His case histories of autistic savants leave a reader with strangely mixed feelings of incredulity and awe, sadness and delight - much the same effect that his extraordinary people have on those who share their daily lives.
Perhaps Treffert's best known subject is Leslie Lemke, a 37-year-old man whose baffling musical genius resides in the mind of an undeveloped child.
Leslie was profiled on "60 Minutes" in 1983, and no one who saw that segment is likely to forget it.
Clinically, Leslie's mental limitations are severe enough to certify him for an institution. Statistically, however, he is among the estimated 0.06 percent of the acutely impaired population who also fit the gifted savant syndrome.
But more about Leslie shortly. Since the same statistical estimates show only one autistic savant in seven is born female, let's first examine the even more extraordinary case of Harriet B.
Harriet was an obstreperous, destructive child with a measurable IQ of only 73. Diagnosed autistic, she did not talk until her ninth year.
But at seven months, Harriet astonished her father by spontaneously humming the showpiece Caro Nome aria from Verdi's "Rigoletto," negotiating its difficult coloratura runs with perfect pitch.
Five years before she said her first word, Harriet could play piano,
violin, clarinet, trumpet and French horn, though she'd never had a music lesson.
When Harriet finally did speak, she was able to recite the precise weather report for every day she'd heard it announced on the radio since infancy.
Harriet's grasp of the musical masterworks was encyclopedic. She could improvise at the piano in the style of one composer with her right hand while simultaneously ad-libbing in the style of yet another composer with her left hand. Her musicality was so sensitive, she would actually feel physical pain at the sound of a wrong note.
Tragically, this sensitivity eventually cost Harriet the unique little corner of genius her otherwise defective brain inhabited. When an injury forced her to stop playing at age 40, she was left confused and suicidal, and finally had to be institutionalized.
Fortunately, Leslie Lemke's life has encountered no such disruption, although it began with even less promise than Harriet's.
Given up for adoption at birth in 1952, Leslie spent his early infancy in the Milwaukee County Home for Children, where he lost his sight before he was 6 months old. When he was placed with his adoptive mother - an extraordinary person herself, by all conventional standards - Leslie was in such poor health, doctors feared he would soon die.
"Not in my house!" vowed May Lemke, then 55, with five grown children of her own.
In addition to being blind, a birth injury had left Leslie with cerebral palsy. Doctors said he'd never be able to use his left arm. But here, too, his foster mother refused to accept their prognosis.
Through instinct and inexhaustible patience, May Lemke developed a program of therapy that gave Leslie almost full use of the afflicted arm. With an improvised harness binding him to her waist - so he shared her every step - he also learned to walk.
Gradually, as if drawing on the force of her love, Leslie learned to talk and to sing. One night, May found him under the bed, plucking at the springs to coax tonal contrasts from their reverberations.
Again heeding instinct, she bought a used piano. Guiding his fingers, May watched Leslie swiftly master the keyboard. She didn't realize she had tapped into an inexplicable reservoir of genius!
Wednesday's column will examine that miracle.