A novel homozygous variant in ZFP36L2 cause female infertility due to oocyte maturation defect

Normal oocyte maturation is an important requirement for the success of human reproduction, and defects in this process will lead to female infertility and repeated IVF/ICSI failures. In order to identify genetic factors that are responsible for oocyte maturation defect, we used whole exome sequencing in the affected individual with oocyte maturation defect from a consanguineous family and identified a homozygous variant c.853_861del (p.285_287del) in ZFP36L2. ZFP36L2 is a RNA-binding protein, which regulates maternal mRNA decay and oocyte maturation. In vitro studies showed that the variant caused decreased protein levels of ZFP36L2 in oocytes due to mRNA instability and might lead to the loss of its function to degrade maternal mRNAs. Previous study showed that the pathogenic variants in ZFP36L2 were associated with early embryonic arrest. In contrast, we identified a novel ZFP36L2 variant in the affected individual with oocyte maturation defect, which further broadened the mutational and phenotypic spectrum of ZFP36L2, suggesting that ZFP36L2 might be a genetic diagnostic marker for the affected individuals with oocyte maturation defect.     

Genotype of congenital adrenal hyperplasia patients with testicular adrenal rest tumor

Testicular adrenal rest tumor (TART) is one of the important complications that can cause infertility in male patients with congenital adrenal hyperplasia (CAH) and should therefore be diagnosed and treated at an early age. The factors that result in TART in CAH have not been completely understood. The aim of this study is to evaluate the genotype-phenotype correlation in CAH patients with TART.MethodAmong 230 malepatients with CAH who were followed upwith regular scrotal ultrasonography in 11 different centers in Turkey, 40 patients who developed TARTand whose CAH diagnosis was confirmed by genetic testing were included in this study. Different approaches and methods were used for genotype analysis in this multicenter study. A few centers first screened the patients for the ten most common mutations in CYP21A2 and performed Sanger sequencing for the remaining regions only if these prior results were inconclusive while the majority of the departments adopted Sanger sequencing for the whole coding regions and exon-intron boundaries as the primary molecular diagnostic approach for patients with either CYP21A2 orCYP11B1 deficiency. The age of CAH diagnosis and TART diagnosis, type of CAH, and identified mutations were recorded.ResultsTART was detected in 17.4% of the cohort [24 patients with salt-wasting (SW) type, four simple virilizing type, and one with nonclassical type with 21-hydroxylase (CYP21A2) deficiency and 11 patients with 11-beta hydroxylase (CYP11B1) deficiency]. The youngest patients with TART presenting with CYP11B1 and CYP21A2 deficiency were of 2 and 4 years, respectively. Eight different pathogenic variants in CYP21A2were identified. The most common genotypes were c.293-13C>G/c.293-13C>G (31%) followed by c.955C>T/c.955C>T(27.6%) and c.1069C>T/c.1069C>T (17.2%). Seven different pathogenic variants were identified in CYP11B1. The most common mutation in CYP11B1 in our study was c.896T>C (p.Leu299Pro).ConclusionWe found that 83% TART patients were affected with SW typeCYP21A2 deficiency,and the frequent mutations detected were c.955C>T (p.Gln319Ter), c.293-13C>G in CYP21A2 and c.896T>C (p.Leu299Pro) inCYP11B1. Patients with CYP11B1 deficiency may develop TART at an earlier age. This study that examined the genotype–phenotype correlation in TART may benefit further investigations in larger series.     

ZP2 pathogenic variants cause in vitro fertilization failure and female infertility

PurposeThe oocyte-borne genetic causes leading to fertilization failure are largely unknown. We aimed to identify novel human pathogenic variants (PV) and genes causing fertilization failure.MethodsWe performed exome sequencing for a consanguineous family with a recessive inheritance pattern of female infertility characterized by oocytes with a thin zona pellucida (ZP) and fertilization failure in routine in vitro fertilization. Subsequent PV screening of ZP2 was performed in additional eight unrelated infertile women whose oocytes exhibited abnormal ZP and similar fertilization failure. Expression of ZP proteins was assessed in mutant oocytes by immunostaining, and functional studies of the wild-type and mutant proteins were carried out in CHO-K1 cells.ResultsTwo homozygous s PV (c.1695-2A>G, and c.1691_1694dup (p.C566Wfs*5), respectively) of ZP2 were identified in the affected women from two unrelated consanguineous families. All oocytes carrying PV were surrounded by a thin ZP that was defective for sperm-binding. Immunostaining indicated a lack of ZP2 protein in the thin ZP. Studies in CHO cells showed that both PV resulted in a truncated ZP2 protein, which might be intracellularly sequestered and prematurely interacted with other ZP proteins.ConclusionWe identified loss-of-function PV of ZP2 causing a structurally abnormal and dysfunctional ZP, resulting in fertilization failure and female infertility.     

Maturation arrest of human oocytes as a cause of infertility: case report

Maturation arrest of human oocytes may occur at various stages of the cell cycle. A total failure of human oocytes to complete meiosis is rarely observed during assisted conception cycles. We describe here a case series of infertile couples for whom all oocytes repeatedly failed to mature during IVF/ICSI. Eight couples, all presenting with unexplained infertility, underwent controlled ovarian stimulation followed by oocyte retrieval and IVF/ICSI. The oocytes were stripped of cumulus cells prior to the ICSI procedure and their maturity status was defined. In each couple, oocyte maturation was repeatedly arrested at the germinal vesicle (GV) (n = 1), metaphase I (MI) (n = 4) and metaphase II (MII) (n = 3) stage. Oocyte maturation arrest may be the cause of infertility in some couples previously classified as having unexplained infertility. The recognition of oocyte maturation arrest as a specific medical condition may contribute to the characterization of the yet poorly defined entity currently known as 'oocyte factor'. The cellular and genetic mechanisms causing oocyte maturation arrest should be the subject of further investigation.     

Novel variants in ACTL7A and PLCZ1 are associated with male infertility and total fertilization failure

Total fertilization failure (TFF), which refers to fertilization failure in all mature oocytes, accounting for 5%–10% of in vitro fertilization (IVF) cycles and 1%–3% of intracytoplasmic sperm injection (ICSI) cycles in human. In this study, we recruited three unrelated primary infertile men with repeated cycles of TFF and performed whole-exome sequencing to identify the potential pathogenic variants. We identified homozygous or compound-heterozygous variants of paternal-effect genes ACTL7A and PLCZ1 that followed a Mendelian recessive inheritance pattern. Novel homozygous nonsense variant in ACTL7A [c.C146G: p.S49*] was identified in case 1, who came from a consanguineous family. Ultrastructural observation of ACTL7A-mutated spermatozoa by transmission electron microscopy (TEM) indicated that apparent increased thickness of perinuclear matrix and the acrosome was detached from the nuclear envelop. Besides, two novel compound-heterozygous variants in PLCZ1 were identified in case 2 [c.1174+3A>C:p.?; c.A1274G:p.N425S] and case 3 [c.136-1G>C:p.?; c.G1358A:p.G453D]. Mutated spermatozoa from case 2 with reduced expression of PLCZ1 showed apparent acrosome detachment by TEM analysis. And ICSI with assisted oocyte activation (ICSI-AOA) treatment can partly rescue the TFF. Taken together, our findings revealed that novel biallelic variants in the paternal-effect genes ACTL7A and PLCZ1 were associated with human TFF, which expanding the spectrum of genetic causes and facilitating the genetic diagnosis of male infertility with TFF.     

Caffey disease is associated with distinct arginine to cysteine substitutions in the proα1(I) chain of type I procollagen

PurposeInfantile Caffey disease is a rare disorder characterized by acute inflammation with subperiosteal new bone formation, associated with fever, pain, and swelling of the overlying soft tissue. Symptoms arise within the first weeks after birth and spontaneously resolve before the age of two years. Many, but not all, affected individuals carry the heterozygous pathogenic COL1A1 variant (c.3040C>T, p.(Arg1014Cys)).MethodsWe sequenced COL1A1 in 28 families with a suspicion of Caffey disease and performed ultrastructural, immunocytochemical, and biochemical collagen studies on patient skin biopsies.ResultsWe identified the p.(Arg1014Cys) variant in 23 families and discovered a novel heterozygous pathogenic COL1A1 variant (c.2752C>T, p.(Arg918Cys)) in five. Both arginine to cysteine substitutions are located in the triple helical domain of the proα1(I) procollagen chain. Dermal fibroblasts (one patient with p.(Arg1014Cys) and one with p.(Arg918Cys)) produced molecules with disulfide-linked proα1(I) chains, which were secreted only with p.(Arg1014Cys). No intracellular accumulation of type I procollagen was detected. The dermis revealed mild ultrastructural abnormalities in collagen fibril diameter and packing.ConclusionThe discovery of this novel pathogenic variant expands the limited spectrum of arginine to cysteine substitutions in type I procollagen. Furthermore, it confirms allelic heterogeneity in Caffey disease and impacts its molecular confirmation.     

Identification of TMC1 as a relatively common cause for nonsyndromic hearing loss in the Saudi population

Hearing loss (HL) is the most common sensory disorder worldwide and genetic factors contribute to approximately half of congenital HL cases. HL is subject to extensive genetic heterogeneity, rendering molecular diagnosis difficult. Mutations of the transmembrane channel‐like 1 (TMC1) gene cause hearing defects in humans and mice. The precise function of TMC1 protein in the inner ear is unknown, although it is predicted to be involved in functional maturation of cochlear hair cells. TMC1 mutations result in autosomal recessive (DFNB7/11) and sometimes dominant (DFNA36) nonsyndromic HL. Mutations in TMC1 are responsible for a significant portion of HL, particularly in consanguineous populations. To evaluate the importance of TMC1 mutations in the Saudi population, we used a combination of autozygome‐guided candidate gene mutation analysis and targeted next generation sequencing in 366 families with HL previously shown to lack mutations in GJB2. We identified 12 families that carried five causative TMC1 mutations; including three novel (c.362+3A > G; c.758C > T [p.Ser253Phe]; c.1396_1398delACC [p.Asn466del]) and two reported mutations (c.100C > T [p.Arg34Ter]; c.1714G > A [p.Asp572Asn]). Each of the identified recessive mutation was classified as severe, by both age of onset and severity of HL. Similarly, consistent with the previously reported dominant variant p.Asp572Asn, the HL phenotype was progressive. Eight families in our cohort were found to share the pathogenic p.Arg34Ter mutation and linkage disequilibrium was observed between p.Arg34Ter and SNPs investigated. Our results indicate that TMC1 mutations account for about 3.3% (12/366) of Saudi HL cases and that the recurrent TMC1 mutation p.Arg34Ter is likely to be a founder mutation.     

First Analysis of <Emphasis Type="Italic">SERPING1</Emphasis> Gene in Patients with Hereditary Angioedema in Colombia Reveals Two Genotypic Variants in a Highly Symptomatic Individual

Hereditary angioedema (HAE) is a heterogeneous genetic disease caused by a deficit in C1 inhibitor (C1-INH) and clinically characterized by sudden events of edema, swelling, and pruritus. Here, we describe the first SERPING1 genotyping in 22 subjects from 4 non-related families, all from southern Colombia. The previously reported heterozygous gene mutations, c.1081C>T (p.Gln361*), c.1396C>G (p.Arg466Gly), c.1029+84G>A, or c.106_107del (p.Ser36Phefs*21), were found in 12 patients. Of note, a single patient clinically characterized as severe HAE type 2 expressed mutations in exon 8 and intron 6, whereas all the others have type 1 HAE and expressed one pathogenic variant. One of the subjects, a 5-year-old girl was discovered to have a pathogenic variant, and she is still asymptomatic. This is the first report focused on HAE genetic analysis in a Colombian population.     

Computational biology insights into genotype-clinical phenotype-protein phenotype relationships between novel SLC26A2 variants identified in inherited skeletal dysplasias

BackgroundPathogenic variants in the transmembrane sulfate transporter protein SLC26A2 are associated with different phenotypes of inherited chondrodysplasias. As limited data is published from India, in this study we sought to elucidate the molecular basis of inherited chondrodysplasias in an Indian cohort.MethodsMolecular screening of 32 fetuses with antenatally diagnosed lethal skeletal dysplasia was performed by next generation sequencing and Sanger sequencing. The genotype-protein phenotype characterization was done using computational biology techniques like homology modelling, stability and pathogenicity predictions.ResultsWe identified five rare autosomal recessive SLC26A2 [NM_000112.4] variants, including three homozygous c.796dupA(p.Thr266Asnfs*12), c.1724delA(p.Lys575Serfs*10), and c.1375_1377dup(p.Val459dup) and two heterozygous variants (c.532C > T(p.Arg178*)) and (c.1382C > T(p.Ala461Val)) in compound heterozygous form in a total of four foetuses. Genotype-protein phenotype annotations highlighted that the clinically severe achondrogenesis 1B causative c.796dupA(p.Thr266Asnfs*12) and c.1724delA(p.Lys575Serfs*10)variants impact SLC26A2 protein structure by deletion of the protein core and transmembrane STAS domains, respectively. In clinically moderate atelosteogenesis type 2 phenotype, the c.1382C > T(p.Ala461Val) variant is predicted to distort alpha helix conformation and alter the bonding properties and free energy dynamics of transmembrane domains and the c.532C > T(p.Arg178*) variant results in loss of both core transmembrane and STAS domains of the SLC26A2 protein. The c.1375_1377dup(p.Val459dup) variant identified in clinically milder atelosteogenesis type II-diastrophic dysplasia spectrum lethal phenotype is predicted to decrease the Qualitative Model Energy Analysis (QMean), which affects major geometrical aspects of the SLC26A2 protein structure.ConclusionWe expand the spectrum of SLC26A2 related lethal chondrodysplasia and report three novel variants correlating clinical severity and protein phenotype within the lethal spectrum of this rare dysplasia. We demonstrate the relevance of structural characterization to aid novel variant reclassification to provide better prenatal management and reproductive options to families with lethal antenatal skeletal disorder.     

Extrusion pump ABCC1 was first linked with nonsyndromic hearing loss in humans by stepwise genetic analysis

PurposeTo determine the genetic etiology of deafness in a family (HN-SD01) with autosomal dominant nonsyndromic hearing loss (NSHL).MethodsStepwise genetic analysis was performed on family HN-SD01, including hotspot variant screening, exome sequencing, virtual hearing loss gene panel, and genome-wide linkage analysis. Targeted region sequencing was used to screen ABCC1 in additional cases. Cochlear expression of Abcc1 was evaluated by messenger RNA (mRNA) and protein levels. Computational prediction, immunofluorescence, real-time quantitative polymerase chain reaction, and flow cytometry were conducted to uncover functional consequences of candidate variants.ResultsStepwise genetic analysis identified a heterozygous missense variant, ABCC1:c.1769A>G (p.Asn590Ser), cosegregating with phenotype in HN-SD01. Screening of ABCC1 in an additional 217 cases identified candidate pathogenic variants c.692G>A (p.Gly231Asp) in a sporadic case and c.887A>T (p.Glu296Val) in a familial proband. Abcc1 expressed in stria vascularis and auditory nerve of mouse cochlea. Immunofluorescence showed p.Asn590Ser distributed in cytomembrane and cytoplasm, while wild type was shown only in cytomembrane. Besides, it generated unstable mRNA and decreased efflux capacity of ABCC1.ConclusionStepwise genetic analysis is efficient to analyze the genetic etiology of NSHL. Variants in ABCC1 are linked with NSHL and suggest an important role of extruding pumps in maintaining cochlea function.     

Next-generation sequencing of 12 obesity genes in a Portuguese cohort of patients with overweight and obesity

We examined 12 monogenic obesity genes in 72 Portuguese individuals with overweight and obesity (class 1 and class 2), some of which with suspected genetic obesity, to identify known or unknown potential obesity variants. Genomic DNA was analyzed for variants in genes LEP, LEPR, MC4R, POMC, PCSK1, BDNF, NTRK2, SIM1, SH2B1, UCP3, GCG and ADCY3 through next generation sequencing (NGS). The impact of the rare variants was investigated in the ClinVar database and using in silico tools for prediction of pathogenicity. Four potential pathogenic missense variants were detected at the heterozygous state in five individuals: two in the ADCY3 gene, NM_004036.5:c.1153G > A (p.Val385Ile) (rs756783003) and NM_004036.5:c.1222G > A (p.Gly408Arg) (rs201606553), one in gene SH2B1, NM_001145795.1:c.127C > A (p.Arg43Ser) (rs547678855), and the fourth in gene POMC NM_000939.4:c.706C > G (p.Arg236Gly) (rs28932472), which was found in two individuals. Moreover, six rare variants near splicing sites were also identified, as well as eight rare synonymous variants. In summary, some potential pathogenic rare missense variants were identified, two of them in ADCY3 gene, the most recently identified gene as having a role in monogenic obesity. Further analysis should be performed to confirm the clinical relevance of these variants.     

Spectrum and frequency of CHEK2 variants in breast cancer affected and general population in the Baltic states region,initial results and literature review

BackgroundWhile BRCA1/2 gene mutational spectrum and clinical features are widely studied, there is limited data on breast cancer-predisposing non-BRCA pathogenic/likely pathogenic variants (PV/LPVs) in the Baltic states region. According to previous studies, CHEK2 is the most frequent moderate-risk breast cancer predisposition gene. The study aimed to analyse the frequency and mutational spectrum of CHEK2 PV/LPVs in the Baltic states region and perform a literature review on the subject.MethodsThe study includes two cohorts - population-based Estonian biobank (EstBB) (N-152 349) and breast cancer affected cases from Latvia (N-105). In the cohort from Latvia, CHEK2, BRCA1, BRCA2, PALB2 testing with next-generation sequencing (NGS) was carried out in selected breast cancer cases. In the EstBB, the full SNP genotyped dataset Global Screening Array (GSA) (N-152 349) was used to screen CHEK2 PV/LPVs and variants c.319+2T > A (p.(?)), c.444+1G>A (p.(?)), c.433C > T (p.Arg145Trp), c.283C > T (p.Arg95*) in CHEK2 are reported from this dataset. In addition, a subset of the EstBB (N-4776) underwent whole-genome sequencing (WGS, N-2420) and whole-exome sequencing (WES, N-2356) and founder variants c.470T > C (p.Ile157Thr), c.444+1G>A (p.(?)), c.1100delC (p.Thr367Metfs*15) in CHEK2 were reported from this dataset. Moreover, a literature overview was performed on April 1, 2021, using the PubMed search of keywords ‘CHEK2’, ‘breast cancer’, ‘Estonia’, ‘Lithuania’, ‘Latvia’, ‘Poland’, ‘Belarus’ and ‘Russia’.ResultsIn the breast cancer affected cohort from Latvia 6 CHEK2 variants, classified as PV/LPVs, were observed (6/105; 5.7%), including recurrent ones c.470T > C (p.Ile157Thr) (1.9%) and del5395(ex9-10del; (p.Met304Leufs*16)) (1.9%), as well as single ones – c.1100delC (p.Thr367Metfs*15) (1%) and c.444+1G>A (p.(?)) (1%). From EstBB NGS data (N-4776) CHEK2 variant c.470T > C (p.Ile157Thr) was detected in 8.6% of cases, c.1100delC (p.Thr367Metfs*15) in 0.6% and c.444+1G>A (p.(?)) in 0.2% of cases. In the EstBB full cohort of SNP array data (N-152 349) CHEK2 variant c.444+1G>A (p.(?)) was detected in 0.02% of cases, c.319+2T > A (p.(?)) in 0.09% of cases, c.433C > T (p.Arg145Trp) in 0.02% of cases and c.283C > T (p.Arg95*) in <0.001% of cases. For the literature review altogether, 49 PubMed articles were found, 23 of which were relevant, representing CHEK2 PV/LPVs in the population of interest. Ten publications are from Poland, eight from Russia, three from Latvia and two from Belarus.ConclusionsThis study is the first combined report on complete CHEK2 PV/LPVs screening in selected breast cancer affected cases in Latvia and large-scale population screening in Estonia, providing insight into the CHEK2 mutational spectrum in the Baltic states region. The initial results are in line with other studies that CHEK2 PV/LPVs frequency is around 5–6% of selected breast cancer cases. Here we report three CHEK2 PV/LPV - c.319+2T > A (p.(?)), c.433C > T (p.Arg145Trp), c.283C > T (p.Arg95*), that are novel for the Baltic states region. This is also the first report on c.1100delC (p.Thr367Metfs*15) and c.444+1G>A (p.(?)) from the Baltic states. High population frequency of c.470T > C (p. Ile157Thr) (8.6%) continues to question the variant's pathogenicity in particular populations. Other findings are concordant with previous reports from Latvia and neighbouring populations.     

Maternal SLE and brachytelephalangic chondrodysplasia punctata in a patient with unrelated de novo RAF1 and SIX2 variants

Our improved tools to identify the aetiologies in patients with multiple abnormalities resulted in the finding that some patients have more than a single genetic condition and that some of the diagnoses made in the past are acquired rather than inherited. However, limited knowledge has been accumulated regarding the phenotypic outcome of the interaction between different genetic conditions identified in the same patients. We report a newborn girl with brachytelephalangic chondrodysplasia punctata (BCDP) as well as frontonasal dysplasia, ptosis, bilateral hearing loss, vertebral anomalies, and pulmonary hypoplasia who was found, by whole exome sequencing, to have a de novo pathogenic variant in RAF1 (c.770C>T, [p.Ser257Leu]) and a likely pathogenic variant in SIX2 (c.760G>A [p.A254T]), as well as maternal systemic lupus erythematosus (SLE). This case shows that BCDP is most probably not a diagnostic entity and can be associated with various conditions associated with CDP including maternal SLE.     

Mapping the TYR gene reveals novel and previously reported variants in Eastern Indian patients highlighting preponderance of the same changes in multiple unrelated ethnicities

Oculocutaneous albinism (OCA) is a group of congenital autosomal recessive disorders with seven known subtypes (OCA1–OCA7) characterized by loss or absence of pigmentation in the skin, hair, and eyes. OCA1, caused by pathogenic variations in the tyrosinase (TYR) gene, has been documented to be the most prevalent subtype across the world including India. In the present study, we recruited 53 OCA-affected individuals from 45 unrelated families belonging to 20 different marriage groups/ethnicities of 15 different districts of West Bengal. We took a targeted sequencing-based approach to find the causal variations in the TYR gene. We report here identification of two novel potentially pathogenic variations [NM_000372.4:c.614C>T, NP_000363.1:p.(Pro205Leu), and NM_000372.4:c.1036+1=/G>T], one novel synonymous TYR variant [NM_000372.4:c.204=/A>G, NP_000363.1:p.(Gln68=)], two pathogenic variations documented for the first time in Indian OCA cases [NM_000372.4:c.1147G>A, NP_000363.1:p.(Asp383Asn), and NM_000372.4:c.585G>A, NP_000363.1:p.(Trp195*)], along with nine previously reported pathogenic variants in 36 out of 53 (∼68%) patients recruited. We report common haplotype backgrounds for the two most prevalent variations [NM_000372.4:c.124G>A, NM_000372.4:c.832C>T] in cases belonging to different marriage/ethnic groups, suggesting a possible founder effect. To our knowledge, this is the most comprehensive genetic study on OCA1 from India, firmly establishing OCA1 as the commonest form of albinism in this part of the world.     

ZNF142 mutation causes neurodevelopmental disorder with speech impairment and seizures: Novel variants and literature review

The ZNF142 gene on chromosome 2q35 contains ten exons and encodes a zinc finger protein 142 with 31 C2H2-type zinc fingers domain. Pathogenic variants in ZNF142 result in an autosomal recessive neurodevelopmental disorder with impaired speech and developmental delay. Here, we report two novel variants (NM_001105537: c.25C > T/c.1741C > T, p.Gln9*/p.Arg581Cys) in ZNF142 in an Iranian family identified by Whole-Exome sequencing and confirmed by Sanger sequencing. These variants are categorized as “pathogenic” and “variant of unknown significance” based on the standards for the interpretation of sequence variations recommended by ACMG, respectively. The proband is a five-year-old male born to consanguineous parents. The compound heterozygous variant (NM_001105537: c.25C > T/c.1741C > T, p.Gln9*/p.Arg581Cys) in ZNF142 was identified in the proband with moderate intellectual disability, global developmental delay, speech impairment, and seizures. This paper reported the sixth family in the world with novel pathogenic variants in the ZNF142 gene as the reason for neurodevelopmental Disorder with Impaired Speech and Hyperkinetic Movements (NEDISHM) and determining the phenotype spectrum of this disease. In this study, we also reviewed the phenotype of the former cases. In contrast to the Malaysian cases, proband in the present paper does not manifest any facial features similar to the patients in the initial study. Further studies on the NEDISHM patients could be valuable to determine the phenotype precisely.     

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.