Down's syndrome

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Mental retardation due to trisomy of chromosome 21, associated with characteristic facies and habitus.

Description

Down’s syndrome is one of the most common causes of mental retardation. It is due to trisomy of chromosome 21. Its main features are mental retardation and associated characteristic facies and habitus.
The affected person is usually of short stature, 145-160 cm for adults. Birth weight usually 10-20 % below normal. Sloping forehead, small ear canals, grey or very light yellow spots as periphery or iris (Brushfield’s spots), short broad hand with a single palmar crease (simian crease), a flat nose or absent bridge, low-set ears, and generally dwarfed physique.

Mental retardation (100 %) becomes evident to parent at end of first year of life. The intelligence quotient in adults is most often below 50. Usually, child is happy, affable, and affectionate; walking; speech, and toilet training delayed until 2 to 3 years of age. Delayed puberty, early menopause.

Some patients (ca 2,4 %) show mosaicism - a mixture of normal and trisomic cell lines - and in them the IQ can be in the 70s and the physical abnormalities may not be so marked.

Patients who survive into the fourth and fifth decades develop the pathological changes of Alzheimer’s disease of the brain.

The only known etiological factor is high birth age. Women at high risk of giving birth to a child with Down syndrome are those over 40; those who have had a previous child with the syndrome; and those who themselves have Down syndrome (pregnancy is rare in this condition).

The occurrence of Down syndrome per 1000 living births is approximately 0,5 for a woman under 25 years of age, 0,7 under the age of 30, 5 under 35 years, 25 under 40 years, and 34,6 for mothers over the age of 45. Still, against popular belief, most children with Down’s syndrome are born to young mothers: 51 % to mothers under 30, 72 % to women under 35.

The deviation is registered in all races and affects both sexes. The term mongolism comes from the upward slanting eyes which give the impression of an oriental person. The typical phenotype is recognisable in pictures from the middle ages.

When Down in 1866 described the syndrome that bears his name he was surprised that it had not been described earlier. Later investigations in medical history, however, have proved him wrong. The first description was made in 1838 by Jean Etienne Dominique Esquirol (1772-1840), a founder of modern alienism. Another clinical description was made by Édouard Séguin (1812-1880) in 1844. Langdon Down did a more elaborate description in 1866. The chromosome aberration was discovered in 1959 by the French human geneticist Jérôme Jean Louis Marie Lejeune (1926-1994).

    «The face is flat and destitute of prominence. Cheeks are roundish and extended laterally. The eyes are obliquely placed and the internal canthi more than normally distant from one another. The palpebral fissure is very narrow. The lips are large and thick with transverse fissures. The tongue is long, thick and much roughened. The nose is small.»
See also Siegert's sign, under Ferdinand Siegert, German paediatrician, 1865-1946.

Bibliography

  • Jean Etienne Dominique Esquirol:
    Des maladies mentales considerées sous le rapport médicale, hygiènique et médico-legal.
    2 volumes and atlas. Paris, J. B. Baillière, 1938.
    Esquirol succeeded Philippe Pinel (1745-1826) at Salpêtrière, and was the first lecturer on psychiatry. After Pinel he was a founder of the French School. This is the first modern textbook on psychiatry. It is notable for its striking illustrations of the insane.
    On page 264, volume 2, is a classic description of paresis. Esquirol regarded general paralysis as a complication of various forms of mental disorder.
    English translation, without illustrations, Philadelphia 1845. Reprinted 1965.
  • Édouard Séguin:
    Traitement moral, hygiène et éducation des idiots et des autres enfants arriérés. Paris, Baillière, 1846.
    Séguin was the first to outline a complete plan for the training of mental defectives.
  • J. L. H. Down:
    Marriages in Consanguinity in Relation to Degeneration of Race.
    Clinical lectures and reports by the medical and surgical staff of the London Hospital, 1866, 3: 224-236.
  • Patricia A. Jacobs and J. A. Strong:
    A Case of Human Intersexuality Having a Possible XXY Sex-determining Mechanism. Nature, 1959, 183: 302-303.
    Jacobs and Strong discovered the chromosome aberration independently of Lejeune et al.
  • J. Lejeune, R. Turpin and M. Gautier:
    Le mongolisme. Premier example d'aberration autosomique humaine.
    Annales de génétique, Paris, 1958/1959, 1: 41-49.
  • J. Lejeune, Marthe Gautier, and Raymond Alexandre Turpin:
    Mongolisme; une maladie chromosomique (trisomy).
    Bulletin de l'Académie nationale de médecine, Paris, 1959, 143, 256-265.

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