Hereditary hypophosphatemic rickets and craniosynostosis

The current understanding of germline predisposition in non-syndromic sagittal craniosynostosis: a systematic review

PURPOSE

The objective of this literature review was to provide a comprehensive and up-to-date overview of the current understanding of the genetic etiology for non-syndromic sagittal craniosynostosis.

METHODS

Using the PubMed database and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), we systematically reviewed relevant records on germline genetics in children with non-syndromic sagittal craniosynostosis.

RESULTS

Two hundred two records were identified, of which 25 were included following title and abstract screening and subsequent full-text review. The 25 records in combination included 829 children with non-syndromic sagittal craniosynostosis. A likely pathogenic or pathogenic germline variant was reported for 9.8% of the 827 patients for whom germline genetic testing was performed. The reported variants were distributed across 50 different genes, with more than one variant detected in 13 genes.

CONCLUSION

Based on the existing literature, genetic predisposition is likely to play a role in at least 9% of children with non-syndromic sagittal craniosynostosis. Future studies will benefit from international consensus in terms of diagnostic nomenclature and a higher level of standardization across study methodologies and bioinformatic approaches.

Complications in craniosynostosis surgery in patients with rickets: illustrative case and systematic review of literature

BACKGROUND

Craniosynostosis (CSS) is the premature fusion of calvarial sutures associated with identified genetic mutations or secondary to alterations in intracranial pressure, brain, or bone growth patterns. Of the metabolic etiologies implicated in CSS, X-linked hypophosphatemic rickets (XLHR) is the most common, with dysfunctional bone mineralization leading to progressive hyperostosis and delayed synostosis. There is a paucity of literature discussing the unique surgical considerations for XLHR-related CSS.

OBSERVATIONS

A 26-month-old male with XLHR-related sagittal CSS underwent cranial vault remodeling (CVR). Surgery was complicated by the presence of diploic hypertrophy with significant intraoperative estimated blood loss (EBL). EBL greatly exceeded reference ranges for CVR in all-cause CSS. As a result, the surgical goals were modified and the complete planned procedure aborted. Subsequent review of preoperative imaging revealed multiple fine vascular lacunae within the bone. A systematic literature review was conducted to identify reported complications relating to surgical intervention for rickets-associated CSS.

LESSONS

Future considerations for patients with XLHR-related CSS should emphasize awareness of metabolic risk factors with associated complications, and the need for selection of approach and operative management techniques to avoid EBL. Further research is required to elucidate underlying mechanisms and determine whether the encountered phenomenon is characteristic across this patient population and potentially minimized by preoperative medical therapy.

Approach to Hypophosphatemic Rickets

Hypophosphatemic rickets typically presents in infancy or early childhood with skeletal deformities and growth plate abnormalities. The most common causes are genetic (such as X-linked hypophosphatemia), and these typically will result in lifelong hypophosphatemia and osteomalacia. Knowledge of phosphate metabolism, including the effects of fibroblast growth factor 23 (FGF23) (an osteocyte produced hormone that downregulates renal phosphate reabsorption and 1,25-dihydroxyvitamin-D (1,25(OH)2D) production), is critical to determining the underlying genetic or acquired causes of hypophosphatemia and to facilitate appropriate treatment. Serum phosphorus should be measured in any child or adult with musculoskeletal complaints suggesting rickets or osteomalacia. Clinical evaluation incudes thorough history, physical examination, laboratory investigations, genetic analysis (especially in the absence of a guiding family history), and imaging to establish etiology and to monitor severity and treatment course. The treatment depends on the underlying cause, but often includes active forms of vitamin D combined with phosphate salts, or anti-FGF23 antibody treatment (burosumab) for X-linked hypophosphatemia. The purpose of this article is to explore the approach to evaluating hypophosphatemic rickets and its treatment options.

Craniosynostosis in a patient with Fanconi-Bickel syndrome: a case report

OBJECTIVES

Craniosynostosis may be a rare but severe complication of Fanconi-Bickel syndrome (FBS). Both conditions can be associated with feeding intolerance in young children. Prompt recognition and correction of increased intracranial pressure may lead to improved dietary tolerance in FBS patients and decrease morbidity.

CASE PRESENTATION

We present the case of a child with genetically confirmed FBS, severe feeding intolerance and evidence of metabolic bone disease. At two years of age, a diagnosis of multi-sutural craniosynostosis with increased intracranial pressure was made. The patient underwent cranial vault expansion using distraction osteogenesis, after which his feeding intolerance completely resolved.

CONCLUSIONS

This case highlights the importance of monitoring for secondary craniosynostosis in patients with FBS and frequent emesis. Objective markers of bone health may help identify children at highest risk, though the actual mechanism of development is likely multifactorial. Increased awareness of this potential association should prompt more routine screening and improve outcomes.

Growth in height and body proportion from birth to adulthood in hereditary hypophosphatemic rickets: a retrospective cohort study

PURPOSE

Patients with hereditary hypophosphatemic rickets are short and disproportionate and very little information is available on segmental growth, but the body disproportion at adulthood leads us to think that the growth velocity of legs is slower.

METHODS

A total of 96 children were included and molecular testing was carried out in 42. Children who reached adult height were classified into two groups according to their compliance to conventional treatment (phosphate supplement and calcitriol). Individual growth records of height and sitting height/height were plotted using Argentine reference data in 96 children and growth curves were estimated by fitting Preece-Baines Model 1 in 19 of the children.

RESULTS

Molecular testing revealed sequence deleterious alterations or large deletions in 36/42 patients. During childhood, 76% of children grew below - 1.88 standard deviation score (SDS) and 97% had body disproportion. During adolescence, the mean peak height velocity for the good and poor compliance to treatment groups was 7.8 (0.6) and 5.4 (0.4) cm/year in boys and 7.0 (0.7) and 5.2 (0.8) cm/year in girls, respectively. At adulthood, the median sitting height/height ratio was 2.32 and 6.21 SDS for the good and poor compliance to treatment groups, respectively. The mean pubertal growth spurt of the trunk was -0.8 (1.4) SDS, with a short pubertal growth spurt of - 1.8 (0.4) SDS for limbs in the good compliance group. Median adult height in 13/29 males and 30/67 females was -4.56 and -3.16 SDS, respectively.

CONCLUSION

For all patients the growth spurt was slower, secondary to a short growth spurt of limbs, reaching a short adult height with body disproportion that was more prominent in the poor compliance group.