[Henry Hubert Turner (1892–1970), chair of medicine at the University of Oklahoma, secretary and president of the Endocrine Society]

= nondisjunction of sex chromosomes as

1. Complete monosomy (45,XO)
2. Partial monosomy (structurally altered 2^nd X chromosome)
3. Mosaicism (XO + another sex karyotype)

Prevalence: 1÷3,000–5,000 livebirths

Associated with: coarctation (20–36% affected), aortic stenosis, horseshoe kidney (most common)

• sexual infantilism (spontaneous puberty in 5–15%):
  • primary amenorrhea
  • absent secondary sex characteristics
• short stature; absence of prepubertal growth spurt
• webbed neck; low irregular nuchal hair line
• shield-shaped chest + widely spaced nipples
• mental deficiency (occasionally); high palate; thyromegaly
• multiple pigmented nevi; keloid formation
• idiopathic hypertension; elevated urinary gonadotropins
• Cardiovascular
  • dilatation of ascending aorta (40%)
  • juxtaductal coarctation / pseudocoarctation of aortic arch (10%); aortic stenosis; bicuspid aortic valve; elongation of aortic arch; partial anomalous pulmonary venous return
• General
  • normal skeletal maturation with growth arrest at skeletal age of 15 years
  • delayed fusion of epiphyses >age 20 years
  • osteoporosis during / after 2^nd decade ← gonadal hormone deficiency
  • coarctation of aorta (10%); aortic stenosis
  • renal ectopia / horseshoe kidney
  • lymphedema
• Skull
  • basilar impression; basal angle >140°
  • parietal thinning
  • small bridged sella
  • hypertelorism
• Axial skeleton
  • hypoplasia of odontoid process + C1
  • osteochondrosis of vertebral plates
  • squared lumbar vertebrae; kyphoscoliosis
  • deossification of vertebrae
  • small iliac wings; late fusion of iliac crests
  • android pelvic inlet with narrowed pubic arch + small sacrosciatic notches
• Chest
  • thinning of lateral aspects of clavicles
  • thinned + narrowed ribs with pseudonotching
• Hand + arm
  • “positive metacarpal” sign = relative shortening of 3^rd and 4^th metacarpal
  • “positive carpal” sign = narrowing of scaphoid-lunate-triquetrum angle <117°
  • phalangeal preponderance = length of proximal + distal phalanx exceeds length of 4^th metacarpal by >3 mm
  • shortening of 2^nd + 5^th middle phalanx (also in Down syndrome)
  • “drumstick” distal phalanges = slender shaft + large distal head
  • “insetting” of epiphyses into bases of adjacent metaphyses (phalanges + metacarpals)
  • Madelung deformity = shortening of ulna / absence of ulnar styloid process
  • cubitus valgus = bilateral radial tilt of articular surface of trochlea
  • deossification of carpal bones
• Knee
  • tibia vara = enlarged medial femoral condyle + depression of medial tibial plateau (DDx: Blount disease)
  • small exostosis-like projection from medial border of proximal tibial metaphysis
• Foot
  • deossification of tarsal bones
  • shortening of 1^st, 4^th, and 5^th metatarsals
  • pes cavus

US:

• prepubertal uterus
• nonvisualized / streaky ovaries (in complete monosomy); normal ovaries (in mosaic karyotype)

OB-US:

• large nuchal cystic hygroma
• lymphangiectasia with generalized hydrops
• symmetrical edema of dorsum of feet
• CHD (20%): coarctation of aorta (70%), left heart lesions
• horseshoe kidney