A novel dominant COL11A1 mutation in a child with

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Mar 16, 2017 - including hypermobility, scoliosis, platyspondyly, and ar- thropathy that may present as joint pain in early life and ar- thritis later on [1–4].

Osteoporos Int DOI 10.1007/s00198-017-4229-3

CASE REPORT

A novel dominant COL11A1 mutation in a child with Stickler syndrome type II is associated with recurrent fractures M. G. Vogiatzi 1 & D. Li 2 & L. Tian 2 & J. P. Garifallou 2 & C. E. Kim 2 & H. Hakonarson 2 & M. A. Levine 1

Received: 10 July 2017 / Accepted: 14 September 2017 # International Osteoporosis Foundation and National Osteoporosis Foundation 2017

Abstract Summary This case describes a child with blindness, recurrent low-impact fractures, low bone mass, and intermittent joint pain who was found to have a novel missense mutation in COL11A1, consistent with Stickler syndrome type II. The case illustrates the phenotypic variability of the syndrome, which may include increased fragility in childhood. Introduction Stickler syndrome type II is an autosomal dominant disorder caused by mutations in the gene that encodes the type XI collagen chain α1 (COL11A1). Manifestations include craniofacial dysmorphology and ocular abnormalities that may lead to blindness, hearing loss, and skeletal anomalies that range from joint pain and arthritis to scoliosis and hypermobility. Methods Herein, we describe a child who carried the presumed diagnosis of osteoporosis-pseudoglioma syndrome because of the combined findings of recurrent low-impact fractures due to low bone mass and blindness. The child also suffered from joint pain but had no facial dysmorphism or hearing loss. Results Targeted sequencing and deletion analysis of the LRP5, COL1A1, and COL1A2 genes failed to identify any mutations, and whole exome sequence analysis revealed a novel missense Maria G. Vogiatzi and Dong Li contributed equally to this work Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00198-017-4229-3) contains supplementary material, which is available to authorized users. * M. G. Vogiatzi [email protected]

1

Division of Endocrinology and Diabetes, Children’s Hospital of Philadelphia, 3401 Civic Center Blvd., Suite 11NW 30, Philadelphia, PA 19104, USA

2

Center for Applied Genomics, The Children’s Hospital of Philadelphia, Philadelphia, PA 19104, USA

mutation (c.3032C>A:p.P1011Q) in COL11A1, consistent with Stickler type II. Conclusion This case highlights the phenotypic variability of Stickler type II, broadens the list of differential diagnosis of increased bone fragility in childhood, and highlights utility of unbiased genetic testing towards establishing the correct diagnosis in children with frequent fractures. Keywords Col11A1 . Fragility . Low bone mass . Stickler . Zoledronic acid

Introduction Stickler syndrome is an autosomal dominant connective tissue disorder that is characterized by distinctive facial features, ocular abnormalities, hearing loss, and skeletal involvement, including hypermobility, scoliosis, platyspondyly, and arthropathy that may present as joint pain in early life and arthritis later on [1–4]. The typical facial features of Stickler syndrome usually suggest the diagnosis and manifest as midface hypoplasia and the Pierre Robin sequence [1–4]. Nevertheless, significant phenotypic variability occurs among affected individuals, and the diagnosis of the syndrome is often delayed or missed [1–4]. Several types of Stickler syndrome with some variation in phenotypic characteristics have been described. Type I (OMIM #108300) is the most common form and occurs approximately in 80 to 90% of cases [1]. It is caused by heterozygous mutations in the COL2A1 gene that disrupt production of the alpha-1 chain of type II collagen [1]. Type II (OMIM #604841) is present in about 10–20% of Stickler patients and is associated with dominant mutations in COL11A1 encoding the alpha-1 chain of type XI collagen [1–4]. Stickler types III, IV, V, and VI are extremely rare and account for the remaining of cases [1].

Osteoporos Int

Herein, we describe a child who was initially diagnosed with osteoporosis-pseudoglioma syndrome (OPPG; OMIM 259770) due to a history of recurrent low-impact fractures, low bone density, and right eye blindness [5, 6]. Studies of the lowdensity lipoprotein receptor-related protein 5 (LRP5) gene were normal, but whole exome sequence analysis revealed a novel missense mutation in COL11A1, thereby identifying Sticker type II as the correct diagnosis. Beyond the novelty of the mutation, this case expands the phenotypic presentation of Stickler syndrome to include increased bone fragility and low bone density.

Clinical case The child presented for evaluation of metabolic bone disease at age 12 years. He was the product of a non-consanguineous, uncomplicated full-term pregnancy. Birth weight and length were normal. As an infant, he received physical therapy for hypotonia and did not begin to walk until 18 months. Development was otherwise normal. He experienced linear growth deceleration in early childhood, and pertinent evaluation included normal thyroid function and growth hormone secretion. The child suffered from frequent, debilitating ankle and knee pain, typically after minor traumas such as Brolling^ an ankle. He would frequently use a walker or cane after such episodes.

Table 1 Age

Anthropometric and DXA data on presentation and during follow up Height Weight L1-L4 z z z

L1-L4 z height adjusted

Femur Femur neck z Comments neck z height adjusted

12 years − 2.4 and 1 month

− 1.33

− 4.39* − 2.99

− 5.02 − 4.01

− 2.4

− 0.68

− 3.0

− 1.35

− 4.05 − 3.03

− 2.2 − 1.32

− 0.98 − 0.88

− 3.18 − 2.8

− 1.62 − 1.69

− 3.13 − 2.18 − 2.89 − 2.36

− 1.24

− 0.4

− 2.8

− 1.63

− 2.18

− 1.69 − 1.61

− 2.96 − 2.57 − 3.08 − 2.72

12 years and 11 months 14 years 15 years and 1 month 16 years

Evaluation revealed joint hyperextensibility but no other pathology. Furthermore, he experienced recurrent long bone fractures that were associated with low-impact trauma. His first fracture was a buckle fracture of the right distal tibia and fibula, after a blow to the leg during playing at age 7 years. At age 8 years, he had a spiral fracture of the left tibia while skiing. The fracture was casted and after 8 weeks of non-weight bearing, he sustained a distal femoral epiphyseal fracture of the same extremity while running. At age 10 years, he fractured his right tibia while playing and subsequently had a right distal radius buckle fracture after falling. Beyond the skeletal manifestations, the child had ocular findings. Retinal dysplasia and persistent hyperplasic primary vitreous (PHPV) of the right eye were noted after birth. He subsequently developed closed angle glaucoma at the same eye, which did not respond to medical therapy. Laser photocoagulation at age 8 months was unable to restore sight. Myopia was present on the other eye. Hearing was normal. The family history was negative for osteoporosis or frequent fractures. Physical examination at age 12 years revealed proportionate short statute (height z = − 2.4; Table 1) and a body mass index at the 75th percentile. His mid-parental height was on the 78th percentile. He had no dysmorphic features. Right eye microphalmia was present, while sclera and dentition were normal. Subtle leg length discrepancy and generalized joint laxity were noted. He was prepubertal.

− 0.99 17 years and 1 month

Prepubertal: PH T1, testis 2–3 ml Laboratory evaluation: Calcium serum = 9.5 mg/dL (8.8–10.1), phosphate serum = 5.3 mg/dL (3.3–5.4), intact PTH = 21 pg/mL (9–52), 25-hydroxy-vitamin D = 33 ng/mL, 1,25-dihydroxy-vitamin D = 40 pg/mL, free thyroxine = 1.0 ng/dL (0.9–1.67), TSH = 2.53 μIU/mL (0.5–4.3), spot calcium/creatinine urine = 0.22 (< 0.22)

Fully pubertal (PH T5, testis 20 ml)

All DXA measurements were performed using Hologic, model Discovery W. The height adjusted z scores were calculated based on data from the Bone Mineral Density in Childhood study at https://bmdcs.nichd.nih.gov/ PH pubic hair, PTH parathyroid hormone, TSH thyroid-stimulating hormone, T1= Tanner Stage 1, T5= Tanner Stage 5 *Therapy with zoledronic acid was started at age 12 years and 1 month and continued until the age of 17. The patient was treated with doses of 0.05 mg/ kg every 6 months. Due to compliance issues, he received only one dose of zoledronic acid between ages 14 to 17

Osteoporos Int

Radiological evaluation of his spine revealed mild dextro-curve of the thoracic spine and demineralization with a suggestion of vertebral body flattening. Initial evaluation and medical management Bone densitometry by dual-energy x-ray absorptiometry (DXA) revealed low bone mineral density (BMD) and reduced height-adjusted BMD z scores (Table 1). Biochemical evaluation did not reveal a secondary cause for the low bone mass (Table 1). Analysis of the LRP5, COL1A1, and COL1A2 genes failed to identify any deleterious mutation indicative of OPPG or common forms of osteogenesis imperfecta. The patient was treated with intravenous zoledronate with improvement of bone density (Table 1). He sustained no additional fractures.

Exome sequencing and results We isolated genomic DNA from the blood obtained from the proband and his unaffected mother and sister, who provided written consent/assent. The father refused to participate. The study was approved by the institutional review board. We performed exome capture, sequencing, and analysis as previously described (Fig. 1) [7, 8]. A heterozygous mutation (c.3032C>A; p.P1011Q) in the COL11A1 gene was identified that was not inherited from his mother and was absent in his healthy sibling (Fig. 1). His father was unavailable for testing. However, as his father had no reported skeletal or ocular symptoms, it is likely that the COL11A1 mutation occurred de novo in the proband. The mutation was predicted to be pathogenic by PolyPhen-2, LRT, FATHMM, MutationTaster, MetaSVM, and MetaLR algorithms [9]. There is no other occurrence of this variant in existing sequencing data from > 3000 subjects in our database or any public databases, including the 1000 Genomes Project, NHLBI ESP6500SI, and the Genome Aggregation Database (gnomAD). Furthermore, a close scrutiny of known genes associated with low bone mass was unrevealing [10–12]. The average depth of coverage for every gene is listed in Supplementary Table S1.

Discussion Stickler syndrome is one of the most common connective tissue disorders with prevalence rates of 1–3 per 10,000 births [1]. Nevertheless, due to the absence of strict diagnostic criteria, Stickler syndrome is likely to be under-diagnosed. Here, we describe a subject with an unusual form of Stickler syndrome type II that is associated with a novel heterozygous COL11A1 mutation. COL11A1 mutations are present in

Fig. 1 Pedigree and mutation validation by Sanger sequencing demonstrated that proband carries the COL11A1 mutation and healthy mother and sister are wild type. Exome capture, sequencing, as well as read processing, mapping to human genome reference (GRCh37-derived alignment set used in 1000 Genomes Project), variant calling, annotations, and filtering for rare variants affecting the coding sequence and/or consensus splice sites were performed as previously described [7, 8]. Variants previously reported in dbSNP, the 1000 Genomes Project, and the National Heart, Lung and Blood Institute (NHLBI) Exome Sequencing Project (ESP) Exome Variant Server with a minor allele frequency > 0.5% were excluded. We focused our variant analysis primarily on nonsynonymous, splice-altering variants, and frameshift variants. Subsequent gene prioritization was on basis of deleterious prediction, biological and clinical relevance by referring to existing databases (i.e., OMIM and HGMD)

patients with Stickler type II, Marshall syndrome (OMIM 154780) [13], and fibrochondrogenesis 1 (OMIM 228520) [14]. Notably, our case shows significant overlap with the OPPG syndrome, in which early-onset osteoporosis and ocular defects are due to biallelic loss-of-function mutations of the gene encoding LPR5 [5, 6]. The later regulates bone mass through the canonical wnt signaling pathway [5]. Both Stickler type II and OPPG feature ocular defects that lead to impaired vision or blindness, although the underlying mechanisms differ. Specifically, the ocular changes in OPPG are secondary to a defect in retinal vascularization and range from congenital phthisis bulbi to milder vitreoretinal changes [6]. By contrast, the typical eye abnormalities in Stickler II relate to changes in collagen XI synthesis, which leads to a Bbeaded^ vitreous and is associated with myopia, vitreous clouding, and glaucoma [1]. Regardless, significant phenotypic variation has been observed in both Stickler syndrome and OPPG, and as demonstrated in this report, it may be difficult to establish the correct diagnosis without molecular information. Stickler syndrome is a form of Bcollagenopathy,^ a diverse group of heritable disorders caused by defects in collagen

Osteoporos Int

structure. Patients with Stickler syndrome type II have mutations in the COL11A1 gene that impair formation of type XI collagen, a minor fibrillar collagen that is primarily present in articular cartilage but also found in parts of the inner ear and vitreous body of the eye [15]. Type XI collagen is heterotrimer that is encoded by the COL11A1, COL11A2, and COL2A1 genes [15]. These chains form a right-handed triple helix that is stabilized by its high content of proline occupying the Y position of canonical Gly-X-Y triad [16]. Collagen alpha1(XI) then copolymerizes with collagen alpha 1 (II) to form heterotypic fibrils within the articular cartilage and vitreous body of the eye [15, 17]. Therefore, the absence or abnormal structure of a collagen alpha-1(XI) molecule may result in abnormal fibril development in the articular cartilage or vitreous body, thus leading to the ocular and joint manifestations that are seen in Stickler syndrome. In this case, the P1011Q substitution identified in the helical domain of the alpha 1(XI) collagen chain is a residue at Y position of a characteristic GlyX-Y repeat, and thus, it may affect collagen stability. Beyond the above considerations, recent research indicates that collagen XI regulates bone formation and mineralization [18–20]. Absence of Col11a1 during embryogenesis results in bone abnormalities in the mouse characterized by thickened trabecular bone, incompletely formed vertebral bodies, and a mineralization defect [18]. In addition, heterotypic molecules of alpha 1 type XI chain with alpha 1 chain of collagen V have been isolated from both cartilage and bone [19]. Furthermore, Col11a1 isoforms regulate osteoblast function in vivo [20]. Our patient had many of the typical characteristics of Stickler syndrome type II, such as its ocular involvement with the presence of glaucoma, joint hypermobility and pain, scoliosis, and short stature [1–4]. Furthermore, he also manifested low bone mass and recurrent fractures, which are not typical of Stickler type II. Osteopenia and decreased bone mineralization have been described in case reports of Stickler syndrome type I [21, 22], albeit the disease severity and resultant fragility are not as pronounced as in the case we describe. Collectively, this case along with the animal data implies a role of alpha 1 chain of type XI collagen on bone remodeling, the mechanism of which needs to be clarified with additional studies.

References

Acknowledgments We thank the family involved in this study for their participation. We acknowledge Fengxiang Wang, James Snyder, and Harsh Kanwar, who helped in the DNA sample extraction and handling, and Cuiping Hou and Tiancheng Wang who provided technical assistance.

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Compliance with ethical standards

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Conflict of interest The authors declare that they have no conflict of interest.

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