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Chromosomal Disorders

From Mediwikis

Down Syndrome

Patau (T13) & Edwards' (T18) Syndromes

Approximately 1:6000 live births

Clinically similar,

  • Learning difficulties
  • Pronounced occiput
  • Severe cleft lip & palate
  • Microcephaly
  • Polydactyly
  • Congenital heart disease, including:
    • Ventricular Septal Defect (VSD)
    • Patent Ductus Arteriosus (PDA)
    • Pulmonary Stenosis (PS)
    • Dextrocardia (heart apex is positioned on the right rather than the left)

Triploidy(69 XXX,XXY,XYY)

  • Three of every chromosome
  • Common in spontaneous abortions- usually incompatible with life
  • Severe intrauterine growth restriction, poor prognosis post birth

Klinefelter Syndrome (47 XXY)

1 in 1000 males

Clinical Features

  • Learning difficulties, clumsiness
  • Taller than average
  • Gynaecomastia
  • Infertility
  • Osteoporosis
  • Leg ulcers
  • Breast cancer risk later in life

Turner Syndrome (45 X0)

Incidence = 1:2000 live female births.

99% of fetuses with this syndrome are thought to spontaneously abort, and this could make up 15% of all spontaneous abortions

This syndrome is causde by their only being one of the sex chromosomes, an X chromosome, so the karyotype is XO, therefore it only affects girls.

Clinical Features

  • Pre-natal- Hydrops fetalis, nuchal cyst
  • Normal appearance at birth
  • Normal intelligence
  • Short stature
  • Webbed neck
  • Widely spaced nipples
  • Poor secondary sexual characteristics- need oestrogen therapy
  • Primary amenorrhoea & infertility due to ovarian failure
  • Congenital heart disease, associated with:
    • Coarctation of the Aorta (narrowing of the aorta)
    • Aortic Stenosis

Noonan Syndrome

Incidence = 1:2000 live births, the genetic aetiology is not completely understood. It can occur sporadically or act as an autosomal dominant condition.

Clinical features are very similar to Turner Syndrome, but it can occur in boys as well as girls. It is associated with different congenital heart disease (Hypertrophic Cardiomyopathy and Pulmonary Stenosis - seen in up to 50% of cases).

25% have developmental problems.

Fragile X Syndrome

FRAXA- FMR-1 gene

Increase in trinucleotide repeat sequences represents a premutation

  • This creates a carrier- at risk of late onset neuro problems- tremor/ ataxia

Those with over 200 trinucleotide repetitions have syndrome

Clinical Features

The penetrance of these features depends on the level of FMR-1 mutation.

  • Wide spectrum of normal to impaired intellectual ability
  • Autism
  • Recurrent otitis media
  • ADHD
  • Hypersensitivity to stimuli
  • Visual problems
  • Seizures
  • Physical characteristics
    • Long face
    • Protruding ears
    • Flat feet
    • Larger testes