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

Abstract

Objective: X-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.

Methods: For 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.

Results: The 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.

Conclusions: Our 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.

Figure 1. Pedigree of the familial patients with XLH.

Black symbols represent the affected individuals, and open symbols represent the unaffected individuals. Circles and squares represent the females and males, respectively. The arrows identify the probands in the families.

Figure 2. Radiology results for the patients.

(A): A general decrease in bone density, widened metaphyses, bilateral femoral distal metaphysis epiphyseal line blurred, and similar features in the lower tibia are shown. (B): A high bone mineral density, genu varum deformities in the lower limbs, and a Looser Zone in the bilateral femoral shaft are shown. (C): A general decrease in the bone density of the vertebrae and pelvis, bilateral hip and knee joint degeneration, and multiple vertebral wedge changes are shown. (D): Widened metaphyses is shown. (E): A high bone mineral density and anterior bowing of the lower limbs are shown. (F): A general decrease in the bone density of the vertebrae and pelvis, an enlargement of the epiphyseal and metaphyseal portions of the under section of the femoral, a short and wide femoral neck, and a large capital femoral epiphyses are shown.

Figure 3. PHEX gene mutation sequencing diagram.

(A): A nonsense mutation c.1980G>A in exon 20 was detected in Proband (II-2) from family 1. (B): Proband’s father (I-1) was hemizygous for a nonsense mutation, c.1980G>A in exon 20 from family 1. (C): A novel missense mutation, c.1751A>C in exon 17, was identified in proband (IV-1) and her mother (III-2) from family 2. (D): A novel missense mutation, c.1183G>C in exon 11, was identified in III-2 from family 2. (E): A nonsense mutation, c.1332G>A in exon 12, was identified in proband (I-2) and her daughter (II-2) from family 3. (F): A putative aberrant splicing mutation, c.1646-2A>T in intron 15, was identified in proband (III 2), his mother (II2), and his grandmother (I2) from family 4. (G): A putative aberrant splicing mutation, c.1174-1G>A in intron 10, was identified in proband (II1) and his mother (I2) from family 5. (H): A deletion mutation, c.1694delA in exon 16, was identified in proband (II1) and her mother (I2) from family 6. (I): A splicing mutation, c.1768+2T>G in intron 17, was identified in proband (III1) from family 7. (J): A del-insertion mutation, c.2077_*4delinsAin exon 21, was identified in proband (III1) from family 8. (K): A nonsense mutation, c.1645C>T in exon 15, was identified in proband (III1) from family 9.

Figure 4. Partial amino acid sequences of the PHEX gene from 9 species.

The amino acids at p.395 in exon 11 (A) and p.584 in exon 17 (B) are highly conserved in 9 different species.