resemble their peers in the general, undiagnosed population than those diagnosed ten years ago. Let us pause and really unpack what that means, because it is a vital statistical concept. Think of a classic bell curve representing a set of human behavioral traits, such as social communication styles or attentional control. In the general population, most people fall somewhere in the broad, average middle of the curve, while a small number of people fall at the extreme ends. Ten years ago, the diagnostic threshold for autism or ADHD was set very far out on that extreme end. The children who received a diagnosis were those whose behaviors were highly distinct and dramatically separated from the average middle of the bell curve. But as diagnostic patterns shifted and broader identification took hold, clinicians began setting the diagnostic threshold closer to the middle of the curve. They started diagnosing children with more moderate, subtle presentations of ADHD and autism. Because the diagnostic net was cast much wider, it began capturing children who, while still facing challenges, possess traits that are much closer to the average human baseline. As a result, when you look at the entire group of children diagnosed with ADHD or autism today, their average characteristics—their cognitive profiles, their social behaviors, their general functioning—are much more similar to the average of the general population than was the case for the highly distinct group diagnosed a decade ago. This finding is a game-changer for how we interpret the diagnostic surge. It strongly suggests that the rising rates of autism and ADHD do not simply reflect a sudden, mysterious increase in the underlying biological conditions themselves. Instead, the shift is driven in large part by changing diagnostic patterns and broader clinical identification. We are looking at the world with a much more sensitive, inclusive lens. Children who ten years ago might have been labeled as merely quiet, shy, hyperactive, or daydreamers are today being recognized as being on the autism or ADHD spectrum, allowing them to access support that was previously denied to them. However, the study also contains an important element of scientific caution. The researchers note that these shifting diagnostic patterns may *partly* explain the rising rates of diagnoses. In science, explaining uncertainty is just as important as reporting findings. The study does not rule out the possibility that there could also be a genuine, underlying increase in some biological or environmental factors contributing to these conditions. But what it does prove is that we cannot talk about the rise in ADHD and autism without acknowledging that the clinical definitions themselves have fundamentally expanded, drawing a much wider, more diverse, and less "atypical" group of children into the diagnosed population. This macro-level broadening of the diagnostic umbrella is a beautiful step forward for societal inclusion and support. But it also creates a major clinical challenge. If the labels of "autism" and "ADHD" are becoming wider and more diverse, how do we ensure that we are still identifying the highly specific, unique biological needs of the individuals within that massive group? This is where we must transition from the macro level of behavioral observations to the micro level of medical genetics, and look at the second major study in our shortlist. While behavioral diagnoses like autism are based on observing outward actions and traits, genetic diagnoses are based on identifying specific physical differences in our biological makeup. Over the past several years, geneticists have discovered that while autism is a incredibly broad behavioral spectrum, it is often underpinned by a wide variety of distinct, specific genetic disorders. One of the most significant of these is Phelan-McDermid syndrome. Phelan-McDermid syndrome is a genetic disorder that is closely, deeply linked to autism. Individuals with this syndrome often exhibit developmental delays, speech difficulties, and sensory processing differences that perfectly match the clinical criteria for an autism diagnosis. Because of this, if you look at a person with Phelan-McDermid syndrome through a purely behavioral lens, they will almost certainly be diagnosed with autism. For a long time, Phelan-McDermid syndrome was classified as an extremely rare, obscure condition—something that most doctors would rarely, if ever, encounter in their careers. But a major new analysis has completely shattered this assumption, revealing that this genetic disorder is actually far, far more common than scientists previously thought. According to the findings of this major analysis, Phelan-McDermid syndrome may affect about 1 in 7,300 people. To put that number into perspective, that means there are more than 45,000 Americans currently living with this genetic disorder. If you think about a condition that affects tens of thousands of people across a single country, that is no longer a rare, clinical curiosity. That is a significant public health reality. This statistical revelation immediately presents us with a profound mystery: If Phelan-McDermid syndrome is this common, affecting tens of thousands of people, why have we believed for so long that it was rare? Where are all of these people, and why are they not on our medical radars? The researchers behind the analysis provide a stark, urgent warning to explain this discrepancy: thousands of cases of Phelan-McDermid syndrome remain completely hidden because genetic testing is often not performed. To understand why this happens, we have to look at the typical real-world clinical journey of a family seeking answers for a child with developmental or behavioral challenges. When parents notice that their child is failing to meet language milestones, struggling with social interactions, or exhibiting highly repetitive behaviors, they take them to a specialist—a pediatrician, a psychologist, or a developmental neurologist. The specialist conducts behavioral assessments, observes the child, interviews the parents, and determines whether the child meets the clinical criteria for autism. Once that behavioral diagnosis of autism is made, the clinical workflow for many families and healthcare providers often comes to a complete halt. The focus shifts entirely to the immediate, practical steps of managing the child's challenges. The family works to secure special education services at school, speech therapy, occupational therapy, and behavioral interventions. Because autism is diagnosed behaviorally, and because the immediately available therapies are behavioral, many clinicians do not see a pressing need to investigate the underlying biological "why." They may view genetic testing as an expensive, unnecessary extra step that will not change the day-to-day management of the child's condition. If the behavioral therapies are going to be the same regardless of what is in the child's genes, why bother testing? As a result of this clinical habit, the genetic testing that could identify Phelan-McDermid syndrome is simply skipped. The child receives a generic diagnosis of autism, and their specific, underlying genetic disorder remains entirely invisible, hidden beneath the broad, expanding behavioral umbrella of the autism spectrum. They become one of the thousands of "hidden cases" warned about in the study. This omission of genetic testing might have been understandable in the past, but the new analysis reveals why it is rapidly becoming a critical, tragic bottleneck in modern medicine. The researchers highlight a massive paradigm shift currently taking place: targeted treatments for Phelan-McDermid syndrome are now moving into clinical trials. This is a vital concept that represents the future of medicine. To understand its importance, we must contrast symptomatic treatments with targeted therapeutics. A symptomatic treatment is designed to manage the outward signs or behavioral expressions of a condition. For example, if a child with autism or ADHD struggles with focus, anxiety, or sleep, a doctor might prescribe medications or behavioral strategies to help manage those specific symptoms. While these treatments are incredibly valuable, they do not change the underlying, physical biology of the condition. They are, in essence, addressing the smoke rather than the fire. A targeted treatment, however, is entirely different. It is designed to go straight to the root of the problem. In a genetic disorder like Phelan-McDermid syndrome, a specific genetic difference disrupts a precise biological pathway in the brain, leading to the developmental and behavioral differences we observe. A targeted treatment is engineered to address that specific, molecular pathway—aiming to correct, bypass, or compensate for the underlying genetic disruption. But here is the catch: targeted treatments can only work if we know exactly who needs them. You cannot treat a specific genetic pathway if you do not know the patient has that genetic variation. Currently, as these promising targeted treatments move into clinical trials, researchers need to recruit participants who have been genetically confirmed to have Phelan-McDermid syndrome. If thousands of individuals with this condition remain hidden because they were only ever given a broad behavioral diagnosis of autism and never received genetic testing, they cannot participate in these trials. They cannot help scientists test and refine these breakthroughs. Even worse, when these targeted treatments eventually complete their clinical trials and become approved, widely available medical therapies, those hidden individuals will completely miss out on life-changing, precise medical care. Because their medical charts only read "autism"—a broad, behavioral description—and not "Phelan-McDermid syndrome," no one will know that they are eligible for these highly specific, molecular treatments. Their under-testing will directly lead to under-treatment. When we step back and look at both of these studies together, we can see that they are not unrelated discoveries. Instead, they are two sides of the exact same coin, representing the dual fronts of a massive paradigm shift in how we understand neurodiversity. On one hand, the massive Danish study shows us that our behavioral definitions of neurodevelopmental conditions like autism and ADHD are expanding. This expansion is a positive, humanistic development. It means we are recognizing the vast diversity of human minds, identifying challenges earlier, and offering support to a wider, more varied group of people who resemble the general population. But on the other hand, the Phelan-McDermid analysis acts as a vital, urgent warning that we cannot rely *only* on broad, behavioral labels. Within that massive, expanding spectrum of individuals diagnosed with autism, there are distinct, biological subgroups that have highly specific genetic profiles. If we treat the entire spectrum as a single, uniform behavioral category, we risk leaving thousands of people behind. We risk failing to identify the individuals who have specific, treatable genetic conditions like Phelan-McDermid syndrome, denying them access to the targeted molecular therapies of tomorrow. The future of neurodevelopmental science and clinical practice lies in our ability to hold both of these truths at once. We must embrace the macro-level understanding of the spectrum—acknowledging that human behavioral traits exist on a wide, sliding scale and that diagnostic patterns are shifting to be more inclusive. At the very same time, we must aggressively pursue micro-level genetic precision. We must make genetic testing a routine, standard part of the diagnostic process for neurodevelopmental conditions, ensuring that we uncover the hidden genetic realities of the individuals within that spectrum. By combining the macro-level compassion of the spectrum with the micro-level precision of genetics, we can build a medical and social framework that truly supports every neurodivergent individual. We can provide broad behavioral support, educational accommodations, and societal acceptance to the entire spectrum, while simultaneously delivering precise, targeted, life-changing molecular treatments to those with specific genetic needs. Thank you for listening to this episode of the jFunk42 Science Brief. We hope this deep dive into the changing landscape of diagnostics and genetics has given you a clearer, more nuanced understanding of the incredible science shaping our view of the human mind. Until next time, stay curious, keep asking questions, and we will see you on the next brief.