Analysis of phenotypic variation in psoriasis as a function of age at onset and family history

To evaluate the relationship between psoriasis disease severity, age at onset, and family history, we analyzed 537 US psoriatics, most of whom were from Michigan. Total body surface area involvement (%TBSA), presence or absence of joint complaints, and nail involvement were measured. Analysis of familial psoriatics revealed that %TBSA was 15.1% when onset was early, but only 8.7% when onset was late ( P=0.00003). The opposite trend was seen when psoriasis was sporadic: %TBSA was 14.3% when onset was early (