Burosumab Provides Sustained Improvement in Phosphorus Homeostasis and Heals Rickets in Children Aged 1 to 4 Years With X-Linked Hypophosphatemia (XLH)

XLH is the most common heritable rickets. Affected children have high levels of circulating FGF23 that cause hypophosphatemia with consequent rickets and lower limb deformity. Burosumab, a fully human monoclonal antibody that binds FGF23, is FDA-approved for the treatment of XLH in children ≥6 months old and adults. Herein, we report final, 3-year safety and efficacy data from an open-label, phase 2 study of burosumab in children 1 to <5 years old at baseline (NCT02750618).

Eligibility required hypophosphatemia and radiographic evidence of rickets. The primary efficacy endpoint was change from baseline in fasting serum phosphorus (Pi). Secondary endpoints included Rickets Severity Score (RSS) and Radiographic Global Impression of Change (RGI-C). Patients received burosumab subcutaneous Q2W starting at 0.8 mg/kg for 160 weeks (64-week treatment + 96-week treatment extension periods).

All 13 enrolled patients completed the 64-week treatment period; 1 left the study to transition to commercially available burosumab, and 12 completed all 160 weeks. Baseline mean (SD) age was 2.9 (1.1) years; 69% were boys; all had previously received oral phosphate salts and active vitamin D.

Burosumab rapidly corrected fasting serum Pi with mean (SD) levels of 2.5 (0.3) mg/dL at Baseline, 3.7 (0.5) mg/dL at Week 1 (W1), 3.4 (0.5) mg/dL at W64, and 3.4 (0.5) mg/dL at W160 (normal range: 3.2–6.1 mg/dL). Lower RSS indicated improved rickets. Total RSS decreased from 2.9 (1.4) at Baseline to 1.2 (0.5) at W40 and to 0.9 (0.5) at W64 and was maintained through W160 [1.0 (0.6)]. Positive RGI-C scores indicate healing rickets relative to Baseline. Global RGI-C scores indicating substantial healing (≥+2) at W40 [+2.2 (0.3)] and W64 [+2.2 (0.4)] were maintained through W160 [+2.2 (0.4)]. Similarly, lower limb deformity RGI-C scores were +1.2 (0.6) at W40 and +1.5 (0.5) at W64, and sustained healing was evident at W160 [+2.0 (0.3)]. Wrist and knee RSSs and RGI-C scores similarly improved. The upper limit of normal for serum ALP ranged from 297 to 345 U/L depending on the child’s age and sex. Mean ALP was 549 (194) U/L at Baseline, normalized by W40 [335 (88) U/L], and was sustained through W160 [302 (71) U/L].

The burosumab safety profile over 160 weeks resembled previous pediatric studies; no new safety concerns emerged. All patients had ≥1 treatment-emergent adverse event (TEAE). All TEAEs were mild (Grade 1) or moderate (Grade 2) except for one patient with a grade 3 TEAE (food allergy) and one with a grade 3 TEAE (increased serum amylase, 92% salivary/8% pancreatic). One patient had a serious TEAE (dental abscess leading to hospitalization). These grade 3 and serious TEAEs were considered unrelated to study drug.

Burosumab rapidly restored Pi homeostasis, improved rickets, and normalized serum ALP in children with XLH aged 1 to <5 years with no new safety concerns. Improvements were maintained during the 3 years of treatment.

SAT-384 Identification of Heterozygous LRP5 Mutation and a TGFβ-1 Variant of Unknown Significance in a Patient with Hearing Loss, High Bone Mass, and Oropharyngeal Exostoses

Background: Manifestations of the high bone mass (HBM) disorders not only include strong bones, but also excessive bones causing cranial nerve palsies and oropharyngeal exostoses. Due to overlap of clinical phenotype in dense bone diseases, one or more distinct genes may be involved. Up-regulation in bone formation can result from gain of function mutation of the low-density lipoprotein receptor-related protein 5 (LRP5), which mediates activation of the canonical Wnt pathway via co-binding with the frizzled protein, but may also be a consequence of activating mutations in the transforming growth factor β1 (TGFβ-1) gene that associate with stimulated osteogenesis. Clinical Case: Here we report a 41 year-old woman referred for incidentally found dense bones on screening dual-energy X-ray absorptiometry (DXA) that led to subsequent revelation of several family members sharing similar histories including inability to float in water, strong bones on skeletal surgery, and presence of palatal exostoses. Her childhood history included mandibular pain developing at age 15 years due to bony overgrowth of her lower jaw requiring multiple drilling for removal. At age 33, she manifested trigeminal neuralgia initially responsive to medical management but eventually needed microvascular decompression for unremitting pain. Preoperative brain magnetic resonance imaging (MRI) noted significant hyperostosis of the skull as well as mild narrowing of internal auditory canals, for which auditory testing showing mild mixed hearing loss in her right ear. Skeletal survey revealed diffuse thickening of axial and appendicular skeleton with characteristic endosteal hyperostosis. DXA demonstrated Z scores of +8.3 and +5.3 in the lumbar spine and total hip, respectively. Torus palatinus was also identified on exam. Mutational analysis disclosed a heterozygous LRP5 missense mutation, c.844A>G, p.Met282Val, together with a variant of unknown significance in TGFβ-1 (c.887G>A, p.Arg296Gln) possibly linked to Camurati-Engelmann disease (progressive diaphyseal dysplasia). As transmission in both conditions follows an autosomal dominant pattern, multigenerational family history was elicited from patient that her mother, who underwent knee replacement in her 80’s, was described by the surgeon as “having bones of a 30-year old man,” and that her deceased maternal grandmother possibly had “thickened” bones. Half of patient’s 18 siblings reportedly also carry features suggestive of high bone mass phenotype. Genetic testing of family members is planned. Conclusion: While HBM disorders protect against fractures, it is important to recognize that these relatively benign conditions may present with neurological and oropharyngeal complications prompting the need for their surveillance and surgical precautions during orthopedic procedures.

SAT-LB085 First Report of Burosumab (Anti-FGF23 Monoclonal Antibody) for Rickets Complicating HRAS-Associated Cutaneous Skeletal Hypophosphatemia Syndrome

Background: Cutaneous skeletal hypophosphatemia syndrome (CSHS) is caused by somatic mosaicism of a RAS family gene (ie. HRAS, NRAS, KRAS). CSHS features: 1) congenital epidermal, melanocytic, or sebaceous nevi, 2) elevated circulating FGF23 levels that cause renal phosphate wasting and skeletal hypomineralization, and 3) focal bone lesions ipsilateral to the nevi as a possible source of excess FGF23. Conventional therapy for rickets in CSHS (phosphate salts and bioactive vitamin D) mirrors treatment for X-linked hypophosphatemia (XLH) with elevated circulating FGF23. Current therapy aims to treat signs and symptoms rather than the etiology. Clinical Case: A 21-month-old boy with left, widespread, unilateral nevus sebaceous developed bilateral lower extremity bowing with a wide-based gait. His serum phosphorus level was low at 2.1 mg/dl (Nl: 3-6) and FGF23 was elevated at 279 RU/mL (Nl: < 230). We prescribed conventional therapy for hypophosphatemic rickets and diagnosed linear sebaceous nevus syndrome, confirmed by mutation analysis of affected skin harboring HRAS p.Q61R (c.182A>G). Adherence to medical therapy was problematic, and he sustained 3 major long-bone fractures. By age 6 years, a walker was required to ambulate short distances with mostly wheelchair-dependence from pain and muscle weakness. Based on his elevated FGF23 level and clinical decline, burosumab (anti-FGF23 fully human monoclonal antibody), FDA-approved in 2018 for XLH, was initiated off-label. After weaning conventional therapy, burosumab was administered subcutaneously as a single dose of 0.8 mg/kg (20 mg) and decreased to 0.3 mg/kg (6 mg) two weeks later. Burosumab was then given every 2 weeks and adjusted by 0.1 mg/kg to maintain fasting serum phosphorus in the low-normal range for age (3.5 - 4.5 mg/dL). Laboratory and clinic follow-up occurred just prior to each injection for 3 months until serum phosphorus was stable as he received approximately 0.4 mg/kg (8 mg per dose). Biochemical testing and clinic visits will occur monthly for 3 months and are planned for quarterly afterwards, with repeat radiological imaging every 3-6 months for the first year of therapy. Duration of burosumab treatment has been 5 months. After his initial burosumab dose, serum phosphorus increased from 1.7 to 3.7 mg/dL and remained normal [Nl: 3.0 - 6.0 mg/dL] thereafter. Radiographs of his wrists and knees 3 months into therapy revealed striking improvement of his rickets but persisting focal bone lesions, characteristic of CSHS, on the left side. He now walks independently with endurance, strength, and resolving pain. Quality-of-life is markedly improved. Burosumab treatment is being tolerated well without side effects. Conclusion: Burosumab seems to be an effective therapy for FGF23-mediated rickets in pediatric CSHS. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

Mucopolysaccharidosis IVA: correlation between genotype, phenotype and keratan sulfate levels

Mucopolysaccharidosis IVA (MPS IVA) is caused by deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS), leading to systemic skeletal dysplasia because of excessive storage of keratan sulfate (KS) in chondrocytes. In an effort to determine a precise prognosis and personalized treatment, we aim to characterize clinical, biochemical, and molecular findings in MPS IVA patients, and to seek correlations between genotype, phenotype, and blood and urine KS levels. Mutation screening of GALNS gene was performed in 55 MPS IVA patients (severe: 36, attenuated: 13, undefined: 6) by genomic PCR followed by direct sequence analysis. Plasma and urine KS levels were measured by ELISA method. Genotype/phenotype/KS correlations were assessed when data were available. Fifty-three different mutations including 19 novel ones (41 missense, 2 nonsense, 4 small deletions, 1 insertion, and 5 splice-site) were identified in 55 patients and accounted for 93.6% of the analyzed mutant alleles. Thirty-nine mutations were associated with a severe phenotype and ten mutations with an attenuated one. Blood and urine KS concentrations in MPS IVA patients were age-dependent and markedly higher than those in age-matched normal controls. Plasma and urine KS levels in MPS IVA patients with the severe phenotype were higher than in those with an attenuated form. This study provides evidence for extensive allelic heterogeneity of MPS IVA. Accumulation of mutations as well as clinical descriptions and KS levels allows us to predict clinical severity more precisely and should be used for evaluation of responses to potential treatment options.

Prevention of human immunodeficiency virus mother-to-child transmission in Israel

The objective of the study was to investigate the HIV-mother-to-child transmission (MTCT) rate in Israel. This was a retrospective study of HIV-infected pregnant women, mainly immigrants from Ethiopia, in six Israeli AIDS centres, in 2000-2005. Medical records of mothers and newborns were evaluated for HIV status, treatment and MTCT rates. Three hundred pregnancies of 241 HIV-infected women, resulting in 304 live births, were studied. In 86/241(36%) women, HIV diagnosis was made during the current pregnancy or shortly after labour. Thirty others were diagnosed during previous pregnancies. Highly active antiretroviral therapy (HAART) was prescribed in 76% of pregnancies. The mean viral load before labour was 23,000 +/- 100,000 copies/mL with a mean CD4 of 406 +/- 223 (range 4-1277) cells/mm(3). Caesarian sections were preformed in 175/300 pregnancies (103/175 with viral load <1000 copies/mL). During labour, azidothymidine (AZT) was given to 80% and nevirapine to 8% of the women. Eighty-eight percent of the neonates received AZT for six weeks. The overall HIV-MTCT rate was 3.6%. MTCT correlated significantly with delayed HIV diagnosis, low CD4, lack of HAART during pregnancy and lack of perinatal treatment. HIV treatment of mothers and their newborns throughout pregnancy, labour and perinatal period are crucial for effective prevention of MTCT, emphasizing the need for early HIV screening, diagnosis and treatment.

"Unresolving pneumonia" as the main manifestation of atypical Kawasaki disease

Two cases of atypical Kawasaki disease (KD) manifested as persistent lobar lung consolidation, prolonged fever, and active inflammatory laboratory markers unresponsive to antibiotic treatment are reported. One of the children developed a giant coronary aneurysm. Atypical KD should be considered in the differential diagnosis of young children with prolonged fever and lobar consolidation unresponsive to antibiotics.

Eosinophilic cystitis in a 4-year-old boy: successful long-term treatment with cyclosporin A

A 4-year-old Jewish boy presented with dysuria, urinary dribbling, increased urinary frequency, and new onset of diurnal enuresis. An infiltrating solid mass involving the entire bladder wall was found. Biopsy revealed "tumor-forming" eosinophilic cystitis, a rare bladder lesion of unclear cause. Antitoxocariasis treatment was unsuccessful. High-dose corticosteroids failed. The child's clinical condition and bladder sonographic findings continued to deteriorate. Treatment with cyclosporin A was given for 8 months, with a complete clinical, radiologic, and histopathologic cure and no side effects. Two years of follow-up showed a complete recovery.

Genotypic variation of HIV-1 reverse transcriptase and protease: comparative analysis of clade C and clade B

OBJECTIVE

To compare drug-resistant variants from untreated (naive) and treated patients infected with clade B or C virus.

METHODS

Consecutive samples (165) from patients throughout Israel were analyzed. All those in the treated group were failing highly active antiretroviral therapy.

RESULTS

There were 87 clade B (14 naive) and 78 clade C (20 naive) [corrected] with significant differences in the prevalence of known drug-resistance mutations between the clades: in naive patients in the protease region M36I 7% and 95% (P < 0.0001), K20R 0% and 27% (P = 0.063), A71V 18% and 0% (P = 0.063), M46I 0% and 13%, and V77I 18% and 0% (P = 0.063), respectively, and in the reverse transcriptase region A98G/S 0% and 20% (P = 0.12), respectively. Most clade C viruses also showed significant differences from clade B consensus sequence at additional protease sites: R41K 100%, H69K/Q 85%, L89M 95% and I93L 80% (P < 0.0001). There were also significant differences (P < 0.03 to < 0.0001) in treated patients in clades B and C: in the protease region L10I 40% and 12%, M36I 26% and 95%, L63P 67% and 40%, A71I 38% and 7%, G73I and V77I 18% and 0%, I84V 16% and 3%, and L90M 40% and 12%, respectively; in the reverse transcriptase M41L 41% and 17%, D67N 41% and12%, K70R 30% and 7%, T215Y 48% and 29%, K219Q 21% and 7%, and A98G/S 3% and 24%, respectively.

CONCLUSION

Significantly differences between clade B and C viruses may be associated with development of differing resistance patterns during therapy and may affect drug utility in patients infected with clade C.

Clinic-based study of plexiform neurofibromas in neurofibromatosis 1

Individuals with neurofibromatosis 1 (NF1) develop both benign and malignant tumors at an increased frequency. One of the most common benign tumors in NF1 is the plexiform neurofibroma. These tumors cause significant morbidity and mortality on account of their propensity to grow and affect adjacent normal tissues. To determine the clinical profile of plexiform neurofibromas in NF1, we conducted a retrospective review of 68 NF1 patients with plexiform neurofibroma. In our series, 44% of tumors were detected by 5 years of age and most were located in the trunk and extremities. Only two patients developed malignant peripheral nerve sheath tumors in their preexisting plexiform neurofibromas. Lastly, we demonstrate that there were no specific clinical features of NF1 associated with the presence of plexiform neurofibroma. These results underscore the importance of careful serial examinations in the evaluation of patients with NF1.

Childhood brucellosis in Israel

BACKGROUND

Brucellosis has become a major medical problem in Israel particularly in the Muslim Arab population.

METHODS

Eighty-eight children with acute brucellosis are described. Sixty-seven were studied retrospectively during 1987 through 1988, and 21 children were studied prospectively during 1989 through 1992. Epidemiologic, clinical and laboratory features were evaluated, and the outcome of 4 antimicrobial regimens are compared.

RESULTS

Although the clinical manifestation varied, the classical triad of fever (91%), arthralgia or arthritis (83%) and hepato- and/or splenomegaly (63%) characterized most patients. Sixty-one percent of the children had elevated liver enzymes. Brucella melitensis was isolated from 61% of blood cultures. The relapse rate in patients who were treated with monotherapy (doxycycline) was 43% compared with 14% with regimens of combined therapy with rifampin and doxycycline, streptomycin and doxycycline or rifampin and trimethoprim-sulfamethoxazole (P < 0.049). Eleven children (33%) who were treated for 3 weeks had relapse compared with 1 patient (3.5%) treated for 4 weeks or longer. The total relapse or reinfection rate was 20%. All patients with relapse recovered after a second course of antibiotic therapy. During the 2 years of follow-up one child progressed to chronic osteomyelitis.

CONCLUSIONS

Combination therapy and extending treatment for 4 weeks or longer gave significantly better results than monotherapy or shorter courses of therapy and resulted in fewer relapses.

Tolerance to experimental contact sensitivity induced by T cell vaccination

It was shown previously that experimental autoimmune diseases could be prevented or treated specifically by administering suitably attenuated autoimmune T lymphocytes to animals, a process termed T cell vaccination (Cohen, I. R., Sci. American 1988. 256: 52). We now report that T cell vaccination is an effective way of inducing tolerance to contact sensitivity to simple chemical haptens. Vaccines were prepared from populations of lymph node cells from specifically sensitized mice by activating the T cells with the T cell mitogen concanavalin A and then treating the T cell blasts with glutaraldehyde. The vaccinated mice showed decreased delayed sensitivity responses to the specific sensitizing antigen and developed significant delayed sensitivity responses to the T cells of the same specificity as those used for vaccination. Thus, T cell vaccination against contact sensitivity reactions appears to function similarly to T cell vaccination against autoimmune disease.