Non-concordance by gender for schizophrenia and related disorders in sibships.

We analysed gender-concordance rates among 29 prospectively sampled schizophrenic probands and their 39 affected and 71 unaffected siblings. We did not find any unusual concordance rates. We found no same-gender concordance particularly in siblings affected by schizophrenia and related disorders. We considered unaffected siblings in an additional attempt to make valid and unbiased comparisons between genders, but this reduced the number of informative sibships to 20. We stratified the siblings of probands by sibship and by the proband's gender in order to check gender distribution within families. The data do not support hypotheses that schizophrenia is pseudo-autosomal or male-female chromosomally transmitted.