Identification of a de novo PUF60 variant associated with craniofacial microsomia.

Craniofacial microsomia (CFM), also known as the oculo-auriculo-vertebral spectrum, is a congenital disorder characterized by hypoplasia of the mandible and external ear due to tissue malformations originating from the first and second branchial arches. However, distinguishing it from other syndromes of branchial arch abnormalities is difficult, and causal variants remain unidentified in many cases. In this report, we performed an exome sequencing analysis of a Brazilian family with CFM. The proband was a 12-month-old boy with clinical findings consistent with the diagnostic criteria for CFM, including unilateral mandibular hypoplasia, microtia, and external auditory canal abnormalities. A heterozygous de novo nonsense variant (c.713C>G, p.S238*) in PUF60 was identified, which was predicted to be pathogenic in silico. PUF60 has been reported as a causal gene in Verheij syndrome, but not in CFM. Although the boy showed craniofacial abnormalities and developmental delay that overlapped with Verheij syndrome, the facial asymmetry with unilateral hypoplasia of the mandible observed in this case did not match the previously reported phenotypes of PUF60 variants. Our findings expand the phenotypic range of PUF60 variants that cover CFM and Verheij syndrome.

Identification of a novel LRRK1 mutation in a family with osteosclerotic metaphyseal dysplasia.

Osteosclerotic metaphyseal dysplasia (OSMD) is a rare skeletal dysplasia characterized by osteosclerotic metaphyses with osteopenic diaphyses of the long tubular bones. Our previous study identified a homozygous elongation mutation in leucine-rich repeat kinase 1 gene (LRRK1) in a patient with OSMD and showed that Lrrk1 knockout mice exhibited phenotypic similarity with OSMD. Here we report a second LRRK1 mutation in Indian sibs with OSMD. They had homozygous mutation (c.5971_5972insG) that produces an elongated mutant protein (p.A1991Gfs*31) similar to the first case. The sibs had normal stature, normal intelligence and recurrent fractures. The common radiographic feature was asymmetric and variable sclerosis of vertebral end plates, pelvic margin and metaphyses of tubular bones. One of the sibs had facial dysmorphisms, dentine abnormalities and acro-osteolysis. A comparison between the three OSMD cases with LRRK1 mutations with different ages suggested that the sclerotic lesions resolved with age. Our findings further support that LRRK1 would cause a subset of OSMD cases.

Osteogenesis imperfecta type V: clinical and radiographic manifestations in mutation confirmed patients.

Osteogenesis imperfecta (OI) type V is a specific OI phenotype with interosseous membrane calcification of the forearm and hyperplastic callus formation as typical features. The causative gene mutation for OI type V has been recently discovered. The purpose of this report is to review the clinical and radiographic characteristics of mutation confirmed OI type V in detail. Sixteen (nine familial and seven sporadic) patients were enrolled in the study. Blue sclera and dentinogenesis imperfecta were not evident in any patient. However, hypodontia in the permanent teeth, ectopic eruption, and short roots in molars were additionally observed in 11 patients. Of the radiographic abnormalities, cortical thickening and bony excrescence of interosseous margin of the ulna was the most common finding, followed by overgrowth of the olecranon and/or coronoid process of the ulna. Slender ribs and sloping of the posterior ribs with or without fractures were also a consistent finding. Hyperplastic callus was detected in 75% of patients and was commonly encountered at the femur. Heterotopic ossification in the muscles and tendon insertion sites were noted in four patients, which resulted in bony ankylosis or contracture of joints. The current study confirms common clinical and radiographic findings of OI type V and reports additional phenotypic information. These observations provide clues to recognize OI type V more promptly and guide to direct targeted molecular study. © 2013 Wiley Periodicals, Inc.

Identification of six novel variants from nine Chinese families with hypophosphatemic rickets.

BACKGROUND: Hypophosphatemic rickets (HR) is a rare genetic disorder associated with renal phosphate wasting and characterized by bone defects. Inactivating mutations in the phosphate regulating endopeptidase homolog X­linked gene (PHEX) account for most cases of HR. The aim of this study was to identify causative variants in nine unrelated Chinese families associated with HR, and to determine potential pathogenicity of the identified variants. METHODS: Genomic DNA was isolated from the peripheral blood of HR patients and their healthy relatives, followed by next-generation sequencing and/or Sanger sequencing. In silico prediction combined with conservation analysis was performed to assess the effects of the variants, and 3D protein modeling was conducted to predict the functional effects on the encoded protein. RESULTS: All HR patients recruited in this study displayed bone deformities and tooth agenesis, as well as reduced serum phosphate levels and elevated urine phosphate levels. Nine PHEX variants were identified in eight families, including four novel variants (c.1661_1726del, c.980A > G, c.1078A > T, and c.1017_1051dup). Of the nine identified PHEX variants, five caused a truncated protein, two caused an altered amino acid, and the other two were the canonical splicing variants. Novel variants c.1336G > A and c.1364 T > C in SLC34A3 were also found in one family. Conservation analysis showed that all the amino acids corresponding to the missense variants were highly conserved. In silico analysis and 3D protein structure modeling confirmed the pathogenicity of these variants. CONCLUSIONS: This study identified four novel variants in PHEX and two novel variants in SLC34A3 in a Chinese cohort with HR. Our findings highlight the dominant role of PHEX in HR, and expand the genotypic and phenotypic spectra of this disorder.

Clinical and radiographic delineation of odontochondrodysplasia.

The association of dentinogenesis imperfecta (DI) with a distinct form of chondrodysplasia in a boy was reported by Goldblatt et al. [1991; Am J Med Genet 39:170-172] and has been given the name of Goldblatt syndrome or odontochondrodysplasia (ODCD; OMIM#184260). Since the original description, only four further individuals have been reported (one sib pair and two unrelated cases). We report on an additional six individuals, including a second sib pair (brother and sister), with clinical and radiographic features that cluster and thus confirm the nosologic status of this entity. The main radiographic features are congenital platyspondyly with coronal clefts, severe metaphyseal changes particularly of the hands, wrists, and knees, mesomelic limb shortening, and coxa valga. The main physical signs are short stature, joint laxity, narrow chest, scoliosis, and DI. This combination of clinical and radiographic findings allows clear recognition of this syndrome in early childhood. Of note, the signs that are present in the newborn period are not entirely specific and the differential diagnosis includes spondylometaphyseal dysplasia (SMD) Sedaghatian type or platyspondylic lethal dysplasia (PSLD) Torrance type. The occurrence of two sib pairs in a group of only 11 patients suggests an autosomal recessive inheritance pattern. Overmodification of cartilage-extracted collagen 2 has been reported in two sibs, but mutation analysis of COL2A1 as well as of COMP, FGFR3, RMRP, and SBDS in one or more patients have given negative results, and the molecular etiology is as yet unknown.

A novel type II collagen gene mutation in a family with spondyloepiphyseal dysplasia and extensive intrafamilial phenotypic diversity.

The purpose of this study was to describe a family with spondyloepiphyseal dysplasia caused by a novel type II collagen gene (COL2A1) mutation and the family's phenotypic diversity. Clinical and radiographic examinations of skeletal dysplasia were conducted on seven affected family members across two generations. The entire coding region of COL2A1, including the flanking intron regions, was analyzed with PCR and direct sequencing. The stature of the subjects ranged from extremely short to within normal height range. Hip deformity and advanced osteoarthritis were noted in all the subjects, ranging from severe coxa plana to mild acetabular dysplasia. Atlantoaxial subluxation combined with a hypoplastic odontoid process was found in three of the subjects. Various degrees of platyspondyly were confirmed in all subjects. Genetically, a novel COL2A1 mutation (c.1349G>C, p.Gly450Ala) was identified in all the affected family members; however, it was not present in the one unaffected family member tested. We described a family with spondyloepiphyseal dysplasia and a novel COL2A1 mutation (c.1349G>C, p.Gly450Ala). Phenotypes were diverse even among individuals with the same mutation and within the same family.

Molecular pathogenesis of spondylocheirodysplastic Ehlers-Danlos syndrome caused by mutant ZIP13 proteins.

The zinc transporter protein ZIP13 plays critical roles in bone, tooth, and connective tissue development, and its dysfunction is responsible for the spondylocheirodysplastic form of Ehlers-Danlos syndrome (SCD-EDS, OMIM 612350). Here, we report the molecular pathogenic mechanism of SCD-EDS caused by two different mutant ZIP13 proteins found in human patients: ZIP13(G64D), in which Gly at amino acid position 64 is replaced by Asp, and ZIP13(ΔFLA), which contains a deletion of Phe-Leu-Ala. We demonstrated that both the ZIP13(G64D) and ZIP13(ΔFLA) protein levels are decreased by degradation via the valosin-containing protein (VCP)-linked ubiquitin proteasome pathway. The inhibition of degradation pathways rescued the protein expression levels, resulting in improved intracellular Zn homeostasis. Our findings uncover the pathogenic mechanisms elicited by mutant ZIP13 proteins. Further elucidation of these degradation processes may lead to novel therapeutic targets for SCD-EDS.

The zinc transporter SLC39A13/ZIP13 is required for connective tissue development; its involvement in BMP/TGF-beta signaling pathways.

BACKGROUND: Zinc (Zn) is an essential trace element and it is abundant in connective tissues, however biological roles of Zn and its transporters in those tissues and cells remain unknown. METHODOLOGY/PRINCIPAL FINDINGS: Here we report that mice deficient in Zn transporter Slc39a13/Zip13 show changes in bone, teeth and connective tissue reminiscent of the clinical spectrum of human Ehlers-Danlos syndrome (EDS). The Slc39a13 knockout (Slc39a13-KO) mice show defects in the maturation of osteoblasts, chondrocytes, odontoblasts, and fibroblasts. In the corresponding tissues and cells, impairment in bone morphogenic protein (BMP) and TGF-beta signaling were observed. Homozygosity for a SLC39A13 loss of function mutation was detected in sibs affected by a unique variant of EDS that recapitulates the phenotype observed in Slc39a13-KO mice. CONCLUSIONS/SIGNIFICANCE: Hence, our results reveal a crucial role of SLC39A13/ZIP13 in connective tissue development at least in part due to its involvement in the BMP/TGF-beta signaling pathways. The Slc39a13-KO mouse represents a novel animal model linking zinc metabolism, BMP/TGF-beta signaling and connective tissue dysfunction.

Acrodysostosis with unusual iridal color changing with age.

Acrodysostosis is a rare congenital anomaly syndrome characterized by peculiar facial appearance with a small nose and an open mouth, short stature, short metacarpotarsal, and phalangeal bones with cone-shaped epiphyses, advanced bone-age, and variable degrees of mental retardation. It is most likely that the disease is inherited in an autosomal dominant mode, its pathogenesis has remained unknown. We report a 4-year-old Japanese girl who suffered from acrodysostosis with unusual iridal color. The color of patient's irides was gray-bluish in her infancy but became light-brownish by age 4 years. Of eight Japanese patients reported, four had abnormal eye color: a 7-month-old boy with blue irides and his 2-year-old elder sister with light-blue eyes a 6-year-old girl with gray-brownish irides, and a 4-year-old girl (present case) with blue-brownish irides. The degree of iris pigmentation in acrodysostosis patients may change with age. It is likely that the putative gene for acrodysostosis might play a role not only in remodeling of bones but also in iris pigmentation.

PLAP-1/asporin, a novel negative regulator of periodontal ligament mineralization.

Periodontal ligament-associated protein-1 (PLAP-1)/asporin is a recently identified novel member of the small leucine-rich repeat proteoglycan family. PLAP-1/asporin is involved in chondrogenesis, and its involvement in the pathogenesis of osteoarthritis has been suggested. We report that PLAP-1/asporin is also expressed specifically and predominantly in the periodontal ligament (PDL) and that it negatively regulates the mineralization of PDL cells. In situ hybridization analysis revealed that PLAP-1/asporin was expressed specifically not only in the PDL of an erupted tooth but also in the dental follicle, which is the progenitor tissue of the PDL during tooth development. Overexpression of PLAP-1/asporin in mouse PDL-derived clone cells interfered with both naturally and bone morphogenetic protein 2 (BMP-2)-induced mineralization of the PDL cells. On the other hand, knockdown of PLAP-1/asporin transcript levels by RNA interference enhanced BMP-2-induced differentiation of PDL cells. Furthermore co-immunoprecipitation assays showed a direct interaction between PLAP-1/asporin and BMP-2 in vitro, and immunohistochemistry staining revealed the co-localization of PLAP-1/asporin and BMP-2 at the cellular level. These results suggest that PLAP-1/asporin plays a specific role(s) in the periodontal ligament as a negative regulator of cytodifferentiation and mineralization probably by regulating BMP-2 activity to prevent the periodontal ligament from developing non-physiological mineralization such as ankylosis.

Metaphyseal dysplasia of Braun-Tinschert type: report of a Japanese girl.

We report on a 7-year-old Japanese girl with metaphyseal dysplasia (MD) of Braun-Tinschert type, a recently recognized, autosomal dominant sclerosing bone dysplasia. All individuals with the disorder from four families in the literature originated from a small town in Bohemia or its vicinity. The occurrence of the disorder in a Japanese girl indicates that it is not restricted to Germans. The radiographic hallmarks of the disorder include metaphyseal undermodeling (Erlenmeyer-flask deformity); osteosclerosis of the chondroosseous junctions, metaphyseal cortices, and epiphyseal margins; and exostosis-like bone excrescences at the metaphyseal-diaphyseal junctions. In the girl we described, the latter two findings were conspicuous at age 4 years, but became less prominent with increasing age. The metaphyseal trabeculae were somewhat coarse. The humeri exhibited varus deformity, and the ulnae and fibulae mild bowing. The mean bone mineral density of the lumbar spine was lower than that of age-matched controls. The patient exhibited premature loss of primary teeth, likely to be a sign of increased periodontal bone resorption. Markers of bone formation and resorption were both increased, an indication of a high rate of bone turnover.