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Rett syndrome

Rett Syndrome Definition

Rett syndrome is a rare genetic disorder linked to a mutation in the gene, MECP2, on the X chromosome.

Genetic Info

It typically affects girls and usually recognized in children aged 6 to 18 months. Some of the symptoms include loss of speech, loss of purposeful use of hands, loss of mobility (or gait impairment),  Rett “episodes” (seizures), scoliosis, breathing impairment, and sleep disturbances. (Ref.1) The severity of the condition depends on the location, type, and extent of the mutation and X-inactivation. (Ref. 1)

The syndrome was first described by Andreas Rett, a pediatrician, in 1954. He noticed that his patients who were girls were making the same repetitive behavior, i.e. doing hand-washing motions, and having similar developmental and clinical histories.  Thus, he went on to find similar cases throughout Europe and published his medical findings in 1966. (Ref. 2) In 1960, Bengt Hagberg similarly found the same symptoms in some of the girls and published about it in 1982. Hagberg described 35 patients, all girls from 3 countries (France, Portugal, and Sweden), with a uniform and striking, progressive encephalopathy. After normal development up to the age of 7 to 18 months, developmental stagnation occurred, followed by rapid deterioration of high brain functions. Within 1.5 years this deterioration progressed to severe dementia, autism, loss of purposeful use of the hands, jerky truncal ataxia, and ‘acquired’ microcephaly. Thereafter, a period of apparent stability lasted for decades. Additional neurologic abnormalities intervened insidiously, mainly spastic paraparesis, vasomotor disturbances of the lower limbs, and epilepsy. A striking deceleration of growth has been found across all measurements in 85 to 94% of girls with Rett syndrome and may provide the earliest clinical indication of this disorder. Hagberg estimated that the frequency of the disorder was about 1:15,000 in southwestern Sweden. Hagberg’s report incited increased awareness of the condition. Later, the condition was named Rett syndrome in honor of Andreas Rett as the pioneering researcher. (Ref.2 ) In 1999, the mutant gene associated with the condition was identified by Ruthie Amir, a research fellow at Baylor University in Houston, Texas. The gene was at the Xq28 site on the X chromosome. Rett syndrome, thus, is an X-linked dominant disorder. (Ref. 2)

The metabolic rate in patients with Rett syndrome is often lower while sleeping but rates while actively awake do not differ between affected and control groups. The presence of metatarsal and metacarpal abnormalities in some patients with Rett syndrome prompted radiologic studies of 17 cases. Short fourth and/or fifth metatarsals were identified in 11 (65%) and short fourth and/or fifth metacarpals in 8 of 14 (57%). Reduced bone density in the hands was found in 12 of 14 cases (86%). The exclusive involvement of females is best explained by X-linked dominant inheritance with lethality in the hemizygous males. By this hypothesis, all cases are new mutations. One instance of 2 affected half-sisters born to the same mother is known. This is explicable on the basis of gonadal mosaicism or X-autosome translocation in the mother. However, no chromosomal abnormality was found. Another possible mechanism for only female cases is the so-called metabolic interference. According to this suggestion, the homozygous female and the hemizygous male are normal, the heterozygous female is abnormal because of an adverse interaction of the gene products from the two X chromosomes. Because of lyonization, these products would be produced in different cells.

Pathology

Light-microscopy shows evidence of white matter disease and ultrastructurally, many neurons and oligodendroglia contained membrane-bound electron-dense inclusions with a distinct lamellar and granular substructure with a striking decrease in the dendritic trees of selected cortical areas, chiefly projection neurons of the motor, association, and limbic cortices.

Clinical features:

  • progressive encephalopathy
  • severe dementia
  • autism
  • loss of purposeful hand use
  • jerky truncal ataxia
  • spastic paraparesis
  • vasomotor disturbances of legs
  • seizures
  • acquired microcephaly

Inheritance: x-linked dominant with lethality in hemizygous males.

Incidence: approximately 1 in 15,000

References:

  1. What is Rett Syndrome? | Rettsyndrome.org. (2019, August 5). Rettsyndrome.Org. https://www.rettsyndrome.org/about-rett-syndrome/what-is-rett-syndrome/#:~:text=Rett%20syndrome%20is%20a%20rare,near%20constant%20repetitive%20hand%20movements.
  2. History of Rett | Rettsyndrome.org. (2020, April 23). Rettsyndrome.Org. https://www.rettsyndrome.org/about-rett-syndrome/history-of-rett/