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CHAPTER
55
Osteogenesis Imperfecta: Maintenance
of
Adult Bone Heal
th
Jay R. Shapiro and Feng-Shu Brennen
Kennedy Krieger Institute and Johns Hopkins University School of Medicine, Baltimore, MD, USA
INTRODUCTION
OI phenotypes: bone formation and resorption may
remain coupled. However, in the adult, aging decreases
osteoblastic bone formation and increases osteoclastic
bone resorption thus accentuating late onset bone loss
and increasing the fracture risk as the individual ages.
Although increasing information is available as to the
significant role of osteocytes in regulating bone metab-
olism, this has not been investigated in OI.
1
However,
we lack detailed information as to the mechanisms
whereby cellular aging alters skeletal homeostasis
under normal circumstances and limited information
which specifically addresses the effect of aging in OI on
bone cell metabolism.
Aging effects specifically related to OI may encom-
pass the following: age-related changes in type I col-
lagen, age-related effects on osteoblast, osteoclast or
osteocyte function, and changes in matrix composition
affecting proteoglycan synthesis (see Chapter 8).
Bone mass and bone strength decline with age.
As categorized by Manologas,
2
small bone size, dis-
rupted bone architecture, the potential for delayed
repair of fatigue microdamage and suppressed bone
turnover in adults with OI are additional factors that
increase age-related susceptibility to fracture. The age-
related decline in cortical bone tensile strength may be
caused by deterioration of type I collagen, resulting
from lost crosslinking between the component chains
3
and accumulation of advanced glycation end prod-
ucts
4
- another general feature of the aging process
which has not been assessed in bone from OI individu-
als.
2
Studying osteoblast gap junctions, Genetos et al.
observed no effect of age
per se
upon osteoblastic Cx43
mRNA, protein or gap junctional intercellular com-
munication (GJIC). However, the authors have dem-
onstrated an age-related impairment in the capacity of
Experience dictates that (1) the medical literature
contains relatively few references to the treatment of
adults with osteogenesis imperfect (OI) and (2) the pri-
mary care physician has, at best, limited or no expe-
rience in treating adults with OI. As a result, when
medical problems occur in the OI individual they may
be approached apart, or out of context, from a patient's
systemic connective tissue disorder. Other chapters in
this text cover certain disorders found in adults with
aging, dental care (Chapter 33), osteoarthritis (Chapter
38) and hearing (Chapter 32). This chapter will focus on
the maintenance of bone health in adults with OI. The
role of vitamin D and the maintenance of normal vita-
min D levels and calcium metabolism are discussed in
Chapter 56 but are included here as vitamin D and cal-
cium metabolism impact bone health in adults with OI.
However, when discussing bone health in adults with
OI, it is important to note that there is little information
that accurately describes the changes in bone mineral
density or in fracture rate.
BONE METABOLISM IN ADULT AGING
AND IN ADULTS WITH OI
The skeleton is subject to deleterious effects from
aging which can predispose an individual to osteo-
porosis and related fractures. This burden of aging
is superimposed upon the diminished bone mass
in adults with OI and is potentially complicated by
the presence of skeletal deformities which alter bone
structure and weaken bone strength. In children, bone
turnover is generally increased in moderate to severe
