Fragile X Mental Retardation Syndrome

Alternative Names

  • Fragile X Syndrome
  • Mental Retardation, X-Linked, Associated With marXq28
  • X-Linked Mental Retardation and Macroorchidism
  • Marker X Syndrome
  • Martin-Bell Syndrome
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WHO-ICD-10 version:2010

Congenital malformations, deformations and chromosomal abnormalities

Chromosomal abnormalities, not elsewhere classified

OMIM Number

300624

Mode of Inheritance

X-linked dominant

Gene Map Locus

Xq27.3

Description

Fragile X Syndrome is the most common inherited form of mental retardation among all racial and ethnic groups. It is so named, because in patients with this syndrome, the X chromosome appears to be physically constricted at a point, giving it a fragile appearance. The disease affects boys more severely than girls. Affected patients display mental impairment, ranging from learning disabilities to mental retardation, attention deficit and hyperactivity, anxiety, and occasional seizures. DNA testing for detection of Fragile X Syndrome has been available since 1992.

Fragile X syndrome is generally associated with a fragile site at Xq 27.3, which can be observed in the metaphase chromosome following selective culture conditions. At the molecular level, the fragile X syndrome is associated with an amplification of CGG repeat sequence of the FMR1 gene. 

Epidemiology in the Arab World

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Other Reports

Bahrain

Al-Arrayed and Mohammed (1990) described a Bahraini family in which four of its eight male children were diagnosed with Fragile X Mental Retardation Syndrome. 

Kuwait

Tayel et al. (1999)  screened 306 adult males suffering from inherited mental retardation of unknown etiology (MROUE) for features correlated with Fragile X syndrome  in Kuwait. DNA analysis confirmed that 20 out of 182 mentally retarded patients were positive for fragile X syndrome, giving an incidence of 11% among Kuwaiti patients. Eleven subjects were found to be cytogenetically positive for Fragile X syndrome. 

[Tayel SM, Al-Naggar RL, Bastaki L, Ali FE, Al-Wadaani MA, Al-Awadi SA. Two-step fragile x-screening programme in mentally retarded males. The Kuwait Medical Journal 1999, 31 (3): 257-262.]

In 2004, Bastaki et al. conducted a prospective study that included 182 mentally retarded male patients who fulfilled 5 or more clinical criteria of fragile X syndrome.  DNA analysis confirmed that 20 out of 182 mentally retarded patients were positive for fragile X syndrome, giving an incidence of 11% among Kuwaiti patients. 

Lebanon

Zafatayeff et al. (1998) conducted a retrospective study on nine Lebanese families with fragile X syndrome and indicated that the incidence rate of the disease in the country is estimated at 1/4000 boys.

Oman

Jan (1992) reported the case of a 9-year-old boy with fragile X syndrome and intercurrent chest infection. Fragile X syndrome was diagnosed by chromosomal analysis which showed absence of long arm of chromosome X. 

[Jan A. Fragile X syndrome. Oman Med J. 1992; 9(2):37-8.]

Saudi Arabia

In 2000, Al Husain et al. determined the prevalence rate of fragile X syndrome among cases with mental retardation in a hospital setting in Riyadh. Of 94 cases, six male probands (6.4%) showed the classic fragile X chromosome and another six (including a four-year-old girl) were detected, following extension of the cytogenetic studies to all 32 first-degree relatives. Affection of more than one sibling was ascertained in four families. One family had four brothers with fragile X syndrome, whereas another formed part of a large kindred with twelve males and five females who were mentally retarded. 

Tunisia

Falik-Zaccai et al. (1997) found the fragile X syndrome in 36 apparently unrelated pedigrees of Tunisian Jewish descent. They suggested that the high prevalence of disease among Tunisian Jews could be due to a founder effect.

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