Exome sequencing reveals a novel homozygous splice site variant in the WNT1 gene underlying osteogenesis imperfecta type 3

Update on the Genetics of Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) is a heterogeneous heritable skeletal dysplasia characterized by bone fragility and deformity, growth deficiency, and other secondary connective tissue defects. OI is now understood as a collagen-related disorder caused by defects of genes whose protein products interact with collagen for folding, post-translational modification, processing and trafficking, affecting bone mineralization and osteoblast differentiation. This review provides the latest updates on genetics of OI, including new developments in both dominant and rare OI forms, as well as the signaling pathways involved in OI pathophysiology. There is a special emphasis on discoveries of recessive mutations in TENT5A, MESD, KDELR2 and CCDC134 whose causality of OI types XIX, XX, XXI and XXI, respectively, is now established and expends the complexity of mechanisms underlying OI to overlap LRP5/6 and MAPK/ERK pathways. We also review in detail new discoveries connecting the known OI types to each other, which may underlie an eventual understanding of a final common pathway in OI cellular and bone biology.

Effectiveness of whole exome sequencing analyses in the molecular diagnosis of osteogenesis imperfecta

OBJECTIVES

Osteogenesis imperfecta (OI) is a group of phenotypically and genetically heterogeneous connective tissue disorders that share similar skeletal anomalies causing bone fragility and deformation. This study aimed to investigate the molecular genetic etiology and to determine the relationship between genotype and phenotype in OI patients with whole exome sequencing (WES).

METHODS

Multiplex-Ligation dependent Probe Amplification (MLPA) analysis of COL1A1 and COL1A2 and WES were performed on cases between the ages of 0 and 18 whose genetic etiology could not be determined before using a targeted next-generation sequencing panel, including 13 genes (COL1A1, COL1A2, IFITM5, SERPINF1, CRTAP, P3H1, PPIB, SERPINH1, FKBP10, SP7, BMP1, MBTPS2, PLOD2) responsible for OI.

RESULTS

Twelve patients (female/male: 4/8) from 10 different families were included in the study. In 6 (50 %) families, consanguineous marriage was noted. The clinical typing based on Sillence classification; 3 (25 %) patients were considered to be type I, 7 (58.3 %) type III, and 2 (16.7 %) type IV. Deletion/duplication wasn't detected in the COL1A1 and COL1A2 genes in the MLPA analysis of the patients. Twelve patients were molecularly analyzed by WES, and in 6 (50 %) of them, a disease-causing variant in three different genes (FKBP10, P3H1, and WNT1) was identified. Two (33.3 %) detected variants in all genes have not been previously reported in the literature and were considered deleterious based on prediction tools. In 6 cases, no variants were detected in disease-causing genes.

CONCLUSIONS

This study demonstrates rare OI types' clinical and molecular features; genetic etiology was determined in 6 (50 %) 12 patients with the WES analysis. In addition, two variants in OI genes have been identified, contributing to the literature.

Sequence Variants in the WNT10B Underlying Non-Syndromic Split-Hand/Foot Malformation

Introduction

Split hand and foot malformation (SHFM) or ectrodactyly is a rare limb deformity characterized by median cleft of the hand and foot with impaired or missing central rays. It can occur as an isolated anomaly or in association with abnormalities of other body parts.

Methods

After delineating the clinical features of two families (A-B), with non-syndromic SHFM, exome and Sanger sequencing were employed to search for the disease-causing variants.

Results

Analysis of exome and Sanger sequencing data revealed two causative variants in the WNT10B gene in affected members of the two families. This included a novel missense change [c.338G>C; p.(Gly113Ala)] in family A and a previously reported frameshift variant [c.884-896delTCCAGCCCCGTCT; p.(Phe295Cysfs*87)] in family B.

Conclusion

Our findings add a novel variant in WNT10B gene as the underlying cause of SHFM. The finding adds to the growing body of knowledge about the genetic basis of developmental disorders and provides valuable insights into the molecular mechanisms that regulate limb development.

Early-Onset Osteoporosis: Rare Monogenic Forms Elucidate the Complexity of Disease Pathogenesis Beyond Type I Collagen

Early-onset osteoporosis (EOOP), characterized by low bone mineral density (BMD) and fractures, affects children, premenopausal women and men aged <50 years. EOOP may be secondary to a chronic illness, long-term medication, nutritional deficiencies, etc. If no such cause is identified, EOOP is regarded primary and may then be related to rare variants in genes playing a pivotal role in bone homeostasis. If the cause remains unknown, EOOP is considered idiopathic. The scope of this review is to guide through clinical and genetic diagnostics of EOOP, summarize the present knowledge on rare monogenic forms of EOOP, and describe how analysis of bone biopsy samples can lead to a better understanding of the disease pathogenesis. The diagnostic pathway of EOOP is often complicated and extensive assessments may be needed to reliably exclude secondary causes. Due to the genetic heterogeneity and overlapping features in the various genetic forms of EOOP and other bone fragility disorders, the genetic diagnosis usually requires the use of next-generation sequencing to investigate several genes simultaneously. Recent discoveries have elucidated the complexity of disease pathogenesis both regarding genetic architecture and bone tissue-level pathology. Two rare monogenic forms of EOOP are due to defects in genes partaking in the canonical WNT pathway: LRP5 and WNT1. Variants in the genes encoding plastin-3 (PLS3) and sphingomyelin synthase 2 (SGMS2) have also been found in children and young adults with skeletal fragility. The molecular mechanisms leading from gene defects to clinical manifestations are often not fully understood. Detailed analysis of patient-derived transiliac bone biopsies gives valuable information to understand disease pathogenesis, distinguishes EOOP from other bone fragility disorders, and guides in patient management, but is not widely available in clinical settings. Despite the great advances in this field, EOOP remains an insufficiently explored entity and further research is needed to optimize diagnostic and therapeutic approaches. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Early-Onset Osteoporosis

Osteoporosis is a skeletal disorder with enhanced bone fragility, usually affecting the elderly. It is very rare in children and young adults and the definition is not only based on a low BMD (a Z-score < - 2.0 in growing children and a Z-score ≤ - 2.0 or a T-score ≤ - 2.5 in young adults) but also on the occurrence of fragility fractures and/or the existence of underlying chronic diseases or secondary factors such as use of glucocorticoids. In the absence of a known chronic disease, fragility fractures and low BMD should prompt extensive screening for secondary causes, which can be found in up to 90% of cases. When fragility fractures occur in childhood or young adulthood without an evident secondary cause, investigations should explore the possibility of an underlying monogenetic bone disease, where bone fragility is caused by a single variant in a gene that has a major role in the skeleton. Several monogenic forms relate to type I collagen, but other forms also exist. Loss-of-function variants in LRP5 and WNT1 may lead to early-onset osteoporosis. The X-chromosomal osteoporosis caused by PLS3 gene mutations affects especially males. Another recently discovered form relates to disturbed sphingolipid metabolism due to SGMS2 mutations, underscoring the complexity of molecular pathology in monogenic early-onset osteoporosis. Management of young patients consists of treatment of secondary factors, optimizing lifestyle factors including calcium and vitamin D and physical exercise. Treatment with bone-active medication should be discussed on a personalized basis, considering the severity of osteoporosis and underlying disease versus the absence of evidence on anti-fracture efficacy and potential harmful effects in pregnancy.

Homozygous missense variant in POPDC3 causes recessive limb girdle muscular dystrophy type 26

BACKGROUND

Limb-girdle muscular dystrophy (LGMD) is a heterogeneous group of diseases, which affects different muscles, predominantly skeletal muscles and cardiac muscles of the body. LGMD is classified into two main sub-types A and B, which are further sub-classified into eight dominant and thirty recessive sub-types. Three genes, mainly POPDC1, POPDC2 and POPDC3, encodes popeye domain-containing protein (POPDC), and the variants of POPDC1 and POPDC3 genes have been associated with LGMD.

METHODS

In this study, we performed whole-exome sequencing (WES) analysis on a single-family to investigate the hallmark features of LGMD. The results of WES were further confirmed by Sanger sequencing and 3D protein modeling was also performed.

RESULTS

WES data analysis and sanger sequencing revealed a homozygous missense variant (c.460A>G; p.Lys154Glu) at a highly conserved amino acid position in the POPDC3. Mutations in the POPDC3 gene have been previously associated with recessive limb-girdle muscular dystrophy type 26. 3D protein modeling further suggested that the identified variant might affect the POPDC3 structure and proper function.

DISCUSSION/CONCLUSIONS

This study confirms the role of POPDC3 in LGMD, and will facilitate in genetic counseling of the family to mitigate the risks of the carrier or affected in future pregnancies.

Osteogenesis Imperfecta: Mechanisms and Signaling Pathways Connecting Classical and Rare OI Types

Osteogenesis imperfecta (OI) is a phenotypically and genetically heterogeneous skeletal dysplasia characterized by bone fragility, growth deficiency, and skeletal deformity. Previously known to be caused by defects in type I collagen, the major protein of extracellular matrix, it is now also understood to be a collagen-related disorder caused by defects in collagen folding, posttranslational modification and processing, bone mineralization, and osteoblast differentiation, with inheritance of OI types spanning autosomal dominant and recessive as well as X-linked recessive. This review provides the latest updates on OI, encompassing both classical OI and rare forms, their mechanism, and the signaling pathways involved in their pathophysiology. There is a special emphasis on mutations in type I procollagen C-propeptide structure and processing, the later causing OI with strikingly high bone mass. Types V and VI OI, while notably different, are shown to be interrelated by the interferon-induced transmembrane protein 5 p.S40L mutation that reveals the connection between the bone-restricted interferon-induced transmembrane protein-like protein and pigment epithelium-derived factor pathways. The function of regulated intramembrane proteolysis has been extended beyond cholesterol metabolism to bone formation by defects in regulated membrane proteolysis components site-2 protease and old astrocyte specifically induced-substance. Several recently proposed candidate genes for new types of OI are also presented. Discoveries of new OI genes add complexity to already-challenging OI management; current and potential approaches are summarized.

Biallelic variant in DACH1, encoding Dachshund Homolog 1, defines a novel candidate locus for recessive postaxial polydactyly type A

Polydactyly or hexadactyly is characterized by an extra digit/toe with or without a bone. Currently, variants in ten genes have been implicated in the non-syndromic form of polydactyly. DNA from a single affected individual having bilateral postaxial polydactyly was subjected to whole exome sequencing (WES), followed by Sanger sequencing. Homology modeling was performed for the identified variant and advance microscopy imaging approaches were used to reveal the localization of the DACH1 protein at the base of primary cilia. A disease-causing biallelic missense variant (c.563G > A; p.Cys188Tyr; NM_080760.5) was identified in the DACH1 gene segregating perfectly within the family. Structural analysis using homology modeling of the DACH1 protein revealed secondary structure change that might result in loss of function or influence downstream interactions. Moreover, siRNA-mediated depletion of DACH1 showed a key role of DACH1 in ciliogenesis and cilia function. This study provides the first evidence of involvement of the DACH1 gene in digits development in humans and its role in primary cilia. This signifies the importance and yet unexplored role of DACH1.

SAP30BP gene is associated with the susceptibility of rotator cuff tear: a case-control study based on Han Chinese population

Background

Multiple studies have indicated that genetic components contribute significantly to the risk of rotator cuff tears. Previous studies have suggested that the SAP30BP gene may play an essential role in the development of rotator cuff tears. The aim of this study was to evaluate the potential association of the SAP30BP gene with the susceptibility to rotator cuff tears in a Han Chinese population.

Methods

A total of 394 patients with rotator cuff tears and 998 healthy controls were included in the study. Twelve tag single nucleotide polymorphisms (SNPs) located in the region of the SAP30BP gene were selected for genotyping. Genetic association analyses were performed using χ² tests for each SNP. Significant associations were searched in the GTEx database for their functional consequences.

Results

SNP rs820218 was significantly associated with rotator cuff tears (χ² = 9.49, P = 0.0021, OR [95% CI] = 0.67 [0.52–0.87]). In addition, SNP rs820218 was found to be significantly associated with the gene expression level of SAP30BP in whole blood (NES = 0.12, P = 1.00 × 10⁻⁶).

Conclusion

Our study has shown that the genetic polymorphism of SAP30BP contributes to the risk of rotator cuff tears in Chinese Han people. Individuals with the A allele for SNP rs820218 were less susceptible to developing rotator cuff tears.

Biallelic variants in four genes underlying recessive osteogenesis imperfecta

Osteogenesis imperfecta (OI) is an inherited heterogeneous rare skeletal disorder characterized by increased bone fragility and low bone mass. The disorder mostly segregates in an autosomal dominant manner. However, several rare autosomal recessive and X-linked forms, caused by mutations in 18 different genes, have also been described in the literature. Here, we present five consanguineous families segregating OI in an autosomal recessive pattern. Affected individuals in the five families presented severe forms of skeletal deformities. It included frequent bone fractures with abnormal healing, short stature, facial dysmorphism, osteopenia, joint laxity, and severe scoliosis. In order to search for the causative variants, DNA of at least one affected individual in three families (A-C) were subjected to whole exome sequencing (WES). In two other families (D-E), linkage analysis using highly polymorphic microsatellite markers was followed by Sanger sequencing. Sequence analysis revealed two novels and three previously reported disease-causing variants. The two novel homozygous variants including [c.824G > A; p.(Cys275Tyr)] in the SP7 gene and [c.397C > T, p.(Gln133*)] in the SERPINF1 gene were identified in families A and B, respectively. The three previously reported homozygous variants including [c.497G > A; p.(Arg166His)] in the SPARC gene, (c.359-3C > G; intron 2) and [c.677C > T; p.(Ser226Leu)] in the WNT1 gene were identified in family C, D, and E. In conclusion, our findings provided additional evidence of involvement of homozygous sequence variants in the SP7, SERPINF1, SPARC and WNT1 genes causing severe OI. It also highlights the importance of extensive genetic investigations to search for the culprit gene in each case of skeletal deformity.

Association Between Genetic Polymorphisms of CR2 Gene and the Risk of Steroid-Induced Osteonecrosis of the Femoral Head in the Chinese Han Male Population

Background: Multiple lines of evidence have suggested that genetic factors may contribute to steroid-induced osteonecrosis of the femoral head (SONFH). Complement receptor 2 (CR2), constituting a family of regulators of complement activation, has been recently reported to be associated with osteonecrosis of the femoral head (ONFH) in Koreans. The aim of this study was to evaluate the relationships between polymorphisms of the CR2 gene and susceptibility to SONFH in the male Han Chinese population. Materials and Methods: A total of 468 SONFH patients and 1224 healthy controls were recruited for this study. Ten tag single nucleotide polymorphisms (SNPs) located within the CR2 gene were genotyped. Genetic association analyses, including SNP and haplotypic analyses, were performed for the 10 SNPs. Furthermore, bioinformatic analyses were conducted to examine the functional consequences of SNPs shown to be significantly associated with SONFH. Results: An intronic SNP, rs311306, was identified to be significantly associated with the risk of SONFH (p = 0.0008, odds ratio = 1.44). Allelic analyses showed that the C allele of this SNP significantly elevated the risk of SONFH, which was replicated in genotypic association analyses. Moreover, a 3-SNP haplotype was significantly associated with SONFH (rs311306-rs17044576-rs3767933, p = 7.49 × 10^-8). Furthermore, bioinformatic analyses indicated limited functional consequences of SNP rs311306, but a complex interaction network was constructed for the protein encoded by the SLC44A2 gene and proteins encoded by the CD19, CD81, and C3 genes. Conclusion: Our findings shed new light on the link between the CR2 gene and SONFH in Han Chinese males, providing clues as to the nature of the mechanisms involved in the etiology of ONFH.

Evaluation of Common Variants in the AKNA Gene and Susceptibility to Knee Osteoarthritis Among the Han Chinese

Background: Osteoarthritis (OA) is a complex degenerative joint disease that is associated with both genetic and environmental factors. The AKNA gene, located at 9q32, has recently been identified as being associated with knee osteoarthritis (KOA) in the Mexican population. Our aim was to investigate the relationship of common variants in this gene with the risk of KOA in a large Han Chinese population. Methods: A total of 2,500 Han Chinese subjects were recruited, consisting of 824 KOA patients and 1,676 controls. Eight tag single nucleotide polymorphisms (SNPs) located within the ANKA gene were selected for genotyping. Single marker-based association analyses were conducted using multiple modes of inheritance, including genotypic, allelic, dominant, and recessive. Haplotype-based association analyses were also performed. Plink was utilized for genetic association analyses. In addition, we examined the GTEx database to test the expression quantitative loci effects of the significant SNPs within the AKNA gene. Results: Among these eight SNPs evaluated we identified one, rs10817595, as being significantly associated with the risk of KOA. Compared to the CC genotype at this locus, the odds ratio (95% confidence interval) for KOA with the AA genotype was 1.58 (1.23-2.01)-fold greater. A linkage disequilibrium block that included this SNP was also determined to be significantly associated with the risk of KOA (χ² = 25.08, p = 3.58 × 10^-6). In general, the minor allele A of SNP rs10817595 was associated with an increased risk of KOA. Conclusion: This study is the first to present evidence for a potential link between the risk of KOA and an AKNA gene polymorphism among persons with a Han Chinese ancestry. Future functional analyses based on animal models and sequencing-based population studies are needed to elucidate the biological plausibility and genetic architecture of AKNA for KOA susceptibility.

A homozygous missense variant in the homeobox domain of the NKX6-2 results in progressive spastic ataxia type 8 associated with lower limb weakness and neurological manifestations

BACKGROUND

Progressive spastic ataxia is a heterogeneous disorder characterized by cerebellar ataxia and limb spasticity associated with other severe neurological complications. Spastic ataxia is classified into pure and complex types, inherited in both an autosomal recessive and autosomal dominant manner. It is caused by pathogenic variants in at least eight different genes, including NKX6-2 (MIM 607063) located on chromosome 10q26.3. The present study aimed to identify the genetic variant(s) underlying progressive spastic ataxia and to establish the genotype-phenotype correlation.

METHODS

We collected a large consanguineous family having four affected individuals segregating progressive spastic ataxia in an autosomal recessive manner. To investigate the molecular cause of the disease, genomic DNA of three affected individuals underwent whole exome sequencing.

RESULTS

All of the affected individuals showed progressive clinical features such as spastic ataxia, lower limb weakness and other mild neurological abnormalities. Whole exome sequencing data were analyzed using different filters. Filtering of rare and shared homozygous variants revealed a novel homozygous missense variant (c.545C>T; p.Ala182Val) in a highly conserved homeobox domain of the NKX6-2 protein.

CONCLUSIONS

The findings of the present study add a novel variant to the NKX6-2 mutation spectrum and provide evidence that homozygous variants in the NKX6-2 cause progressive spastic ataxia associated with other abnormalities.

Ptosis as a unique hallmark for autosomal recessive WNT1-associated osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable connective tissue disorder, mainly characterized by bone fragility and low bone mass. Defects in the type I procollagen-encoding genes account for the majority of OI, but increasingly more rare autosomal recessive (AR) forms are being identified, which are caused by defects in genes involved in collagen metabolism, bone mineralization, or osteoblast differentiation. Bi-allelic mutations in WNT1 have been associated with a rare form of AR OI, characterized by severe osteoporosis, vertebral compression, scoliosis, fractures, short stature, and variable neurological problems. Heterozygous WNT1 mutations have been linked to autosomal dominant early-onset osteoporosis. In this study, we describe the clinical and molecular findings in 10 new patients with AR WNT1-related OI. Thorough revision of the clinical symptoms of these 10 novel patients and previously published AR WNT1 OI cases highlight ptosis as a unique hallmark in the diagnosis of this OI subtype.

SGCD Homozygous Nonsense Mutation (p.Arg97∗) Causing Limb-Girdle Muscular Dystrophy Type 2F (LGMD2F) in a Consanguineous Family, a Case Report

Background: Limb-girdle muscular dystrophy (LGMD) is an increasingly heterogeneous category of inherited muscle diseases, mainly affecting the muscles of shoulder areas and the hip, segregating in both autosomal recessive and dominant manner. To-date, thirty-one loci have been identified for LGMD including seven autosomal dominant (LGMD type 1) and twenty four autosomal recessive (LGMD type 2) inherited loci.

Methodology/Laboratory Examination: The present report describes a consanguineous family segregating LGMD2F in an autosomal recessive pattern. The affected individual is an 11-year-old boy having two brothers and a sister. Direct targeted next generation sequencing was performed for the single affected individual (VI-1) followed by Sanger sequencing.

Results: Targeted next generation sequencing revealed a novel homozygous nonsense mutation (c.289C>T; p.Arg97^∗) in the exon 3 of the delta-sarcoglycan (SGCD) gene, that introduces a premature stop codon (TCA), resulting in a nonsense mediated decay or a truncated protein product.

Discussion and Conclusion: This is the first report of LGMD2F caused by an SGCD variant in a Pakistani population. The mutation identified in the present investigation extends the body of evidence implicating the gene SGCD in causing LGMD2F and might help in genetic counseling, which is more important to deliver the risk of carrier or affected in the future pregnancies.

Biallelic Missense Mutation in the ECEL1 Underlies Distal Arthrogryposis Type 5 (DA5D)

Distal arthrogryposis (DA) is a heterogeneous sub-group of arthrogryposis multiplex congenita (AMC), mostly characterized by having congenital contractures affecting hands, wrists, feet, and ankles. Distal arthrogryposis is mostly autosomal dominantly inherited, while only one sub-type DA type 5D is inherited in an autosomal recessive manner. Clinically, DA5D is described having knee extension contractures, micrognathia, distal joint contractures, clubfoot, ptosis, contractures (shoulders, elbows, and wrists), and scoliosis. Using whole exome sequencing (WES) followed by Sanger sequencing, we report on a first familial case of DA5D from Pakistani population having a novel biallelic missense mutation (c.158C>A, p.Pro53Leu) in the ECEL1 gene. Our result support that homozygous mutations in ECEL1 causes DA5D and expands the clinical and allelic spectrum of ECEL1 related contracture syndromes.

Clinical Genetics of Polydactyly: An Updated Review

Polydactyly, also known as hyperdactyly or hexadactyly is the most common hereditary limb anomaly characterized by extra fingers or toes, with various associated morphologic phenotypes as part of a syndrome (syndromic polydactyly) or may occur as a separate event (non-syndromic polydactyly). Broadly, the non-syndromic polydactyly has been classified into three types, i.e.; preaxial polydactyly (radial), central polydactyly (axial), and postaxial polydactyly (ulnar). Mostly inherited as an autosomal dominant entity with variable penetrance and caused by defects that occur in the anterior-posterior patterning of limb development. In humans, to-date at least 10 loci and six genes causing non-syndromic polydactyly have been identified, including the ZNF141, GLI3, MIPOL1, IQCE, PITX1, and the GLI1. In the present review, clinical, genetic and molecular characterization of the polydactyly types has been presented including the recent genes and loci identified for non-syndromic polydactyly. This review provides an overview of the complex genetic mechanism underlie polydactyly and might help in genetic counseling and quick molecular diagnosis.

Novel WNT1 mutations in children with osteogenesis imperfecta: Clinical and functional characterization

INTRODUCTION

Biallelic mutations in WNT1 can give rise to a rare form of moderate to severe OI. Here we report on 12 children (age 2 to 16 years; 5 girls) with biallelic WNT1 mutations.

METHODS

Genomic DNA was analyzed either by targeted next-generation sequencing or Sanger sequencing. Mutations were modeled on the WNT1 protein structure. The in vitro functional effect of WNT1 mutations on WNT signaling was assessed in HEK293 cells using the topflash reporter assay system.

RESULTS

All patients had lower extremity deformities and vertebral compression fractures. Seven individuals had upper extremity deformities. Intellectual development appeared normal in 11 children, but was clearly impaired in a 3-year old boy. Ptosis was noted in 7 patients. Height z-scores varied widely, from -7.2 to +1.5. A total of 11 disease-causing WNT1 variants (7 missense mutations, 4 mutations leading to premature termination codons) were identified, of which 9 were novel. Three-dimensional protein modeling suggested that each of the missense mutations led to structural modifications. Functional in vitro studies revealed that all observed missense mutations led to decreased ability of WNT1 to induce WNT signaling via the canonical WNT pathway.

CONCLUSIONS

The reported biallelic WNT1 variants cause loss of WNT1 function and lead to a severe bone fragility phenotype with conspicuous involvement of the spine.

The most 5' truncating homozygous mutation of WNT1 in siblings with osteogenesis imperfecta with a variable degree of brain anomalies: a case report

Background

WNT1 mutations cause bone fragility as well as brain anomalies. There are some reported cases of WNT1 mutations with normal cognition. Genotype and phenotype correlation of WNT1 mutations has not been established.

Case presentation

Here we present two female siblings with osteogenesis imperfecta (OI) born to a consanguineous couple. Both sustained severe bone deformities. However, only the younger had severe brain anomalies resulting in an early death from pneumonia, while the older had normal intellectual development. Next generation sequencing showed a homozygous mutation, c.6delG, p.Leu3Serfs*36 in WNT1. To our knowledge, it is the most 5′ truncating mutation to date.

Conclusion

This report emphasizes the intrafamilial variability of brain anomalies found in this OI type and suggests that WNT1 may not be necessary for normal human cognitive development.