= MAROTEAUX-LAMY DISEASE

= autosomal recessive inherited disorder of primary spongiosa; probably variant of cleidocranial dysostosis

Genetics: mutation in cathepsin-K gene (= lysosomal cysteine proteinase expressed in osteoclasts and required for degradation of collagen)

Age: often diagnosed in infancy / early childhood; M÷F = 2÷1

• dwarfism; mental retardation (10%)
• no concurrent anemia ← preserved medullary cavities
• generalized osteosclerosis of long bones with thickened cortices (resembling osteopetrosis but with preservation of medullary canal)
• multiple spontaneous fractures ← brittle bones
• Skull
  • yellowish discoloration of teeth
  • CHARACTERISTIC dysmorphic facies: beaked nose, receding jaw
  • brachycephaly + platybasia
  • wide cranial sutures, wormian bones
  • thick skull base
  • hypoplasia of mandible + obtuse mandibular angle
  • hypoplasia + nonpneumatization of paranasal sinuses
• Hands
  • widened hands + feet; dystrophic nails
  • hypoplastic tapered terminal tufts (= acroosteolysis)
• Spine
  • nonsegmentation of C1/C2 and L5/S1
  • kyphoscoliosis with increased lumbar lordosis
  • dense vertebral bodies with CHARACTERISTIC sparing of transverse processes
• Chest
  • pectus excavatum
  • clavicular dysplasia

DDx:

1. Osteopetrosis (no dwarfism, no mandibular / skull abnormality, no phalangeal hypoplasia, no transverse metaphyseal bands, anemia, Erlenmeyer flask deformity; “bone-within-bone” appearance)
2. Cleidocranial dysostosis (no dense bones / terminal phalangeal hypoplasia, short stature)