Search

Context: The natriuretic peptide receptor 2 gene (NPR2) is a causative gene of idiopathic short stature (ISS) with an incidence rate of 2% to 6%. The clinical characteristics of patients with NPR2 heterozygous mutations are atypical, and data on the efficacy of recombinant human growth hormone (rhGH) treatment in patients with NPR2 mutations are limited., Objectives: This work reports 6 cases with NPR2 mutation and explores the characteristics of patients with an NPR2 mutation and their therapeutic response to rhGH., Design, Settings, and Patients: Six Chinese short-stature patients in our hospital with NPR2 mutations by whole-exome sequencing were included. We also searched all previously published NPR2 mutation cases as of August 10, 2020, and information about their medical history, mutations, and rhGH treatment were recorded and summarized., Results: The clinical characteristics of patients with an NPR2 heterozygous mutation mainly included short stature, facial anomalies, and skeletal dysplasia. Skeletal dysplasia mainly included brachydactyly (56.2%), shortened metacarpals or metatarsals (particularly fourth to fifth; 26.1%), and clinodactyly (21.7%). rhGH treatment significantly improved the height SD score (SDS) of patients with NPR2 heterozygous mutations (median, -2.1 vs -2.9, P < .001), especially in girls. The height SDS change correlated negatively with initial age of treatment (r = -0.477; P = .034), and height SDS change of patients with NPR2 heterozygous mutations in the carboxyl-terminal guanylyl cyclase catalytic domain was significantly higher than that of the extracellular ligand-binding region domain (median, 1.9 vs 0.6, P = .019)., Conclusions: ISS patients with skeletal deformities should be tested for an NPR2 mutation. rhGH treatment is beneficial for short-stature patients with NPR2 heterozygous mutations and needs further study., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Context: The C-type natriuretic peptide receptor encoded by the NPR2 gene is a paracrine regulator of the growth plate; heterozygous NPR2 variants cause short stature with possible presence of different signs of bone dysplasia. To date, the effect of growth hormone (GH) treatment has been described in a few individuals with NPR2 gene variants with inconsistent results., Objectives: To identify NPR2 gene variants among children with familial short stature (FSS) and to describe their phenotype, including GH treatment response., Design, Settings and Patients: Out of 747 patients with short stature treated with GH in a single center, 87 with FSS met the inclusion criteria (pretreatment height ≤ -2 standard deviation in both the patient and the shorter parent, unknown genetic etiology). Next-generation sequencing methods were performed to search for NPR2 gene variants. The results were evaluated using the American College of Medical Genetics and Genomics guidelines. The GH treatment response (growth velocity improvement and height standard deviation score development over the first 5 years of treatment) was evaluated., Results: In 5/87 children (5.7%), a (likely) pathogenic variant in the NPR2 gene was identified (p.Ile558Thr [in 2], p.Arg205*, p.Arg557His, p.Ser603Thr). Two children had disproportionate short-limbed short stature, 1 a dysplastic 5th finger phalanx. The growth velocity in the first year of GH treatment accelerated by 3.6 to 4.2 cm/year; the height improved by 1.2 to 1.8 SD over 5 years of treatment., Conclusions: NPR2 gene variants cause FSS in a significant proportion of children. Their GH treatment response is promising. Studies including final height data are necessary to assess the long-term efficacy of this therapy., (© Endocrine Society 2020. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The RING finger protein TRAIP protects genome integrity and its mutation causes Seckel syndrome. TRAIP encodes a nucleolar protein that migrates to UV-induced DNA lesions via a direct interaction with the DNA replication clamp PCNA. Thus far, mechanistically how UV mobilizes TRAIP from the nucleoli remains unknown. We found that PCNA binding is dispensable for the nucleolus-nucleoplasm shuttling of TRAIP following cell exposure to UV irradiation, and that its redistribution did not rely on the master DNA damage kinases ATM and ATR. Interestingly, I-PpoI-induced ribosomal DNA damage led to TRAIP exclusion from the nucleoli, raising the possibility that active ribosomal DNA transcription may underlie TRAIP retention in the nuclear sub-compartments. Accordingly, chemical inhibition of RNA polymerase I activity led to TRAIP diffusion into the nucleoplasm, and was coupled with marked reduction of DNA/RNA hybrids in the nucleoli, suggesting that TRAIP may be sequestered via binding to nucleic acid structures in the nucleoli. Consistently, cell pre-treatment with DNase/RNase effectively released TRAIP from the nucleoli. Taken together, our study defines a bipartite mechanism that drives TRAIP trafficking in response to UV damage, and highlights the nucleolus as a stress sensor that contributes to orchestrating DNA damage responses.

JMJD3 (KDM6B) is an H3K27me3 demethylase and counteracts polycomb-mediated transcription repression. However, the function of JMJD3 in vivo is not well understood. Here we show that JMJD3 is highly expressed in cells of the chondrocyte lineage, especially in prehypertrophic and hypertrophic chondrocytes, during endochondral ossification. Homozygous deletion of Jmjd3 results in severely decreased proliferation and delayed hypertrophy of chondrocytes, and thereby marked retardation of endochondral ossification in mice. Genetically, JMJD3 associates with RUNX2 to promote proliferation and hypertrophy of chondrocytes. Biochemically, JMJD3 associates with and enhances RUNX2 activity by derepression of Runx2 and Ihh transcription through its H3K27me3 demethylase activity. These results demonstrate that JMJD3 is a key epigenetic regulator in the process of cartilage maturation during endochondral bone formation., (© The Author (2015). Published by Oxford University Press on behalf of Journal of Molecular Cell Biology, IBCB, SIBS, CAS. All rights reserved.)

This study tested whether elevated levels of IGF-II in the postnatal period can rescue the dwarfism in IGF-I-deficient mice. Heterozygous Igf1 mutant mice [I(+/-) II(wt)] were crossed with heterozygous Igf1 mutant, phosphoenolpyruvate carboxykinase promoter IGF-II transgenic mice [I(+/-) II(tg)], and [I(+/+) II(wt)], [I(+/+) II(tg)], [I(-/-) II(wt)], and [I(-/-) II(tg)] offspring were investigated. IGF-II levels were 11- and 6-fold higher in male and female [I(-/-) II(tg)] vs. [I(-/-) II(wt)] animals. Western ligand blot analysis revealed markedly reduced activities of 30- and 32-kDa IGF binding proteins (IGFBPs) (most likely IGFBP-1 and IGFBP-2) and the 39- to 43-kDa IGFBP-3 double band in serum from IGF-I-deficient mice. These binding proteins were partially restored by overexpression of IGF-II. Analysis of weight data from the early postnatal period until d 60 showed that, in the absence of IGF-I, elevated levels of IGF-II have no effect on body weight gain. A detailed analysis of body proportions, bone parameters, and organ weights of 60-d-old mice also failed to show effects of IGF-II with one important exception: in Igf1 mutant and also Igf1 intact male mice, IGF-II overexpression significantly increased absolute (+32.4 and +28.6%; P < 0.01) and relative kidney weights (+29.0 and +22.4%; P < 0.001). These changes in kidney weight were associated with reduced phosphorylation of p38 MAPK. In summary, our genetic model shows that substantial amounts of IGF-II in the circulation do not rescue the postnatal growth deficit of IGF-I-deficient mice but increase absolute and relative kidney weights of normal and IGF-I-deficient male mice, suggesting a gender-specific role of IGF-II for kidney growth.

Profound somatotroph hypoplasia in the dwarf (dw/dw) rat is accompanied by an estrogen-dependent induction of prolactin secretion by the GH secretagogue, GHRP-6. Using electron microscopy, we demonstrated that the reduction in the somatotroph population in the dw/dw pituitary is accompanied by the presence of a morphologically distinct lactotroph subpopulation. In these cells, which did not coexpress GH, the size, shape, and number of the secretory granules were between those of the type I and type II lactotrophs. We therefore called these cells intermediate lactotrophs. The intermediate lactotrophs accounted for up to 30% of the total prolactin-positive cell population in dw/dw males and up to 12% in females. Using tannic acid to quantify the fusion of secretory granules, we have shown that the intermediate lactotrophs are unresponsive to either GH-releasing factor (GRF) or TRH but exhibit a sexually dimorphic secretory response to acute ghrelin treatment, granular fusions being 4-fold higher in females. No cell matching the morphology of the novel lactotroph subpopulation was observed in the pituitary of the GRF-insensitive lit/lit mouse. However, ablation of GRF neurons with neonatal monosodium glutamate treatment had no effect on the population of intermediate lactotrophs in the dw/dw rat. Thus, the presence of the intermediate lactotrophs in the dw/dw pituitary appears to be independent of the function of the GRF neurons.

Clinical and laboratory investigations starting in 1958 of a group of dwarfed children resembling isolated GH deficiency but who had very high serum levels of GH led to the description of the syndrome of primary GH resistance or insensitivity (Laron syndrome) and subsequently to the discovery of its molecular defects residing in the GH receptor and leading to an inability of IGF-I generation. With the biosynthesis of IGF-I in 1986, therapeutic trials started. Continuously more and more patients are being diagnosed in many parts of the world with a variety of molecular defects. This syndrome proved to be a unique model that enables the study of the consequences of GH receptor defects, the physiopathology of GH-IGF-I disruption, and comparison of the GH-independent IGF-I effects. This review presents the personal experience gained from the study follow-up and treatment of the 60 patients followed up for many years in the Israeli cohort.

Longitudinal bone growth is determined by endochondral ossification at the growth plate, which is located at both ends of long bones and vertebrae, and involves many systemic hormones and local regulators. C-type natriuretic peptide (CNP), a third member of the natriuretic peptide family, occurs at the growth plate and acts locally as a positive regulator of endochondral ossification through the intracellular accumulation of cyclic GMP (cGMP). The increase in cGMP concentrations is known to activate different signaling mediators, such as cyclic nucleotide phosphodiesterases, cGMP-regulated ion channels, and cGMP-dependent protein kinases (cGKs). The type II cGK (cGKII)-deficient mice (Prkg2(-/-) mice) develop dwarfism as a result of impaired endochondral ossification, suggesting that cGKII is important for the CNP-mediated endochondral ossification. However, given that Prkg2(-/-) mice differ from CNP-deficient mice (Nppc(-/-) mice) in the growth plate histology, which downstream mediator(s) of cGMP play key roles in the process is still an enigma. Here we show that targeted expression of CNP in the growth plate chondrocytes fails to rescue the skeletal defect of Prkg2(-/-) mice. Using cultured fetal mouse tibias, an in vitro model system of endochondral ossification, we also demonstrated that CNP cannot increase the longitudinal bone growth, and chondrocytic proliferation and hypertrophy, and cartilage matrix synthesis in Prkg2(-/-) mice. This study provides in vivo and in vitro genetic evidence that cGKII plays a critical role in CNP-mediated endochondral ossification.

The actions of insulin-like growth factor-I (IGF-I) are modulated by IGF binding proteins (IGFBPs). The effects of IGFBP-1 in vivo are insufficiently known, with respect to inhibitory or stimulatory actions on IGF-induced growth of specific organs. Therefore, we studied the effects of IGFBP-1 on IGF-I-induced somatic and organ growth in pituitary-deficient Snell dwarf mice. Human GH, IGF-I, IGFBP-1, and a preequilibrated combination of equimolar amounts of IGF-I and IGFBP-1 were administered sc during 4 weeks. Treatment with IGF-I alone induced a significant increase in body length (108% of control) and weight (112%) as well as an increase in weight of the submandibular salivary glands (135%), kidneys (124%), femoral muscles (111%), testes (129%), and spleen (126%) compared with saline-treated controls. IGFBP-1 alone induced a significant increase in weight of the kidneys (152% of control). Coadministration of IGF-I with IGFBP-1 neutralized the stimulating effects of IGF-I on body length and weight as well as on the femoral muscles and testes. In contrast, the weights of the submandibular salivary glands (143%) were not significantly different from those of IGF-I-treated animals, whereas the weights of the kidneys (171%) and spleen (156%) were significantly increased compared with IGF-I-treated mice. The effect of IGFBP-1 plus IGF-I on kidney weight was not significantly greater than the effect of IGFBP-1 alone. Western ligand blotting showed induction of the IGFBP-3 doublet as well as IGFBPs with molecular masses of 24 kDa, most probably IGFBP-4, by human GH, IGF-I alone, and IGF-I in combination with IGFBP-1. Our data show that coadministration of IGFBP-1 inhibits IGF-I-induced body growth of GH-deficient mice but significantly stimulates the growth promoting effects of IGF-I on the kidneys and the spleen. These data warrant further investigation because differences in concentrations of IGFBP-1 occurring in vivo may influence IGF-I-induced anabolic processes.

To evaluate GH's role in cardiac physiology and its interrelationship with the beta-adrenergic system, we studied GH-deficient dwarf (dw/dw) and control rats in 4 groups of 20 each: dwarf group receiving placebo, dwarf-GH group receiving 2 mg/kg GH, dwarf-GH-propranolol group receiving 2 mg/kg GH and 750 mg/liter propranolol, and a control group of Lewis rats receiving placebo. Dwarf rats showed reduced left ventricular weight and myocyte cross-sectional area, and impaired cardiac performance in vitro. Left ventricular pressure-volume curves showed a shift upward and leftward, indicating reduced distensibility. These abnormalities reversed after GH treatment regardless of concomitant propranolol administration. Although isoproterenol responsiveness was reduced in dwarf rats, there were no differences in beta-adrenergic receptor density, affinity, Na+,K+-adenosine triphosphatase activity, or adenylyl cyclase activity. In summary, myocyte size, cardiac structure, myocardial contractility, and distensibility are abnormal in GH deficiency. The effects of GH are not mediated by the beta-adrenergic pathway, which, in turn, is unaffected by changes in the GH-insulin-like growth factor I axis. Thus, GH plays a regulatory role in normal cardiac physiology that is independent of the beta-adrenergic system.

Background: The compensatory increase in glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) which follows a reduction in renal mass may be mediated by growth hormone, a renal vasodilator., Methods: GFR, ERPF and glomerular morphometry were assessed in the dwarf rat, selectively deficient in GH, and compared its Lewis base strain. Studies were performed 21-days after sham-operation, unilateral nephrectomy or subtotal nephrectomy in age-matched animals. GFR and ERPF were assessed from the renal clearance of inulin and p-aminohippurate measured under barbiturate anaesthesia., Results: The dwarf rat had a lower GFR and ERPF than the Lewis rat, in proportion to its lower body weight and lower kidney weight. Kidneys from the dwarf rat had a similar number of glomeruli to the Lewis, but smaller glomerular components in proportion to a lower kidney weight. Following unilateral nephrectomy, GFR (dwarf + 58%, Lewis + 53%) and ERPF (dwarf + 58%, Lewis + 52%) increased to a similar degree in both rat strains. Glomerular diameter, volume and capillary surface area increased in proportion to kidney growth, although compensatory renal growth (dwarf + 62%, Lewis + 78%) was somewhat lower in the dwarf. Following 5/6 subtotal nephrectomy, GFR (dwarf + 143%, Lewis + 171%) increased to a similar degree in both rat strains while ERPF (dwarf + 108%, Lewis + 48%) and compensatory renal growth (dwarf + 115%, Lewis + 86%) were greater in the dwarf than the Lewis rat. Subtotal nephrectomy was also associated with an increase in the thickness of the glomerular basement membrane in both rat strains., Conclusions: The results do not support a role for GH in the compensatory increase in renal function or hypertrophy which follows a reduction in renal mass, excluding this as a potential mechanism for GH-dependent renal scarring.

To determine the effects of lactogenic hormones on pancreatic islet size and numbers, islets of 3-month-old female mice were intravitally stained by an ip injection of an alkaline-alcohol solution of diphenylthiocarbazone (dithizone; 100 micrograms/g BW). After 15 min, animals were killed, and pancreases were removed, diced, cleared in glycerol, and whole mounted on slides. Major and minor axes of Zn dithizoate-stained islets were measured at x40 magnification. Islet areas and volumes were calculated. Animals and appropriate controls studied included 16-day pregnant, two lines of human GH-expressing transgenic, and two lines of pituitary PRL- and GH-deficient dwarf mice. Islet numbers per pancreas ranged from about 500-1200 in all groups except the transgenic mice, in which two of five animals in one group and one of five in the other showed significant increases in islet numbers (> 3 x SD control mean). In all cases, significant (P < 0.05) changes in both islet area and volume occurred. Area increased 2-fold in both pregnant and transgenic mice and decreased by a similar amount in dwarf mice. Islet volume increased 2- and 3-fold in pregnant and transgenic animals, respectively, and decreased 2- to 5-fold in dwarf mice. Analysis of the distributions of islet sizes revealed that almost all of the volume increases in the pregnant and transgenic mice and the decreases in dwarf mice were accounted for by alterations in the numbers and sizes of large (diameter, > 150 microns) islets. Our results with dwarf mice show that maintenance of islet numbers is not dependent upon pituitary PRL or GH; however, results with transgenic mice suggest that prolonged high levels of lactogens may induce islet neogenesis. The islet area and volume results for all of the mice studied support the hypothesis that lactogenic hormones are potent regulators of islet mass.

Hypothalamic expression of growth hormone-releasing hormone (GHRH) was quantified morphologically in dwarf mice which exhibit spontaneous genetic GH absence. Mouse GHRH mRNA was assessed by in situ hybridization; densitometric evaluation of total mRNA in dwarfs showed levels 2.3-fold higher than in phenotypically normal siblings (p < 0.01); assessment of mRNA per neuron by autoradiographic grain counting indicated a 2.5-fold increase per cell in dwarfs (p < 0.005). GHRH peptide was evaluated immunocytochemically using a new mouse-specific antiserum; numbers of neurons containing detectable levels were 3-fold higher in dwarfs (p < 0.005). The increase in GHRH mRNA corroborates that reported previously in the GH-deficient little mouse, and after hypophysectomy in rats; GHRH peptide increase contrasts with previous reports of the effect of acute GH removal by hypophysectomy, in which GHRH levels fell. The results suggest that chronic GH deficiency is accompanied by increased translation as well as transcription of GHRH.

GH is the hormone primarily responsible for regulating body size within the genetic program. While GH has pleiotropic actions on cellular growth and metabolism, most of its effects are believed to be mediated by a single GH receptor. This receptor is not functional in tissues from patients with Laron dwarfism. We used human T-cell leukemia virus-immortalized T-lymphoblast cell lines from Laron dwarfs and normal individuals to examine the mechanism of GH-induced insulin resistance at the cellular level. GH (5-500 micrograms/L) caused a profound decrease in the sensitivity of normal T-lymphoblasts in response to all insulin concentrations (P < 0.0001 vs. insulin alone); pretreatment with GH and GH receptor antibody significantly improved sensitivity to all concentrations of insulin (P = NS vs. insulin alone). Preincubation with GH and PRL receptor antibody was associated with partial improvement in insulin sensitivity (P = 0.004 vs. insulin alone). Thus, in normal T-cell lines, the major pathway of GH-induced insulin resistance appears to be directed by the GH receptor, with a smaller effect mediated through the PRL receptor. While T-cell lines from Laron dwarfs do not respond to GH in clonal proliferation assays, GH (50 and 100 micrograms/L) caused profound insulin resistance in these cells (P = 0.008 and P < 0.0001, respectively, vs. insulin alone). GH receptor antibody did not abrogate this effect at any insulin concentration (P = NS vs. insulin alone), but there was partial restoration of insulin sensitivity when GH and PRL receptor antibody were coincubated (P = 0.0069 vs. insulin alone). Thus, in Laron T-cell lines, PRL and perhaps other lactogenic receptors appear to mediate GH-induced insulin resistance. The kinetics of GH-induced insulin resistance in Laron T-cells were also distinct from the pattern seen in normal T-cells, and unlike in normal cells, GH had no effect on insulin-like growth factor-I-induced clonal expansion of Laron T-cell lines (P = NS vs. insulin-like growth factor-I alone). These results provide evidence for an alternative pathway of GH action revealed in cells lacking classical growth responses to GH.

A new mutant GH-deficient dwarf rat has been used to study the effects of iv infusions of human GH (hGH) and recombinant human insulin-like growth factor I (hIGF-I). This animal has only about 5% of normal pituitary GH content, low circulating GH levels, and no regular GH surges. The defect seems to be specific for GH. Infusions of hIGF-I at 180 micrograms/day for 9 days elevated serum IGF-I concentrations significantly over those in the saline-infused controls (713 +/- 20 ng/ml vs. 395 +/- 31 ng/ml); hGH infusions did not raise IGF-I levels significantly (435 +/- 20 ng/ml). Gel filtration of serum samples showed that the high-dose hIGF-I infusions increased free IGF concentrations, without apparently altering the pattern of IGF-I binding whereas hGH infusions increased the amount of high mol wt IGF-I binding protein. Neither IGF-I nor hGH infusions affected the small amounts of rat GH present in the dwarf rat pituitary glands. Continuous iv infusions of hGH (200 mU/day for 9 days) stimulated body wt gain (2.1 +/- 0.2 g/day) and bone growth (96 +/- 9 microns/day) significantly compared to saline-infused dwarf rats (1.2 +/- 0.3 g/day and 43 +/- 3 microns/day). Infusions of hIGF-I at 180 micrograms/day produced a body wt gain (2.1 +/- 0.5 g/day) similar to that seen in the hGH-infused group but a significantly smaller stimulation of bone growth (63 +/- 3 microns/day). Infusion of a 5-fold lower dose of hIGF-I (36 micrograms/day for 9 days) had no effect on body wt or bone growth. Food intake was unaffected by either hGH or hIGF-I infusions. The pattern of tissue growth was affected differentially by hGH and IGF-I infusions that produced the same overall body wt gain. hGH induced a relatively proportional growth in most of the organs studied, whereas hIGF-I infusion at 180 micrograms/day stimulated a disproportionately greater growth of the kidney, adrenals, and spleen. In some of the animals, tissues were extracted for RIA of IGF-I; the amounts of IGF-I in the liver were similar in control, hGH, or IGF-I-infused animals, whereas kidney and adrenals from IGF-I infused animals contained larger amounts of immunoreactive IGF-I than did those tissues from hGH-treated rats. Thus, both hGH and hIGF-I can promote growth in the mutant dwarf rat, but they differ both quantitatively and qualitatively in their pattern of actions.

Snell-type dwarf mice were injected with TSH, GH, or both hormones together for 6 days. GH induced an increase in body weight but not in the weight of the thyroid gland itself; on the contrary, TSH caused an increase in the weight of the thyroid but no increase in body weight. After TSH injection, the relative volume of the thyroid parenchyme was enhanced by 45% compared to that in untreated dwarf mice, and the radius of the follicles and follicular lumina increased by 50% and 48%, respectively. The major effect of TSH was an increase in cellular volume (+93%), and the mean number of cells in the average follicle was doubled, without a reduction in the number of follicles. GH had almost the same effect as TSH on the relative volume of the parenchyme and caused the radius of follicles and of the follicular lumina to increase by 61% and 69%, respectively. However, GH did not influence cellular volume. Its primary effect was to stimulate cellular division (cells were increased about 5 times in the average follicle) and to reduce the number of follicles. The nucleo-cytoplasmic ratio increased with GH but decreased with TSH. T4 serum levels increased to a much lesser extent with GH than with TSH, while normal values were obtained with both hormones together. At a morphological level, the combined administration of TSH and GH produced the same qualitative effects as separate administration, inducing an increase in cell volume and number which was less than the sum of the effects of each hormone administered separately.

Tissues from patients with Laron dwarfism are resistant to the actions of endogenous or exogenous GH. As a result, insulin-like growth factor I (IGF-I) levels are low, possibly contributing to the severe growth deficiency that occurs in patients with this syndrome. In this study, we found that erythroid progenitor cells and permanently transformed T-cell lines from two patients with Laron dwarfism responded in vitro to added IGF-I in concentrations ranging between 1-10 ng/mL despite no stimulatory response to added GH in concentrations of up to 500 ng/mL. Normal or near-normal responsiveness to insulin was also demonstrated. The persistence of GH resistance in the cultured T-cell lines confirms the primary genetic nature of the defect in Laron dwarfism. The preservation of in vitro growth responsiveness to IGF-I in hematopoietic tissue from the Laron dwarfs suggests that affected individuals are sensitive to this factor and may respond to it in vivo.

Acromegaloidism is a syndrome characterized by features of acromegaly without biochemical evidence of excessive GH or somatomedin production. We searched for a growth factor in the serum of patients with this syndrome. Growth-promoting activity was measured by determining the stimulatory effect of whole and fractionated serum on colony formation by human erythroid progenitors in vitro. Sera from five subjects with acromegaloidism gave a mean (+/- SEM) stimulated colony growth of 211 +/- 4.0 colonies, in contrast to normal sera which yielded a mean colony growth of 100 +/- 11.0 (n = 9; P less than 0.001). When serum was chromatographed on a Sephadex G-200 column, the maximal stimulation of colony growth was found in the fractions coinciding with the descending slope of the second protein peak. Based on gel filtration chromatography, the estimated molecular weight was 70,000 daltons. Epidermal growth factor, nerve growth factor, fibroblast growth factor, and platelet-derived growth factor resulted in no substantial stimulation of colony growth under the conditions used. Although the erythroid progenitor cells of a Laron dwarf were unresponsive to 200 ng/ml human GH, they were clearly stimulated by serum from a patient with acromegaloidism. The present study describes the presence of a heretofore unidentified growth factor in the serum of subjects with acromegaloidism. This factor also stimulated the erythroid precursor cells of a Laron dwarf whose cells were unresponsive to GH. The physiological role of this growth factor in normal man as well as its pathogenic role in subjects with acromegaloidism remain to be established.

Leprechaunism is a rare inherited disorder characterized by severe intrauterine growth retardation and insulin resistance. Cultured skin fibroblasts from an infant with Leprechaunism were previously reported to show decreased stimulation of DNA synthesis by insulin despite apparently normal binding of [125I]insulin and [125I]somatomedin C. We have now further investigated the growth of this patient's fibroblasts and compared their metabolic responses to insulin and various peptide growth factors with responses in normal foreskin-derived fibroblasts. The doubling time of Leprechaun fibroblasts was prolonged (90 vs. 29 h), and their morphology was abnormal. Stimulation of [3H]glucose uptake was minimal with low insulin levels (1--10 ng/ml) relative to controls, but was comparable at higher insulin concentrations (1--10 micrograms/ml). Stimulation of [3H] aminoisobutyric acid uptake by insulin, epidermal growth factor (EGF), multiplication-stimulating activity, and somatomedin C (Sm-C) in Leprechaun cells was diminished relative to control cells at all concentrations tested. Furthermore, stimulation of [3H]thymidine incorporation in Leprechaum cells by EGF, Sm-C, and fibroblast growth factor was also subnormal. Binding of [125I]EGF to Leprechaun fibroblasts was not decreased. It is concluded that fibroblasts from this patient are resistant to the metabolic effects of insulin, EGF, Sm-C, and fibroblast growth factor. Since receptors for three of these peptides are apparently normal, it is likely that the defect in these cells is at the postreceptor level, perhaps involving a metabolic pathway common to the action of multiple growth factors.

Two siblings with Cockayne syndrome (CS) had extremely severe and early onset cachectic dwarfism, developmental delay, cataracts, microcephaly, peripheral neuropathy, and spastic quadriplegia. In order to study the inherited DNA-repair defect known to be present in cultured CS cells, a lymphoblastoid line was established from the younger sibling. Tissue culture studies revealed the line to have a hypersensitivity to the lethal effects of 254-nm ultraviolet radiation (UV) equivalent to that of lymphoblastoid lines from CS patients who had either the usual severity or a very mild form of CS. Autopsy of the older sibling at six years of age showed the brain to be severely atrophic, with particularly severe cerebellar atrophy. There was a marked reduction in the number of granule cells in the cerebellum and irregular patchy myelination throughout the brain. Many astrocytes contained either a large, bizarre-shaped nucleus or multiple nuclei. Some Purkinje cells of the cerebellum and pyramidal neurons of the hippocampus were binucleated. It is suggested that the DNA-repair defect of CS causes abnormalities in nuclear DNA replication and cell division which result in cell death and in the observed nuclear abnormalities.

A case of leprechaunism is described. This is thought to be the first reported in a black child.

Myelin in the central nervous system of 19-day-old Snell's dwarf mice was studied morphologically and biochemically. The number of myelinated axons per unit area in the corticospinal tract and anterior commissure of dwarf mice was significantly decreased. The distribution of myelinated fibers based upon sheath thickness was normal. The yield of isolated myelin was decreased by 56% in the dwarf but its compositions of lipids, proteins, glycoproteins and 2', 3'-cyclic nucleotide 3'-phosphohydrolase activity was nearly equivalent to that of control myelin.