目的:X连锁低磷酸盐血症病(XLH)是由于X染色体(PHEX)上磷酸盐调节内肽酶同源物的功能缺失突变导致成纤维细胞生长因子23(FGF23)产生增加。FGF23过量导致肾脏磷酸盐消耗和1,25-二羟维生素D(1,25(OH)2D)合成不足,肠道磷酸盐吸收减少,最终导致慢性低磷酸盐血症。XLH患儿表现出典型的骨骼损伤,下肢畸形,发育不良,身材矮小,骨痛,和身体机能障碍。Burosumab,一种与FGF23结合以抑制其活性的完全人IgG1单克隆抗体,与磷酸盐补充剂和维生素D活性代谢物的常规治疗相比,更有效地改善XLH的生化和临床体征。在过渡到成年期间,XLH青少年的数据很少。在这个前瞻性案例系列中,我们旨在评估burosumab在停止长期常规治疗的XLH青少年患者中的安全性和有效性.
方法:五名白人青少年(4名男性,招募1名女性;平均年龄15.4±1.5岁)的XLH患者,并从常规治疗转为burosumab(0.8至1.2mg/kg,s.c.QW2)。Burosumab持续12至48个月,一旦停产,随访6~12个月.在所有患者中,血清钙,磷酸盐,碱性磷酸酶(ALP),甲状旁腺激素(PTH),和1,25(OH)2D水平,和肾小管磷酸盐重吸收(TmP/GFR)值在入口和期间进行评估。在进入时测量完整的FGF23血浆水平。患者报告的结果(PRO)在进入时和每3-6个月进行评估,以评估下肢疼痛的影响,刚度,和执行日常活动的困难。
结果:在入门时,所有患者都出现低磷血症,增加完整的FGF23水平,降低TmP/GFR,1,25(OH)2D水平不足,五分之四的ALP水平升高。两名患者有病的放射学征象。在burosumab期间,所有患者均显示血清磷酸盐和1,25(OH)2D水平显着增加,和TmP/GFR值(P<0.05-P<0.0001)。血清ALP水平显著下降(P<0.05)至正常值。burosumab期间未发现血清钙和PTH水平的变化(P=NS)。所有患者的PRO均显著改善(P<0.02-P<0.0001)。四名患者在18岁或19岁时停止了burosumab,而一名患者在研究期间仍小于18岁,因此继续治疗。4例暂停服用burosumab的患者血清磷酸盐和1,25(OH)2D水平以及TmP/GFR值迅速下降;血清ALP水平升高,和PROs逐渐恶化,生活质量显着降低。在继续burosumab治疗的患者中未观察到这些后果。
结论:我们的数据表明,常规治疗仅部分改善了XLH的体征和症状。Burosumab耐受性良好,可有效改善磷酸盐代谢,骨骼健康,和PROS。burosumab的所有好处在停药后都失去了。这些结果表明,在XLH患者过渡到成年期间,需要继续使用burosumab才能实现和维持治疗的临床益处。
OBJECTIVE: X-linked hypophosphatemic rickets (XLH) is due to loss-of-function mutations in the phosphate-regulating endopeptidase homologue on the X chromosome (PHEX) that lead to increased fibroblast growth factor 23 (FGF23) production. FGF23 excess causes renal phosphate wasting and insufficient 1,25-dihydroxyvitamin D (1,25(OH)2D) synthesis with reduced intestinal phosphate absorption, ultimately resulting in chronic hypophosphatemia. Children with XLH show typical skeletal lesions of rickets, deformities of the lower limbs, stunted growth with disproportionate short stature, bone pain, and physical dysfunctions.
Burosumab, a fully human IgG1 monoclonal antibody that binds to FGF23 to inhibit its activity, is more effective to improve the biochemical and clinical signs of XLH than conventional treatment with phosphate supplements and vitamin D active metabolites. Data on adolescents with XLH during the transition period to young adulthood are few. In this prospective case series, we aimed to assess safety and efficacy of burosumab in adolescents with XLH who discontinued long-term conventional therapy.
METHODS: Five Caucasian adolescents (4 males, 1 female; mean age 15.4 ± 1.5 years) with XLH were recruited and switched from conventional treatment to burosumab (0.8-1.2 mg/kg, s. c. QW2). Burosumab was continued for 12-48 months and, once discontinued, patients were followed-up for 6-12 months. In all patients, serum calcium, phosphate, alkaline phosphatase (ALP), parathyroid hormone (PTH), and 1,25(OH)2D levels, and renal tubular reabsorption of phosphate (TmP/GFR) values were assessed at entry and during burosumab. Intact FGF23 plasma levels were measured at entry. Patient-reported outcomes (PROs) were assessed at entry and every 3-6 months to evaluate the impact of low extremity pain, stiffness, and difficulties performing daily activities.
RESULTS: At entry, all patients showed hypophosphatemia, increased intact FGF23 levels, reduced TmP/GFR, insufficient 1,25(OH)2D levels, and in four out of five increased ALP levels. Two patients had radiological signs of rickets. During
burosumab, all patients showed a significant increase in serum phosphate and 1,25(OH)2D levels, and in TmP/GFR values (P < 0.05 - P < 0.0001). Serum ALP levels significantly declined (P < 0.05) to normal values. No changes of serum calcium and PTH levels (PNS) were found during
burosumab. PROs significantly improved (P < 0.02 - P < 0.0001) in all patients. Four patients discontinued burosumab when they turned 18 or 19, whereas one continued the treatment since he was still younger than 18 during the study period. Four patients who suspended burosumab showed a rapid decline in serum phosphate and 1,25(OH)2D levels and in TmP/GFR values; serum ALP levels increased, and PROs progressively worsened with a significant reduction in quality of life. These consequences were not observed in the patient who continued
burosumab treatment.
CONCLUSIONS: Our data showed that conventional treatment improved only in part the signs and symptoms of XLH. Burosumab was well tolerated and was effective in improving phosphate metabolism, bone health, and PROs. All the benefits of
burosumab were lost after its discontinuation. These results suggested that continuing burosumab is required to achieve and maintain the clinical benefits of the treatment during the transition to young adulthood in patients with XLH.