What is Kennedy disease (KD)?

Updated: Sep 30, 2019
  • Author: Paul E Barkhaus, MD, FAAN, FAANEM; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

Kennedy disease (KD) is named after William R. Kennedy, MD, who described this entity in an abstract in 1966. The full report followed in 1968. [1] The history of this entity is summarized briefly here by way of a personal memoir from Dr Kennedy to the author.

Three months after completing his residency in neurology at the Mayo Clinic in 1964, Dr Kennedy examined a 57-year-old man of French and Native American ancestry from Minnesota who had been having problems with weakness for over 20 years. At that time, Dr. Kennedy had just taken a faculty position at the University of Minnesota where he has remained for his professional career. Other affected family members were identified, and an extensive pedigree developed. Dr Kennedy recalled, "This was an exciting patient! As a resident I had reviewed the entire Mayo Clinic film collection of patients, and every muscle and nerve biopsy taken before 1964, but I had not encountered this disease. I thought I knew how to document this patient. But I had never performed a muscle biopsy, had never photographed a patient, and had never used a motion picture camera."

Two months later, a similar patient, a 68-year-old man from Iowa, was referred for evaluation. Again, the patient's family history was positive, and Dr Kennedy noted that this patient's clinical picture closely resembled that of the previous patient. Evaluation of both families included his loading an electromyograph (EMG) into a car and driving to Iowa. (The present author had a similar experience when evaluating another affected family with Dr Kennedy in northern Minnesota in 1979. Performing clinical evaluations and EMG in the field is challenging work.)

Dr Paul Delwaide, a Belgian neurologist, first used the appellation Kennedy disease in a 1979 paper. [2] In the author's discussions over the years with Dr Kennedy, he tended to downplay the use of eponyms for diseases. When the author recently asked him again about "his disease," he admitted that now, as he grows older, "It feels kind of good."

In 1982, Harding et al reclassified the disease as X-linked bulbospinal neuronopathy to reflect the sensory conduction abnormalities noted in several of their cases. [3] Although the concept of the disease has been broadened, it remains an X-linked disorder with the hallmark of progressive weakness of the limb and bulbar musculature and is more commonly known as spinal and bulbar muscular atrophy (SBMA) . Additional neurologic features include sensory abnormalities, tremor of the upper extremities, and a quivering chin. A number of patients also have various endocrinologic abnormalities, such as diabetes, testicular atrophy, gynecomastia, oligospermia, and erectile dysfunction. [4]

In 1986, Fischbeck et al reported the genetic defect to be at the DXYS1 marker on the proximal long arm of the X chromosome. [5] This was later characterized as an expanded tandem (cytosine-adenine-guanine [CAG]) repeat in the first exon of the androgen receptor gene. [6, 7, 8]


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