A rare cause of rickets

Sophia Sakka; Suma Uday; Tabitha Randell; Justin H Davies; Ved Bushan Arya; Caroline Brain; Jeremy Allgrove; Wolfgang Hogler; Nick J Shaw

doi:10.1530/boneabs.6.P048

Background: The development of hypophosphataemic rickets in infants fed with the elemental formula (EF) Neocate^® has been recently reported. We present seven cases of exclusively Neocate-fed babies who developed hypophosphataemic rickets.

Presenting problem: Three patients (P1,3,4) had incidental findings of rickets on chest X-rays, two (P2,6) developed leg deformities and rickets was confirmed on X-rays, and two (P5,6) presented with femur fractures. Patient 7 was found to have low phosphate concentrations on routine blood testing and was further investigated. All patients (age 5 months – 3.2 years) were exclusively fed on Neocate at presentation and had normal serum calcium and parathyroid hormone concentrations, raised alkaline phosphatase and hypophosphataemia. Vitamin D deficiency and renal phosphate wasting were excluded (Table 1).

Clinical management: Following exclusion of other causes of rickets, reduced intestinal phosphate absorption due to EF was considered. Patients 1–6 were treated with phosphate supplements after diagnosis of rickets. Patient 6 was previously on long term steroids and received one course of bisphosphonates after the fracture. Formula was changed eventually in all patients and phosphate concentrations normalized after 1 week-4 months. Clinical and/or radiological improvement of rickets was noted in P2,3,4. No X-ray confirmation of improvement is available so far in the others.

Table 1 Clinical and biochemical characteristics of patients.
	Patient 1	Patient 2	Patient 3	Patient 4	Patient 5	Patient 6	Patient 7
Gestational age	31w	27w	33w	39w+3	31w	term	34w+4
Diagnosis	Presumed cow’s milk allergy	GORD, cow’s milk intolerance	Pierre-Robin Syndrome, cleft palate, CP, GORD, NJ fed	CHARGE syndrome, GORD, PEG fed	FTT, GORD, PEG-NJ fed	SCID, BMT, GVHD on steroids, refusing feed	SOD, GORD, 8q12.3del, tectal plate glioma, NJ fed
Age at presentation	6 months	10 months	11 months	18 months	9 months	3 years 2 m	5 months
Exclusively on Neocate before presentation (duration)	3 months	10 months	>8 months	>6 months	5 months	15 months	5 months
Ca(mmol/L)	2.48	2.52	2.6	2.49	2.57	2.47	2.38
Phosphate (mmol/L)	1.23	0.68	0.83	1.04	0.84	1.34	0.63
ALP (IU/L)	1000	1000	3469	431	1653	419	2206
PTH (ng/L)	24	19.8	17	5.6	21	31	Normal
25-OH-VitaminD (nmol/L)	59.7	86	88	347	76	131	110
TRP (%)	99.5	–	99.8	>97	NA	NA	NA
Abbreviations: GORD: gastro-oesophageal reflux disease; CP: cerebral palsy; NJ: naso-jejunal; PEG: percutaneous endoscopic gastrostomy; FTT: failure to thrive; SCID: severe combined immunodeficiency; BMT: bone marrow transplant; GVHD: graft versus host disease; SOD: septo-optic dysplasia;.NA: not available.

Discussion: The fact that serum phosphate improved following weaning of Neocate supports its role in the causation of hypophosphataemia; poor intestinal absorption of phosphate is the assumed mechanism in infants exclusively fed with Neocate. Clinicians should exercise caution in the use of EF in the absence of clear clinical indications. Infants who are being exclusively fed on Neocate should have close clinical and biochemical monitoring of bone profile, in accordance with existing guidance.

Disclosure: The authors declared no competing interests.

Bone Abstracts

P048