The etiology of substance-induced psychotic disorder (SIPD) is an important research area to study.

It is aimed to investigate clinical risk status for psychosis, schizotypal features and neurocognitive functions in siblings of the patients who have been diagnosed as SIPD and who have no family history of psychotic spectrum disorder.

This study included 41 healthy siblings of patients who have been diagnosed as SIPD according to DSM-V and 41 healthy controls without family history of psychiatric disorders (matched on age, gender, and years of education). The data collected with sociodemographic and clinical data form, Digid Span Test, Trail Making Test A, Trail Making Test B, Verbal Fluency Test and Stroop Test, Comprehensive Assesment of At-Risk Mental States (CAARMS) and Structured Interview for Schizotypy-Revised.

It is determined that %41.5 of siblings and %7.3 of healthy controls are in one of the clinical high risk groups for psychosis according to CAARMS. There is significant difference in Trail Making Test A error and Trail Making Test B error and correction, verbal fluency test- lexical fluency-perseveration mean scores between siblings of patients and healthy controls.

Siblings of patients with SIPD have more schizotypal features than healthy control group and they take part more frequent in one of high risk group for psychosis. Schizotypal features are known as trait factor and show genetic predisposition. Siblings who are in high risk groups have more schizotypal features and it may point that predisposition to psychosis is more related to underlying genetic predisposition than environmental factors and social stressors.

No significant relationships.

Advanced paternal age is associated with increased risk of schizophrenia. This study aimed to explore whether older paternal age is associated with earlier onset among co-affected schizophrenia sib-pairs with the same familial predisposition.

A total of 1297 patients with schizophrenia from 630 families, which were ascertained to have at least two siblings affected, throughout Taiwan were interviewed using the Diagnostic Interview for Genetic Studies. Both inter-family comparisons, a hierarchical regression model allowing for familial dependence and adjusting for confounders, and within-family comparisons, examining the consistency between onset order and birth order, were performed.

An inverted U shape was observed between paternal age and onset of schizophrenia. Affected offspring with paternal age of 20–24 years had the oldest onset. As paternal age increased over 25 years, older paternal age exhibited a linear decrease in the onset of schizophrenia. On average, the onset was lowered by 1.5 years for paternal age of 25–29 years and by 5.5 years for paternal age ⩾50 years (p = 0.04; trend test). The proportion of younger siblings with earlier onset (58%) was larger than that of older siblings with earlier onset (42%) (p = 0.0002).

These findings indicate that paternal age older than 25 years and younger than 20 years were both associated with earlier onset among familial schizophrenia cases. The associations of advanced paternal age with both increased susceptibility to schizophrenia and earlier onset of schizophrenia are consistent with the rate of increases in spontaneous mutations in sperm as men age.