Child molesters, exhibitionists and rapists have a "surprising number" of biological abnormalities that may help account for their deviant sexual behavior, according to a preliminary study by Johns Hopkins University researchers.

"This raises a lot of questions about the nature of unconventional sexual compulsions," says Dr. Fred S. Berlin. "Early life experiences may be a factor, but there is suggestive evidence that this is not the whole story."

In a preliminary study, Berlin found that 31 out of 41 men diagnosed with sexual disorders had one or more biological abnormalities. Fourteen had elevated levels of the male hormone testosterone, and seven had chromosomal defects, including several with Klinefelter's syndrome. Klinefelter's syndrome is an inherited chromosomal trait. Its possessors have an extra female sex chromosome and appear to be boys, but develop some feminine characteristics at puberty and have lower levels of testosterone.

Testosterone, the hormone which is principally responsible for male sex characteristics at puberty, has been studied primarily by doctors attempting to solve fertility problems and impotence, according to Berlin. Some researchers have claimed that high levels of testosterone are linked to aggression, but these statements have not been conclusively proved, he said.

Klinefelter's syndrome, first described in 1942, is associated with low levels of testosterone. Although it has been studied by medical researchers, Berlin noted that little is known about the prevalence of sex-related disturbances in this group. He said, however, that in prison populations, there have been observations of a high number of patients with chromosomal disorders, including Klinefelter's syndrome.

How these biological characteristics of sex offenders might be related to their offenses, if at all, is so far unknown. But the intriguing results of the preliminary research have led the Hopkins Biosexual Psychohormonal Clinic to launch an unusual large-scale study that will allow researchers to look at the brains of hundreds of male sex offenders.

The Hopkins researchers will take advantage of a new brain-scanning machine that allows scientists to watch regions of the working brain for the first time using PET--or Positron Emission Tomography--an expensive technique available at only a handful of U.S. research centers.

Berlin, a psychiatrist who is co-director of the well-known Hopkins clinic, said that starting next spring he plans to study 25 sex offenders a year over a five-year period and compare them with a control group of heterosexual men. He will see if there are any differences in the way their brains function.

"It is a speculative question, but the PET scanner may give us some answers. It will provide the opportunity to study the brains of people with conventional and unconventional sexual preferences. We will be able to observe brain metabolism under controlled conditions, to see what differences exist."

Berlin spoke today at a science writers' seminar celebrating the opening of a new Center for Psychiatry and the Neurosciences. Hopkins' medical school is one of the first to join research and patient care in psychiatry and neurosciences under one roof.

In addition to PET measurements, the comparative study will use more conventional brain scanning equipment to measure brain structure and sample male and female sex hormone levels, brain electrical activity, and genetic makeup.

In addition to seeking a better understanding of the possible biological contributions to sexual identity, Berlin plans to do a controlled study of the use of drug treatment as a "sexual appetite suppressant."