Retrospective Reports of Skill Attainment and Loss in Phelan-McDermid Syndrome.
Expect both early delays and later skill regression, even after age 10, in Phelan-McDermid syndrome.
01Research in Context
What this study did
Farmer et al. (2025) asked parents to look back and list when their kids gained or lost skills.
They collected reports on 581 people with Phelan-McDermid syndrome, a rare genetic condition that causes severe delays.
Parents noted if a skill appeared, stayed, or disappeared at any age.
What they found
Almost everyone learned milestones late, and many lost skills they once had.
Skill loss still happened after age 10, long after most kids stop regressing.
The picture is mostly negative: delays plus later setbacks.
How this fits with other research
Schertz et al. (2016) saw a similar late slide in Williams syndrome: IQ held steady, but daily-living scores dropped in the teen and adult years.
Austin et al. (2015) found the opposite trend in preschool autism: big IQ gains and small adaptive jumps between diagnosis and kindergarten.
Together the papers draw a lifespan map. Early childhood can bring fast gains in some disorders, yet single-gene syndromes like Phelan-McDermid and Williams can still show fresh losses in adolescence or adulthood.
Why it matters
Do not assume a teen with Phelan-McDermid has plateaued. Build adaptive-skill goals into the teen and adult plans, and watch for new losses. Re-assess often, add supports quickly, and teach replacement skills before gaps widen.
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02At a glance
03Original abstract
Phelan-McDermid syndrome (PMS) is a genetic condition associated with profound neurodevelopmental disabilities. This study described patterns of onset and loss of developmental milestones and associated skills using questionnaire data from the PMS International Registry (N = 374) and clinician-led assessment data from the Developmental Synaptopathies Consortium natural history study (N = 207). Across studies, an overwhelming proportion of people with PMS were reported to have delays in acquiring basic skills, and regression or loss of skills was commonly reported across multiple developmental domains, including some after the age of 10. The current descriptive study synthesizes two complementary data sources showing loss occurring in the context of significant delays and frequent lack of milestone attainment in people with PMS. Further work to elucidate mechanisms is needed.
American journal on intellectual and developmental disabilities, 2025 · doi:10.1352/1944-7558-130.5.362