Explorative function in Prader-Willi syndrome analyzed through an ecological spatial task

This study was aimed at evaluating the spatial abilities in individuals with Prader-Willi syndrome (PWS) by using an ecological large-scale task with multiple rewards. To evaluate the extent of spatial deficit in PWS individuals, we compare their performances with those of individuals with Williams Syndrome (WS) in which the spatial deficits have been widely described. Participants had to explore an open space to search nine rewards placed in buckets arranged according to three spatial configurations: a Cross, a 3×3 Matrix and a Cluster composed by three groups of three buckets each. PWS individuals exhibited an explorative deficit in Cluster and Cross configurations, while WS participants in Matrix and Cross configurations. The findings indicate that the structural affordances of the environment influence the explorative strategies and can be related to how spatial information is processed.

Metabolic syndrome in adult patients with Prader-Willi syndrome

BACKGROUND AND AIMS

Prader-Willi syndrome (PWS), the most common genetic cause of obesity, is characterized by elevated morbility and mortality in all ages. In this context, non-obese PWS children showed low frequency of metabolic syndrome (MetS), while a comparable prevalence was observed in obese PWS and obese controls. Aim of this study was to estimate the occurrence of MetS and its components in a large group of PWS adults, according to obesity status.

METHODS AND RESULTS

A cross-sectional study was performed in 108 PWS aged 18.0-43.2 years (87 obese and 21 non-obese) and in 85 controls with nonsyndromic obesity matched for age, gender, and BMI with obese PWS. Non-obese PWS showed lower waist circumference, insulin, HOMA-index, triglycerides, diastolic blood pressure, and higher HDL-C than both obese PWS and obese controls (p < 0.017). Obese PWS showed higher glucose and systolic blood pressure than both non-obese PWS and obese controls (p < 0.017). MetS was found in 1/21 (4.8%) non-obese PWS, 36/87 (41.4%) obese PWS and 39/85 (45.9%) obese controls. Non-obese PWS showed lower frequency for each MetS component as compared with obese PWS and obese controls. PWS patients with deletion of the chromosome 15q11-13 showed a lower risk for low HDL-C (p < 0.01) and a trend towards a lower MetS risk (p < 0.06) compared to subjects without deletion.

CONCLUSION

Our findings suggest the main role that obesity status plays on the individual metabolic risk clustering in PWS adults. Early identification of MetS could be helpful to improve morbidity and prevent mortality in such patients.

Multiple forms of hypogonadism of central, peripheral or combined origin in males with Prader-Willi syndrome

BACKGROUND

Hypogonadism in Prader-Willi syndrome (PWS) is generally attributed to hypothalamic dysfunction or to primary gonadal defect, but pathophysiology is still unclear.

OBJECTIVES

To investigate the aetiology of hypothalamic-pituitary-gonadal axis dysfunction in PWS males.

METHODS

Clinical examination and blood sampling for luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, inhibin B and sexhormone-binding globulin (SHBG) were performed in 34 PWS patients, age 5·1-42·7 years, and in 125 healthy males of same age range. All participants were divided into two groups : < or ≥13·5 years.

RESULTS

Pubertal PWS patients showed an arrest of pubertal development. Patients <13·5 years had normal LH, FSH, testosterone and 7/10 had low inhibin B. Among those ≥13·5 years, 8/24 patients had normal LH and testosterone, high FSH and low inhibin B. 5/24 had low FSH, LH, testosterone and inhibin B; one showed normal LH and FSH despite low testosterone and inhibin B; 4/24 had low testosterone and LH but normal FSH despite low inhibin B; 6/24 showed high FSH, low inhibin B and normal LH despite low testosterone. Compared with controls, patients <13·5 years had lower LH, inhibin B, similar FSH, testosterone, SHBG levels and testicular volume; those ≥13·5 years had smaller testicular volume, near-significantly lower LH, testosterone, SHBG, inhibin B and higher FSH.

CONCLUSION

PWS patients display heterogeneity of hypogonadism: (i) hypogonadotropic hypogonadism of central origin for LH and/or FSH; (ii) early primary testicular dysfunction (Sertoli cells damage); and (iii) a combined hypogonadism (testicular origin for FSH-inhibin B axis and central origin for LH-T axis).

Computer use, free time activities and metabolic control in patients with type 1 diabetes

We investigated the influence of computer's use on metabolic control in 115 patients with type 1 diabetes (DM1). Multiple linear regression showed that HbA1c% was not related to age, DM1 duration, TV watching or computer use but was independently and negatively related to the weekly hours spent on physical exercise.

A survey on Prader-Willi syndrome in the Italian population: prevalence of historical and clinical signs

Clinical criteria for the diagnosis of Prader-Willi Syndrome (PWS) were established by consensus in 1993 (Holm et al.). Specific molecular testing is now available and the purpose of diagnostic criteria has shifted to identify individuals to test, thus avoiding the expense of unnecessary analysis. The aim of this study was to find clinical indicators to select patients with suspected PWS for laboratory testing. We analyzed the prevalence of clinical signs and symptoms in 147 genetically diagnosed Italian patients with PWS (67 males and 80 females), aged from 9 months to 34.6 years (13.6 +/- 8.3 years), using the consensus diagnostic criteria, and according to age, sex and type of genetic abnormality. The prevalence of several clinical features changed significantly with age, but very few with sex. According to genetic subtypes (deletion vs UPD), only hypopigmentation and acromicria were more frequent in patients with deletion. Some criteria considered as minor or supportive by Holm et al. have higher prevalence than some major criteria. In conclusion, in order to identify patients with suspected PWS to submit to laboratory testing, we recommend a classification of clinical criteria according to age, giving more attention to those so-called minor or supportive criteria.

BioEnterics intragastric balloon for treatment of morbid obesity in Prader-Willi syndrome: specific risks and benefits

BACKGROUND

Obesity in Prader-Willi Syndrome (PWS) is progressive, severe, and resistant to dietary, pharmacological, and behavioral treatment. A body weight reduction is mandatory to reduce the risk of cardio-respiratory and metabolic complications. The aim of the study was to assess risks and benefits of BioEnterics Intragastric Balloon (BIB) for treatment of morbid obesity in PWS patients.

METHODS

Twenty-one BIB were positioned in 12 PWS patients (4 M, 8 F), aged from 8.1 to 30.1 years, and removed after 8 +/- 1.4 months (range: 5-10 months). Auxological, clinical, and nutritional evaluations were performed every 2 months. Variations in body composition were analysed by dual energy X-ray absorbiometry (DXA).

RESULTS

One patient (28.5 years, BMI: 59.3 kg/m(2)) died 22 days after BIB positioning because of gastric perforation. In another case (26.2 years, BMI: 57.6 kg/m(2)), BIB was surgically removed after 25 days because of symptoms suggesting gastric perforation (not confirmed). The remaining ten patients showed a significant decrease of BMI (p = 0.005) and of fat tissue as measured by DXA (p = 0.012). No significant modifications in bone mineral density (BMD) occurred, but a slight loss in lean body mass (p = 0.036) was documented. In five patients, BIB treatment was repeated more than once.

CONCLUSION

This study shows that when noninvasive pharmacological therapies fail, BIB may be effective to control body weight in PWS patients with morbid obesity, particularly when treatment is started in early childhood. However, careful clinical follow-up and close collaboration with parents are crucial to avoid severe complications, which can be caused by persisting unrestrained food intake.

Multidimensional triple resonance NMR spectroscopy of isotopically uniformly enriched proteins: a powerful new strategy for structure determination

A procedure is described that affords complete 1H, 13C and 15N resonance assignment in proteins of up to about 25 kDa. The new approach requires uniform isotopic enrichment of the protein with 13C and 15N and correlates resonances of adjacent nuclei using the relatively large and well-resolved one-bond J couplings. Spectral overlap, a common problem in the application of two-dimensional NMR, is removed by increasing the dimensionality of the new methods to three or four, without increasing the number of observed resonances. With complete 1H, 13C and 15N resonance assignments available, the nuclear Overhauser effect (NOE)-based interproton distance constraints can be extracted in a very straightforward manner from four-dimensional NOE spectra.

The effects of calcitriol and nicotinamide on residual pancreatic beta-cell function in patients with recent-onset Type 1 diabetes (IMDIAB XI)

BACKGROUND

A number of recent studies underline the importance of vitamin D in the pathogenesis of Type 1 diabetes (T1D).

AIMS

The aim of this study was to investigate whether supplementation with the active form of vitamin D (calcitriol) in subjects with recent-onset T1D protects residual pancreatic beta-cell function and improves glycaemic control (HbA(1c) and insulin requirement).

METHODS

In this open-label randomized trial, 70 subjects with recent-onset T1D, mean age 13.6 years +/- 7.6 sd were randomized to calcitriol (0.25 microg on alternate days) or nicotinamide (25 mg/kg daily) and followed up for 1 year. Intensive insulin therapy was implemented with three daily injections of regular insulin + NPH insulin at bedtime.

RESULTS

No significant differences were observed between calcitriol and nicotinamide groups in respect of baseline/stimulated C-peptide or HbA1c 1 year after diagnosis, but the insulin dose at 3 and 6 months was significantly reduced in the calcitriol group.

CONCLUSIONS

At the dosage used, calcitriol has a modest effect on residual pancreatic beta-cell function and only temporarily reduces the insulin dose.

A two year observational study of nicotinamide and intensive insulin therapy in patients with recent onset type 1 diabetes mellitus

BACKGROUND AND AIMS

A number of trials have evaluated residual beta-cell function in patients with recent onset type 1 diabetes mellitus (DM1) treated with nicotinamide in addition to intensive insulin therapy (IIT). In most studies, only a slight decline of C-peptide secretion was observed 12 months after diagnosis; however, no data is available on C-peptide secretion and metabolic control in patients continuing nicotinamide and IIT for up to 2 years after diagnosis.

PATIENTS AND METHODS

We retrospectively analysed data from 25 patients (mean age 14.7 years +/- 5 SD) with DM1 in whom nicotinamide at a dose of 25 mg/kg b. wt. was added from diagnosis (< 4 weeks) to IIT (three injections of regular insulin at meals + one NPH at bed time) and continued for up to 2 years after diagnosis. Data were also analysed from patients (n = 27) in whom IIT was introduced at diagnosis and who were similarly followed for 2 years. Baseline C-peptide as well as insulin dose and HbA1c levels were evaluated at 12 and 24 months after diagnosis.

RESULTS

In the course of the follow-up, patients on nicotinamide + IIT or IIT alone did not significantly differ in terms of C-peptide secretion (values at 24 months in the two groups were 0.19 +/- 0.24 nM vs 0.19 +/- 0.13 nM, respectively). Insulin requirement (0.6 +/- 0.3 U/kg/day vs 0.7 +/- 0.2 U/kg/day at 24 months, respectively) did not differ between the two groups. However, HbA1c was significantly lower 2 years after diagnosis in patients treated with nicotinamide + IIT (6.09 +/- 0.9% vs 6.98 +/- 0.9%, respectively, p < 0.01). No adverse effects were observed in patients receiving nicotinamide for 2 years.

CONCLUSION

Implementation of IIT with the addition of nicotinamide at diagnosis continued for 2 years improves metabolic control as assessed by HbA1c. In both nicotinamide and control patients, no decline in C-peptide was detected 2 years after diagnosis, indicating that IIT preserves C-peptide secretion. We conclude that nicotinamide + IIT at diagnosis of DM1 prolonged for up to 2 years can be recommended, but longer follow-up is required to determine whether nicotinamide should be continued beyond this period.

A randomized trial of nicotinamide and vitamin E in children with recent onset type 1 diabetes (IMDIAB IX)

OBJECTIVE

Various adjuvant therapies have been introduced along with intensive insulin therapy in patients with recent onset type 1 diabetes. Nicotinamide (NA), administered at diagnosis of the disease, can have beneficial effects on the clinical remission rate, improve metabolic control and preserve or slightly increase beta-cell function, probably by reducing toxicity due to free oxygen radicals. Vitamin E, a known antioxidant, inhibits lipid peroxidation; this can lead to protection of islet beta cells from the combined effects of interleukin 1, tumor necrosis factor and gamma interferon. The aim of the present study was to investigate whether the addition of vitamin E to NA could improve metabolic control and the residual beta-cell function, as measured by C-peptide secretion, in children and adolescents with recent onset type 1 diabetes; patients were followed-up for 2 years after diagnosis.

PATIENTS AND STUDY DESIGN

Recent onset type 1 diabetes patients (n=64, mean age 8.8 years) were recruited by participating centres of the IMDIAB group. Thirty-two patients were randomized to NA (25 mg/kg body weight) plus vitamin E (15 mg/kg body weight); 32 patients acted as controls and received NA only at the same dose as above. Intensive insulin therapy was applied to both treatment groups.

RESULTS

There were three drop outs during the 2-year follow-up period. Overall, patients assigned to the NA+vitamin E group or the NA group did not significantly differ in terms of glycated hemoglobin (HbA1c) levels, insulin requirement or baseline C-peptide secretion. Patients diagnosed at an age of less than 9 years showed significantly reduced C-peptide levels compared with those aged over 9 years at diagnosis and at the 2-year follow-up but there were no differences between the NA and NA+vitamin E treated groups. However at 6 months, patients over 9 years of age treated with NA+vitamin E showed significantly higher C-peptide compared with the NA group (P<0.003). In both age groups and in the different treatment groups, C-peptide levels found at diagnosis were preserved 2 years later.

CONCLUSIONS

The use of NA alone, or in combination with vitamin E, along with intensive insulin therapy is able to preserve baseline C-peptide secretion for up to 2 years after diagnosis. This finding is of particular interest for pre-pubertal children with type 1 diabetes and has never been reported before.

Hypogonadism and pubertal development in Prader-Willi syndrome

Genital abnormalities and disorders of pubertal development such as hypogonadism are common in Prader-Willi Syndrome (PWS). Depending on age, PWS patients present genital hypoplasia and delayed or incomplete gonadal maturation. Nevertheless, only a few evaluations have been made of these findings in this syndrome; in the cases previously reported the diagnosis of PWS has often been based only on clinical criteria and not confirmed by genetic analysis. In this paper we describe both external genital findings and spontaneous pubertal development in 84 patients aged from 2.1 to 35.4 (42 males, 42 females) affected by PWS. Diagnosis was made using the Holm and Cassidy criteria and was confirmed by genetic analysis (methylation test and/or FISH). We evaluated the presence of cryptorchidism, scrotal development, length of penis and volume of testis in males and outlook of labia minora and/or clitoris, age of menarche and features of menses (when present) in females; in both sexes we also evaluated the onset of puberty. All recruited males showed cryptorchidism, which was bilateral in 36 out of 42 patients (86%); 38 patients (90%) underwent orchidopexy. Small testes and scrotal hypoplasia were present in 76% and 69% of cases, respectively. In 76% of females, hypoplasia or absence of labia minora and/or clitoris was described. Spontaneous menarche occurred only in 14/32 cases (44%) over the age of 15 years, but menstrual cycles were often a periodical vaginal spotting. Primary amenorrhea was diagnosed in 56% of cases. Isolated premature pubarche was present in six males and in six females (14% of cases) while one male and two females were affected by precocious puberty (3.6%).

CONCLUSION

Hypogonadism represents a common clinical feature in PWS, confirming the importance of such a major diagnostic criterion. Cryptorchidism was consistently present in all our cases. Patients with PWS commonly fail to spontaneously complete puberty, although some patients may have early pubarche or, more rarely, precocious puberty. In older subjects, hormonal replacement therapy is not always necessary and it must be reserved for selected patients.

The Continuous Glucose Monitoring System (CGMS) in type 1 diabetic children is the way to reduce hypoglycemic risk

BACKGROUND

Diabetic children treated with intensive insulin therapy are showing a dangerous increase in severe hypoglycemic episodes. The Continuous Glucose Monitoring System (CGMS) allows glycemic profiles to be monitored over a 72-h period. The aim of the present study was to evaluate whether this system is sufficiently sensitive to detect asymptomatic hypoglycemia, and to determine if its periodic application would help to minimize the hypoglycemic risk in children with type 1 diabetes mellitus (T1DM).

METHODS

Twenty-seven T1DM children (age range 6-13.1 years) were enrolled in the study. The sensor was inserted subcutaneously in each patient and the standard four or five registrations of capillary glycemia per day were performed. Eighteen patients continued in the study and the glucose sensor was again inserted after a 6-week interval. At the beginning and end of the study, fructosamine, glycosylated hemoglobin (HbA(1c)), median glycemia, number and duration of hypoglycemic events and insulin requirement were evaluated.

RESULTS

A significantly higher number of asymptomatic hypoglycemic events was revealed by CGMS in comparison with the standard system (3.6 +/- 2.3 vs 0.7 +/- 0.9; p < 0.0001). In patients who continued in the study, insulin therapy adjustments reduced the incidence of hypoglycemic events (2.5 +/- 1.7 vs 3.9 +/- 2.2; p < 0.05). At the 6-week point, the fructosamine level was reduced (330 +/- 30 vs 349 +/- 24 micro mol/l; p < 0.05).

CONCLUSIONS

The CGMS is a useful device not only for detecting unrecognized hypoglycemia, but also for modifying insulin therapy in order to reduce hypoglycemic events. The system appears to be useful in avoiding long exposure to hypoglycemia.

Accuracy of fine needle aspiration biopsy of thyroid nodules in detecting malignancy in childhood: comparison with conventional clinical, laboratory, and imaging approaches

In childhood the traditional diagnostic approach to thyroid nodules consists of clinical, laboratory, and imaging evaluations. A safe and accurate procedure is needed to promptly identify patients who require surgery. In regard to the usefulness of fine needle aspiration biopsy, the data in the literature concerning children and adolescents are scanty. The aim of this study was to evaluate and compare the diagnostic accuracies of clinical, laboratory, and imaging data collected retrospectively in a group of pediatric patients with thyroid nodules submitted to fine needle aspiration biopsy. Forty-two patients who underwent surgery for thyroid nodules, recruited in 9 Italian pediatric endocrine units, were retrospectively studied. According to histological diagnosis, they were divided into 2 groups, 22 patients with benign lesions and 20 patients with malignant lesions. From clinical records we obtained data about 1) symptoms of neck compression; 2) cervical adenopathy; 3) thyroid function, calcitonin level, and antithyroid antibody titers; 4) ultrasonography; 5) (99m)Tc scintiscanning; and 6) cytology obtained with fine needle aspiration biopsy. Patients and nodule characteristics were analyzed statistically for associations with the presence of thyroid cancer. Among clinical findings, only adenopathy was significantly higher in the group with cancer (8 of 22 benign lesions vs. 16 of 20 malignant lesions; P = 0.006). Thyroid function and antibody titers were similar in the 2 groups, whereas the serum calcitonin level was elevated only in 1 patient with malignant lesions. Among ultrasonography findings, no significant statistical difference was found between the 2 groups with regard to number, dimensions, growth progression, or hypoechogenic pattern of the nodules. Regarding scintigraphic findings, no significant difference was found between the 2 groups. However, a positive correlation (r = 0.90; P < 0.0001) was found between fine needle aspiration biopsy cytological findings and histological diagnoses. The sensitivity, specificity, and accuracy of fine needle aspiration biopsy were 95%, 86.3%, and 90.4%, respectively. A multiple regression analysis showed that only fine needle aspiration biopsy (beta coefficient = 0.963; P < 0.0001) significantly contributed to detecting malignancy (multiple r = 0.973; P < 0.0001). This study provides strong evidence that fine needle aspiration biopsy is a safe technique even in childhood and adolescence, offering the best sensitivity, specificity, and accuracy in detecting malignancy compared with conventional approaches.

No effect of oral insulin on residual beta-cell function in recent-onset type I diabetes (the IMDIAB VII). IMDIAB Group

AIMS/HYPOTHESIS

Induction of tolerance to insulin is achievable in animal models of Type I (insulin-dependent) Diabetes mellitus by oral treatment with this hormone, which can lead to prevention of the disease. In the Diabetes Prevention Trial of Type I diabetes (DPT-1), oral insulin is given with the aim of preventing disease insurgence. We investigated whether if given at diagnosis of Type I diabetes in humans, oral insulin can still act as a tolerogen and therefore preserve residual beta-cell function, which is known to be substantial at diagnosis.

METHODS

A double-blind trial was carried out in patients (mean age +/- SD: 14 +/- 8 years) with recent-onset Type I diabetes to whom oral insulin (5 mg daily) or placebo was given for 12 months in addition to intensive subcutaneous insulin therapy. A total of 82 patients with clinical Type I diabetes ( < 4 weeks duration) were studied. Basal C peptide and glycated haemoglobin were measured and the insulin requirement monitored every 3 months up to 1 year. Insulin antibodies were also measured in 27 patients treated with oral insulin and in 18 patients receiving placebo at the beginning of the trial and after 3, 6 and 12 months of treatment.

RESULTS

The trial was completed by 80 patients. Overall and without distinction between age at diagnosis, at 3, 6, 9 and 12 months baseline mean C-peptide secretion in patients treated with oral insulin did not differ from that of those patients treated with placebo. In patients younger than 15 years a tendency for lower C-peptide values at 9 and 12 months was observed in the oral insulin group. Insulin requirement at 1 year was similar between the two groups as well as the percentage of glycated haemoglobin. Finally, IgG insulin antibodies were similar in the two groups at each time point.

CONCLUSION/INTERPRETATION

The results of this study indicate that the addition of 5 mg of oral insulin does not modify the course of the disease in the first year after diagnosis and probably does not statistically affect the humoral immune response against insulin.

A multi-centre randomized trial of two different doses of nicotinamide in patients with recent-onset type 1 diabetes (the IMDIAB VI)

BACKGROUND

Intensive insulin therapy is the gold standard by which Type 1 diabetes is treated. In addition to this therapy, administration of nicotinamide (NA) can be beneficial. This concept is reinforced by the results of a recent meta-analysis of the use of NA in patients with recent-onset Type 1 diabetes.

METHODS

In this study we compared two different doses of NA in 74 patients with duration of Type 1 diabetes <4 weeks (mean age 13 years). Patients were randomly allocated in blind to two treatment groups: 38 patients received a dose of 25 mg/kg (b.w.) of NA and 36 patients received a dose of 50 mg/kg (b.w.) of NA. Intensive insulin therapy was carried out in order to optimize metabolic control as soon as possible after diagnosis and to maintain blood glucose level as near to normal as possible. Response to therapy was monitored throughout the study by investigating the occurrence of clinical (complete) remission defined, according to the recommendations of the International Diabetes Immunotherapy Group, as restoration of normal fasting and post-prandial blood glucose without any insulin administration for more than 2 weeks. Moreover, the integrated measures of metabolic control (C-peptide, HbA(1c) and insulin dose) were analysed at 3- month intervals up to 1 year after diagnosis.

RESULTS

There were no significant differences in the integrated measures of metabolic control between the two NA treated groups either at onset of the disease or at each 3-month interval up to 1 year after diagnosis, although there was a tendency toward higher insulin dosages in the 50 mg NA group. No significant differences were observed in the rate of clinical remission between the two groups.

CONCLUSION

We conclude that patients with recent-onset Type 1 diabetes treated with two different doses of NA, in addition to intensive insulin therapy, show similar residual beta-cell function 1 year later. Since both doses of NA are likely to be effective in reducing beta-cell dysfunction, the smaller dose of 25 mg/kg NA would be sufficient as a higher dose may induce insulin resistance.

AB023, novel polyene antibiotics. II. Isolation and structure determination

AB023, a complex of new polyene antibiotics, was isolated from a soil Streptomyces strain. The two main components, pentaene antibiotics AB023a and AB023b, were separated and purified by preparative chromatographic methods and their structures were determined by extensive NMR and mass spectrometric studies.

Secondary structure and side-chain 1H and 13C resonance assignments of calmodulin in solution by heteronuclear multidimensional NMR spectroscopy

Heteronuclear 2D and 3D NMR experiments were carried out on recombinant Drosophila calmodulin (CaM), a protein of 148 residues and with molecular mass of 16.7 kDa, that is uniformly labeled with 15N and 13C to a level of greater than 95%. Nearly complete 1H and 13C side-chain assignments for all amino acid residues are obtained by using the 3D HCCH-COSY and HCCH-TOCSY experiments that rely on large heteronuclear one-bond scalar couplings to transfer magnetization and establish through-bond connectivities. The secondary structure of this protein in solution has been elucidated by a qualitative interpretation of nuclear Overhauser effects, hydrogen exchange data, and 3JHNH alpha coupling constants. A clear correlation between the 13C alpha chemical shift and secondary structure is found. The secondary structure in the two globular domains of Drosophila CaM in solution is essentially identical with that of the X-ray crystal structure of mammalian CaM [Babu, Y., Bugg, C. E., & Cook, W.J. (1988) J. Mol. Biol. 204, 191-204], which consists of two pairs of a "helix-loop-helix" motif in each globular domain. The existence of a short antiparallel beta-sheet between the two loops in each domain has been confirmed. The eight alpha-helix segments identified from the NMR data are located at Glu-6 to Phe-19, Thr-29 to Ser-38, Glu-45 to Glu-54, Phe-65 to Lys-77, Glu-82 to Asp-93, Ala-102 to Asn-111, Asp-118 to Glu-127, and Tyr-138 to Thr-146. Although the crystal structure has a long "central helix" from Phe-65 to Phe-92 that connects the two globular domains, NMR data indicate that residues Asp-78 to Ser-81 of this central helix adopt a nonhelical conformation with considerable flexibility.