Bilateral coronal and sagittal synostosis in X-linked hypophosphatemic rickets: a case report

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.

Whole exome sequencing identifies two novel variants in PHEX and DMP1 in Malaysian children with hypophosphatemic rickets

BACKGROUND

Hypophosphatemic rickets (HR) is a genetic disease of phosphate wasting that is characterized by defective bone mineralization. The most common cause of the disease is mutations in the phosphate regulating gene with homologies to endopeptidases on the X chromosome (PHEX) gene. The aims of this study were to identify the gene variants responsible for HR in three cases of Malaysian origin from three independent families and to describe their clinical, biochemical, and radiological features.

METHODS

Whole exome sequencing (WES) was performed on all patients and their parents, followed by Sanger sequencing validation. Bioinformatics tools were used to provide supporting evidence for pathogenicity of variants. To confirm that a mutation is de novo, paternity test was carried out. High resolution melting curve analysis was performed to assess the allele frequency in normal controls for mutations that were found in the patients.

RESULTS

The patients showed typical characteristics of HR including lower limb deformity, hypophosphatemia, and elevated alkaline phosphatase. WES revealed two variants in the PHEX gene and one variant in the dentin matrix protein 1 (DMP1) gene. Two of the three variants were novel, including c.1946_1954del (p.Gly649_Arg651del) in PHEX and c.54 + 1G > A in DMP1. Our data suggests that the novel p.Gly649_Arg651del variant is likely pathogenic for HR disease.

CONCLUSIONS

This study extends the variant spectrum of the PHEX and DMP1 genes. Our findings indicate that WES is an advantageous approach for diagnosis of genetic diseases which are heterogeneous.

Orthopedic and neurosurgical care of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is due to mutations in the PHEX gene leading to unregulated production of FGF23 and uncontrollable hypophosphatemia. XLH is characterized in children by rickets, short stature, waddling gait, and leg bowing of variable morphology and severity. Phosphate supplements and oral vitamin D analogs partially or, in some cases, fully restore the limb straightness. XLH patients may also be affected by premature, complete, or partial ossification of sutures between cranial bone, which could eventually result in cranial dysmorphia, decreased intracranial volume, and secondary abnormally high intracranial pressure with a cerebral compression. Our goal is to address the criteria and the management of the skeletal complications associated with XLH, mainly orthopedic and neurosurgical care, and reflect on decision-making and follow-up complexities.

Hereditary hypophosphatemic rickets and craniosynostosis

BACKGROUND

Craniosynostosis is an underdiagnosed complication associated with hypophosphatemic rickets. The study aims to describe the clinical and auxological characteristic of children with hypophosphatemic rickets and craniosynostosis, describe the usual treatment, and compare the characteristics with those of children without craniosynostosis.

METHODS AND PATIENTS

An observational and retrospective cohort study was conducted. Clinical notes and cranial images were reviewed. Out of 96 children, only the 50 patients who had skull images were included.

RESULTS

Out of 50 patients, 26 (15 males) had craniosynostosis (52%). No differences were observed in birth size, age, height, body proportions, alkaline phosphatase, serum phosphate, or percent tubular reabsorption of phosphate at first appointment among children with or without craniosynostosis. Among patients with craniosynostosis, dolichocephaly was prevalent. The sagittal suture was affected in all patients with craniosynostosis, with 19 of 26 children (73%) affected with isolated scaphocephaly. Pan-sutural craniosynostosis was present in 7 children (27%). None of the children had microcephaly, 7 of them presented macrocephaly and, in the remaining subjects, head circumference was normal. Five patients had undergone at least 1 cranial remodeling surgery. One patient with craniosynostosis was diagnosed with a Chiari I malformation. Molecular characterization of PHEX gene was performed in 14 cases.

CONCLUSIONS

Craniosynostosis is an underdiagnosed complication of hypophosphatemic rickets. Many patients with normal head size and growth may go undiagnosed, thus it is important to consider this association for early diagnosis and possible surgical treatment. A multidisciplinary approach is necessary for a correct long-term follow-up.

The Use of Distraction Osteogenesis in the Treatment of Rickets-Associated Craniosynostosis

BACKGROUND

Craniosynostosis has a known association with rickets. Because of abnormal bone development and a tendency for patients with rickets to present at an older age than most patients with craniosynostosis, repair may be complicated by inadequate cranial expansion and greater risk of sutural re-fusion. We present 2 cases of rickets-associated sagittal craniosynostosis and show the effectiveness of distraction osteogenesis in the surgical management of this condition.

CASE DESCRIPTION

Two 3-year-old boys with rickets presented with sagittal synostosis and marked scaphocephalic deformity. Cranial osteotomies were performed followed by placement of 2 internal distractors. The devices were activated daily for 30 days to achieve a target transverse cranial distraction of 30 mm. A subsequent period of 10-12 weeks allowed for adequate bone consolidation. At the time of device removal, the final breadth of distraction and the quality of new bone formed was assessed. Distraction distance in both cases was verified intraoperatively to be 30 mm. Clinical examination confirmed that the distraction gaps were bridged by solid bone. The treatment protocol resulted in a significant improvement in cranial proportion in both patients, which was maintained at long-term follow-up. Estimated blood loss was high in both cases, presumably related to the hyperemic nature of rickets bone.

CONCLUSIONS

Distraction osteogenesis promotes bone growth and cranial remodeling in patients with craniosynostosis caused by rickets. The technique allows for continuous incremental expansion of both bone and scalp tissue. We recommend consideration of distraction osteogenesis in the treatment of older children with severe deformity related to craniosynostosis, including those with rickets.

High Incidence of Cranial Synostosis and Chiari I Malformation in Children With X-Linked Hypophosphatemic Rickets (XLHR)

X-linked hypophosphatemic rickets (XLHR) represents the most common form of genetic hypophosphatemia and causes rickets and osteomalacia in children because of increased FGF23 secretion and renal phosphate wasting. Even though cranial vault and craniovertebral anomalies of potential neurosurgical interest, namely early closure of the cranial sutures and Chiari type I malformation, have been observed in children with XLHR, their actual incidence and characteristics are not established. The aims of this study were to analyze the incidence of cranial and cervico-occipital junction (COJ) anomalies in children with XLHR and describe its features. This is a retrospective study of CT scans of the head and skull in 44 XLHR children followed at the French Reference Center for Rare Diseases of the Calcium and Phosphate Metabolism. Forty-four children with XLHR, 15 boys and 29 girls, aged 8.7 ± 3.9 years at time of CT scan, were studied. We found that 59% of XLHR children had a complete or partial fusion of the sagittal suture and 25% of XLHR children showed protrusion of the cerebellar tonsils. A history of dental abscesses was associated with craniosynostosis, and craniosynostosis was associated with abnormal descent of cerebellar tonsils. Only 2 patients showed neurologic symptoms. Four of 44 patients (9%) required neurosurgery. This study highlights that sagittal suture fusion and Chiari type I malformation are frequent complications of XLHR. The incidence of sagittal synostosis in XLHR is actually extremely high and was probably underestimated so far. Chiari type I malformation is also frequent. Because diagnosis of craniovertebral anomalies can be underestimated on a purely clinical basis, radiological studies should be considered in XLHR children if a proper diagnosis is warranted. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

Mutation Screening of Candidate Genes in Patients with Nonsyndromic Sagittal Craniosynostosis

BACKGROUND

Craniosynostosis is a condition that includes the premature fusion of one or multiple cranial sutures. Among various craniosynostosis forms, sagittal nonsyndromic craniosynostosis is the most prevalent. Although different gene mutations have been identified in some craniosynostosis syndromes, the cause of sagittal nonsyndromic craniosynostosis remains largely unknown.

METHODS

To screen for candidate genes for sagittal nonsyndromic craniosynostosis, the authors sequenced DNA of 93 sagittal nonsyndromic craniosynostosis patients from a population-based study conducted in Iowa and New York states. FGFR1-3 mutational hotspots and the entire TWIST1, RAB23, and BMP2 coding regions were screened because of their known roles in human nonsyndromic or syndromic sagittal craniosynostosis, expression patterns, and/or animal model studies.

RESULTS

The authors identified two rare variants in their cohort. A FGFR1 insertion c.730_731insG, which led to a premature stop codon, was predicted to abolish the entire immunoglobulin-like III domain, including the ligand-binding region. A c.439C>G variant was observed in TWIST1 at its highly conserved loop domain in another patient. The patient's mother harbored the same variant and was reported with jaw abnormalities. These two variants were not detected in 116 alleles from unaffected controls or seen in the several databases; however, TWIST1 variant was found in a low frequency of 0.000831 percent in Exome Aggregation Consortium database.

CONCLUSIONS

The low mutation detection rate indicates that these genes account for only a small proportion of sagittal nonsyndromic craniosynostosis patients. The authors' results add to the perception that sagittal nonsyndromic craniosynostosis is a complex developmental defect with considerable genetic heterogeneity.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, II.

Hypophosphatemic rickets and craniosynostosis: a multicenter case series

OBJECTIVE This study examines a series of patients with hypophosphatemic rickets and craniosynostosis to characterize the clinical course and associated craniofacial anomalies. METHODS A 20-year retrospective review identified patients with hypophosphatemic rickets and secondary craniosynostosis at 3 major craniofacial centers. Parameters examined included sex, age at diagnosis of head shape anomaly, affected sutures, etiology of rickets, presenting symptoms, number and type of surgical interventions, and associated diagnoses. A review of the literature was performed to optimize treatment recommendations. RESULTS Ten patients were identified (8 males, 2 females). Age at presentation ranged from 1 to 9 years. The most commonly affected suture was the sagittal (6/10 patients). Etiologies included antacid-induced rickets, autosomal dominant hypophosphatemic rickets, and X-linked hypophosphatemic (XLH) rickets. Nine patients had undergone at least 1 cranial vault remodeling (CVR) surgery. Three patients underwent subsequent surgeries in later years. Four patients underwent formal intracranial pressure (ICP) monitoring, 3 of which revealed elevated ICP. Three patients were diagnosed with a Chiari Type I malformation. CONCLUSIONS Secondary craniosynostosis develops postnatally due to metabolic or mechanical factors. The most common metabolic cause is hypophosphatemic rickets, which has a variety of etiologies. Head shape changes occur later and with a more heterogeneous presentation compared with that of primary craniosynostosis. CVR may be required to prevent or relieve elevated ICP and abnormalities of the cranial vault. Children with hypophosphatemic rickets who develop head shape abnormalities should be promptly referred to a craniofacial specialist.

X-linked hypophosphatemic rickets and sagittal craniosynostosis: three patients requiring operative cranial expansion: case series and literature review

PURPOSE

A defect in a phosphate-regulating gene leads to the most common form of rickets: X-linked hypophosphatemic rickets (XLH) or vitamin D-resistant rickets (VDDR). XLH has been associated with craniosynostosis, the sagittal suture being the most commonly involved.

METHODS

We present three patients with rickets and symptomatic sagittal suture craniosynostosis all of whom presented late (>2 years of age). Two had a severe phenotype and papilledema, while the third presented with an osseous bulging near the anterior fontanel and experienced chronic headaches.

RESULTS

All underwent successful cranial vault expansion.

CONCLUSIONS

Rachitic patients with scaphocephaly should be screened for craniosynostosis.