Mutations In PHEX Gene Research Articles

Raquitismo hipofosfatémico ligado al cromosoma X: un reto diagnóstico y terapéutico

X-linked hypophosphatemia is a genetic disorder caused by PHEX gene mutations, which affects the encoding of a metalloprotease whose function is to inhibit fibroblastic growth factor —23 (FGF-23), promoting phosphate renal loss. Following we describe the case of a teenager diagnosed with a PHEX gene mutation. The same genetic alteration was found in the mother of the patient, considering a spontaneous mutation that was transmitted to her son, which makes the case, even rarer, where the diagnostic challenge needs to overcome administrative, economic and social difficulties. A timely diagnosis and treatment could help optimize the finalheight and minimize the skeletal deformities presented in both the mother and the child. Currently, there is a traditional treatment and a novel one that was ordered for the pediatric patient in this report.

Pulp chamber features, prevalence of abscesses, disease severity, and PHEX mutation in X-linked hypophosphatemic rickets.

Rickets, growth failure, and recurrent periapical abscesses with fistulae are main signs in patients with X-linked hypophosphatemic rickets (XLH). Prevalence of abscesses, pulp chamber features, biochemical findings, disease severity, and PHEX gene mutation were examined. Pulp chambers size, shape, and morphology were assessed by orthopantomography in XLH patients (n = 24, age 5.8 ± 1.6years) and in sex and age-matched healthy controls (n = 23, age 6.2 ± 1.4years). XLH patients received conventional treatment (3.5 ± 1.9years). Pulp chamber features were assessed in teeth of primary dentition and in the permanent left mandibular first molar and compared with those of controls. Rickets severity score was assessed at wrist, knee, and ankle. The mean pulp chamber area/tooth area ratio, mean pulp chamber height/pulp chamber width ratio, and prominence of pulp horns into the tooth crown in primary and secondary molars were significantly higher in patients than in controls and in patients suffered abscesses than in patients without abscesses. Sixteen patients (67%) had a history of abscesses; incisors were affected more than canines and molars. Severity of rickets and mean serum parathyroid hormone (PTH) levels were significantly higher, and mean serum 1,25-dihydroxyvitamin D [1,25(OH)2D] levels significantly lower in patients suffered abscesses than in patients without abscesses. PHEX gene mutations were not correlated with dental phenotype and disease severity. Enlarged pulp chambers with altered shape and morphology affected the majority of XLH patients predisposing to recurrent periapical abscesses with fistulae. Dental phenotype was associated with severity of rickets, high serum PTH, and low serum 1,25(OH)2D levels.

Congenital Conditions of Hypophosphatemia Expressed in Adults.

The main congenital conditions of hypophosphatemia expressed in adulthood include several forms of hereditary hypophosphatemic rickets and a congenital disorder of vitamin D metabolism characterized by osteomalacia and hypophosphatemia in adult patients. Hypophosphatemia in adults is defined as serum phosphate concentration < 0.80mmol/L. The principal regulators of phosphate homeostasis, as is well known, are parathyroid hormone (PTH), activated vitamin D, and Fibroblast Growth Factor 23 (FGF23). Differential diagnosis of hypophosphatemia is based on the evaluation of mechanisms leading to this alteration, such as high PTH activity, inadequate phosphate absorption from the gut, or renal phosphate wasting, either due to primary tubular defects or high FGF23 levels. The most common inherited form associated to hypophosphatemia is X-linked hypophosphatemic rickets (XLH), caused by PHEX gene mutations with enhanced secretion of the FGF23. Until now, the management of hypophosphatemia in adulthood has been poorly investigated. It is widely debated whether adult patients benefit from the conventional treatments normally used for pediatric patients. The new treatment for XLH with burosumab, a recombinant human IgG1 monoclonal antibody that binds to FGF23, blocking its activity, may change the pharmacological management of adult subjects with hypophosphatemia associated to FGF23-dependent mechanisms.

SAT-069 Advantages of Next Generation Sequencing (NGS) in Hypophosphatemic Disorders Diagnosis. First Case of SLC9A3R1 Gene Pathogenic Variant Detected in a Pediatric Patient

Background: Hereditary hypophosphatemic rickets (HHR) is a group of inherited disorders characterized by hypophosphatemia due to renal-phosphate wasting and impairment of vitamin D metabolism, rickets and disproportioned short stature. Different genetic defects are known to cause HHR, but similar clinical and biochemical features were reported. Dominant-X-linked HR (XLHR) is the most frequent form, with an incidence of 1 in 20.000, although dominant and recessive autosomal forms are also described. XLHR is caused by inactivating mutations in the PHEX gene (located at Xp22.1), encoding a endopeptidase which regulates the phosphaturic secretion. Affected individuals present with a broad phenotypic spectrum, ranging from isolated hypophosphatemia up to severe symptoms of rickets. Therefore NGS studies represent an useful tool for molecular diagnosis characterization Aim: to develop a reliable NGS diagnostic tool for HHR and related disorders. Patients and Methods: we develop a NGS panel including 13 genes related with HHR or other hypophosphatemic disorders, using Illumina TruSeq Custom Amplicon technology.We analyzed 12 patients which have been sent to our laboratory for molecular genetic testing under suspicion of HHR based on clinical phenotype and laboratory studies but with no proven mutation in PHEX gene by Sanger sequencing or MLPA analysis or other hypophosphatemic disorder. Results: A previously reported pathogenic variant (p.Arg153Gln) was found in SLC9A3R1 gene encoding NHERF1cotransporter, which interact with phosphate and sodium renal transporter NaPi2a in a 13 months old girl. There are only 5 reported cases with alterations in this gene and all of them were adult patients with nephrolithiasis. The patient was referred to our hospital due to hypercalcemia. She had poor weight gain and laboratory findings showed high serum calcium (16,6 mg/dl), mild serum phosphate (3.9 mg/dl), very low parathyroid hormone (PTH) (< 3 ng/ml), normal 25OHvit D (40 ng/ml) levels, and elevated urinary calcium/ creatinine rate (2), and low phosphate tubular reabsorption (85%). Ultrasound showed nephrolithiasis. Since she had hypophosphatemia and renal phosphate wasting with symptomatic severe PTH independent hypercalcemia probably secondary to excessive calcitriol production with hypercalciuria, a molecular alteration of CYP24A1 or SLC34A1genes was suspected. Conclusion: NGS allowed to report for the first time the identification of a mutation in the SLC9A3R1 gene in a pediatric patient. An early diagnosis might improve long term outcome starting the right therapy to avoid progression of nephrolithiasis and nephrocalcinosis and chronic renal failure.

SAT-373 A Case of X Linked Hypophosphatemic Rickets Due to DE Novo Phex Gene Mutation

IntroductionRickets is a condition that can affect bones of infants and children. It is characterized by growth plate demineralization and can occur secondary to, most commonly, vitamin D deficiency or various problems with vitamin D, Calcium or Phosphate metabolism.Hypophosphatemic rickets (HR) is a type of rickets that is inherited by X linked dominant pattern mainly however it can be also inherited by autosomal dominant and recessive patterns in rare cases. X linked dominant type (XLH) affects about 1 in 20,000 newborns. Each of the other hereditary forms of HR has been identified in only a few families.Clinical features of XLH is similar to other types of rickets including metaphyseal widening, palpable rachitic rosaries, frontal prominence, malformation of the horizontal depression along the lower border of the chest, insufficient weight gain and leg bowing.Case presentation:A 10-month-old infant presented to endocrinology with vitamin D deficiency, low serum phosphorus and hyperparathyroidism. Physical examination showed macrocephaly with frontal bossing, widening of the wrists and rachitic rosaries. His lab results showed low 25 OH vitamin D (11 ng/ml) (N:20-50 ng/ml), low phosphorus (PO4) (3.3 mg/dl) (N:4-6.5 mg/dl), high PTH (113 pg/ml) (N: 20-65pg/ml), high alkaline phosphatase (ALP) (836 IU/L) (N: 135-518 IU/L) and normal calcium (Ca2+) (9.6 mg/dl) (N:9-11 mg/dl). Vitamin D treatment was started however his follow up lab results showed persistent hypophosphatemia for age (2.8mg/dl) and elevated ALP (600IU/l) despite normalization of vitamin D (38 ng/ml). Additional lab tests were done showing high PO4 excretion (19.5 mg/dl)(N:1:3.5 mg/dl), Ca/Cr ratio 0.005 (N <0.14), inappropriately normal FGF23 level (129 RU/ml) (N: >124 RU/mL). Genetic testing showed de novo mutation in PHEX gene (871C>T) which is consistent with XLH.PHEX gene mutation is the most common mutation associated with XLH. Normally this gene can directly or indirectly regulate a protein called fibroblast growth factor 23 (produced from FGF23 gene). This protein normally inhibits renal reabsorption of phosphate into the bloodstream. Gene mutations increase the production or reduce the breakdown of fibroblast growth factor 23 leading to an overactivation of this protein and reduction of phosphate reabsorption by the kidneys, resulting in hypophosphatemia.The patient was maintained on Burosomab (0.4 mg/kg biweekly); a recombinant human monoclonal antibody (IgG1) that binds to and inhibits the activity of fibroblast growth factor 23 (FGF23) and increases the phosphate reabsorption in the renal tubules.Conclusion:XLH due to PHEX gene mutation should be considered in rachitic children who have persistently low phosphate levels despite treating vitamin D deficiency.

SAT-360 Out of Sight, out of Mind: PHEX 3’-UTR C.*231A&amp;gt;G X-Linked Hypophosphatemia in Adults: A Case Study of One Family Pedigree with a Widely Variable Phenotype

Title: Out of Sight, Out of Mind: PHEX 3’-UTR c.*231A>G X-Linked Hypophosphatemia in Adults: A Case Study of One Family Pedigree with a Widely Variable PhenotypeX-linked hypophosphatemia (XLH) is an inherited form of hypophosphatemia that is part of a group of disorders that leads to impaired bone mineralization, which can manifest as rickets in children and osteomalacia in adults. Mutations in PHEX, DMP1, ENPP1, and activating mutations in FGF23 have each been shown as genetic causes for XLH. PHEX is a zinc metallopeptidase which reduces expression of FGF23 through mechanisms that are not fully understood. Inactivating mutations in the PHEX gene cause elevated levels of FGF23, resulting in renal phosphate-wasting, impaired conversion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D and impaired bone mineralization with osteomalacia. Though the clinical significance of FGF23 levels is not clearly understood, it has also been shown that FG23 increases with age.XLH has a reported prevalence of 3.9–5 per 100,000. We speculate that this may be under recognized and that diagnosis may be delayed for many years in those with mild forms of XLH due to non-specific symptoms. Diagnosis may be complicated by normal or low-normal serum phosphorus levels. Adults may be mistakenly diagnosed with ankylosing spondylitis, polyarthritis, osteoarthritis, diffuse idiopathic skeletal hyperostosis and other disorders that cause stiffness. Some clinical manifestations of XLH in adults include dental disease, skeletal and spinal disease, sensorineural hearing loss, kidney stones, renal impairment, and hyperparathyroidism. The PHEX 3’-UTR c.231A>G near the polyadenylation signal has been previously described to cause milder severity in men and seemingly unaffecting women, but data for comparison is limited.We present a large, multigenerational family with a mutation in the PHEX gene (3’-UTR c.*231A>G) demonstrating variable penetrance in the pedigree. Of the members positive for the mutation, the most common symptoms were sensorineural hearing loss, enthesopathy, and dental disease. Most had normal or low-normal phosphorus levels in both genders. Two patients had prior diagnoses of ankylosing spondylitis/ seronegative spondyloarthropathy. In general, males with the mutation had more severe symptoms than females. However, females with a severe phenotype and low phosphorus was also observed. The disease burden was cumulative over time and correlated with serum phosphorus levels. Musculoskeletal symptoms were increased in the members over the age of 60.Sources:Chesher, Douglas et al. Outcome of Adult Patients with X-Linked Hypophosphatemia Caused by PHEX Gene Mutations. Vol. 41. Dordrecht: Springer Netherlands, 2018. Web.Zhang, Cong et al. Clinical and Genetic Analysis in a Large Chinese Cohort of Patients with X-Linked Hypophosphatemia. Vol. 121. Elsevier Inc, 2019. Web.

On X-linked hypophosphatemia at the European society of pediatric endocrinology meeting, Vienna, Austria; september 19–21, 2019

X-linked hypophosphatemia (XLH) is the most common form of inherited hypophosphatemic rickets. Phosphate wasting results in weak, soft and deformed bones, impaired growth, and affected mobility. It is mainly caused by a loss of function mutation in PHEX gene that leads to elevated fibroblast growth factor-23 which mediates the phosphate wasting. During the 58th annual meeting of the European Society of Pediatric Endocrinology (ESPE) held in Vienna between September 19, 2019 and 21, 2019, nearly 100 free communications and a dedicated symposium focused on XLH. The authors attended the conference and wished to share its highlights pertaining to XLH and burosumab therapy to extend the benefit to other professionals who did not attend.

X-linked hypophosphatemia: Management and treatment prospects.

X-linked hypophosphatemia (XLH), due to a PHEX gene mutation, is the most common genetic form of rickets and osteomalacia. Manifestations in children consist of rickets, lower-limb bone deformities, bone pain, failure to thrive, dental abscesses, and/or craniostenosis. Adults may present with persistent bone pain, early osteoarthritis, hairline fractures and Looser zones, enthesopathy, and/or periodontitis. Regardless of whether the patient is an infant, child, adolescent or adult, an early diagnosis followed by optimal treatment is crucial to control the clinical manifestations, prevent complications, and improve quality of life. Treatment options include active vitamin D analogs and phosphate supplementation to correct the 1.25(OH)2 vitamin D deficiency and to compensate for the renal phosphate wasting, respectively. The recently introduced FGF23 antagonist burosumab is designed to restore renal phosphate reabsorption by the proximal tubule and to stimulate endogenous calcitriol production. In Europe, burosumab is licensed for use in pediatric patients older than 1 year who have XLH. This review discusses the diagnosis and treatment of XLH and describes the indications of the various available treatments.

Mutation analysis of four pedigrees affected with hypophosphatemic rickets through targeted next-generation sequencing

To detect potential mutations of PHEX gene in four pedigrees affected with hypophosphatemic rickets (HR) and provide prenatal diagnosis for a fetus at 13th gestational week. The coding regions and exon/intron boundaries of PHEX, FGF23, DMP1, ENPP1, CLCN5 and SLC34A3 genes of the probands were analyzed by targeted next-generation sequencing (NGS). Suspected mutations were verified by Sanger sequencing among unaffected relatives and 200 unrelated healthy individuals. Deletions were confirmed by multiplex ligation-dependent probe amplification (MLPA) detection of probands, unaffected relatives and 20 unrelated healthy individuals. Prenatal diagnosis for a fetus with high risk was carried out through MLPA analysis. Four PHEX mutations were respectively detected in the pedigrees, which included c.850-3C>G, exon 11 deletion, exon 13 deletion and c.1753G>A (p.G585R). Among these, exon 11 deletion, exon 13 deletion and c.1753G>A (p.G585R) were novel mutations and not found among unaffected relatives and healthy controls. In pedigree 3, the same mutation was not found in the fetus. Mutations of the PHEX gene probably underlies the disease among the four pedigrees. NGS combined with Sanger sequencing and/or MLPA detection can ensure accurate diagnosis for this disease.

Analysis of PHEX gene mutations in three pedigrees affected with hypophosphatemic rickets

To explore the molecular basis for three pedigrees affected with hypophosphatemia vitamin D resistant rickets (X-linked hypophosphatemia, XLH). Peripheral blood samples from the three pedigrees were collected. Following DNA extraction, the 11 exons and flanking regions of the PHEX gene were subjected to PCR amplification and direct sequencing. Pathogenicity of identified mutations was evaluated through genotype-phenotype correlation. For pedigrees 1 and 2, pathogenic mutations were respectively identified in exon 8 (c.871C>T, p.R291X) and exon 15 (c.1601C>T, p.P534L) of the PHEX gene. For pedigree 3, a novel mutation (c.1234delA, p.S412Vfs*12) was found in exon 11 of the PHEX gene, which caused shift the reading frame and premature termination of protein translation. The three mutations probably account for the XLH in the affected pedigrees. The discovery of novel mutations has enriched the spectrum of PHEX gene mutations.

Outcome of adult patients with X-linked hypophosphatemia caused by PHEX gene mutations

X-linked hypophosphatemia (XLH) is the most common monogenic disorder causing hypophosphatemia. This case-note review documents the clinical features and the complications of treatment in 59 adults (19 male, 40 female) with XLH. XLH is associated with a large number of private mutations; 37 different mutations in the PHEX gene were identified in this cohort, 14 of which have not been previously reported. Orthopaedic involvement requiring surgical intervention (osteotomy) was frequent. Joint replacement and decompressive laminectomy were observed in those older than 40 years. Dental disease (63%), nephrocalcinosis (42%), and hearing impairment (14%) were also common. The rarity of the disease and the large number of variants make it difficult to discern specific genotype-phenotype relationships. A new treatment, an anti-FGF23 antibody, that may affect the natural history of the disease is currently being investigated in clinical trials.

Molecular and Biochemical Aspects of Hypophosphatemic Rickets; an Updated Review

Rickets is associated with aberrant mineralization in growth plates leading to the deformity of bone structure. The two main types of rickets are phosphopenic and calcipenic rickets. Phosphopenic rickets is found in a variety of sorts; the most common is the X-linked dominant hypophosphatemic rickets (HR) caused by a mutation in PHEX gene. The FGF23, DMP1, and PHEX are among the most important genes in the etiology of HR disorder. The interaction of these genes is essential for proper bone mineralization. However, the underlying mechanism is not comprehensively known. For data collection, we searched the most recent articles in Science Direct, PubMed and Google Scholar using hypophosphatemia, mutation, PHEX and FGF23 as keywords. The search results revealed that most of the articles have mainly focused on various types of mutations causing hypophosphatemia in different populations. However, there was a lack of enough studies elucidating the interaction of genes involved in this disorder. This review mainly focuses on the various types of phosphopenic rickets and genetic mutations of various agents crucial for bone mineralization and how these mutations exert their effects on biochemical agents like vitamin D and parathyroid hormone (PTH) . It also reviews the available treatment and molecular techniques for managing this disorder.

Identification of a novel splicing mutation of PHEX gene in a pedigree affected with X-linked hypophosphatemia

To identify potential mutation of PHEX gene in two patients from a family affected with X-linked hypophosphatemia (XLH). PCR and Sanger sequencing were performed on blood samples from the patients and 100 healthy controls. Reverse transcription-PCR (RT-PCR) was used to determine the mRNA expression in patient samples. A splicing site mutation, IVS21+2T>G, was found in the PHEX gene in both patients but not among the 100 healthy controls. RT-PCR confirmed that exon 21 of the PHEX gene was deleted. The novel splicing mutation IVS21+2T>G of the PHEX gene probably underlies the XLH in this pedigree. At the mRNA level, the mutation has led to removal of exon 21 and shift of the open reading frame (p.Val691fsx), resulting in premature termination of protein translation.

Hypertension is a characteristic complication of X-linked hypophosphatemia.

X-linked hypophosphatemia (XLH) is a group of rare disorders caused by defective proximal tubular reabsorption of phosphate. Mutations in the PHEX gene are responsible for the majority of cases. There are very few reports of long-term complications of XLH other than skeletal and dental diseases. The aim of this study was to identify the phenotypic presentation of XLH during adulthood including complications other than skeletal and dental diseases. The clinical and biochemical phenotype of 22 adult patients with a PHEX gene mutation were examined retrospectively from their medical records. 6 patients had hypertension. The average age of hypertension onset was 29.0 years. Secondary hyperparathyroidism preceded the development of hypertension in 5 patients. 1 patient developed tertiary hyperparathyroidism. 15 patients had nephrocalcinosis. 2 patients had chronic renal dysfunction. Patients with hypertension had a significantly lower eGFR (p=0.010) compared to patients without hypertension. No significant difference was found in any other parameters. To examine the genotype-phenotype correlation, 10 adult males were chosen for analysis. No significant genotype-phenotype correlation analysis was revealed in any of the complications. However, there was a possibility that the age at nephrocalcinosis onset was younger in the non-missense mutation group than in the missense mutation group (p=0.063). This study corroborated the view that early-onset hypertension could be one of the characteristic complications seen in XLH patients. Considering the limited number of our patients, further study is necessary to address a potential cause of hypertension. XLH patients require careful lifelong treatment.

Seven novel and six de novo PHEX gene mutations in patients with hypophosphatemic rickets.

Inactivating mutations in phosphate-regulating gene with homologies to endopeptidase on the X chromosome (PHEX) have been identified as a cause of X-linked hypophosphatemic rickets (XLH; OMIM 307800). In the present study, we enrolled 43 patients from 18 unrelated families clinically diagnosed with hypophosphatemic rickets and 250 healthy controls. For each available individual, all 22 exons with their exon-intron boundaries of the PHEX gene were directly sequenced. The levels of serum fibroblast growth factor 23 (FGF23) were measured as well. Sequencing analysis detected 17 different PHEX gene mutations, and 7 of these were identified as novel: 3 missense mutations, including c.304G>A (p.Gly102Arg) in exon 3, c.229T>C (p.Cys77Arg) in exon 3 and c.824T>C (p.Leu275Pro) in exon 7; 2 deletion mutations, including c.528delT (p.Glu177LysfsX44) in exon 5 and c.1234delA (p.Ser412ValfsX12) in exon 11; and 2 alternative splicing mutations, including c.436_436+1delAG in intron 4 at splicing donor sites and c.1483-1G>C in intron 13 at splicing acceptor sites. Moreover, 6 mutations were proven to be de novo in 6 sporadic cases and the probands were all females. No mutations were found in the 250 healthy controls. The serum levels of FGF23 varied widely among the patients with XLH, and no significant difference was found when compared with those of the healthy controls. On the whole, the findings of this study provide new insight into the spectrum of PHEX mutations and provide potential evidence of a critical domain in PHEX protein. In addition, the finding of an overlap of the serum FGF23 levels between the patients with XLH and the healthy controls indicates its limited diagnostic value in XLH.

Mutation Survey of the PHEX Gene and Oral Manifestation in a Chinese Family with X-linked Dominant Hypophosphatemic Ricket

Objective: X-linked dominant hypophosphatemic rickets is the most common genetic disorder of renal phosphate wasting with an approximate prevalence of 1 in 20,000 in humans. Until now, no more than 15 mutations in the PHEX gene have been reported in Chinese patients with familial XLH among the all the 338 PHEX mutations. The aim of this study is describe the oral manifestation of a Chinese XLH family, analyze the dentin structure alteration and gene mutation. Methods: In this XLH family, the oral manifestation was described by panoramic tomograph and oral photographs, dentin structure alteration was studied by both tooth section and 3D morphology measurement laser microscope, the gene mutation was studied by PCR technique. Results: Pulp infection and teeth loss were facilitated in XLH patients due to the anatomy change, hypophosphatemic dentin alterations in deciduous teeth displayed as large interglobular spaces between the unmerged calcospherites. A nonsense gene mutation c.1645 (p.Arg549X) was detected in this study. Conclusions: We found a PHEX gene mutation in this XLH Chinese family. Our findings are useful for understanding the oral manifestation, dentin alteration and genetic basis of Chinese patients with XLH.

A pilot study of gene testing of genetic bone dysplasia using targeted next-generation sequencing

Molecular diagnosis of genetic bone dysplasia is challenging for non-expert. A targeted next-generation sequencing technology was applied to identify the underlying molecular mechanism of bone dysplasia and evaluate the contribution of these genes to patients with bone dysplasia encountered in pediatric endocrinology. A group of unrelated patients (n=82), characterized by short stature, dysmorphology and X-ray abnormalities, of which mucopolysacharidoses, GM1 gangliosidosis, mucolipidosis type II/III and achondroplasia owing to FGFR3 G380R mutation had been excluded, were recruited in this study. Probes were designed to 61 genes selected according to the nosology and classification of genetic skeletal disorders of 2010 by Illumina's online DesignStudio software. DNA was hybridized with probes and then a library was established following the standard Illumina protocols. Amplicon library was sequenced on a MiSeq sequencing system and the data were analyzed by MiSeq Reporter. Mutations of 13 different genes were found in 44 of the 82 patients (54%). Mutations of COL2A1 gene and PHEX gene were found in nine patients, respectively (9/44=20%), followed by COMP gene in 8 (18%), TRPV4 gene in 4 (9%), FBN1 gene in 4 (9%), COL1A1 gene in 3 (6%) and COL11A1, TRAPPC2, MATN3, ARSE, TRPS1, SMARCAL1, ENPP1 gene mutations in one patient each (2% each). In conclusion, mutations of COL2A1, PHEX and COMP gene are common for short stature due to bone dysplasia in outpatient clinics in pediatric endocrinology. Targeted next-generation sequencing is an efficient way to identify the underlying molecular mechanism of genetic bone dysplasia.

Novel de novo nonsense mutation of the PHEX gene (p.Lys50Ter) in a Chinese patient with hypophosphatemic rickets

X-linked hypophosphatemic rickets (XLHR), the most common form of inherited rickets, is a dominant disorder characterized by hypophosphatemia, abnormal bone mineralization, and short stature. Mutations in the PHEX gene are major causes of XLHR. Herein, we clinically characterized four unrelated families with hypophosphatemia, bone abnormalities, short stature, and dentin malformation. Mutational analysis of the PHEX gene using Sanger sequencing revealed three recurrent mutations (c.2197T>C, c.1646G>C, and c.2198G>A) and a de novo nonsense mutation (c.148A>T). The novel mutation was not found in any of the unaffected family members or in the 100 healthy controls and was predicted to produce a truncated protein (p.K50X), a truncated form of the PHEX protein caused by nonsense mutations has been frequently detected in XLHR individuals. Thus, our work indicated that the c.148A>T (p.K50X) mutation was the likely pathogenic mutation in individual III-2 in family 2, and that PHEX gene mutations were responsible for XLHR in these Chinese families. These findings expand the mutation spectrum of PHEX and may help us to understand the molecular basis of XLHR in order to facilitate genetic counseling.

Identification of two novel mutations in the PHEX gene in Chinese patients with hypophosphatemic rickets/osteomalacia.

ObjectiveX-linked dominant hypophosphatemia (XLH) is the most prevalent form of inherited rickets/osteomalacia in humans. The aim of this study was to identify PHEX gene mutations and describe the clinical features observed in 6 unrelated Chinese families and 3 sporadic patients with hypophosphatemic rickets/osteomalacia.MethodsFor this study, 45 individuals from 9 unrelated families of Chinese Han ethnicity (including 16 patients and 29 normal phenotype subjects), and 250 healthy donors were recruited. All 22 exons and exon-intron boundaries of the PHEX gene were amplified by polymerase chain reaction (PCR) and directly sequenced.ResultsThe PHEX mutations were detected in 6 familial and 3 sporadic hypophosphatemic rickets/osteomalacia. Altogether, 2 novel mutations were detected: 1 missense mutation c.1183G>C in exon 11, resulting in p.Gly395Arg and 1 missense mutation c.1751A>C in exon 17, resulting in p.His584Pro. No mutations were found in the 250 healthy controls.ConclusionsOur study increases knowledge of the PHEX gene mutation types and clinical phenotypes found in Chinese patients with XLH, which is important for understanding the genetic basis of XLH. The molecular diagnosis of a PHEX genetic mutation is of great importance for confirming the clinical diagnosis of XLH, conducting genetic counseling, and facilitating prenatal intervention, especially in the case of sporadic patients.

A Novel PHEX Gene Mutation in a Patient with Sporadic Hypophosphatemic Rickets.

Phosphate regulating gene with homologies to endopeptidases on the X-chromosome (PHEX) is a common cause of X-linked hypophosphatemic (XLH) rickets. Diverse PHEX gene mutations have been reported; however, gene mutations in sporadic rickets are less common than in XLH rickets. Herein, we describe a 50-year-old female patient with sporadic hypophosphatemic rickets harboring a novel splicing-site mutation in the PHEX gene (c.663+1G>A) at the exon 5-intron 5 boundary. The patient had recently suffered from right thigh pain and an aggravated waddling gait. She also presented with very short stature, generalized bone pain, and muscle weakness. Despite low serum phosphate levels, her phosphate reabsorption rate was lower than normal. Additionally, her 1,25-dihydroxyvitamin D3 concentration was lower than normal, although FGF23 level was normal. After treatment with alfacalcidol and elemental phosphate, her rachitic symptoms subsided, and callus formation was observed in the fracture site on the right femur.