Late diagnosis in severe and mild intellectual disability in adulthood.
One extra diagnostic round in adulthood can still find the missing cause for a quarter of adults with ID.
01Research in Context
What this study did
Kittler et al. (2004) looked at Finnish adults who already carried an intellectual disability label. The team ran a fresh round of genetic, metabolic, and brain-imaging tests to see how many still lacked a clear cause.
They treated the work-up as a clinical service, not an experiment. Every adult got the same step-by-step protocol.
What they found
One in four adults still had no known reason for their disability years after the first diagnosis. Missing a cause meant missing targeted care and family counselling.
When a cause was finally pinned down, families could receive accurate risk information and, in some cases, specific medical follow-up.
How this fits with other research
Konstantareas et al. (1999) built a tree-style checklist that maps each cause to the time the brain was injured. P et al. used that same logic to guide their adult testing, showing the old tool still works in grown-ups.
DeRoma et al. (2004) studied Pakistani children and also found half of mild cases had no known cause. The two papers together suggest the gap is global and lasts across the lifespan.
Warburg (2001) warned that visual problems in adults with ID are missed even more often. Add P’s 24 % unknown aetiology and you get a double blind spot: we may be overlooking both the cause and a treatable side-effect.
Why it matters
If you serve adults with ID, do not trust the dusty file. Ask for a fresh genetics or metabolic consult whenever the record says ‘cause unknown.’ One referral can turn ‘undiagnosed’ into a care plan and give the family facts they can use.
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02At a glance
03Original abstract
BACKGROUND: The diagnosis of intellectual disability (ID) is highly dependent on a comprehensive personal and family medical history, a complete physical examination and a careful developmental assessment of the patient. Our study intended to: (1) classify the aetiology of mild and severe ID in an adult population of 140 Italian subjects; (2) evaluate the frequency of associated medical conditions; (3) evaluate the age of diagnosis in both groups; and (4) underline the importance of aetiological diagnosis for adult ID patients also. METHODS: The study involved 140 consecutive adult Italian ID inpatients and outpatients neurologically investigated at the Neurological Institute C. Mondino of Pavia Service for Mental Retardation. A total of 80 patients had mild ID (MID group) (39 females, 41 males), mean age 34 years (range 19-61 years), mean IQ = 64 (range 51-75), and 60 had severe ID (SID group) (32 females, 28 males), mean age 30 years (range 19-69 years). They underwent a complete diagnostic work-up that comprised prenatal, perinatal and postnatal history, physical examinations, laboratory investigations, genetic survey and neuroradiological investigations to determine the aetiology of ID and to evaluate the presence of associated medical conditions. RESULTS: ID aetiology was classified as prenatal in 34% of the MID and 28% of the SID group. Perinatal and postnatal events were found in 6% of the MID and in 5% of the SID group. Associated medical conditions were found in 97 patients (47% MID and 26% SID). A genetic diagnosis was possible in 6% of patients above 20 years of age and in 5% of patients above 40 years. A diagnosis of cerebral dysgenesis was possible in 5% of patients above 20 years and 4% of patients above 40 years. CONCLUSIONS: A long interval between the diagnosis of ID and the aetiological definition can be observed in a significant percentage (24%) of our population, leading to unfortunate consequences of late diagnosis: late onset of a specific therapeutic program, genetic counselling that is frequently no more useful, and ineffective prenatal diagnosis, leading to the birth of other affected subjects (for familiar ID).
Journal of intellectual disability research : JIDR, 2004 · doi:10.1111/j.1365-2788.2003.00593.x