fragile X syndrome

Examples of fragile X syndrome in the following topics:

• Intellectual Disabilities

  • Intellectual disability can be either syndromic (in which intellectual deficits are present along with other medical and behavioral signs and symptoms), or non-syndromic (in which intellectual deficits appear without other abnormalities).
  • Down syndrome and fragile X syndrome are examples of syndromic intellectual disabilities.
  • The most prevalent genetic conditions include Down syndrome, Klinefelter's syndrome, fragile X syndrome (common among boys), neurofibromatosis, congenital hypothyroidism, Williams syndrome, phenylketonuria (PKU), and Prader-Willi syndrome.
  • Down syndrome is one of the more common genetic causes of intellectual disability.

• Neurodevelopmental Disorders: Autism and ADHD

  • Some, like Down Syndrome, cause intellectual deficits, while others specifically affect communication, learning, or the motor system.
  • Patients with some forms of the disorder (e.g., Fragile X syndrome) also have intellectual disability.
  • Except for some well-characterized, clearly-genetic forms of autism (e.g., Fragile X and Rett Syndrome), the causes of ASD are largely unknown.

• Prenatal Diagnostic Tests

  • For example, Down Syndrome is associated with cardiac defects that may need intervention immediately upon birth.
  • The other types of conditions commonly screened for include neural tube defects, chromosome abnormalities, genetic diseases, spina bifida, cleft palate, Tay-Sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, and fragile X syndrome.
  • The results of the blood tests are then combined with the NT ultrasound measurements, maternal age, and gestational age of the fetus to yield a risk score for Down syndrome, trisomy 18, and trisomy 13.
  • This karyotype indicates that the fetus has Down Syndrome as it has three of chromosome 21 instead of two.

• X-Inactivation

  • The presence of extra X chromosomes in a cell is compensated for by X-inactivation in which all but one X chromosome are silenced.
  • So how does X-inactivation help alleviate the effects of extra X chromosomes?
  • The XXY genotype, corresponding to one type of Klinefelter syndrome, corresponds to phenotypically male individuals with small testes, enlarged breasts, and reduced body hair .
  • More complex types of Klinefelter syndrome exist in which the individual has as many as five X chromosomes.
  • This individual with cri-du-chat syndrome is shown at two, four, nine, and 12 years of age.

• Respiratory Distress Syndrome

  • Acute respiratory distress syndrome (ARDS) is a serious reaction to various forms of injuries or acute infection to the lung.
  • Acute respiratory distress syndrome (ARDS), also known as respiratory distress syndrome (RDS) or adult respiratory distress syndrome, is a serious reaction to various forms of injuries or acute infection to the lung.
  • ARDS is a severe lung syndrome (not a disease) caused by a variety of direct and indirect issues.
  • An X-ray of a patient with ARDS is shown in Figure 1.
  • If the underlying disease or injurious factor is not removed, the amount of inflammatory mediators released by the lungs in ARDS may result in a systemic inflammatory response syndrome (or sepsis if there is lung infection).

• Hair and Hormones

  • In time, hair becomes thinner and its overall volume is reduced, resembling fragile vellus hair or "peach fuzz" until, finally, the follicle falls dormant and ceases producing hair completely.
  • Some of the genes involved are X-linked, although other genes are also involved.
  • High glucose levels and de novo hepatic lypogenesis and an interaction with liver fats cause SHBG levels to fall independantly of insulin levels and is the likely link between caloric excess, metabolic syndrome, and baldness.

• Impingement Syndrome

  • Shoulder impingement syndrome occurs when the tendons of the rotator cuff muscles become irritated and inflamed.
  • Shoulder impingement syndrome, also called painful arc syndrome, supraspinatus syndrome, swimmer's shoulder, and thrower's shoulder, is a clinical syndrome that occurs when the tendons of the rotator cuff muscles become irritated and inflamed as they pass through the subacromial space, the passage beneath the acromion.
  • Anything that causes further narrowing of this space can result in impingement syndrome.
  • Impingement syndrome can usually be diagnosed by history and physical exam.
  • Plain x-rays of the shoulder can be used to detect some joint pathology and variations in the bones, including acromioclavicular arthritis, variations in the acromion, and calcification.

• Sudden Infant Death Syndrome (SIDS)

  • Sudden infant death syndrome (SIDS) is marked by the sudden death of an infant that is not predicted by medical history.
  • Sudden infant death syndrome (SIDS) is marked by the sudden death of an infant that is not predicted by medical history and remains unexplained after a thorough forensic autopsy and detailed death scene investigation.
  • The cause of SIDS is unknown, but some characteristics associated with the syndrome have been identified.
  • Supporting evidence for an X-linkage is found by examining other causes of infant respiratory death, such as suffocation by inhalation of food or other foreign objects.

• Primary Immunodeficiency Diseases

  • A number of syndromes, including the following, escape formal classification but are otherwise recognisable by particular clinical or immunological features:
  • DNA repair defects not causing isolated SCID; for example ataxia telangiectasia and ataxia-like syndrome
  • Various immuno-osseous dysplasias (abnormal development of the skeleton with immune problems);for example, cartilage-hair hypoplasia, Schimke syndrome
  • Immunodeficiency with hypopigmentation or albinism; for example, Chediak-Higashi syndrome, Griscelli syndrome type two
  • Many manifest themselves as periodic fever syndromes.

• Disorders in Chromosome Number

  • Aneuploidy often results in serious problems such as Turner syndrome, a monosomy in which females may contain all or part of an X chromosome.
  • Klinefelter syndrome is a trisomy genetic disorder in males caused by the presence of one or more X chromosomes.
  • Down syndrome is the only autosomal trisomy in humans that has a substantial number of survivors one year after birth.
  • Trisomy in chromosome 21 is the cause of Down syndrome; it affects 1 infant in every 800 live births.