Autosomal recessive disorder

Etiology: cystathionine B synthetase deficiency results in defective methionine metabolism with accumulation of homocystine + homocysteine in blood and urine; causes defect in collagen / elastin structure

• thromboembolic phenomena due to stickiness of platelets
• ligamentous laxity
• downward + inward dislocation of lens (DDx: upward + outward dislocation in Marfan syndrome)
  

  Differences between Homocystinuria and Marfan

  Homocystinuria Marfan Syndrome Inheritance autosomal recessive autosomal dominant Biochemical defect cystathionine synthetase not known Osteoporosis yes no Spine biconcave vertebrae scoliosis Lens dislocation downward upward Arachnodactyly 33% 100%

• mild / moderate mental retardation; malar flush
• crowding of maxillary teeth and protrusion of incisors
• arachnodactyly in ⅓ (DDx: Marfan syndrome)
• microcephaly
• enlarged paranasal sinuses
• osteoporosis of vertebrae (biconcave / flattened / widened vertebrae)
• scoliosis
• pectus excavatum / carinatum (75%)
• osteoporosis of long bones (75%) with bowing + fracture
• children: metaphyseal cupping (50%); enlargement of ossification centers in 50% (knee, carpal bones); epiphyseal calcifications (esp. in wrist, resembling phenylketonuria); delayed ossification
• Harris lines = multiple growth lines
• genu valgum, coxa valga, coxa magna, pes cavus
• premature vascular calcifications

Prognosis: death from occlusive vascular disease / minor vascular trauma