LSDG

• Down syndrome (Trisomy 21)

  The most common autosomal trisomy compatible with life
• Causes of Down syndrome

  • Trisomy 21 (95%)
  • Translocation
  • Mosaicism (about 2%)
• Karyotype of Down syndrome

  47, XX+21 or 47, XY+21
• Characteristic appearance of Down syndrome

  • Hypotonia with tendency to keep mouth open and protrude the tongue
  • Excessive mobility, flexibility of joints
  • Relatively small, short stature with awkward gait
• Central nervous system effects of Down syndrome

  • Mental retardation (mean IQ< 50)
  • Developmental delay
  • Hypotonia
  • Alzheimer-like dementia
  • Signs of hypothyroidism
  • Leukemia
• Physical features of Down syndrome

  • Microcephaly (small brain)
  • Brachycephaly (short skull) with relatively flat occiput
  • Flat facial profile
  • Short, up slanting palpebral fissures
  • Small nose with flat nasal bridge
  • Brushfield, speckled spots of the iris
  • Inner epicanthal folds
  • Small mandible, small mouth with protruding tongue
  • Small ears with abnormal shape
  • Late closure of fontanels
  • Small nose with flat nasal bridge
  • Inner epicanthal folds
  • Rough skin
  • Mentally retarded
  • Small round face
  • Protruding tongue
  • Impotency in males
  • Short lifespan
• Cardiac effects of Down syndrome

  • Atrioventricular Septal Defect (AV-Canal)
• With early intervention and special education, many with Down syndrome learn to read and write and participate in various childhood activities
• Trisomy 18 (Edwards syndrome)

  • Incidence 1/8000
  • Severe mental retardation and many physical birth defects
  • Over 90% dead in 1st year
• Prenatal features of Trisomy 18

  • Polyhydramnios
  • Small placenta
  • Intrauterine growth retardation
• Postnatal features of Trisomy 18

  • Craniofacial dysmorphism (strawberry-shaped head)
  • Microcephaly
  • Micrognathia (small mandible)
  • Overlap of second finger on third, fourth finger on fifth
  • Fixed finger contractures
  • Weak cry
  • Small sternum, small nipples and pelvis
  • Hypoplasia of skeletal muscle, subcutaneous and adipose tissue
  • Congenital heart defects, horseshoe kidney, and omphalocele
• Trisomy 13 (Patau syndrome)

  • Severe birth defects
  • Mental retardation
  • Intrauterine growth retardation
• Features of Trisomy 13

  • Open scalp lesion, scalp defect (cutis aplasia)
  • Cleft palate (may be bilateral)
  • Microcephaly
  • Malformed ears
  • Microphthalmos
  • Central nervous system malformations, midline brain defect, holoprosencephaly
  • Variety of cardiac defects
• 50% of Patau syndrome patients die before 1 month of age, 70% die before age 6 months, 90% die before age 1 year
• Turner syndrome


  • Affects 1 in 2500 newborn girls
  • One X chromosome is either missing or abnormal
• Karyotypes of Turner syndrome

  • 45, X (55%)
  • Altered structure of one X chromosome (25%)
  • Mosaicism (15%)
• Physical features of Turner syndrome

  • Short female
  • Broad chest with wide space of nipples
  • Congenital lymphedema of hands and feet at birth
  • Shield-shaped chest
  • Webbing of the neck
  • Appearance of short neck
  • Low posterior hairline
  • Cubitus valgus (increased carrying angle)
  • Short stature (adult height ~135 cm)
  • Renal anomalies (40%)
  • Congenital heart defects (20%)
• Life span is probably normal in most cases of Turner syndrome
• Klinefelter syndrome


  • Hypogenitalism and hypogonadism
  • Long legs, dull mentality, and/or behavioral issues
• Klinefelter syndrome karyotypes


  • 47,XXY (80%)
  • 48,XXXY; 48,XXYY; 49,XXXXY (20%)
  • 46,XY/47,XXY mosaicism
• Features of Klinefelter syndrome

  • Puberty occurs at normal age but testes remain small
  • Develop secondary sex characters late
  • 50% develop gynecomastia
  • Taller stature
  • Often goes undiagnosed until adulthood when infertility aids identification
  • 46,XY/47,XXY have better prognosis for testicular function