When children have intellectual and developmental disabilities (IDD), doctors often turn to genetic testing for answers. They trust that genetics can help them gather information and find a diagnosis. Unfortunately, the same can’t be said for adults with similar conditions. Doctors rarely consider genetic evaluations for adults with IDD. Whether due to outdated clinical guidelines, limited awareness of adult testing benefits, or a lack of nearby clinical geneticists, genetic testing is much less common for adults with IDD.

At SequenceMD, we recently dug into data from our clinic to learn more about the impact of genetic evaluations on adults with IDDs. In particular, we set out to study the diagnostic and clinical values of modern genetic testing technologies for these patients. This post outlines what we learned and how we arrived at our conclusions.

Our Data

Our team looked at data from 69 adults who underwent genetic testing at SequenceMD between 2022 and 2024. The patients ranged from 18 to 83. They were all referred to us due to signs of an intellectual or developmental disability. Everyone included had a neurodevelopmental (NDD) assessment and received genetic test results. We did not include any patients who already had a confirmed IDD diagnosis. We also excluded patients whose test results were pending.

Our Findings

We presented our research and findings at the 2025 ACMG Annual Clinical Genetics Meeting. Here is some of what we shared.

37.7% Diagnosis Rate

Of the 69 patients, 26 gained a diagnosis via genetic testing. That’s 37.7% of the people tested. This diagnostic rate for adults is on par with what is expected when testing children. Among the SequenceMD patients, adults over 50 had the highest diagnostic rates.

Comprehensive Testing Performed Best

Whole exome or genome sequencing (WES/WGS), the most thorough type of genetic testing, was responsible for 19 diagnoses (73% of the total). WES/WGS had the highest diagnostic efficiency and was almost three times more efficient than gene panels. WES/WGS also required fewer follow-ups and had a broader clinical impact. Although gene panels were widely ordered (with 68 tests in total), they produced fewer definitive diagnoses.

Clear Benefits of Genetic Diagnosis

For 27.5% of our patients, a genetic diagnosis led to improved immediate management and surveillance of their condition. Patients were able to start targeted therapies they weren’t receiving before. In 15% of cases, patients benefited from actionable medication implications. 

For 34.8% of our patients, the genetic diagnosis gave doctors the insights to start preventive care. These disease-specific monitoring protocols, screenings, and risk-reduction strategies can reduce healthcare costs and improve outcomes. The diagnoses also helped link patients to specialists for their care.

The diagnosis helped 37.7% of patients with long-term personal and family planning. This ranged from starting reproductive counseling to coordinating resources and social services for current and future support. Multiple families also did cascade testing to learn if they shared the genetic mutation. 

Broad Spectrum of Disorders

Genetic testing revealed a variety of conditions among the 69 adults. Three patients also received a dual diagnosis. Categories for the 29 conditions we found are below.

  • Neurological Disorder: 34.5% (10/29)
  • Deletion/Duplication Syndrome: 27.6% (8/29)
  • Monogenic Syndrome: 24.1% (7/29)
  • Cerebrovascular Malformation: 3.4% (1/29)
  • Endocrinopathy: 3.4% (1/29)
  • Inborn Error of Metabolism: 3.4% (1/29)
  • Mitochondrial Disorder: 3.4% (1/29)

Systemic Barriers and Equity

Adults in more remote areas are unlikely to have access to genomic services nearby, limiting their ability to receive care. In our study, 83% of the patients lived within 50 miles of our Denver clinic. Insurance is also vital in allowing patients to receive testing, with 46.8% of the patients tested using Medicaid. Commercial providers such as BCBS, Cigna, and United evenly distributed the other insurance providers.

Our Conclusions and Recommendations

Our study reaffirms that genetic testing in adults with IDD can have diagnostic yields on par with pediatrics, especially when using WES/WGS. The diagnoses provided real value to our patients, including immediate therapeutic interventions. Patients also started preventive care likely to reduce costs and morbidity. Additionally, patients were connected with valuable support services and gained insights for themselves and their families. As the science continues to improve, follow-up visits can also help give patients increasingly personalized and effective care.

While geographic disparities remain an obstacle, we believe telemedicine and regional genetics outreach could bridge this gap. Insurance can also be a barrier. The dominance of Medicaid in our study highlighted that many adults with IDD face socioeconomic challenges. It is important that insurance of all types cover these tests, particularly WES/WGS. 

By embracing these diagnostic tools and addressing barriers such as insurance limitations and geographic access, care providers can achieve higher diagnostic yields, meaningful clinical interventions, and improved patient outcomes. Ultimately, comprehensive genetic testing offers both cost savings and enhanced care quality for these underserved adults.

Learn more about our research and the ACMG presentation here: https://sequencemd.com/genetic_testing_in_adults_poster/