ERN BOND: The key European network leveraging diagnosis, research, and treatment for rare bone conditions

There is no universally accepted definition for rare diseases: in Europe a disease is considered to be rare when affecting fewer than 1 in 2000 people. European Reference Networks (ERNs) have been the concrete response to address the unmet needs of rare disease patients and many pan-European issues in the field, reducing inequities, and significantly increasing accessibility to high-quality healthcare across Europe. ERNs are virtual networks, involving centres and patient representatives with the general scope to facilitate discussion on complex cases requiring highly specialised competences and trained expertise. ERN BOND - the European Reference Network on rare BONe Diseases - is one of these 24 approved networks with the specific ongoing mission to implement measures facilitating multidisciplinary, holistic, continuous, patient-centred, and participative care provision to patients, and supporting them in the full realisation of their fundamental human rights. ERN BOND includes in 2023 a total of 53 centres of expertise from 20 European countries. Its governing structure installed in March 2017 includes decision-making, operative and consultative committees, which comprise experts in the field and patient representatives ensuring patient's voice and perspectives are taken into account. Over the years, ERN BOND has worked hard to achieve its mission and valuably contribute to the advancement of diagnosis, management, treatment, and research in rare diseases. The network activities are mainly related to (i) the provision of care which collectively involves averagely 2800 patients diagnosed per year, (ii) the development of education for and training of the healthcare personnel consisting until now in the realisation of 7 thematic workshops and 19 webinars, (iii) the dissemination and exchange and spread of knowledge via network's website (https://ernbond.eu/), social media channels, and newsletters, (iv) the management of related data through a disease registry currently mapping over 2300 cases and recording over 600 reported cases, and (v) the enhancement of research which now include two clinical trials endorsed by the network. ERN BOND represents therefore an unprecedented move to improve the healthcare management of patients suffering from rare bone diseases through European collaborations. This network, through the support from the European Health Programme, will continue to pursue its efforts to achieve its goals, always maintaining the patients and their families at the centre of healthcare services.

Unexpected findings in cervical spine in spondylometaphyseal dysplasia Sutcliff type FN1-related

The autosomal dominant spondylometaphyseal dysplasia Sutcliff type or corner fracture type FN1-related is characterized by a combination of metaphyseal irregularities simulating fractures ("corner fractures"), developmental coxa vara, and vertebral changes. It is linked to heterozygous mutations in FN1 and COL2A1. Vertebral changes as delayed vertebral ossification, ovoid vertebral bodies, anterior vertebral wedging, and platyspondyly have been observed in this condition, while odontoid abnormalities have not been reported. We report an odontoid anomaly in a girl with SMD-CF FN1-related showing the heterozygous variant c.505T>A; p.(Cys169Ser), presenting at 11.9 years of age with acute quadriparesis. Images showed spinal cord compression and injury associated with os odontoideum and C1-C2 instability. She required decompression and instrumented occipitocervical stabilization, suffering from residual paraparesis. This paper describes the first case of SMD-CF FN1-related accompanied by odontoid anomalies.

Vitamin D-Dependent Rickets Type 1A in Two Siblings with a Hypomorphic CYP27B1 Variant Frequent in the African Population

Vitamin D-dependent type 1A rickets (VDDR-1A) is a rare autosomal recessive disease due to the inability to convert 25-hydroxyvitamin D [25(OH)D] to the active form 1.25-dihydroxyvitamin D [1.25(OH) 2 D] by the enzyme 25(OH)D-1α-hydroxylase leading to low or low-normal serum levels of [1.25(OH) 2 D]. We report two sisters with rickets in whom the diagnosis of VDDR-1A was a challenge. They had normal 1.25(OH)2D levels, which are unusual with this condition but may be explained by the identified genotype. Both have compound heterozygous for two, most likely, hypomorphic CYP27B1 alleles: the novel p.(Arg117Gly) variant, and p.(Ala129Thr), which are present in 0.43% of the African population. This report illustrates the variability of clinical, laboratory, and radiological presentation between two sisters with the same genotype, during phases of faster or slower growth. Genetic testing was crucial for establishing the diagnosis that optimized the management and genetic counseling.

Characterization of three adults and an adolescent with Osteogenesis Imperfecta type VI and a novel founder SERPINF1 variant

Osteogenesis imperfecta (OI) type VI is an extremely rare form of OI caused by biallelic variants in the SERPINF1 gene, which codes for the pigment-epithelium derived factor (PEDF). We report on four patients (three adults and one adolescent) with a severe deforming form of OI. All patients presented no abnormalities at birth, frequent long bone and vertebrae fractures (mainly during childhood), marked short stature, severe bone deformities, chronic mild to moderate pain, and severe limitation of mobility, with three being completely wheelchair bound. Blue sclera and dentinogenesis imperfecta were absent, although some patients presented tooth, ophthalmological, and/or cardiac features. Radiographic findings included, among others, thin diaphysis and popcorn calcifications, both of which are non-specific to this type of OI. The novel homozygous variants c.816_819del (p.Met272Ilefs*8) and c.283+2T > G in SERPINF1 were identified in three and one patient, respectively. The three patients carrying the frameshift variant were born in nearby regions suggesting a founder effect. Describing the long-term outcomes of four patients with OI type VI, this cohort adds relevant data on the clinical features and prognosis of this type of OI.

Two new patients with acromesomelic dysplasia, PRKG2 type-identification and characterization of the first missense variant

Acromesomelic dysplasia, PRKG2 type (AMDP, MIM 619636), is an extremely rare autosomal recessive skeletal dysplasia characterized by severe disproportionate short stature presenting with acromesomelia, mild metaphyseal widening of the long bones and mild spondylar dysplasia. To date, only four variants have been reported; one nonsense, one splice-site, and two frameshifts in five AMDP families. Here, we report the first missense variant and a second splice-site variant in PRKG2 in two patients with clinical and radiological features of acromesomelic dysplasia. Furthermore, functional studies of the novel missense variant, p.Val470Gly, revealed that it was unable to down-regulate FGF2-induced MAPK signaling and, thus, would be predicted to cause growth delay. Hence, this report expands the mutational spectrum in skeletal dysplasias associated with PRKG2 variants. In addition, we propose recognizable facial features with acromesomelic dysplasia, PRKG2 type.

Evolution of clinical and radiological presentations of spondyloepimetaphyseal dysplasia, RPL13-related: Description of 11 further cases

Spondyloepimetaphyseal dysplasia (SEMD), RPL13-related is caused by heterozygous variants in RPL13, which encodes the ribosomal protein eL13, a component of the 60S human ribosomal subunit. Here, we describe the clinical and radiological evolution of 11 individuals, 7 children and 4 adults, from 6 families. Some of the skeletal features improved during the course of this condition, whilst others worsened. We describe for the first time "corner fractures" as a feature of this dysplasia which as with other dysplasias disappear with age. In addition, we review the heights and skeletal anomalies of these reported here and previously in a total of 25 individuals from 15 families. In this study, six different RPL13 variants were identified, five of which were novel. All were located in the apparently hotspot region, located in intron 5 and exon 6. Splicing assays were performed for two of the three previously undescribed splicing variants. Until now, all splice variants have occurred in the intron 5 splice donor site, incorporating an additional 18 amino acids to the mutant protein. Here, we report the first variant in intron 5 splice acceptor site which generates two aberrant transcripts, deleting the first three and four amino acids encoded by exon 6. Thus, this study doubles the number of SEMD-RPL13-related cases and variants reported to date and describes unreported age-related clinical and radiological features.

Lifetime impact of achondroplasia study in Europe (LIAISE): findings from a multinational observational study

BACKGROUND

Achondroplasia, caused by a pathogenic variant in the fibroblast growth factor receptor 3 gene, is the most common skeletal dysplasia. The Lifetime Impact of Achondroplasia Study in Europe (LIAISE; NCT03449368) aimed to quantify the burden of achondroplasia among individuals across a broad range of ages, including adults.

METHODS

Demographic, clinical and healthcare resource use data were collected from medical records of achondroplasia patients enrolled in 13 sites across six European countries in this retrospective, observational study. Descriptive statistics or event rates per 100 person-years were calculated and compared across age groups as well as by history of limb lengthening. Patient-reported outcomes (quality of life [QoL], pain, functional independence, work productivity and activity impairments) were evaluated using questionnaires at the time of enrolment. An exploratory analysis investigated correlations between height (z-score or centimetres) and patient-reported outcomes.

RESULTS

Overall, 186 study patients were included, with a mean age of 21.7 ± 17.3 years (range 5.0-84.4). At least one complication or surgery was reported for 94.6% and 72.0% of patients, respectively, at a rate of 66.6 and 21.5 events per 100 person-years. Diverse medical and surgical complications were reported for all ages in a bimodal distribution, occurring more frequently in the youngest and oldest age groups. A total of 40 patients had previously undergone limb lengthening (capped at 20% per the study protocol). The most frequent surgery types varied by age, in line with complication profiles. Healthcare resource use was high across all age groups, especially among the youngest and oldest individuals, and did not differ substantially according to history of limb lengthening. Compared to general population values, patients reported impaired QoL particularly for physical functioning domains. In addition, patients reported difficulty carrying out daily activities independently and pain starting in childhood. Patient height correlated with multiple patient-reported outcomes.

CONCLUSIONS

The findings of this study suggest that, across an individual's lifetime, achondroplasia is associated with multisystem complications, reduced QoL and functionality, and increased pain. These results highlight the large amount of healthcare resources that individuals with achondroplasia require throughout their lifespans and provide novel insights into current achondroplasia management practices across Europe. Trial registration ClinicalTrials.gov, NCT03449368, Submitted 14 December 2017 - prospectively registered, https://clinicaltrials.gov/ct2/show/record/NCT03449368.

Case report: A third variant in the 5' UTR of TWIST1 creates a novel upstream translation initiation site in a child with Saethre-Chotzen syndrome

Introduction: Saethre-Chotzen syndrome, a craniosynostosis syndrome characterized by the premature closure of the coronal sutures, dysmorphic facial features and limb anomalies, is caused by haploinsufficiency of TWIST1. Although the majority of variants localize in the coding region of the gene, two variants in the 5' UTR have been recently reported to generate novel upstream initiation codons. Methods: Skeletal dysplasia Next-generation sequencing (NGS) panel was used for genetic analysis in a patient with bicoronal synostosis, facial dysmorphisms and limb anomalies. The variant pathogenicity was assessed by a luciferase reporter promoter assay. Results: Here, we describe the identification of a third ATG-creating de novo variant, c.-18C>T, in the 5' UTR of TWIST1 in the patient with a clinical diagnosis of Saethre-Chotzen syndrome. It was predicted to create an out-of-frame new upstream translation initiation codon resulting in a 40 amino acid larger functionally inactive protein. We performed luciferase reporter promoter assays to demonstrate that the variant does indeed reduce translation from the main open reading frame. Conclusion: This is the third variant identified in this region and confirms the introduction of upstream ATGs in the 5' UTR of TWIST1 as a pathogenic mechanism in Saethre-Chotzen syndrome. This case report shows the necessity for performing functional characterization of variants of unknown significance within national health services.

Precocious puberty and anal stenosis in an African patient with Rothmund-Thomson syndrome

Rothmund-Thomson syndrome (RTS) is a rare autosomal recessive disorder characterized by a rash that progresses to poikiloderma. Other common features include sparse hair, eyelashes and eyebrows, short stature, variable skeletal abnormalities, dental defects, cataracts, hypogonadism, and an increased risk for cancer, especially osteosarcoma and skin cancer. RTS is caused by biallelic pathogenic variants in ANAPC1 (Type 1 RTS) or RECQL4 (Type 2 RTS). We present an African girl with Type 2 RTS caused by a nonsense variant and an intronic variant in RECQL4. The patient presented precocious puberty, which has not been previously reported in RTS and that was treated with a GnRH analog, and anal stenosis, which has only been reported once. This case highlights the need to consider deep intronic variants in patients with RTS when pathogenic variants in the coding regions and exon/intron boundaries are not identified and expands the phenotypic spectrum of this disorder.

New pathogenic variant in DLX5: New clues for a clinical spectrum from split-hand-foot malformation to fibular aplasia, tibial campomelia and oligosyndactyly

Introduction: FATCO (Fibular Aplasia, Tibial Campomelia and Oligosyndactyly) is a very infrequent skeletal dysplasia classified within the limb hypoplasia-reduction defects group whose genetic cause has not yet been identified. The advent of next-generation sequencing is enabling the diagnosis of diseases with no previously known genetic cause. Methods: We performed a thorough autopsy on a fetus whose pregnancy was legally terminated due to severe malformations detected by ultrasound. A trio exome was run to identify the genetic cause and risk of recurrence. Previous literature of similar cases was systematically searched. Results: Anatomopathological analyses revealed complete fibular aplasia, shortened and campomelic tibia, absent ankle joint, club right foot and a split foot malformation, leading to the diagnosis of FATCO. Exome sequencing showed that the female fetus carried a de novo nonsense variant in DLX5. The literature search permitted the collection of information on 43 patients with FATCO, the majority of whom were males diagnosed postnatally. In most cases, lower limbs were affected exclusively, but in 39.5% of cases the upper limbs were also affected. Conclusion: The pathologies associated with DLX5 variants encompass a wide spectrum of manifestations ranging from abnormalities exclusively in the hands and feet to long bones such as the tibia and fibula.

Achondroplasia: Update on diagnosis, follow-up and treatment

Achondroplasia requieres multidisciplinary follow-up, with the aim of preventing and managing complications, improving the quality of life of people who suffer from it and favoring their independence and social inclusion. This review is justified by the multiple publications generated in recent years that have carried out a change in its management. Different guidelines and recommendations have been developed, among which the one made by the American Academy of Pediatrics in 2005 recently updated (2020), the Japanese guide (2020), the first European Consensus (2021) and the International Consensus on the diagnosis, approach multidisciplinary approach and management of individuals with achondroplasia throughout life (2021). However, and despite these recommendations, there is currently a great worldwide variability in the management of people with achondroplasia, with medical, functional and psychosocial consequences in patients and their families. Therefore, it is essential to integrate these recommendations into daily clinical practice, taking into account the particular situation of each health system.

Biochemical algorithm to identify individuals with ALPL variants among subjects with persistent hypophosphatasaemia

Background

Hypophosphatasia (HPP) is a rare and underdiagnosed condition characterized by deficient bone and teeth mineralization. The aim of this study was first, to evaluate the diagnostic utility of employing alkaline phosphatase (ALP) threshold levels to identify adults with variants in ALPL among individuals with persistently low ALP levels and second, to determine the value of also including its substrates (serum pyridoxal-5′-phosphate—PLP—and urinary phosphoetanolamine-PEA) for this purpose in order to create a biochemical algorithm that could facilitate the diagnostic work-up of HPP.

Results

The study population comprised 77 subjects with persistent hypophosphatasaemia. They were divided into two groups according to the presence (+GT) or absence (−GT) of pathogenic ALPL variants: 40 +GT and 37 −GT. Diagnostic utility measures were calculated for different ALP thresholds and Receiver Operating Characteristic (ROC) curves were employed to determine PLP and PEA optimal cut-off levels to predict the presence of variants. The optimal threshold for ALP was 25 IU/L; for PLP, 180 nmol/L and for PEA, 30 µmol/g creatinine. Biochemical predictive models were assessed using binary logistic regression analysis and bootstrapping machine learning technique and results were then validated. For ALP < 25 UI/L (model 1), the area under curve (AUC) and the 95% confidence intervals (CI) was 0.68 (95% CI 0.63–0.72) and it improved to 0.87 (95% CI 0.8–0.9), when PEA or PLP threshold levels were added (models 2 and 3), reaching 0.94 (0.91–0.97) when both substrates were included (model 4). The internal validation showed that the addition of serum PLP threshold levels to the model just including ALP improved significantly sensitivity (S) and negative predictive value (NPV) − 100%, respectively- with an accuracy (AC) of 93% in comparison to the inclusion of urinary PEA (S: 71%; NPV 75% and AC: 79%) and similar diagnostic utility measures as those observed in model 3 were detected when both substrates were added.

Conclusions

In this study, we propose a biochemical predictive model based on the threshold levels of the main biochemical markers of HPP (ALP < 25 IU/L and PLP > 180 nmol/L) that when combined, seem to be very useful to identify individuals with ALPL variants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02253-5.

Pain and health-related quality of life in patients with hypophosphatasemia with and without ALPL gene mutations

BACKGROUND

Low serum alkaline phosphatase levels are the hallmark of hypophosphatasia, a disorder due to pathogenic variants of the ALPL gene. However, some patients do not carry ALPL variants and the cause of low alkaline phosphatase remains unknown. We aimed to determine health-related quality of life in adults with low alkaline phosphatase and explore the differences between patients with and without ALPL mutations.

METHODS

We studied 35 adult patients with persistently low alkaline phosphatase unrelated to secondary acquired causes who had ALPL sequenced, and 35 controls of similar age. Three questionnaires about body pain (Brief Pain Inventory, BPI), physical disability (Health Assessment Questionnaire Disability Index, HAQ-DI), and health-related quality of life (36-item Short-Form Health Survey, SF-36) were delivered by telephone interviews.

RESULTS

The mean BPI intensity and interference scores were higher in the patient group (p=0.04 and 0.004, respectively). All domains of the HAQ instrument tended to score better in the control group, with significant differences in the "reach" score (p=0.037) and the overall mean score (0.23 vs 0.09; p=0.029). Patients scored worse than controls in several SF-36 dimensions (Role physical, p=0.039; Bodily pain p=0.046; Role emotional, p=0.025). Patients with and without pathogenic variants scored similarly across all tests, without between-group significant differences.

CONCLUSIONS

Patients with persistently low levels of alkaline phosphatase have significantly worse scores in body pain and other health-related quality of life dimensions, without differences between patients with and without pathogenic variants identified in ALPL gene. This is consistent with the latter ones carrying mutations in regulatory regions.

High prevalence of variants in skeletal dysplasia associated genes in individuals with short stature and minor skeletal anomalies

OBJECTIVE

Next generation sequencing (NGS) has expanded the diagnostic paradigm turning the focus to the growth plate. The aim of the study was to determine the prevalence of variants in genes implicated in skeletal dysplasias in probands with short stature and mild skeletal anomalies.

DESIGN

Clinical and radiological data were collected from 108 probands with short stature and mild skeletal anomalies.

METHODS

A customized skeletal dysplasia NGS panel was performed. Variants were classified using ACMG recommendations and Sherloc. Anthropometric measurements and skeletal anomalies were subsequently compared in those with or without an identified genetic defect.

RESULTS

Heterozygous variants were identified in 21/108 probands (19.4%). Variants were most frequently identified in ACAN (n = 10) and IHH (n = 7) whilst one variant was detected in COL2A1, CREBBP, EXT1, and PTPN11. Statistically significant differences (P < 0.05) were observed for sitting height/height (SH/H) ratio, SH/H ratio standard deviation score (SDS), and the SH/H ratio SDS >1 in those with an identified variant compared to those without.

CONCLUSIONS

A molecular defect was elucidated in a fifth of patients. Thus, the prevalence of mild forms of skeletal dysplasias is relatively high in individuals with short stature and mild skeletal anomalies, with variants in ACAN and IHH accounting for 81% of the cases. An elevated SH/H ratio appears to be associated with a greater probability in detecting a variant, but no other clinical or radiological feature has been found determinant to finding a genetic cause. Currently, we cannot perform extensive molecular studies in all short stature individuals so detailed clinical and radiological phenotyping may orientate which are the candidate patients to obtain worthwhile results. In addition, detailed phenotyping of probands and family members will often aid variant classification.

Early clinical and radiological improvement in a young boy with metaphyseal anadysplasia type 2

Metaphyseal anadysplasia is a very rare hereditary skeletal dysplasia with onset occurring normally during the second and third years of life, but unlike many other dysplasias, symptoms appear to resolve by adolescence. Two types exist, the more severe form, type 1, with both autosomal dominant and recessive inheritance due to pathogenic variants in MMP13, whilst type 2, an even rarer form is due to biallelic MMP9 variants. To date, only two metaphyseal anadysplasia type 2 families have been reported. We describe a third family, a young boy, born to consanguineous parents, referred at 19 months old for abnormal gait due to bowed legs. Clinical and radiological examination revealed scoliosis, genu varum and metaphyseal abnormalities. A homozygous MMP9 nonsense variant, NM_004994.2:c.1764G>A; p.(Trp588*) was identified. By the age of 39 months, lower limb alignment and metaphyseal features had already significantly improved and scoliosis had disappeared. This case confirms that biallelic MMP9 variants cause this very rare skeletal dysplasia, metaphyseal anadysplasia type 2 but also shows that the skeletal manifestations can improve within a short period time and at an early age.

TCF12 haploinsufficiency causes autosomal dominant Kallmann syndrome and reveals network-level interactions between causal loci

Dysfunction of the gonadotropin-releasing hormone (GnRH) axis causes a range of reproductive phenotypes resulting from defects in the specification, migration and/or function of GnRH neurons. To identify additional molecular components of this system, we initiated a systematic genetic interrogation of families with isolated GnRH deficiency (IGD). Here, we report 13 families (12 autosomal dominant and one autosomal recessive) with an anosmic form of IGD (Kallmann syndrome) with loss-of-function mutations in TCF12, a locus also known to cause syndromic and non-syndromic craniosynostosis. We show that loss of tcf12 in zebrafish larvae perturbs GnRH neuronal patterning with concomitant attenuation of the orthologous expression of tcf3a/b, encoding a binding partner of TCF12, and stub1, a gene that is both mutated in other syndromic forms of IGD and maps to a TCF12 affinity network. Finally, we report that restored STUB1 mRNA rescues loss of tcf12 in vivo. Our data extend the mutational landscape of IGD, highlight the genetic links between craniofacial patterning and GnRH dysfunction and begin to assemble the functional network that regulates the development of the GnRH axis.

Description of four patients with TRIP11 variants expand the clinical spectrum of odontochondroplasia (ODCD) and demonstrate the existence of common variants

More than two decades since the first clinical and radiological description of odontochondroplasia (ODCD) was reported, biallelic loss of function variants in the Thyroid hormone receptor interactor 11 gene (TRIP11) were identified, the same gene implicated in the lethal disorder achondrogenesis (ACG1A). Here we report the clinical and radiological follow-up of four ODCD patients, including two siblings and an adult who interestingly has the mildest form observed to date. Four TRIP11 variants were detected, two previously unreported. Subsequently, we review the clinical and radiological findings of the 14 reported ODCD patients. The majority of ODCD patients are compound heterozygotes for TRIP11 variants, 12/14 have a null allele and a splice variant whilst one is homozygous for an in-frame splicing variant, with the splice variants resulting in residual GMAP activity and hypothesized to explain why they have ODCD and not ACG1A. However, adult patient 4 has two potentially null alleles and it remains unknown why she has very mild clinical features. The c.586C>T; p.(Gln196*) variant, previously shown by mRNA studies to result in p.Val105_Gln196del, is the most frequent variant, present in seven individuals from four families, three from different regions of the world, suggesting that it may be a variant hotspot. Another variant, c.2993_2994del; p.(Lys998Serfs*5), has been observed in two individuals with a possible common ancestor. In summary, although there are clinical and radiological characteristics common to all individuals, we demonstrate that the clinical spectrum of TRIP11-associated dysplasias is even more diverse than previously described and that common genetic variants may exist.

Prenatal Diagnosis of Acromelic Frontonasal Dysostosis

Acromelic frontonasal dysostosis (AFND; MIM #603671) is a rare autosomal dominant genetic disorder caused by a heterozygous mutation in the ZSWIM6 (KIAA1577) gene located at chromosome 5q12.1. It is phenotypically characterized by frontonasal malformation with hypertelorism, telecanthus, nasal clefting or bifid nasal tip, wide fontanels and sutures, brachycephaly, and cleft palate. The patients also present with central nervous system malformations such as encephalocele, agenesis of the corpus callosum, or interhemispheric lipoma. Limb malformations can also be found, including preaxial polydactyly of the feet and sometimes postaxial polydactyly of the hands, talipes equinovarus, or tibia malformations. Here, we present a case of early prenatal diagnosis of AFND with ultrasound and necropsy images which show the phenotypic findings of this syndrome.

Delineation of the clinical and radiological features of Stuve-Wiedemann syndrome childhood survivors, four new cases and review of the literature

Stuve-Wiedemann syndrome (SWS; MIM 601559) is a rare autosomal recessive disease caused by mutations in the leukemia inhibitor factor receptor gene (LIFR). Common clinical and radiological findings are often observed, and high neonatal mortality occurs due to respiratory distress and hyperthermic episodes. Despite initially considered as a lethal disorder during the newborn period, in recent years, several SWS childhood survivors have been reported. We report a detailed clinical and radiological characterization of four unrelated childhood SWS molecularly confirmed patients and review 22 previously reported childhood surviving cases. We contribute to the definition of the childhood survival phenotype of SWS, emphasizing the evolving phenotype, characterized by skeletal abnormalities with typical radiological findings, distinctive dysmorphic features, and dysautonomia. Based on the typical features and clinical course, early diagnosis is possible and crucial to plan appropriate management and prevent potential complications. Genetic confirmation is advisable in order to improve genetic counseling to the patients and their families.

Identification of the third FGF9 variant in a girl with multiple synostosis-comparison of the genotype:phenotype of FGF9 variants in humans and mice

Multiple synostosis syndrome (SYNS) is a heterogeneous group of genetic disorders mainly characterized by multiple joint synostosis due to variants in either NOG, GDF5, FGF9 or GDF6. To date, only two FGF9 variants have been associated with SYNS, characterized with hand and feet joint synostosis and fusion of the elbow and vertebral lumbar joints. Craniosynostosis was also observed in one family. Here, we report the clinical and radiological description of a young girl with a third heterozygous FGF9 variant, NM_002010.2:c.427A>T;p.(Asn143Tyr), which interestingly, is located at the same amino acid as the well characterized spontaneous Eks mouse variant. We also compare the genotype: phenotypes observed between humans and mice with SYNS.

Interaction between KDELR2 and HSP47 as a Key Determinant in Osteogenesis Imperfecta Caused by Bi-allelic Variants in KDELR2

Osteogenesis imperfecta (OI) is characterized primarily by susceptibility to fractures with or without bone deformation. OI is genetically heterogeneous: over 20 genetic causes are recognized. We identified bi-allelic pathogenic KDELR2 variants as a cause of OI in four families. KDELR2 encodes KDEL endoplasmic reticulum protein retention receptor 2, which recycles ER-resident proteins with a KDEL-like peptide from the cis-Golgi to the ER through COPI retrograde transport. Analysis of patient primary fibroblasts showed intracellular decrease of HSP47 and FKBP65 along with reduced procollagen type I in culture media. Electron microscopy identified an abnormal quality of secreted collagen fibrils with increased amount of HSP47 bound to monomeric and multimeric collagen molecules. Mapping the identified KDELR2 variants onto the crystal structure of G. gallus KDELR2 indicated that these lead to an inactive receptor resulting in impaired KDELR2-mediated Golgi-ER transport. Therefore, in KDELR2-deficient individuals, OI most likely occurs because of the inability of HSP47 to bind KDELR2 and dissociate from collagen type I. Instead, HSP47 remains bound to collagen molecules extracellularly, disrupting fiber formation. This highlights the importance of intracellular recycling of ER-resident molecular chaperones for collagen type I and bone metabolism and a crucial role of HSP47 in the KDELR2-associated pathogenic mechanism leading to OI.

Biallelic cGMP-dependent type II protein kinase gene (PRKG2) variants cause a novel acromesomelic dysplasia

Background

C-type natriuretic peptide (CNP), its endogenous receptor, natriuretic peptide receptor-B (NPR-B), as well as its downstream mediator, cyclic guanosine monophosphate (cGMP) dependent protein kinase II (cGKII), have been shown to play a pivotal role in chondrogenic differentiation and endochondral bone growth. In humans, biallelic variants in NPR2, encoding NPR-B, cause acromesomelic dysplasia, type Maroteaux, while heterozygous variants in NPR2 (natriuretic peptide receptor 2) and NPPC (natriuretic peptide precursor C), encoding CNP, cause milder phenotypes. In contrast, no variants in cGKII, encoded by the protein kinase cGMP-dependent type II gene (PRKG2), have been reported in humans to date, although its role in longitudinal growth has been clearly demonstrated in several animal models.

Methods

Exome sequencing was performed in two girls with severe short stature due to acromesomelic limb shortening, brachydactyly, mild to moderate platyspondyly and progressively increasing metaphyseal alterations of the long bones. Functional characterisation was undertaken for the identified variants.

Results

Two homozygous PRKG2 variants, a nonsense and a frameshift, were identified. The mutant transcripts are exposed to nonsense-mediated decay and the truncated mutant cGKII proteins, partially or completely lacking the kinase domain, alter the downstream mitogen activation protein kinase signalling pathway by failing to phosphorylate c-Raf 1 at Ser43 and subsequently reduce ERK1/2 activation in response to fibroblast growth factor 2. They also downregulate COL10A1 and upregulate COL2A1 expression through SOX9.

Conclusion

In conclusion, we have clinically and molecularly characterised a new acromesomelic dysplasia, acromesomelic dysplasia, PRKG2 type (AMDP).

Spondyloepiphyseal dysplasia type Stanescu: Expanding the clinical and molecular spectrum of a very rare type II collagenopathy

Spondyloepiphyseal dysplasia type Stanescu (SED-S) is a very rare type II collagenopathy. We describe an 8-year-old boy who presented with short trunk, C2-C3 vertebral fusion, hand, foot, leg and thigh pain, stiffness and limited joint mobility, and waddling gait. Radiographs showed platyspondyly with anterior wedging and endplate irregularities, broad femoral necks, and large epiphyses and epiphyseal equivalents. Differential diagnosis included progressive pseudorheumatoid dysplasia and SED-S. A skeletal dysplasia custom-designed NGS panel was performed and the heterozygous pathogenic variant c.620G>A; p.(Gly207Glu) in COL2A1 was detected, establishing the diagnosis of SED-S. Vertebral fusions, observed in our patient, have not been previously described in this dysplasia. This variant has not been previously associated with SED-S, but was reported in two other families with spondyloepiphyseal dysplasia. Thus, this case expands the clinical and mutational spectrum of SED-S and demonstrates that SED-S significantly overlaps with other skeletal dysplasias.

Clinical and Molecular Description of 16 Families With Heterozygous IHH Variants

CONTEXT

Heterozygous variants in the Indian hedgehog gene (IHH) have been reported to cause brachydactyly type A1 and mild hand and feet skeletal anomalies with short stature. Genetic screening in individuals with short stature and mild skeletal anomalies has been increasing over recent years, allowing us to broaden the clinical spectrum of skeletal dysplasias.

OBJECTIVE

The objective of this article is to describe the genotype and phenotype of 16 probands with heterozygous variants in IHH.

PATIENTS AND METHODS

Targeted next-generation sequencing or Sanger sequencing was performed in patients with short stature and/or brachydactyly for which the genetic cause was unknown.

RESULTS

Fifteen different heterozygous IHH variants were detected, one of which is the first reported complete deletion of IHH. None of the patients showed the classical phenotype of brachydactyly type A1. The most frequently observed clinical characteristics were mild to moderate short stature as well as shortening of the middle phalanx on the fifth finger. The identified IHH variants were demonstrated to cosegregate with the short stature and/or brachydactyly in the 13 probands whose family members were available. However, clinical heterogeneity was observed: Two short-statured probands showed no hand radiological anomalies, whereas another 5 were of normal height but had brachydactyly.

CONCLUSIONS

Short stature and/or mild skeletal hand defects can be caused by IHH variants. Defects in this gene should be considered in individuals with these findings, especially when there is an autosomal dominant pattern of inheritance. Although no genotype-phenotype correlation was observed, cosegregation studies should be performed and where possible functional characterization before concluding that a variant is causative.

Variable pulmonary manifestations in Chitayat syndrome: Six additional affected individuals

Hand hyperphalangism leading to shortened index fingers with ulnar deviation, hallux valgus, mild facial dysmorphism and respiratory compromise requiring assisted ventilation are the key features of Chitayat syndrome. This condition results from the recurrent heterozygous missense variant NM_006494.2:c.266A>G; p.(Tyr89Cys) in ERF on chromosome 19q13.2, encoding the ETS2 repressor factor (ERF) protein. The pathomechanism of Chitayat syndrome is unknown. To date, seven individuals with Chitayat syndrome and the recurrent pathogenic ERF variant have been reported in the literature. Here, we describe six additional individuals, among them only one presenting with a history of assisted ventilation, and the remaining presenting with variable pulmonary phenotypes, including one individual without any obvious pulmonary manifestations. Our findings widen the phenotype spectrum caused by the recurrent pathogenic variant in ERF, underline Chitayat syndrome as a cause of isolated skeletal malformations and therefore contribute to the improvement of diagnostic strategies in individuals with hand hyperphalangism.

Prenatal diagnosis of fetal skeletal dysplasias in a tertiary Hospital in Spain

OBJECTIVE

To assess the diagnostic accuracy of prenatal ultrasound for detecting fetal skeletal dysplasias and to describe its role in orienting genetic studies.

STUDY DESIGN

Observational study of pregnant women surveyed in our hospital, between 2011 and 2018, with fetal long bones below the 3rd centile (shortened long bones), either as an isolated finding or associated to other skeletal anomalies. We used a systematic protocol for the ultrasound evaluation and selection of those fetuses suspected of having a skeletal dysplasia. We report the demographics of these patients along with the sonographic follow-up of their fetuses, the genetic results and the outcome of the pregnancies and the newborn in the entire group and also compare data between the two sub-groups (isolated shortened long bones vs shortened long bones associated to other anomalies).

RESULTS

A total of 81 pregnancies with a suspected fetal skeletal dysplasia were included, with a complete follow-up available in 75 cases, 22 with isolated shortened long bones and 53 cases that presented shortened long bones with other skeletal anomalies. In the shortened long bones sub-group, a total of five (23 %) were born healthy neonates, 10 (45 %) were small for gestational age or intrauterine growth restricted (one of them of genetic origin) and seven (32 %) had a skeletal dysplasia (6 of them with genetic diagnosis). Whilst among the 53 cases that presented with shortened long bones + other skeletal anomalies, three (6%) were healthy neonates, five (9%) were small for gestational age/intrauterine growth restricted (two of genetic origin) and 45 (85 %) had a skeletal dysplasia (19 genetically confirmed and 26 with a clinical diagnosis). These differences in frequencies between the two sub-groups were determined to be statistically significant (χ²: p = 0.02).

CONCLUSION

Around one third of fetuses with isolated shortened long bones will have a skeletal dysplasia. If abnormal skeletal ultrasound findings are associated with shortened long bones, the risk for skeletal dysplasia is significantly increased (85 %). Prenatal systematic approach in a multidisciplinary unit is useful in the orientation of genetic studies.

Comprehensive Characterization of the Mutational Landscape in Localized Anal Squamous Cell Carcinoma

Anal squamous cell carcinoma (ASCC) is a rare neoplasm. Chemoradiotherapy is the standard of care, with no therapeutic advances achieved over the past three decades. Thus, a deeper molecular characterization of this disease is still necessary. We analyzed 46 paraffin-embedded tumor samples from patients diagnosed with primary ASCC by exome sequencing. A bioinformatics approach focused in the identification of high-impact genetic variants, which may act as drivers of oncogenesis, was performed. The relation between genetics variants and prognosis was also studied. The list of high-impact genetic variants was unique for each patient. However, the pathways in which these genes are involved are well-known hallmarks of cancer, such as angiogenesis or immune pathways. Additionally, we determined that genetic variants in BRCA2, ZNF750, FAM208B, ZNF599, and ZC3H13 genes are related with poor disease-free survival in ASCC. This may help to stratify the patient's prognosis and open new avenues for potential therapeutic intervention. In conclusion, sequencing of ASCC clinical samples appears an encouraging tool for the molecular portrait of this disease.

Clinical and Radiologic Evaluation of an Individual with Hypochondroplasia and a Novel FGFR3 Mutation

Hypochondroplasia (HCH), a skeletal dysplasia caused by mutations in the fibroblast growth factor receptor 3 (FGFR3) gene, is characterized by disproportionate short stature. The p.Asn540Lys (p.N540K) mutation accounts for ∼50 to 70% of cases of HCH, but novel FGFR3 mutations are described. We present a family with disproportionately short stature and mild radiologic findings seen in a major public pediatric hospital in Argentina. A previously undescribed heterozygous missense variant in FGFR3, NM_000142.4:667C > T; p.(Arg223Cys) was identified. The predicted phenotype correlates well with the mild auxologic and radiologic characteristics observed. In this case, disproportionately short stature raised the suspicion of skeletal dysplasia.

Can we identify individuals with an ALPL variant in adults with persistent hypophosphatasaemia?

Background

Hypophosphatasia (HPP) is an inborn error of metabolism characterized by low levels of serum alkaline phosphatase (ALP). Scarce evidence exists about features that should signal the potential association between hypophosphatasaemia and HPP in adults. The aim of this study is to estimate the prevalence of ALPL variants in subjects with persistent hypophosphatasaemia and determine the associated clinical and laboratory features. For this cross-sectional study, laboratory records of 386,353 subjects were screened by measurement of ALP activity. A total of 85 (0.18%) subjects with persistent hypophosphatasaemia (≥2 serum alkaline phosphatase–ALP–measurements ≤35 IU/L and none > 45 IU/L) were included (secondary causes previously discarded). ALPL genetic testing and a systematized questionnaire to retrieve demographic, clinical and laboratory data were performed. Descriptive analysis and logistic regression models were employed to identify the clinical and laboratory characteristics associated with ALPL variants.

Results

Forty subjects (47%) had a variant(s) in ALPL. With regard to clinical characteristics, the presence of an ALPL variant was significantly associated only with musculoskeletal pain (OR: 7.6; 95% IC: 1.9–30.9). Nevertheless, a trend to present more dental abnormalities (OR: 3.6; 95% IC: 0.9–13.4) was observed. Metatarsal stress fractures were also more frequent (4 vs 0; p < 0.05) in this group. Regarding laboratory features, median ALP levels were lower in subjects with ALPL variants (26 vs 29 IU/L; p < 0.005). Interestingly, the threshold of ALP levels < 25 IU/L showed a specificity, positive predictive value and positive likelihood ratio of 97.8, 94.4% and 19.8 to detect a positive ALPL test, respectively.

Conclusions

In subjects with persistent hypophosphatasaemia –secondary causes excluded– one out of two presented ALPL variants. Musculoskeletal pain and ALP levels < 25 IU/L are associated with this variant(s). In this scenario, ALP levels < 25 IU/L seem to be very useful to identify individuals with the presence of an ALPL variant.

First case of compound heterozygous BHLHA9 variants in mesoaxial synostotic syndactyly with phalangeal reduction

Mesoaxial synostotic syndactyly with phalangeal reduction (MSSD) is an extremely rare autosomal recessive limb abnormality characterized by the fusion of third and fourth fingers. To date, only homozygous missense and frameshift mutations have been reported in BHLHA9 associated to MSSD. In this study, we report a patient who presented with clinical and radiological features of MSSD. A customized skeletal dysplasia NGS panel revealed the presence of two novel compounds heterozygous variants in BHLHA9: NM_001164405.1: c.[226A>T][269G>C]; p.[(Lys76*)][(Arg90Pro)]. Thus, this is the first case of MSSD in a nonconsanguineous family.

SHOX Deficiency in Argentinean Cohort: Long-Term Auxological Follow-Up and a Family's New Mutation

A cohort study on the growth of 19 Argentinean children, aged 0 to 18 years, and 11 of their first-degree relatives with alterations in the SHOX gene or its regulatory regions is reported. Children are born shorter and experience a growth delay during childhood with a stunted pubertal growth spurt. Body disproportion, with a sitting height/height ratio above +2 standard deviation score (SDS), was already present as early as 2 years old. Hand length was normal. Shortening of the radius, with a length below -1.9 SDS, was the earliest and most frequent radiological sign detected as early as 45 days old. We found a previously unreported mutation in a family with a highly variable phenotype, the boy had a severe phenotype with a milder presentation in other affected members of the family. We conclude that body disproportion and a shorter radius length on X-ray are useful tools for selecting children to undergo SHOX molecular studies.

Loss of function BMP4 mutation supports the implication of the BMP/TGF-β pathway in the etiology of combined pituitary hormone deficiency

Despite BMP4 signaling being critical to Rathke's pouch induction and maintenance during early stages of pituitary development, its implication in the etiology of combined pituitary hormone deficiency (CPHD) and other clinical presentations of congenital hypopituitarism has not yet been definitely demonstrated. We report here the first CPHD patient with a de novo pathogenic loss-of-function variant in BMP4. A 6-year-old boy, with macrocephaly, myopia/astigmatism, mild psychomotor retardation, anterior pituitary hypoplasia and ectopic posterior pituitary, clinically diagnosed with growth hormone deficiency, and central hypothyroidism, was referred for genetic analysis of CPHD. Targeted NGS analysis with a custom panel (n = 310 genes) identified a novel heterozygous de novo nonsense variant, NM_001202.5:c.794G > A, p.(Trp265*) in BMP4, which introduces a premature stop codon in the BMP4 pro-domain, impairing the transcription of the TGF-β mature peptide domain. Additional relevant variants in other genes implicated in pituitary development signaling pathways such as SMAD4 and E2F4 (BMP/TGF-pathway), ALMS1 (NOTCH-pathway), and TSHZ1 (Prokineticin-pathway), were also identified. Our results support the implication of the BMP/TGF-β signaling pathway in the etiology of CPHD and suggest that oligogenic contribution of additional inherited variants may modify the phenotypic expressivity of BMP4 pathogenic variants.

Missense Mutations of the Pro65 Residue of PCGF2 Cause a Recognizable Syndrome Associated with Craniofacial, Neurological, Cardiovascular, and Skeletal Features

PCGF2 encodes the polycomb group ring finger 2 protein, a transcriptional repressor involved in cell proliferation, differentiation, and embryogenesis. PCGF2 is a component of the polycomb repressive complex 1 (PRC1), a multiprotein complex which controls gene silencing through histone modification and chromatin remodelling. We report the phenotypic characterization of 13 patients (11 unrelated individuals and a pair of monozygotic twins) with missense mutations in PCGF2. All the mutations affected the same highly conserved proline in PCGF2 and were de novo, excepting maternal mosaicism in one. The patients demonstrated a recognizable facial gestalt, intellectual disability, feeding problems, impaired growth, and a range of brain, cardiovascular, and skeletal abnormalities. Computer structural modeling suggests the substitutions alter an N-terminal loop of PCGF2 critical for histone biding. Mutant PCGF2 may have dominant-negative effects, sequestering PRC1 components into complexes that lack the ability to interact efficiently with histones. These findings demonstrate the important role of PCGF2 in human development and confirm that heterozygous substitutions of the Pro65 residue of PCGF2 cause a recognizable syndrome characterized by distinctive craniofacial, neurological, cardiovascular, and skeletal features.

Identification of a limb enhancer that is removed by pathogenic deletions downstream of the SHOX gene

Haploinsufficiency of the human SHOX gene causes Léri-Weill dyschondrosteosis (LWD), characterized by shortening of the middle segments of the limbs and Madelung deformity of the wrist. As many as 35% of LWD cases are caused by deletions of non-coding sequences downstream of SHOX that presumably remove an enhancer or enhancers necessary for SHOX expression in developing limbs. We searched for these active sequences using a transgenic mouse assay and identified a 563 basepair (bp) enhancer with specific activity in the limb regions where SHOX functions. This enhancer has previously escaped notice because of its poor evolutionary conservation, although it does contain 100 bp that are conserved in non-rodent mammals. A primary cell luciferase assay confirmed the enhancer activity of the conserved core sequence and demonstrated that putative HOX binding sites are required for its activity. This enhancer is removed in most non-coding deletions that cause LWD. However, we did not identify any likely pathogenic variants of the enhancer in a screen of 124 LWD individuals for whom no causative mutation had been found, suggesting that only larger deletions in the region commonly cause LWD. We hypothesize that loss of this enhancer contributes to the pathogenicity of deletions downstream of SHOX.

Mutations in TOP3A Cause a Bloom Syndrome-like Disorder

Bloom syndrome, caused by biallelic mutations in BLM, is characterized by prenatal-onset growth deficiency, short stature, an erythematous photosensitive malar rash, and increased cancer predisposition. Diagnostically, a hallmark feature is the presence of increased sister chromatid exchanges (SCEs) on cytogenetic testing. Here, we describe biallelic mutations in TOP3A in ten individuals with prenatal-onset growth restriction and microcephaly. TOP3A encodes topoisomerase III alpha (TopIIIα), which binds to BLM as part of the BTRR complex, and promotes dissolution of double Holliday junctions arising during homologous recombination. We also identify a homozygous truncating variant in RMI1, which encodes another component of the BTRR complex, in two individuals with microcephalic dwarfism. The TOP3A mutations substantially reduce cellular levels of TopIIIα, and consequently subjects' cells demonstrate elevated rates of SCE. Unresolved DNA recombination and/or replication intermediates persist into mitosis, leading to chromosome segregation defects and genome instability that most likely explain the growth restriction seen in these subjects and in Bloom syndrome. Clinical features of mitochondrial dysfunction are evident in several individuals with biallelic TOP3A mutations, consistent with the recently reported additional function of TopIIIα in mitochondrial DNA decatenation. In summary, our findings establish TOP3A mutations as an additional cause of prenatal-onset short stature with increased cytogenetic SCEs and implicate the decatenation activity of the BTRR complex in their pathogenesis.

Heterozygous aggrecan variants are associated with short stature and brachydactyly: Description of 16 probands and a review of the literature

OBJECTIVE

Mutations in the aggrecan gene (ACAN) have been identified in two autosomal dominant skeletal dysplasias, spondyloepiphyseal dysplasia, Kimberley type (SEDK), and osteochondritis dissecans, as well as in a severe recessive dysplasia, spondyloepimetaphyseal dysplasia, aggrecan type. Next-generation sequencing (NGS) has aided the identification of heterozygous ACAN mutations in individuals with short stature, minor skeletal defects and mild facial dysmorphisms, some of whom have advanced bone age (BA), poor pubertal spurt and early growth cessation as well as precocious osteoarthritis.

DESIGN AND METHODS

This study involves clinical and genetic characterization of 16 probands with heterozygous ACAN variants, 14 with short stature and mild skeletal defects (group 1) and two with SEDK (group 2). Subsequently, we reviewed the literature to determine the frequency of the different clinical characteristics in ACAN-positive individuals.

RESULTS

A total of 16 ACAN variants were located throughout the gene, six pathogenic mutations and 10 variants of unknown significance (VUS). Interestingly, brachydactyly was observed in all probands. Probands from group 1 with a pathogenic mutation tended to be shorter, and 60% had an advanced BA compared to 0% in those with a VUS. A higher incidence of coxa valga was observed in individuals with a VUS (37% vs 0%). Nevertheless, other features were present at similar frequencies.

CONCLUSIONS

ACAN should be considered as a candidate gene in patients with short stature and minor skeletal defects, particularly those with brachydactyly, and in patients with spondyloepiphyseal dysplasia. It is also important to note that advanced BA and osteoarticular complications are not obligatory conditions for aggrecanopathies/aggrecan-associated dysplasias.

IHH Gene Mutations Causing Short Stature With Nonspecific Skeletal Abnormalities and Response to Growth Hormone Therapy

CONTEXT

Genetic evaluation has been recognized as an important tool to elucidate the causes of growth disorders.

OBJECTIVE

To investigate the cause of short stature and to determine the phenotype of patients with IHH mutations, including the response to recombinant human growth hormone (rhGH) therapy.

PATIENTS AND METHODS

We studied 17 families with autosomal-dominant short stature by using whole exome sequencing and screened IHH defects in 290 patients with growth disorders. Molecular analyses were performed to evaluate the potential impact of N-terminal IHH variants.

RESULTS

We identified 10 pathogenic or possibly pathogenic variants in IHH, an important regulator of endochondral ossification. Molecular analyses revealed a smaller potential energy of mutated IHH molecules. The allele frequency of rare, predicted to be deleterious IHH variants found in short-stature samples (1.6%) was higher than that observed in two control cohorts (0.017% and 0.08%; P < 0.001). Identified IHH variants segregate with short stature in a dominant inheritance pattern. Affected individuals typically manifest mild disproportional short stature with a frequent finding of shortening of the middle phalanx of the fifth finger. None of them have classic features of brachydactyly type A1, which was previously associated with IHH mutations. Five patients heterozygous for IHH variants had a good response to rhGH therapy. The mean change in height standard deviation score in 1 year was 0.6.

CONCLUSION

Our study demonstrated the association of pathogenic variants in IHH with short stature with nonspecific skeletal abnormalities and established a frequent cause of growth disorder, with a preliminary good response to rhGH.

In-frame Variants in FLNA Proximal Rod 1 Domain Associate With a Predominant Cardiac Valvular Phenotype

INTRODUCTION AND OBJECTIVES

X-linked cardiac valvular dysplasia is a rare form of male-specific congenital heart defect mainly characterized by myxomatous degeneration of the atrioventricular valves with variable hemodynamic consequences. It is caused by genetic defects in FLNA-encoded filamin A, a widely expressed actin-binding protein that regulates cytoskeleton organization. Filamin A loss of function has also been associated with often concurring neurologic and connective tissue manifestations, with mutations in the first half of the Rod 1 domain apparently expressing the full cardiac phenotype. We contribute to previous genotype-phenotype correlations with a multidisciplinary approach in a newly-described family.

METHODS

Cardiologic, dysmorphologic, and genetic evaluation of available members were complemented with transcriptional and X-chromosome inactivation studies.

RESULTS

A novel FLNA mutation c.1066-3C>G cosegregated with a male-expressed, apparently isolated, cardiac phenotype with no skewed X-inactivation pattern in female carriers. This variant was shown to result in an in-frame deletion of 8 amino acid residues near the N-terminal region of the protein.

CONCLUSIONS

A nonimprinted, partial loss of function of filamin A proximal Rod 1 domain seems to be the pathogenetic mechanism of cardiac valvular dysplasia, with some cases occasionally expressing associated extracardiac manifestations.

Multiple SLC26A2 mutations occurring in a three-generational family

Multiple epiphyseal dysplasias (MED) are a group of heterogeneous skeletal dysplasias, which share a common phenotype: short stature, skeletal deformities, joint pain and early onset osteoarthritis. Mutations in COMP account for approximately half of autosomal dominant MED cases whilst SLC26A2 mutations account for ∼25% of the recessive cases in the Caucasian population. We present here an interesting family, which was thought to initially have an autosomal dominant skeletal dysplasia. Using a targeted sequencing skeletal dysplasia panel, the proband was found to be a compound heterozygote for two mutations in SLC26A2, one novel mutation, p.Ser522Phe and the other, the common mutation, p.Arg279Trp. In addition to the classical characteristics of MED, she presented with an atypical feature, bilateral synostoses between the 2nd and 3rd metatarsals. The parents were confirmed to be heterozygous for the two mutations but interestingly, the maternal grandfather, who had MED, was found to be homozygous for the common SLC26A2 mutation.

Copy number variants of Ras/MAPK pathway genes in patients with isolated cryptorchidism

Cryptorchidism is the most common congenital disorder in boys, but the cause for most cases remains unknown. Patients with Noonan Syndrome are characterized by a typical face, growth retardation, congenital heart defects, learning disabilities and cryptorchidism. Copy number variations of Ras/MAPK pathway genes are unusual in patients with several clinical features of Noonan Syndrome; however, they have not been studied in patients with only one feature of this condition, such as cryptorchidism. Our aim was to determine whether patients with isolated cryptorchidism exhibit Ras/MAPK pathway gene copy number variations (CNVs). Fifty-nine patients with isolated cryptorchidism and negative for mutations in genes associated with Noonan Syndrome were recruited. Determination of Ras/MAPK pathway gene CNVs was performed by Comparative Genome Hybridization array. A CNV was identified in two individuals, a ~175 kb microduplication at 3p25.2, partially including RAF1. A similar RAF1 microduplication has been observed in a patient with testicular aplasia. This suggests that some patients with isolated cryptorchidism may harbor Ras/MAPK pathway gene CNVs.

Mutations in C-natriuretic peptide (NPPC): a novel cause of autosomal dominant short stature

PurposeC-type natriuretic peptide (CNP) and its principal receptor, natriuretic peptide receptor B (NPR-B), have been shown to be important in skeletal development. CNP and NPR-B are encoded by natriuretic peptide precursor-C (NPPC) and natriuretic peptide receptor 2 (NPR2) genes, respectively. While NPR2 mutations have been described in patients with skeletal dysplasias and idiopathic short stature (ISS), and several Npr2 and Nppc skeletal dysplasia mouse models exist, no mutations in NPPC have been described in patients to date.MethodsNPPC was screened in 668 patients (357 with disproportionate short stature and 311 with autosomal dominant ISS) and 29 additional ISS families in an ongoing whole-exome sequencing study.ResultsTwo heterozygous NPPC mutations, located in the highly conserved CNP ring, were identified. Both showed significant reductions in cyclic guanosine monophosphate synthesis, confirming their pathogenicity. Interestingly, one has been previously linked to skeletal abnormalities in the spontaneous Nppc mouse long-bone abnormality (lbab) mutant.ConclusionsOur results demonstrate, for the first time, that NPPC mutations cause autosomal dominant short stature in humans. The NPPC mutations cosegregated with a short stature and small hands phenotype. A CNP analog, which is currently in clinical trials for the treatment of achondroplasia, seems a promising therapeutic approach, since it directly replaces the defective protein.