Kennedy's disease (KD) or X-linked spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease associated with mutation of the androgen receptor (AR). The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify Diseases The following is a list of codes for International Statistical Classification of Diseases and Related Health Problems. The Mendelian Inheritance in Man project is a Database that catalogues all the known Diseases with a genetic component, and—when possible—links them The Diseases Database is a free Website that provides information about the relationships between medical conditions Symptoms, and Medications. eMedicine is an online clinical medical knowledge base that was founded in 1996 by Scott Plantz and Richard Lavely two medical doctors The androgen receptor ( AR) also known as NR3C4 (nuclear receptor subfamily 3 group C member 4 is a type of Nuclear receptor which is activated by Because of its endocrine manifestations related to the impairment of the AR, it can be viewed as a variation of the disorders of the androgen insensitivity syndrome (AIS). Androgen insensitivity syndrome (AIS also referred to as androgen resistance syndrome, is a set of disorders of Sexual differentiation caused by Mutations It is also related to other neurodegenerative diseases caused by similar mutations, such as Huntington's disease and the spinocerebellar ataxias. Kennedy's disease is named after W. R. Kennedy, a neurologist who was among the first to describe this disease.

Genetics

Kennedy's disease is inherited in an X-linked recessive pattern. Sex linkage is the phenotypic expression of an Allele that is related to the chromosomal sex of the individual

The androgen receptor gene that is mutated in Kennedy's disease is located on the X chromosome, and the effects of the mutation may be androgen-dependent, thus only males are fully affected. Females are rarely affected; female carriers tend to have a relatively mild expression of the disease if they show symptoms at all.

Pathology

Kennedy's disease patients have muscle cramps and progressive weakness due to degeneration of motor neurons in the brainstem and spinal cord.

As reported in 1991, Kennedy's disease is caused by expansion of a CAG repeat in the first exon of the androgen receptor gene (trinucleotide repeats). An exon is a Nucleic acid sequence that is represented in the mature form of an RNA molecule after a portions of a precursor RNA Introns have been The CAG repeat encodes a polyglutamine tract in the androgen receptor protein. The greater the expansion of the CAG repeat, the earlier the disease onset and more severe the disease manifestations. The repeat expansion likely causes a toxic gain of function in the receptor protein, since loss of receptor function in AIS does not cause motor neuron degeneration. KD may share mechanistic features with other disorders that are caused by polyglutamine expansion, such as Huntington's disease. There is currently no treatment or cure for Kennedy's disease.

Signs and symptoms

Ages of onset and severity of manifestations in affected males vary from adolescence to old age, but most commonly develop in middle adult life. The latest onset was described in a male of 84 years of age. KD does not usually compromise longevity. The syndrome has neuromuscular and endocrine manifestations:

Neuromuscular

Early signs often include weakness of tongue and mouth muscles, fasciculations, and gradually increasing weakness of limb muscles with muscle wasting. In some cases, premature muscle fatigue begins in adolescence. Neuromuscular management is supportive, and the disease progresses very slowly and often does not lead to extreme disability.

Neurological:

• Bulbar signs: The bulbar muscles are those supplied by the motor nerves from the brain stem, which control swallowing, breathing, speech, and other functions of the throat. Bulbar signs are problems with these muscles.
• Lower motor neuron signs: The lower motor neurons are those in the brainstem and spinal cord that directly supply the muscles. Loss of lower motor neurons leads to weakness and wasting of the muscle.
• Primary sensory neuropathy: Loss of sensation and numbness, usually not noticeable.
• Intention tremor: Hand tremor with volitional effort.
• Normal Babinski (plantar) response: When the bottom of the foot is scraped, the toes bend down. An abnormal response would be an upward movement of the toes indicating a problem with higher level (upper) motor neurons.
• Decreased or absent deep tendon reflexes: When a doctor taps the knee with his hammer little or nothing happens.

Muscular:

• Fasciculations: Twitching of muscles when at rest.
• Cramps: Large muscle spasms.
• Muscular atrophy: Loss of muscle bulk that occurs when the lower motor neurons do not stimulate the muscle adequately.

Thoracic:

• Gynecomastia: Breast enlargement.

Endrocrine

• Androgen insensitivity: Loss of masculinizing effect.

Genito-Urinary:

• Impotence
• Erectile dysfunction
• Reduced fertility
• Low sperm count
• Testicular atrophy: Testicles become smaller and less functional.

Miscellaneous Characteristics:

• Late onset: Patients usually develop symptoms in the late 30's or later.
• Slow progression: Nearly normal lifespan
• Symmetry of clinical signs: Muscles are usually affected symmetrically.

Homozygous females

Homozygous females, both of whose X chromosomes have a mutation leading to CAG expansion of the AR gene, have been reported to show only mild symptoms of muscle cramps and twitching. No endocrinopathy has been described.

History

This disorder was described by Kennedy in 1968. In 1991 it was recognized that the AR is involved in the disease process. The disease is probably more common than originally thought. A study in Scandinavia suggested a prevalence of 1. 3/8,500 making KD the most common form of motor neuron disease in the specific area studied; nobody had been diagnosed before 1995. It has been suggested that some men with KD may be misdiagnosed to have amyotrophic lateral sclerosis (ALS, also Lou Gehrig's disease). Amyotrophic Lateral Sclerosis ( ALS, sometimes called Maladie de Charcot, or in the United States Lou Gehrig's Disease) is a progressive

References

• Kennedy WR, Alter M, Sung JH. Progressive proximal spinal and bulbar muscular atrophy of late onset: a sex-linked recessive trait. Neurology 1968;18:671-680. PMID 4233749.
• La Spada A, Wilson EM, Lubahn DB, Harding AE, Fischbeck KH. Androgen receptor gene mutations in X-linked spinal and bulbar muscular atrophy. Nature 1991;352:77-79.
• Fischbeck KH, Lieberman A, Bailey CK, Abel A, Merry DE. Androgen receptor mutation in Kennedy's disease. Phil Trans R Soc Lond B 1999;354:1075-1078.
• Chen CJ, Fischbeck KH: Clinical aspects and the genetic and molecular biology of Kennedy's disease. In: Wells RD, Ashizawa T (eds. ): Genetic Instabilities and Neurological Diseases, Second Edition. San Diego, Academic Press/Elsevier, 2006

External links

• kennedysdisease.org for more information on Kennedy's disease
• http://www.med.upenn.edu/taylor/ for information on Kennedy's Disease research