Increased familiarity of intellectual deficits in early-onset schizophrenia spectrum disorders

Abstract

Objectives. Early-onset schizophrenia is considered to be neurobiologically similar to adult-onset forms, although it represents a more severe expression of the disorder. In the present study, we explored putative larger familial vulnerability of intellectual impairments in early-onset schizophrenia spectrum disorders (EOS) when compared to adult-onset (AOS) families. Methods. A sample of 340 subjects including schizophrenia spectrum disorder patients, their first degree relatives and age-matched healthy controls was assessed on intelligence quotient (IQ). We used linear regression analysis and intraclass correlation coefficients (ICC) to explore familial aggregation of IQ across age at onset groups. Results. The relationship between IQ level of patients and their first-degree relatives showed positive linear association (β = 0.43, P < 0.01). High significant familial aggregation was found for intelligence quotient in EOS families (ICC = 0.618, P < 0.01), while AOS families responded to lower estimates (ICC = 0.204, P = 0.26; between ICC comparison z = 1.993, P < 0.05). Conclusions. High aggregation of intellectual performance in the EOS group suggests larger familial vulnerability in early-onset forms of the disease when cognitive functions are considered. Within a continuum of psychopathology in schizophrenia spectrum disorders, specific genetic effects are discussed for distinct onset forms that might be in line with a neurodevelopmental model of the disease.

Key words::

• Schizophrenia
• early-onset
• intelligence
• vulnerability
• genetics

Acknowledgements

We are deeply grateful to all the participants, whose generosity made this work possible. Ximena Goldberg was supported by a Marie Curie grant from the EUTwinsS Research Training Network, Barcelona Node (European Twin Study Network on Schizophrenia – MRTN-CT-2006-035987).

Funding for this study was provided by: (i) Fundación Alicia Koplowitz (2006), (ii) Ministerio de Ciencia e Innovación (SAF2008-05674-C03-01), (iii) NARSAD - Senior Award (2008), (iv) Ministerio de Ciencia e Innovación, Instituto de Salud Carlos III, Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), (v) Fundació La Marató de TV3 (014430/31). Thanks to Comisionat per a la Universitats i Reserca del DIUE (SGR827).

All funding sources had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Statement of Interest

None to declare