2 Achondrogenesis, Type IB
579
Fraccaro type
Severely shortened long bones with loss of longitudi- nal orientation; unossified fibulas; deficient ossifica- tion of vertebral bodies, pelvis, and sacrum
Frequency: 1 in 50,000 births.
Genetics
Autosomal recessive (OMIM 600972), caused by mutations in the DTDST gene at 5q32-q33
Clinical Features
• Fetal hydrops, polyhydramnios
• Premature birth, stillbirth or death within min- utes in large proportion of cases
• Marked micromelic dwarfism
• Normocephaly, but head appearing large because of small body
• Severe midface hypoplasia
• Low nasal bridge
• Micrognathia
• Short neck
• Short trunk, barrel-shaped chest
• Overdistended abdomen
• Edema of soft tissues
• Prenatal detection of micromelia by ultrasound Differential Diagnosis
• Achondrogenesis, types IA (Houston-Harris) and II
• Hypochondrogenesis
Radiographic Features Spine
• Absent/deficient ossification of vertebral bodies Pelvis
• Small iliac wings
• Small pelvis with flattened acetabula
• Arched lower iliac margins
• Absent/deficient ossification of pubis, ischium, and sacrum
Chest
• Barrel-shaped thorax
• Short, thin, horizontal ribs with widened ends
• Unossified sternum
Extremities
• Extremely short tubular bones, with squared, trapezoid, or stellate appearance
• Wide and cupped ends of the long bones, with lat- eral spurs
• Unossified fibulas Skull
• Ossified or only mildly underossified calvarium
Bibliography
Beluffi G. Achondrogenesis, type I. Rofo Fortschr Geb Rönt- genstr Nuklearmed 1977; 127: 341–4
Borochowitz Z, Lachman R, Adominan GE, Spear G, Jones K, Rimoin DL. Achondrogenesis type I: delineation of further heterogeneity and identification of two distinct subgroups.
J Pediatr 1988; 112: 23–31
Jaeger HJ, Schmitz-Stolbrink A, Hulde J, Novak M, Roggen- kamp K, Mathias K. The boneless neonate: a severe form of achondrogenesis type I. Pediatr Radiol 1994; 24: 319–21 Maroteaux P, Lamy M: Le diagnostic des nanismes chrondro-
dystrophiques chez les nouveau-nés. Arch Fr Pediatr 1968;
25: 241–62
Spranger JW, Langer LO, Wiedemann HR. Bone dysplasias. An atlas of constitutional disorders of skeletal development.
W.B. Saunders Company, Philadelphia, 1974, pp. 24–5 Superti-Furga A, Hastbacka J, Wilcox WR, Cohn DH, van der
Harten HJ, Rossi A, Blau N, Rimoin DL, Steinmann B, Lan- der ES, Gitzelmann R. Achondrogenesis type IB is caused by mutations in the diastrophic dysplasia sulphate trans- porter gene. Nat Genet 1996; 12: 100–2
Tretter AE, Saunders RC, Meyers CM, Dungan JS, Grumbach K, Sun CC, Campbell AB, Wulfsberg EA. Antenatal diagnosis of lethal skeletal dysplasias. Am J Med Genet 1998; 75:
518–22
Van der Harten HJ, Brons JT, Dijkstra PF, Niermeyer MF, Mei- jer CJ, van Giejn HP, Arts NF. Achondrogenesis-hypochon- drogenesis: the spectrum of chondrogenesis imperfecta. A radiological, ultrasonographic, and histopathologic study of 23 cases. Pediatr Pathol 1988; 8: 571–97
Withley CB, Gorlin RJ: Achondrogenesis: nosology with evidence of genetic heterogeneity. Radiology 1983; 148:
693–98
Achondrogenesis, Type IB
A
Achondrogenesis, Type IB / Achondrogenesis, Type II 580
Fig. 3.1. Patient 1, stillborn at 32 weeks’ gestation. The calvari- um is enlarged, with diminished, yet still appreciable, ossifica- tion. The thorax is barrel-shaped, with thin and horizontal ribs. There is no evidence of rib fractures. The scapulae are small and irregular, but the clavicles are normal. The vertebral bodies are severely underossified. The lumbar vertebrae, sacrum, ischia, and pubic bones are totally unossified. The shape of the ilia, with a concave medial and inferior border, is characteristic of this condition. The tubular bones in the limbs are very short and bowed, with cupped ends, but are less se- verely affected than in achondrogenesis type I. The abdomen and soft tissue are prominent
Fig. 2.1 a, b. Patient 1, stillborn.
The skull is ossified. The thorax is barrel shaped. The ribs are short, horizontally oriented, and thin, with splayed ends. There are nor rib fractures. The verte- brae are ossified poorly or not at all. The iliac wings are short, with arched lower iliac margins, and the pubis, ischium, and sacrum are not ossified. The tubular bones in the limbs are extremely short and wide, squared off or trapezoid in appearance, with concave ends and lateral spurs. The fibulas are unossified. The abdomen is enlarged. (Reprinted, with permission, from Beluffi 1977)
a b
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