Elevated rates of schizophrenia in a familial sample with mental illness and intellectual disability.
In families where one member has mild ID, schizophrenia shows up twice as often as mood disorders, so screen early.
01Research in Context
What this study did
Cerutti et al. (2004) looked back at family trees of people with mild intellectual disability (ID).
They counted how many relatives had schizophrenia versus mood problems like depression or bipolar.
The goal was to see if schizophrenia runs in these families more than other mental illnesses.
What they found
Relatives had almost twice as much schizophrenia as mood disorders.
This pattern showed up strongest in families where the main person had mild ID.
How this fits with other research
Ghaziuddin (2005) found a similar schizophrenia signal in Asperger families, stretching the idea beyond ID.
Kirby et al. (2024) followed kids with mild ID into adulthood and saw 56% develop any psychiatric disorder, giving forward-looking weight to the family risk.
Pakenham et al. (2004) reminds us that many early "psychosis" labels in youth with ID get overturned after careful review, so families may talk about symptoms that were never true schizophrenia.
Why it matters
When you assess an adult or teen with mild ID, ask about relatives with schizophrenia. If the family history is positive, watch closely for early signs like social withdrawal, odd beliefs, or hallucinations. A quick screen can lead to faster psychiatric referral and better support for both the client and the family.
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02At a glance
03Original abstract
BACKGROUND: It is unknown whether intellectual disability (ID) is more familially related to psychotic mood disorders or schizophrenia. L. S. Penrose's large sample of families with two or more members admitted to psychiatric hospitals provided a unique opportunity to investigate the familial relationship between mild ID, schizophrenia and psychotic affective disorders. METHOD: There were 183 affected relative pairs comprising probands with mild ID (95 male, 88 female) and their first or second degree relatives with schizophrenia or psychotic affective disorder. RESULTS: There were nearly twice as many relatives with a diagnosis of schizophrenia (n = 121) as relatives with affective disorders (n = 62) among the intellectually impaired probands. This excess of schizophrenia was statistically significant, even after accounting for the increased risk of hospitalization for schizophrenia (P = 0.005), and was fairly constant across the different relative types. First-degree relatives with either mental illness were more likely to be parents (n = 77) than siblings (n = 51) or children (n = 3), but there was no excess of mother-son pairs. CONCLUSIONS: These results suggest a stronger familial relationship of ID with schizophrenia than psychotic affective disorder, and lend some support to the neurodevelopmental hypothesis of schizophrenia.
Journal of intellectual disability research : JIDR, 2004 · doi:10.1111/j.1365-2788.2004.00621.x