Degree of external genital malformation at birth in children with a disorder of sex development and subsequent caregiver distress

PURPOSE

We determined whether the degree of genital malformation at birth in children with a disorder of sex development is related to subsequent caregiver distress, specifically symptoms of depression and anxiety.

MATERIALS AND METHODS

A total of 66 caregivers of children with disorders of sex development were recruited from 3 centers that specialize in disorders of sex development medicine. The caregivers completed the Beck Depression Inventory, 2nd Edition and the Beck Anxiety Inventory. The child's Prader score at birth was determined by the child's treating pediatric endocrinologist and/or pediatric urologist at each institution.

RESULTS

Results from the current study revealed that for caregivers of male children, under masculinization of the child's genitals at birth was significantly related to higher levels of subsequent caregiver depression. In contrast, over masculinization of the genitals of female children at birth was unrelated to caregiver depression or anxiety.

CONCLUSIONS

These findings suggest that caregivers of male children with disorders of sex development may be at increased risk for psychological distress and could benefit from family based psychosocial interventions.

The insulin-like growth factors and growth disorders of childhood

Specific lesions of the growth hormone (GH)/insulin-like growth factor (IGF) axis have been identified in humans, each of which has distinctive auxologic and biochemical features. Measures of circulating IGF-I are useful in diagnosing growth disorders in childhood and in evaluating response to GH therapy. Recombinant human IGF-I is an effective treatment of severe primary IGF deficiency, which is typical of patients with GH receptor defects (Laron syndrome). Such treatment has been limited to a few severely affected patients. Future studies will provide new insight into IGF-I as treatment and into the nature of growth disorders that involve the IGF axis.

Update: consequences of abnormal fetal growth

Intrauterine growth restriction (IUGR) is prevalent worldwide and affects children and adults in multiple ways. These include predisposition to type 2 diabetes mellitus, the metabolic syndrome, cardiovascular disease, persistent reduction in stature, and possibly changes in the pattern of puberty. A review of recent literature confirms that the metabolic effects of being born small for gestational age are evident in the very young, persist with age, and are amplified by adiposity. Furthermore, the pattern of growth in the first few years of life has a significant bearing on a person's later health, with those that show increasing weight gain being at the greatest risk for future metabolic dysfunction. Treatment with exogenous human GH is used to improve height in children who remain short after being small for gestational age at birth, but the response of individuals remains variable and difficult to predict. The mechanisms involved in the metabolic programming of IUGR children are just beginning to be explored. It appears that IUGR leads to widespread changes in DNA methylation and that specific "epigenetic signatures" for IUGR are likely to be found in various fetal tissues. The challenge is to link such alterations with modifications in gene expression and ultimately the metabolic abnormalities of adulthood, and it represents one of the frontiers for research in the field.

A model of delivering multi-disciplinary care to people with 46 XY DSD

In 2006, a consensus statement was jointly produced by the Lawson Wilkins Pediatric Endocrine Society (LWPES) and the European Society of Paediatric Endocrinology (ESPE) concerning the management of disorders of sex development (DSD) [1]. A recommendation provided by this consensus was that evaluation and long-term care for people affected by DSD should be performed at medical centers with multi-disciplinary teams experienced in such conditions. Here we provide our team's interpretation of the 2006 consensus statement recommendations and its translation into a clinical protocol for individuals affected by 46 XY DSD with either female, or ambiguous, genitalia at birth. Options for medical and surgical management, transitioning of care, and the use of mental health services and peer support groups are discussed. Finally, we provide preliminary data to support the application of our model for delivering multi-disciplinary care and support to patients and their families.

Criteria for treating children with idiopathic short stature: laboratory (biochemical)

Idiopathic short stature (ISS) is a diagnosis of exclusion. No specific laboratory test can identify it. Rather, a series of tests that examine a person's genetic, nutritional and hormonal makeup are used to exclude specific diagnoses. However, abnormalities of the growth hormone-insulin-like growth factor (GH-IGF) axis appear to be common in children with ISS. As the only growth-promoting treatments available to children with ISS are either human GH or recombinant human IGF-I, it is plausible that measures of the GH-IGF axis or of growth factor response might be useful in predicting response to therapy or choosing the optimal medical regimen.

Parenting characteristics of female caregivers of children affected by chronic endocrine conditions: a comparison between disorders of sex development and type 1 diabetes mellitus

Rearing a child with a chronic illness is stressful and can potentially affect parenting style, which may result in poorer outcomes for children. The purpose of this study was to compare parenting characteristics of female caregivers rearing children with a disorder of sex development (DSD) to female caregivers rearing children with type 1 diabetes mellitus (T1DM). Caregivers of both groups were matched according to age and compared on measures of stress and parenting practices. Both groups demonstrated significant levels of stress and negative parenting practices. Children with T1DM and male children with non-life-threatening DSD were perceived as more vulnerable by their caregivers. Better understanding of parenting experiences of female caregivers rearing children with DSD, particularly male children, will facilitate the development of individualized interventions to ameliorate negative parenting practices and stress, with the long-term goal of improved health outcomes for their children.

TVs in the bedrooms of children: does it impact health and behavior?

OBJECTIVES

To (1) determine socio-demographic characteristics associated with a TV in the bedroom (BTV) and (2) examine relationship of BTV, independent of total viewing time, with social and behavioral characteristics.

METHODS

Children 6-17 years from the 2007 US National Survey of Children's Health were included (n=48,687). BTV, daily TV viewing time, demographic, behavioral and social outcomes (community involvement, social skills, health habits and status, and family) were examined using logistic regression, and adjusted for total viewing time.

RESULTS

Overall prevalence of BTV was 49.3% in American children. Older age, non-Hispanic Black (71.3%), Hispanics (56.3%), higher level of poverty (>56.2%), non two-parent biological family structure (>62.6%), Midwest (47.1%), Northeast (46.7%), South Atlantic (56.4%) and South Central (59.8%) region of the country were associated with higher odds of BTV. Female gender (52.7%) and residence in Alaska (33.0%) were associated with lower prevalence of BTV. BTV was associated with higher prevalence of exhibiting problematic social behaviors (29%) and overweight status (44%). BTV was significantly associated with lower prevalence of regular family meals (13%), engagement in school (16%), participation in extracurricular activities (31%), regularly sleeping enough (20%), and participation in community service (25%) after adjustment for total viewing time.

CONCLUSIONS

BTV appears associated with more social and behavioral indices than previously reported, in addition to total viewing time.

An Evidence-Based Model of Multidisciplinary Care for Patients and Families Affected by Classical Congenital Adrenal Hyperplasia due to 21-Hydroxylase Deficiency

In 2002 a consensus statement pertaining to the management of classical congenital adrenal hyperplasia due to 21-hydroxylase deficiency was jointly produced by the Lawson Wilkins Pediatric Endocrine Society and the European Society of Pediatric Endocrinology. One of the recommendations of this consensus was that centers should maintain multidisciplinary teams for providing care and support to these patients and their families. However, the specifics for how this should be accomplished were not addressed in the original consensus statement. Here we interpret and translate the 2002 consensus statement recommendations into medical, surgical and mental health protocols. Additionally, we provide preliminary evidence that such protocols result in improved care and support for patients and families.

Gender in childhood obesity: family environment, hormones, and genes

BACKGROUND

The prevalence of obesity among children in the United States represents a pool of latent morbidity. Though the prevalence of obesity has increased in both boys and girls, the causes and consequences differ between the sexes. Thus, interventions proposed to treat and prevent childhood obesity will need to account for these differences.

OBJECTIVE

This review examines gender differences in the presentation of obesity in children and describes environmental, hormonal, and genetic factors that contribute to observed gender differences.

METHODS

A search of peer-reviewed, published literature was performed with PubMed for articles published from January 1974 through October 2008. Search terms used were obesity, sex, gender, hormones, family environment, body composition, adiposity, and genes. Studies of children aged 0 to 18 years were included, and only articles published in English were reviewed for consideration. Articles that illustrated gender differences in either the presentation or underlying mechanisms of obesity in children were reviewed for content, and their bibliographies were used to identify other relevant literature.

RESULTS

Gender differences in childhood obesity have been understudied partially because of how we define the categories of overweight and obesity. Close examination of studies revealed that gender differences were common, both before and during puberty. Boys and girls differ in body composition, patterns of weight gain, hormone biology, and the susceptibility to certain social, ethnic, genetic, and environmental factors.

CONCLUSION

Our understanding of how gender differences in pediatric populations relate to the pathogenesis of obesity and the subsequent development of associated comorbid states is critical to developing and implementing both therapeutic and preventive interventions.

Growth hormone-resistant syndromes: long-term follow-up

Recombinant human IGF-I (rhIGF-I) has been approved as a therapeutic agent for short stature due to primary IGF-I deficiency following clinical trials that lasted more than 10 years. The first children treated with rhIGF-I were those with short stature resulting from defects in growth hormone (GH) action, either due to GH receptor abnormalities or the development of GH-neutralizing antibodies that arose following GH exposure. The administration of rhIGF-I to such children results in improvements in growth rate that are sustained over many years. This appears to improve adult height, but so far the effects are not as robust as when GH-deficient children are treated with human GH. Side effects are common but manageable and seldom necessitate discontinuation of therapy.

Consensus statement on the diagnosis and treatment of children with idiopathic short stature: a summary of the Growth Hormone Research Society, the Lawson Wilkins Pediatric Endocrine Society, and the European Society for Paediatric Endocrinology Workshop

OBJECTIVE

Our objective was to summarize important advances in the management of children with idiopathic short stature (ISS).

PARTICIPANTS

Participants were 32 invited leaders in the field.

EVIDENCE

Evidence was obtained by extensive literature review and from clinical experience.

CONSENSUS

Participants reviewed discussion summaries, voted, and reached a majority decision on each document section.

CONCLUSIONS

ISS is defined auxologically by a height below -2 sd score (SDS) without findings of disease as evident by a complete evaluation by a pediatric endocrinologist including stimulated GH levels. Magnetic resonance imaging is not necessary in patients with ISS. ISS may be a risk factor for psychosocial problems, but true psychopathology is rare. In the United States and seven other countries, the regulatory authorities approved GH treatment (at doses up to 53 microg/kg.d) for children shorter than -2.25 SDS, whereas in other countries, lower cutoffs are proposed. Aromatase inhibition increases predicted adult height in males with ISS, but adult-height data are not available. Psychological counseling is worthwhile to consider instead of or as an adjunct to hormone treatment. The predicted height may be inaccurate and is not an absolute criterion for GH treatment decisions. The shorter the child, the more consideration should be given to GH. Successful first-year response to GH treatment includes an increase in height SDS of more than 0.3-0.5. The mean increase in adult height in children with ISS attributable to GH therapy (average duration of 4-7 yr) is 3.5-7.5 cm. Responses are highly variable. IGF-I levels may be helpful in assessing compliance and GH sensitivity; levels that are consistently elevated (>2.5 SDS) should prompt consideration of GH dose reduction. GH therapy for children with ISS has a similar safety profile to other GH indications.

Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity

CONTEXT

Children with severe IGF-I deficiency due to congenital or acquired defects in GH action have short stature that cannot be remedied by GH treatment.

OBJECTIVES

The objective of the study was to examine the long-term efficacy and safety of recombinant human IGF-I (rhIGF-I) therapy for short children with severe IGF-I deficiency.

DESIGN

Seventy-six children with IGF-I deficiency due to GH insensitivity were treated with rhIGF-I for up to 12 yr under a predominantly open-label design.

SETTING

The study was conducted at general clinical research centers and with collaborating endocrinologists.

SUBJECTS

Entry criteria included: age older than 2 yr, sd scores for height and circulating IGF-I concentration less than -2 for age and sex, and evidence of resistance to GH.

INTERVENTION

rhIGF-I was administered sc in doses between 60 and 120 microg/kg twice daily.

MAIN OUTCOME MEASURES

Height velocity, skeletal maturation, and adverse events were measured.

RESULTS

Height velocity increased from 2.8 cm/yr on average at baseline to 8.0 cm/yr during the first year of treatment (P < 0.0001) and was dependent on the dose administered. Height velocities were lower during subsequent years but remained above baseline for up to 8 yr. The most common adverse event was hypoglycemia, which was observed both before and during therapy. It was reported by 49% of treated subjects. The next most common adverse events were injection site lipohypertrophy (32%) and tonsillar/adenoidal hypertrophy (22%).

CONCLUSIONS

Treatment with rhIGF-I stimulates linear growth in children with severe IGF-I deficiency due to GH insensitivity. Adverse events are common but are rarely of sufficient severity to interrupt or modify treatment.

Acute necrotizing pancreatitis in an adolescent with type 2 diabetes

PURPOSE OF REVIEW

The demographics of diabetes among adolescents are changing, with an increasing prevalence of type 2 diabetes. Since adolescents with type 2 diabetes are susceptible to the same complications that accompany type 2 diabetes in adults, pediatricians are now encountering new diagnosis entities.

RECENT FINDINGS

A 16-year-old Hispanic male presented to the emergency room with new onset diabetes. Laboratory evaluation revealed the diagnosis of hyperglycemic hyperosmolar nonketotic state. Within the next 24 hours, the patient's clinical status deteriorated with multi organ failure, followed by asystole. At autopsy, the pancreas demonstrated acute necrotising pancreatitis. Hyperglycemic hyperosmolar nonketotic state is a life-threatening emergency among adults with type 2 diabetes, and is now occurring more frequently among adolescents. Acute pancreatitis should be considered as a precipitating event, particularly in those with severe hypertriglyceridemia.

SUMMARY

This case illustrates the changing morbidity of diabetes in adolescents and the need to consider acute pancreatitis and hyperglycemic hyperosmolar nonketotic in adolescents with severe metabolic decompensation. Since hypertriglyceridemia is a known risk factor for acute pancreatitis, patients should be monitored, and treated as needed.

Mendelian genetic causes of the short child born small for gestational age

About 5% of newborns are small for gestational age (SGA) and 10-15% of them do not naturally catch up on growth by 2 yr of age. The growth of the fetus from conception to birth results from complex interactions of maternal and fetal genes with the environment, and factors such as malnutrition are well known to influence fetal growth. Specific genetic disorders such as Leprechaunism, Bloom syndrome, Fanconi anemia are inherited, but are very rare causes of intrauterine growth retardation. Recent published research on the actions of IGF-I in humans and the phenotypes of children with genetic defects in the GH/IGF axis establish IGF-I signaling via its receptor (IGF-IR) as the critical growth-controlling element in man. The aim of this article is to review certain SGA disorders of Mendelian genetic origin, with an emphasis on defects in the insulin and IGF pathways which may be implicated in the persistence of short stature in some children born SGA.

Treatment of short children born small for gestational age: US perspective, 2005

Growth hormone (GH) administration to ameliorate growth deficiency of short children born small for gestational age (SGA) is currently approved in the US and the EU. Even though regulatory bodies from each examined similar datasets concerning GH treatment of short SGA children, the specifics of indications for treatment and recommended regimens differed with respect to GH dosage, age at which therapy might be initiated, and the degree of short stature required. US product labeling allows more flexibility but provides less guidance for the practitioner. The EU tends to be more proscriptive, limiting use to shorter children, restricting the dosage, and providing specific guidelines in terms of monitoring during treatment.

Osteoblast-specific expression of insulin-like growth factor-1 in bone of transgenic mice induces insulin-like growth factor binding protein-5

The activities of insulin-like growth factors (IGFs) in bone are modulated by a family of binding proteins (IGFBPs) whose physiological roles remain poorly understood. We have previously shown that targeted overexpression of IGF-I in osteoblasts of transgenic (OC-IGF-I) mice stimulates bone formation. In this model, bone formation is markedly but transiently increased in an age-dependent manner, raising the possibility that IGF-I may be influencing IGFBPs to in turn modulate its paracrine actions within bone. We sought to characterize the IGFBPs in normal mouse bone during development and to determine whether osteoblast-targeted overexpression of IGF-I influenced bone IGFBP abundance in vivo. Femoral bone IGFBP content was assessed in control nontransgenic and OC-IGF-I mice by I125-IGF-I ligand and immunoblotting. Bone IGFBP-5 and IGF-I mRNA abundance was determined using real-time reverse transcription (RT)-PCR. Ligand blot of bone extract showed a 30-kDa band, identified as IGFBP-5 by immunoblot, predominated. The abundance of IGFBP-5 declined with age in both control and transgenic bone. Ligand and immunoblot analysis revealed a 5-fold increase in IGFBP-5 protein levels at 3 weeks in transgenic bone (P<0.0001). The elevated IGFBP-5 protein levels were associated with a similar increase in IGF-I mRNA abundance (4-fold, P<0.01) and a significant increase in IGFBP-5 mRNA abundance (1.5-fold). Despite the age-related decline at 6 weeks, IGFBP-5 remained significantly (P<0.01) more abundant in transgenic bone compared to controls. In contrast, bone IGFBP-4 abundance was relatively unchanged by either age or IGF-I overexpression. These studies demonstrate a distinctive developmental pattern of IGFBP-5 content in mouse bone and show that osteoblast-derived IGF-I determines skeletal IGFBP-5 abundance, at least in part by inducing its synthesis. In that IGFBP-5 is thought to stimulate bone formation, directly or via IGF-I action, such changes in bone IGFBP-5 may be important to ensure robust bone acquisition in the early postnatal period.

Growth hormone treatment of short children born small for gestational age: a US perspective

Research during the last decade shows clearly that growth hormone (GH) therapy causes a sustained increase in growth velocity when applied to short children born small for gestational age (SGA). This occurs even though GH deficiency per se is an unlikely explanation for their lack of catch-up growth. In the United States, children born weighing less than -2 SD for gestational age and who show no growth recovery (usually defined as stature persisting below -2 SD at age 2 years) are eligible for GH treatment using doses up to 0.48 mg/kg per week. The management of these children brings new challenges to the pediatric endocrinologist. Intrauterine growth retardation reflects a variety of etiologies, some of which merit special consideration and may respond variably to GH. The dose of GH used exceeds physiologic replacement and is higher than that commonly used to treat other non-GH-deficient conditions such as Turner syndrome. Thus, what constitutes optimal therapy in terms of dose, timing and patient selection remains an important question. While GH therapy provides a means by which one aspect of the SGA syndrome can be helped, there are other issues for SGA apart from height. Future efforts should include studies that better define how GH should be used in the short child born SGA and address more broadly the medical, social and psychological needs of these patients.

Genetic strategies for elucidating insulin-like growth factor action in bone

While it is universally accepted that IGFs serve important roles in bone acquisition and maintenance, the precise cellular targets and molecular mechanisms responsible for their actions have remained poorly understood. Recent advances in genetic techniques to manipulate the mouse genome have enabled the examination of individual components of the IGF system in vivo. Observations in these mouse models have provided new insights into the skeletal actions of IGF which have significant implications for understanding IGF action in human bone.

IGF-I receptor mutations resulting in intrauterine and postnatal growth retardation

BACKGROUND

Approximately 10 percent of infants with intrauterine growth retardation remain small, and the causes of their growth deficits are often unclear. We postulated that mutations in the gene for the insulin-like growth factor I receptor (IGF-IR) might underlie some cases of prenatal and postnatal growth failure.

METHODS

We screened two groups of children for abnormalities in the IGF-IR gene. In one group of 42 patients with unexplained intrauterine growth retardation and subsequent short stature, we used single-strand conformation polymorphism analysis, followed by direct DNA sequencing of any abnormalities found. A second cohort consisted of 50 children with short stature who had elevated circulating IGF-I concentrations. Complete sequencing of the IGF-IR gene was performed with DNA from nine children. We also studied a control group of 43 children with normal birth weights.

RESULTS

In the first cohort, we identified one girl who was a compound heterozygote for point mutations in exon 2 of the IGF-IR gene that altered the amino acid sequence to Arg108Gln in one allele and Lys115Asn in the other. Fibroblasts cultured from the patient had decreased IGF-I-receptor function, as compared with that in control fibroblasts. No such mutations were found in the 43 controls. In the second group, we identified one boy with a nonsense mutation (Arg59stop) that reduced the number of IGF-I receptors on fibroblasts. Both children had intrauterine growth retardation and poor postnatal growth.

CONCLUSIONS

Mutations in the IGF-IR gene that lead to abnormalities in the function or number of IGF-I receptors may also retard intrauterine and subsequent growth in humans.

International Small for Gestational Age Advisory Board consensus development conference statement: management of short children born small for gestational age, April 24-October 1, 2001

OBJECTIVE

To provide pediatric endocrinologists, general pediatricians, neonatologists, and primary care physicians with recommendations for the management of short children born small for gestational age (SGA).

METHODS

A 13-member independent panel of pediatric endocrinologists was convened to discuss relevant issues with respect to definition, diagnosis, and clinical management of short children born SGA. Panel members convened over a series of 3 meetings to thoroughly review, discuss, and come to consensus on the identification and treatment of short children who are born SGA.

CONCLUSIONS

SGA is defined as birth weight and/or length at least 2 standard deviations (SDs) below the mean for gestational age (<or=-2 SD). Accurate gestational dating and measurement of birth weight and length are crucial for identifying children who are born SGA. Comprehensive pregnancy, perinatal, and immediate postnatal data may help to confirm the diagnosis. Maternal, placental, and fetal causes of SGA should be sought, although the cause is often not clear. Most children who are SGA experience catch-up growth and achieve a height >2 SD below the mean; this catch-up process is usually completed by the time they are 2 years of age. A child who is SGA and older than 3 years and has persistent short stature (ie, remaining at least 2 SD below the mean for chronologic age) is not likely to catch up and should be referred to a pediatrician who has expertise in endocrinology. Bone age is not a reliable predictor of height potential in children who are SGA. Nevertheless, a standard evaluation for short stature should be performed. A diagnosis of SGA does not exclude growth hormone (GH) deficiency, and GH assessment should be performed if there is clinical suspicion or biochemical evidence of GH deficiency. At baseline, insulin-like growth factor-I, insulin-like growth factor binding protein-3, fasting insulin, glucose, and lipid levels as well as blood pressure should be measured, and all aspects of SGA-not just stature-should be addressed with parents. The objectives of GH therapy in short children who are SGA are catch-up growth in early childhood, maintenance of normal growth in childhood, and achievement of normal adult height. GH therapy is effective and safe in short children who are born SGA and should be considered in those older than 2 to 3 years. There is long-term experience of improved growth using a dosage range from 0.24 to 0.48 mg/kg/wk. Higher GH doses (0.48 mg/kg/wk [0.2 IU/kg/d]) are more effective for the short term. Whether the higher GH dose is more efficacious than the lower dose in terms of adult height results is not yet known. Only adult height results of randomized dose-response studies will give a definite answer. Monitoring is necessary to ensure safety of medication. Children should be monitored for changes in glucose homeostasis, lipids, and blood pressure during therapy. The frequency and intensity of monitoring will vary depending on risk factors such as family history, obesity, and puberty.

Paracrine overexpression of IGFBP-4 in osteoblasts of transgenic mice decreases bone turnover and causes global growth retardation

Insulin-like growth factor binding protein 4 (IGFBP-4) is abundantly expressed in bone and is generally believed to function as an inhibitor of IGF action. To investigate the function of locally produced IGFBP-4 in bone in vivo, we targeted expression of IGFBP-4 to osteoblasts using a human osteocalcin promoter to direct transgene expression. IGFBP-4 protein levels in calvaria of transgenic (OC-BP4) mice as measured by Western ligand blot were increased 25-fold over the endogenous level. Interestingly, levels of IGFBP-5 were decreased in the OC-BP4 mice, possibly because of a compensatory alteration in IGF-1 action. Morphometric measurements showed a decrease in femoral length and total bone volume in transgenic animals compared with the controls. Quantitative histomorphometry at the distal femur disclosed a striking reduction in bone turnover in the OC-BP4 mice. Osteoblast number/bone length and bone formation rate/bone surface in OC-BP4 mice were approximately one-half that seen in control mice. At birth, OC-BP4 mice were of normal size and weight but exhibited striking postnatal growth retardation. Organ allometry (mg/g body weight) analysis revealed that, whereas most organs exhibited a proportional reduction in weight, calvarial and femoral wet weights were disproportionally small (approximately 70% and 80% of control, respectively). In conclusion, paracrine overexpression of IGFBP-4 in the bone microenvironment markedly reduced cancellous bone formation and turnover and severely impaired overall postnatal skeletal and somatic growth. We attribute these effects to the sequestration of IGF-1 by IGFBP-4 and consequent impairment of IGF-1 action in skeletal tissue.

Targeted expression of a protease-resistant IGFBP-4 mutant in smooth muscle of transgenic mice results in IGFBP-4 stabilization and smooth muscle hypotrophy

The insulin-like growth factor-binding protein 4 (IGFBP-4), the most abundant IGF-binding protein produced by rodent smooth muscle cells (SMC), is degraded by specific protease(s) potentially releasing IGF-I for local bioactivity. IGFBP-4 protease(s) recognizes basic residues within the midregion of the molecule. We constructed a mutant IGFBP-4 with the cleavage domain substitution 119-KHMAKVRDRSKMK-133 to 119-AAMAAVADASAMA-133. Myc-tagged native and IGFBP-4.7A retained equivalent IGF-I binding affinity. Whereas native IGFBP-4 was cleaved by SMC-conditioned medium, IGFBP-4.7A was completely resistant to proteolysis. To explore the function of the protease-resistant IGFBP-4 in vivo, expression of the mutant and native proteins was targeted to SMC of transgenic mice by means of a smooth muscle alpha-actin promoter. Transgene expression was confined to SMC-rich tissues in all lines. Bladder and aortic immunoreactive IGFBP-4/transgene mRNA ratios in SMP8-BP4.7A mice were increased by 2- to 4-fold relative to SMP8-BP4 mice, indicating that the IGFBP-4.7A protein was stabilized in vivo. SMP8-BP4.7A mice had lower aortic, bladder, and stomach weight and intestinal length relative to SMP8-BP4 counterparts matched for protein expression by Western blotting. Thus, IGFBP-4.7A results in greater growth inhibition than equivalent levels of native IGFBP-4 in vivo, demonstrating a role for IGFBP-4 proteolysis in the regulation of IGF-I action.