When Materials Are at Fault: The Skeletal Collagens, Osteogenesis Imperfecta and Chondrodysplasias

Abstract

Prenatal ultrasound done at week 34 in a 29-old primigravida and primipara reveals bowing of several long bones (tibiae, femurs, and humeri) as well as a suspected fracture of the left femur. The woman and her partner are clinically healthy and non-consanguineous. At week 39, a boy is delivered vaginally. The newborn has bowed limbs, a triangular face, and blue sclerae. On palpation, his skull is soft. Tachypnea (rapid breathing) develops and he is given ventilator support for 24 h. He appears to be comfortable when left quiet but seems to have pain upon handling. As his sucking is weak, a gastric tube is inserted for alimentation. Radiographs show generalized osteopenia; the long bones are expanded and show numerous fractures; the skull is very poorly mineralized. A diagnosis of osteogenesis imperfecta (OI) is made; handling is reduced to a minimum; nonsteroidal anti-inflammatory drug is given for pain control when needed. The baby remains stable and his sucking gains strength, allowing for breastfeeding. He is discharged at age 3 weeks. Over the first months of life, he gains weight but remains intolerant to handling, and his spontaneous movements are very much reduced. His social development seems unaffected, and he follows well with is eyes and develops social smiling.

Note on the nomenclature of collagens: originally, collagen types have been distinguished using Roman numerals (I, II, III, IV, etc.). However, using Roman numerals for newer collagens, such as collagen 27 (“collagen XXVII”), is cumbersome; the collagen genes are numbered using Arabic numerals (e.g., COL27A1); and in the digital age, Roman numerals are easily misinterpreted. For these reasons, only Arabic numerals will be used here.