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Increased blood 1,25 dihydroxyvitamin D levels in infants with Metabolic Bone Disease of Infancy in contested cases of child abuse
⁎Corresponding author: Marvin Miller. marvin.miller@wright.edu
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Metabolic Bone Disease of Infancy (MBDI) is a multifactorial disorder of bone fragility that presents with multiple unexplained fractures (MUF) and is often misdiagnosed as child abuse. The diagnosis of MBDI is made by the finding of radiographic features of healing rickets and risk factors for MBDI. Our anecdotal experience indicates blood 1,25-dihydroxyvitamin D (1,25-DiOHVD) is sometimes elevated. The purpose of this retrospective study was to review cases of MBDI in which child abuse was alleged and the alleged perpetrator denied wrongdoing.
We reviewed forensic cases of MBDI born between 2015 and 2021. The diagnosis was based on radiographic findings of healing rickets. Records were reviewed for blood 1,25-DiOHVD testing.
22 of the 76 infants (29 %) had a blood 1,25-DiOHVD level performed at the time of presentation with fractures. The average age of presentation with fractures was 11 weeks.
3 of the 22 infants (14 %) had a normal 1,25-DiOHVD blood level, and 19 of the 22 infants (86 %) had an elevated level. None had low levels.
Blood 1,25-DiOHVD is often elevated in infants with MBDI. Elevated blood 1,25-DiOHVD levels cause increased bone resorption and decreased bone mineralization, and thus this finding is not unexpected since all infants had evidence of healing rickets on imaging studies. These results indicate blood 1,25-DiOHVD should be done in contested cases of child abuse in infants with MUF as an elevated level indicates bone fragility.
Keywords
Metabolic Bone Disease of Infancy
Healing rickets
1,25 dihydroxyvitamin D
Multiple unexplained fractures
Non-accidental injury
1 Introduction
Metabolic Bone Disease of Infancy (MBDI) is a multifactorial disorder of infant bone fragility in which the presenting feature is multiple unexplained fractures (MUF), and in which child abuse is often incorrectly diagnosed1. The diagnosis of MBDI is suggested by the finding of radiographic features of healing rickets and risk factors for MBDI1. In our review of 75 cases of MBDI diagnosed between 2007 and 2015 we noted that 22 of the 75 infants (28 %) tested for 1,25-Dihydroxyvitamin D (1,25-DiOHVD), 14 were elevated (14/22 = 63 %). Thus, this study suggested that testing for blood 1,25-DiOHVD might be helpful in infants with MUF, because an elevated level suggests a bone fragility disorder1.
A normal blood calcium level is critical for normal neuromuscular, brain, and cardiac function. Blood 1,25-DiOHVD becomes elevated in response to a low blood calcium level which reflects low total body calcium through the action of the parathyroid gland. Low blood calcium causes the release of PTH that stimulates the conversion of 25-Hydroxyvitamin D (25-OHVD) to 1,25-DiOHVD by enhancing its hydroxylation in the kidney. An elevated blood 1,25-DiOHVD level has 4 major consequences that attempt to restore the blood calcium to normal2–4:1.Increased calcium absorption from the GI tract which will slowly increase blood calcium2.Increased calcium reabsorption in the kidney3.Increased bone resorption which will immediately cause calcium to be released in the blood as a result of the osteoclastic-mediated release of calcium from bone, but at the expense of bone mineral content and thus bone strength4.Increased inhibition of bone mineralization which will also immediately decrease calcium incorporation into bone, causing more calcium to remain in the blood and thus further compromising bone strength
The purpose of this study is to analyze a more recent series of infants with MBDI for the following:1.The frequency of 1,25-DiOHVD testing2.If tested, how often the 1,25-DiOHVD was elevated
2 Methods
We reviewed author MM's forensic cases of infants with MUF born between 2015 and 2021 in which we diagnosed MBDI. In all cases the alleged perpetrator denied wrongdoing, but was accused of child abuse. The diagnosis of MBDI was based on the finding of at least two of the previously described 8 radiographic findings of healing rickets1:1.Subperiosteal New Bone Formation (not associated with fractures of the affected bone)2.Growth Plate Mineralization Abnormality3.Ulnar cupping4.Skull Mineralization Abnormality (Craniotabes)5.Rib Mineralization Abnormality (Rachitic Rosary)6.Vertebral Mineralization Abnormality (“Bone in Bone”5)7.Looser Zones8.Osteopenia
Clinical features including gender, gestational age, birth weight, age of presentation with fractures, number of fractures, risk factors for MBDI, and radiographic findings of MBDI were recorded.
We evaluated whether a 1,25-DiOHVD blood level was performed. A 1,25-DiOHVD blood level was considered elevated if it was higher than the upper limit of normal for the range given by the commercial laboratory that performed the test. We also evaluated whether blood calcium, phosphate, alkaline phosphatase (AP), parathyroid hormone (PTH), and 25-Hydroxyvitamin D (25-OHVD) testing were performed.
3 Results
We evaluated 76 infants and 22 of these infants had blood 1,25-DiOHVD levels performed. Table 1 summarizes the clinical, laboratory, and imaging findings of MBDI that were noted in the Methods section in the 19 infants who had an elevated blood 1,25-DiOHVD.
There were 10 males and 9 females; 15 term and 4 preterm infants. The average age of presentation with fractures was 11 weeks (range: 4–36 weeks).
The average number of fractures was 9 (range: 0–36). 14 of the 19 had rib fractures, and 10 had 4 or more rib fractures.
Blood 1,25-DiOH levels: Of these 76 infants, 22 (29 %) had a blood 1,25-DiOHVD level performed at the time of presentation with fractures.
3 of the 22 infants (14 %) had normal 1,25-DiOHVD blood levels: 27, 36, and 75 pg/ml. None had decreased levels. The 3 different commercial labs that performed the 1,25-DiOHVD testing in these 3 infants noted the following normal ranges for their 1,25-DiOHVD testing, respectively: 1. 26–95 pg/ml; 2. 19.9–79.3 pg/ml; 3. 31–87 pg/ml.
19 of the 22 infants (86 %) had elevated 1,25-DiOHVD blood levels that are listed in Table 1. The median blood 1,25-DiOHVD level was 149 pg/ml with a range of 95–352 pg/ml.
Blood calcium levels: Blood calcium levels were normal in 11 cases, not performed in 6 cases, and low in 2 cases.
Blood phosphate levels: Blood phosphate levels were normal in 8 cases, not performed in 10 cases, and high in one case.
Blood AP levels: Blood AP levels were normal in 8 cases, not performed in 6 cases, and, high in 5 cases.
Blood PTH levels: Blood PTH levels were normal in 5 cases, not performed in 6 cases, were high in 7 cases, and low in one case.
Blood 25-OHVD levels: Blood 25-OHVD levels were normal (≥30 ng/ml) in 4 cases, not performed in 5 cases, low in the insufficiency range (between 20 and 30 ng/ml) in 4 cases and low in the deficiency range (less than 20 ng/ml) in 6 cases.
3.1 Imaging examples of healing rickets
The radiographic findings of healing rickets are well-described and illustrated in the older rickets literature of the 1900s in the studies of Eliot and Parks6 the study of Wimberger7 and the more recent study of Miller1. The central finding in healing rickets is the accumulation of nonmineralized bone osteoid/matrix within various growing bone compartments including the skull (craniotabes), costochondral junction of the ribs (rachitic rosary), subperiosteum (subperiosteal new bone formation), vertebral body (bone in bone), and growth plate (perichondral ring and submetaphyseal bands) [1; Figure 13]. The progression of bone mineralization in healing rickets can often be appreciated by comparing the initial skeletal survey with the follow-up skeletal survey, typically done 10–14 days after the initial one.
Fig. 1a–c illustrate several of these radiographic findings which indicate abnormal bone mineralization. We believe that the finding of an elevated blood 1,25-DiOHVD level should prompt a careful review of the skeletal surveys looking for these findings of healing rickets.
![Examples of Healing Rickets from the 19 cases with Elevated Blood 1,25-DiOHVD Levels Fig. 1a (Case 2): 3D CT scan images of the posterior calvarium with MIP image (left) and surface rendered image (right). Both show numerous spherical mineralization defects (several shown in red circles) and parasutural hypomineralization along the lambdoid and sagittal sutures (red arrows). Both are signs of healing rickets. Fig. 1b (Case 6): Lateral chest shows various degrees of cupping of the anterior ribs at the chondro-osseous junction and thickening of the normally delicate zone of provisional calcification (between red arrows), both signs of healing rickets. Fig. 1c (case 7): AP view of the proximal right femur shows 2 distinct lines of the zone of provisional calcification [original (red arrows) and new (green arrows)] at the chondro-osseous junction, separated by a radiolucent zone representing the rachitic intermediate zone. 15 days later the zone continues to expand as healing progresses. Note the content of the rachitic intermediate is less “trabeculated”, giving it a more featureless appearance than that seen in the adjacent metaphysis. This sequence of changes is consistent with healing rickets.](/content/220/2024/58/1/img/S0972978X24002381-gr1.jpg)
4 Discussion
The results of this study indicate that blood 1,25-DiOHVD levels in infants with MBDI were elevated above the normal range in 19 of the 22 (86 %) infants who were tested. The finding of an elevated blood 1,25-DiOHVD level is significant and potentially indicates decreased bone strength and bone fragility. Indeed, we interpreted the fractures in these infants to most likely be fragility fractures because of both the elevated blood 1,25-DiOHVD levels and the imaging studies which showed characteristic features of metabolic bone disease, chiefly healing rickets.
In the 76 infants with MUF in which child abuse was initially diagnosed and we diagnosed MBDI, only 22 of the 76 (30 %) infants had a blood 1,25-DiOHVD level performed, a significant underutilization of a valuable test.
4.1 Significance of elevated 1,25-DiOHVD blood level
1,25-DiOHVD is the active form of vitamin D that binds to the vitamin D receptor (VDR) which is found on a multitude of different human cells8. There are 4 main target cells with VDRs that control blood calcium, and thus total body calcium2–4:1.enterocytes of the small intestines that can absorb calcium by active transport2.renal tubular cells that can reabsorb calcium3.osteoclasts of the bone that control bone resorption4.osteoblasts of the bone that control bone formation
When blood calcium falls below a threshold value of about 9 mg%, there are compensatory mechanisms to restore the blood calcium to a normal value. Elevated blood 1,25-DiOHVD levels can increase blood calcium by mechanisms in both non-bone organs and bone.
Increased blood 1,25-DiOHVD levels can increase blood calcium levels in non-bone organs by increasing calcium absorption in the gastrointestinal tract and by increasing calcium reabsorption in the renal tubules of the kidney.
Increased blood 1,25-DiOHVD levels can increase blood calcium levels by a direct effect on bone osteoclasts and osteoblasts. Fig. 2 shows the well-established association between elevated 1,25-DiOHVD and bone hypomineralization. Elevated blood 1,25-DiOHVD will increase osteoclast activity resulting in increased bone resorption and inhibition of osteoblast activity. Both of these actions cause decreased bone mineralization and bone fragility. Thus, an elevated blood 1,25-DiOHVD level will restore blood calcium to a normal value, but at the expense of bone strength.
Decreased levels of blood calcium are perceived by the calcistat (calcium-sensing receptor) in the parathyroid gland that causes increased secretion of PTH into the blood which increases the activity of CYP27B1 in the kidney. The increased blood levels of 1,25-DiOHVD mediated through increased PTH results in 4 physiologic changes that all increase blood calcium:1.increased intestinal absorption of calcium2.decreased renal excretion of calcium3.increased bone resorption which leeches calcium from the bone, and4.inhibition of bone formation
The latter 2 consequences have an immediate effect to rapidly increase blood calcium compared to the former which requires more time. The elegant transgenic mice studies of Lieben et al. have demonstrated that increased levels of 1,25-DiOHVD not only increase osteoclast activity through RANKL secreted by osteoblasts, but also suppress bone mineralization by increasing the levels of several mineralization inhibitors including the Opn gene and pyrophosphates2,3.
4.2 Temporal relation of elevated PTH and elevated 1,25-DiOHVD
In these 19 cases with elevated 1,25-DiOHVD levels, blood PTH levels were performed in 13 cases: elevated in 7, low in one, normal in 5, and not performed in 6. As noted above and in Fig. 1, elevated PTH increases the enzyme activity of renal CYP27B1.
Venkataraman et al. studied 5 infants ages 4–18 months with vitamin D-deficient rickets who were treated with vitamin D, 400 IUs/day9. They found that serum PTH levels were markedly elevated prior to treatment and quickly normalized by 2 weeks following treatment. However, blood 1,25-DiOHVD levels were high-normal initially and markedly increased following treatment with vitamin and remained significantly elevated for 8 weeks.
Thacher et al. studied 28 Nigerian children with nutritional rickets who had both lower extremity abnormalities and radiographic evidence of rickets10. These infants had markedly elevated blood 1,25-DiOHVD levels initially which remained significantly elevated even after 14 days of treatment with vitamin D. PTH levels were not studied.
Mallet et al. studied a single 13 month old infant with radiographic evidence of nutritional rickets who had both a markedly elevated blood 1,25-DiOHVD level and a markedly elevated blood PTH level prior to treatment with Vitamin D11. After 17 days of vitamin D treatment, the blood PTH level was normal and the blood 1,25-DiOHVD level was even higher than the initial elevated level.
Therefore, there is ample evidence that in infants and children with nutritional rickets treated with vitamin D, the elevated blood 1,25-DiOHVD levels remain elevated significantly longer than the blood PTH level. This likely explains why some of the blood PTH levels in our cases were normal, in spite of elevation of blood 1,25-DiOHVD levels.
There is one difference in our 19 patients and those of Thacher, Mallett Venkataraman. Our patients had healing rickets predominantly related to risk factors of fetal origin; whereas the children in these 3 studies were older and had rickets related to postnatal, nutritional issues.
There are extra-renal tissues that also contain the same CYP27B1 enzyme capable of the 1-hydroxylation of 1,25-DiOHVD including the following: keratinocytes, pulmonary alveolar macrophages, monocytes, and mesenchymal stem cells of bone marrow12. 1,25-DiOHVD levels are also markedly elevated in pregnancy and some autoimmune diseases13. The original belief that the 1-hydroxylation of 1,25-DiOHVD exclusively happens in the kidney via PTH is not valid.
4.3 Normal range for 1,25-DiOHVD
Table 2 summarizes the normal ranges of 1,25-DiOHVD that have been reported for young infants in scientific studies and by commercial labs. These ranges tend to be higher in young infants compared to that of older children and adults. There is variability in the normal ranges of 1,25-DiOHVD for young infants, and the reasons for this likely include: different methods of measurement, different populations with differing frequencies of VDD, and differing ages of the infants. In populations with a greater frequency of young infants with VDD or mothers with VDD during their pregnancy, there would be higher levels of 1,25-DiOHVD.
| Study (Reference) | # infants | Age of Infants (weeks) | Method | Normal 1,25, diOH VD (pg/ml) |
| 1. Seino14 | 8 | 1 week- 6 months | Modified, Competitive protein binding assay of Dokoh | 72 + 9.6 (Mean + 1 sd) |
| 2. Markestad14,15 | 2423 | six week old infantssix month olds | Competitive protein binding assay | Median: 40 Range: 20–110Median: 52 Range: 30-90 |
| 3. Mayo Labs16 | Not Given | Not given | Extraction/Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) | 24-86 (Range) |
| 4. ARUP17 | Not Given | Not given | Quantitative Chemiluminescent Immunoassay | 19.9–79.3 (Range) |
| 5. Labcorp18 | Not Given | 0–6 months | Immunochemiluminometric | 44.3–212.9 (Range) |
Limitations of this study are the following:1.The blood 1,25-DiOHVD levels were not all performed at the same lab.2.There is variation in the range of normal 1,25-DiOHVD blood levels in young infants, and what constitutes levels at risk for adverse physiological consequences. We believe that our methods used reasonably high cut-off values for an abnormally elevated 1,25-DiOHVD blood level, albeit the high cut-off values somewhat varied depending on the lab that performed the test. It is reasonable to assume that the 19 abnormally elevated 1,25-DiOHVD blood levels were truly elevated as they were all associated with poor bone mineralization.3.There was a single radiologist to review the imaging studies for findings of healing rickets.
5 Conclusion
The American Academy of Pediatrics Committee on Child Abuse and Neglect Clinical Report related to fractures in infants (Section on Radiology, Section on Endocrinology, Section on Orthopaedics and the Society for Pediatric Radiology) recommends that in an infant with unexplained fractures have the following blood work at the time of evaluation: calcium, phosphate, alkaline phosphatase, PTH, and 25OH Vitamin D19. They currently make no recommendation for blood 1,25-DiOHVD testing. We believe that the present study indicates blood 1,25-DiOHVD testing should also be done in the infant with MUF because an elevated blood level suggests an underlying metabolic bone fragility disorder. An elevated blood 1,25-DiOHVD level in an infant with MUF should prompt a careful review of both the imaging studies looking for findings of healing rickets and of the history looking for risk factors of metabolic bone disease.
Contributors’ statement
Marvin Miller designed the study and prepared the first draft of the paper. He reviewed and analyzed the cases for the characteristics described in Table 1. He is guarantor and corresponding author.
David Ayoub interpreted the imaging studies. He made additions and corrections to the first draft.
All authors revised the paper critically for intellectual content and approved the final version. All authors agree to be accountable for the work and to ensure that any questions relating to the accuracy and integrity of the paper are investigated and properly resolved.
Funding
None.
Institutional ethical committee approval
Not applicable.
Patient consent
Not applicable.
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