Presentation #1 Elly DeLaney

1. Presentation #1Elly DeLaney Article: Trummer, T., Brenner, R., et al. 2001. Recurrent mutations in the COL1A2 gene in patients with osteogenesis imperfecta. Clin. Genetics. 59:338-343.

2. Background • Osteogenesis imperfecta (OI) is a genetic disorder characterized by bones that break easily for little or no cause. There are 4 main types of OI.

3. Types of Osteogenesis Imperfecta • Type I • Most common and mildest type of OI. • Bones predisposed to fracture. • Most common and mildest type of OI. • Bones predisposed to fracture. • Most fractures occur before puberty. • Normal or near-normal stature. • Loose joints and low muscle tone. • Sclera (whites of the eyes) usually have a blue, purple, or gray tint. • Triangular face. • Tendency toward spinal curvature. • Bone deformity absent or minimal. • Brittle teeth possible. • Hearing loss possible, often beginning in early 20s or 30s. • Collagen structure is normal, but the amount is less than normal.

4. Type II • Most severe form. • Frequently lethal at or shortly after birth, often due to respiratory problems. In recent years, some people with type 2 have lived into young adulthood. • Numerous fractures and severe bone deformity. • Small stature with underdeveloped lungs. • Collagen is improperly formed • Autosomal dominant type (the other 3 are autosomal recessive).

5. Type III • Bones fracture easily. Fractures often present at birth, and x-rays may reveal healed fractures that occurred before birth. • Short stature. • Sclera have a blue, purple, or gray tint. • Loose joints and poor muscle development in arms and legs. • Barrel-shaped rib cage. • Triangular face. • Spinal curvature. • Respiratory problems possible. • Bone deformity, often severe. • Brittle teeth possible. • Hearing loss possible. • Collagen is improperly formed.

6. Type IV • Between Type I and Type III in severity. • Bones fracture easily, most before puberty. • Shorter than average stature. • Sclera are white or near-white (i.e., normal in color). • Mild to moderate bone deformity. • Tendency toward spinal curvature. • Barrel-shaped rib cage. • Triangular face. • Brittle teeth possible. • Hearing loss possible. • Collagen is improperly formed.

7. Variation in OI Estimated range of effected individuals 20,000-50,000 Diagnosis based mainly on clinical features, also biochemical and DNA tests

8. Collagen • Collagen is the most abundant protein in the body. It is composed of a triple helical structure in which glycine, a small amino acid, is essential in every third position for optimal folding. • The genes COL1A1 and COL1A2 are responsible for collagen structure formation.

9. The Patient • Studies in this article were based on a female patient diagnosed with OI type III. During the 1st three years of her life, 22 fractures occurred. She was implanted with rods in her femura and tibia and only 3 more fractures were noticed until she turned 10. Other symptoms demonstrated by the patient included: -slightly blue sclera -severe dentinogenesis imperfecta

10. PICP Test • In the first test, the 10 year old patient was tested for serum levels of procollagen I C-terminal propeptide (PICP). • The patient’s PICP levels were compared with 12 other OI type III patients (ages 4-15) and 24 control patients (ages 4-15).

11. Results • Patient’s Serum Levels – 125 micro-grams per liter. • Control Results – 288 + or – 89 micro-grams per liter. • OI type III patients – 109 + or – 35 micro-grams per liter.

12. Discussion • Reduced serum levels in the patient indicate quantitative consequences of the underlying mutation for collagen type I biosynthesis. • The fact that the patient’s serum levels were within the mean of other OI type III patient indicates that secretion of PICP could play an important role in determining clinical phenotypes of OI.

13. Gene Sequence Variation • The patients genes for COL1A1 and COL1A2 were examined for sequence variations. • Evidence for mutation lead to the discovery of a Gly238Cys substitution due to a mutation in the COL1A2 gene. This proved to be the most N-terminal cystine substitution to date. • All other mutations listed in the literature collated in the database of human collagen mutations were serine substitutions.

14. Some recurrent COL1A1 mutations and their clinical phenotype

15. Some recurrent COL1A2 mutations and their clinical phenotype

16. Discussion • An update shows that: - In COL1A2 mutations, serine and cystine are predominant in glycine substitution. In addition, seven sites were identified as mutational hot spots. - In COL1A1 mutations, serine, cystine and arginine are predominant in glycin substitution. Also, 13 sites were identified as mutational hot spots.

17. Significance of the Article • Identified cystine as a glycine substitute (as opposed to serine) • Raises questions as to why identical mutations in this genetically classical disorder lead to such phenotypic variability.

18. Questions?

19. References • Trummer, T., Brenner, R., et al. 2001. Recurrent mutations in the COL1A2 gene in patients with osteogenesis imperfecta. Clin. Genetics. 59:338-343 • Kuznetsova, N., McBride, D., Leikin, S. 2001. Osteogenesis imperfecta murine: interaction between type I collagen homotrimers. J. Mol. Biol. 309:807-815. • Medical College of Wisconsin. Retrieved March 6, 2002 at www.chorus.rad.mcw.edu • Osteogenesis Imperfecta Foundation. Retrieved Jan. 31, 2002 at www.oif.org