Like Father, Like Daughter - Ectodermal Dysplasia-Syndactyly Syndrome: A Case Report

Ectodermal dysplasia-syndactyly syndrome 1 (EDSS1) is an exceedingly rare condition associated with mutations in the PVL4 gene. It is characterised by sparse, brittle hair, eyebrows and eyelashes, abnormal dentition and nails, along with bilateral cutaneous syndactyly involving the fingers and toes. We report a 2-year-old girl who presented to us with bilateral complete simple syndactyly of the third and fourth web spaces of the hands, along with bilateral syndactyly of both feet involving the second to fourth toes. Upon examination, sparse hair and eyebrows, along with abnormal dentition, were noted. Thorough clinical examination and genetic analysis were conducted on the affected child and her father, who exhibited similar clinical features. Genetic analysis revealed a homozygous nonsense mutation in the PVL4 gene in both individuals. According to the literature, EDSS1 has been reported in only 10 families worldwide, and there are no reported cases from India. Level of Evidence: Level V (Therapeutic).

The pathogenic mechanism of syndactyly type V identified in a Hoxd13Q50R knock-in mice

Syndactyly type V (SDTY5) is an autosomal dominant extremity malformation characterized by fusion of the fourth and fifth metacarpals. In the previous publication, we first identified a heterozygous missense mutation Q50R in homeobox domain (HD) of HOXD13 in a large Chinese family with SDTY5. In order to substantiate the pathogenicity of the variant and elucidate the underlying pathogenic mechanism causing limb malformation, transcription-activator-like effector nucleases (TALEN) was employed to generate a Hoxd13Q50R mutant mouse. The mutant mice exhibited obvious limb malformations including slight brachydactyly and partial syndactyly between digits 2-4 in the heterozygotes, and severe syndactyly, brachydactyly and polydactyly in homozygotes. Focusing on BMP2 and SHH/GREM1/AER-FGF epithelial mesenchymal (e-m) feedback, a crucial signal pathway for limb development, we found the ectopically expressed Shh, Grem1 and Fgf8 and down-regulated Bmp2 in the embryonic limb bud at E10.5 to E12.5. A transcriptome sequencing analysis was conducted on limb buds (LBs) at E11.5, revealing 31 genes that exhibited notable disparities in mRNA level between the Hoxd13Q50R homozygotes and the wild-type. These genes are known to be involved in various processes such as limb development, cell proliferation, migration, and apoptosis. Our findings indicate that the ectopic expression of Shh and Fgf8, in conjunction with the down-regulation of Bmp2, results in a failure of patterning along both the anterior-posterior and proximal-distal axes, as well as a decrease in interdigital programmed cell death (PCD). This cascade ultimately leads to the development of syndactyly and brachydactyly in heterozygous mice, and severe limb malformations in homozygous mice. These findings suggest that abnormal expression of SHH, FGF8, and BMP2 induced by HOXD13Q50R may be responsible for the manifestation of human SDTY5.

Antisense oligonucleotide therapeutic approach for Timothy syndrome

Timothy syndrome (TS) is a severe, multisystem disorder characterized by autism, epilepsy, long-QT syndrome and other neuropsychiatric conditions1. TS type 1 (TS1) is caused by a gain-of-function variant in the alternatively spliced and developmentally enriched CACNA1C exon 8A, as opposed to its counterpart exon 8. We previously uncovered several phenotypes in neurons derived from patients with TS1, including delayed channel inactivation, prolonged depolarization-induced calcium rise, impaired interneuron migration, activity-dependent dendrite retraction and an unanticipated persistent expression of exon 8A2-6. We reasoned that switching CACNA1C exon utilization from 8A to 8 would represent a potential therapeutic strategy. Here we developed antisense oligonucleotides (ASOs) to effectively decrease the inclusion of exon 8A in human cells both in vitro and, following transplantation, in vivo. We discovered that the ASO-mediated switch from exon 8A to 8 robustly rescued defects in patient-derived cortical organoids and migration in forebrain assembloids. Leveraging a transplantation platform previously developed7, we found that a single intrathecal ASO administration rescued calcium changes and in vivo dendrite retraction of patient neurons, suggesting that suppression of CACNA1C exon 8A expression is a potential treatment for TS1. Broadly, these experiments illustrate how a multilevel, in vivo and in vitro stem cell model-based approach can identify strategies to reverse disease-relevant neural pathophysiology.

LRP4 site-specific variants in the third β-propeller domain causes congenital myasthenic syndrome type 17

LRP4 is expressed in many organs. It mediates SOST-dependent inhibition of bone formation and acts as an inhibitor of WNT signaling. It is also a postsynaptic end plate cell surface receptor at the neuromuscular junction and is central to its development, maintenance, and function. Pathogenic variants of LRP4 that specifically affect the canonical WNT signaling pathway are known to be associated with Cenani-Lenz syndactyly syndrome or the overlapping condition sclerosteosis. However, site-specific pathogenic variants of LRP4 have been associated with the congenital myasthenic syndrome (CMS) type 17 with no abnormal bone phenotype. Only two studies reported biallelic variants of LRP4 associated with CMS17 that presented during childhood. All three reported variants (NM_002334.4: p.Glu1233Ala, p.Glu1233Lys, or p.Arg1277His) are located within the 3'-edge of the third β-propeller domain of LRP4. We report on a patient with a biallelic variant of the LRP4 gene presenting with a severe and neonatal lethal phenotype; we also provide a literature review of the previously reported patients. A female neonate, born to healthy consanguineous parents, presented with severe hypotonia, congenital diaphragmatic hernia, pulmonary hypertension, and progressive hypoxemia. Two of her siblings presented with a similar condition in the past, and all three died shortly after birth. Clinical exome sequencing revealed homozygosity for the pathogenic variant NM_002334.4:c.3698A > C (p.[Glu1233Ala]).

International Cohort of Neonatal Timothy Syndrome

INTRODUCTION

Timothy syndrome (TS) is an extremely rare, multisystem disorder classically associated with long QT, syndactyly, ventricular arrhythmias, and hypoglycaemia. A neonatal diagnosis allows maximal medical and device therapy to be implemented to avoid malignant arrhythmias and sudden cardiac death.

METHODS

This was a retrospective case series study of type I TS (TS1) patients using data from the Timothy Syndrome Foundation's international registry, encompassing patients with a genetic diagnosis (CACNA1C variant G406R in exon 8A) recruited over a 28-year period.

RESULTS

Forty-four cases of TS1 were included (26 male; 60%). Mean gestational age (GA) was 35.6 weeks (range 28 weeks - term), with 43% of patients born less than 37 weeks GA. In TS1 patients presenting with foetal bradycardia, mean GA was significantly lower (34.2 weeks, p < 0.05). Foetal bradycardia secondary to atrioventricular block was present in 20 patients (45%), resulting in premature delivery in 14 patients (32%). Fifteen patients (34%) were diagnosed with TS1 as neonates. Long QT at birth helped secure a diagnosis in 25 patients (57%). Syndactyly was seen in most patients (n = 40, 91%). Twenty patients died, with an average age of death of 2.3 years (range 1 month-6 years). Of the 7 patients who died before the first year of life (16%), the average age of death was 2.5 months.

CONCLUSION

TS is associated with high early mortality. TS should be considered in paediatric patients presenting with long QT and syndactyly. Recognition of TS in the neonatal period allows for early intervention to prevent life-threatening arrhythmias.

A novel homozygous missense variant in LRP4 causing Cenani-Lenz syndactyly syndrome and literature review

BACKGROUND

Cenani-Lenzsyndactyly syndrome (CLSS; OMIM 212780) is a rare autosomal recessive acral deformity, which is mainly manifested in the fusion of fingers or toes, disordered phalangeal structure, shortening or fusion of the radius and ulna, and renal hypoplasia.

CASE PRESENTATION

Our report described an individual with mild phenotypes from China. His parents were not consanguineous. The affected individual was non-dysmorphic. Standard X-ray showed that the both hands have only four metacarpal bones. The distal end of the first metacarpal bone on the right was relatively slender, and the distal phalanx was absent. Multiple phalanges and some soft tissues of both hands were fused. Exome sequencing revealed a novel biallelic c.282C⟩Avariant in low-density lipoprotein receptor-related protein 4 (LRP4; OMIM604270; NM_002334.4) causing p. (Asn94Lys) change in the encoded protein. This variant is predicted to be potentially pathogenic, affecting protein structure and function.

CONCLUSION

We report a novel missense variant present in homozygosity in LRP4 to broaden the pathogenic spectrum of LRP4 in syndactyly, and exome sequencing technology is a powerful tool for genetic analysis in prenatal diagnosis and medical research, as a preferred method for the diagnosis of syndactyly and related phenotypes.

A Japanese patient with Teebi hypertelorism syndrome and a novel CDH11 EC1 domain variant

The gene CDH11 encodes cadherin-11, a Type II cadherin superfamily member that contains five extracellular cadherin (EC) domains. Cadherin-11 undergoes trans-dimerization via the EC1 domain to generate cadherin complexes. Compound heterozygous and homozygous loss-of-function CDH11 variants are observed in Elsahy-Waters syndrome (EWS), which shows characteristic craniofacial features, vertebral abnormalities, cutaneous syndactyly in 2-3 digits, genitourinary anomalies, and intellectual disability. Heterozygous CDH11 variants can cause Teebi hypertelorism syndrome (THS), which features widely spaced eyes and hypospadias. We report a THS patient with a novel CDH11 variant involving the EC1 domain. The patient was a 10-month-old male with normal developmental milestones, but had widely spaced eyes, strabismus, hypospadias, shawl scrotum, broad thumbs (right bifid thumb in x-ray), polysyndactyly of the left fourth finger, and cutaneous syndactyly of left third/fourth fingers. Exome sequencing identified a de novo heterozygous CDH11 variant (NM_001797.4:c.229C > T [p.Leu77Phe] NC_000016.9:g.64998856G > A). Clinical features were consistent with previously reported THS patients, but polysyndactyly, broad thumb, and cutaneous syndactyly overlapped phenotypic features of EWS. THS and EWS may represent a spectrum of CDH11-related disorders. Residue Leu77 in this novel CDH11 variant lines a large hydrophobic pocket where side chains of the partner cadherin-11 insert to trans-dimerize, suggesting that the cadherin-11 structure might be altered in this variant.

Thurston syndrome with thalassaemia: a rare case devising a novel molecular and phenotypic variation

A male infant presented with progressive paleness of the body since 3 months of age. On examination, the child had pallor, microcephaly with dysmorphic facies (depressed nasal bridge, low set ears, retrognathia, high arched palate and tongue hamartoma). Postaxial polydactyly in bilateral hands and feet, broad great toes, with syndactyly of left fourth and fifth toes were present. The haemogram showed severe anaemia with a microcytic hypochromic picture. High-performance liquid chromatography (HPLC) was normal. However, the parents' HPLC was suggestive of beta thalassaemia trait. Whole-exome sequencing revealed Thurston syndrome with beta-thalassaemia in homozygous pattern with a novel mutation. It is a rare genetic syndrome exclusively found in the South Asian population. Due to the rarity, identification of this syndrome is often difficult and requires awareness among clinicians. However, it is important to diagnose the disorder accurately in order to provide appropriate genetic counselling and prognostication to the parents.

HOXD13-associated synpolydactyly: Extending and validating the genotypic and phenotypic spectrum with 38 new and 49 published families

PURPOSE

HOXD13 is an important regulator of limb development. Pathogenic variants in HOXD13 cause synpolydactyly type 1 (SPD1). How different types and positions of HOXD13 variants contribute to genotype-phenotype correlations, penetrance, and expressivity of SPD1 remains elusive. Here, we present a novel cohort and a literature review to elucidate HOXD13 phenotype-genotype correlations.

METHODS

Patients with limb anomalies suggestive of SPD1 were selected for analysis of HOXD13 by Sanger sequencing, repeat length analysis, and next-generation sequencing. Literature was reviewed for HOXD13 heterozygotes. Variants were annotated for phenotypic data. Severity was calculated, and cluster and decision-tree analyses were performed.

RESULTS

We identified 98 affected members of 38 families featuring 11 different (likely) causative variants and 4 variants of uncertain significance. The most frequent (25/38) were alanine repeat expansions. Phenotypes ranged from unaffected heterozygotes to severe osseous synpolydactyly, with intra- and inter-familial heterogeneity and asymmetry. A literature review provided 160 evaluable affected members of 49 families with SPD1. Computer-aided analysis only corroborated a positive correlation between alanine repeat length and phenotype severity.

CONCLUSION

Our findings support that HOXD13-protein condensation in addition to haploinsufficiency is the molecular pathomechanism of SPD1. Our data may, also, facilitate the interpretation of synpolydactyly radiographs by future automated tools.

A Recurrent Nonsense Mutation in NECTIN4 Underlying Ectodermal Dysplasia-Syndactyly Syndrome with a Novel Phenotype in a Consanguineous Kashmiri Family

EDSS1, a syndrome characterized by ectodermal dysplasia-syndactyly, is inherited in an autosomal recessive manner due to mutations in the NECTIN4/PVRL4 gene. Clinical manifestations of the syndrome include defective nail plate, sparse to absent scalp and body hair, spaced teeth with enamel hypoplasia, and bilateral cutaneous syndactyly in the fingers and toes. Here, we report a consanguineous family of Kashmiri origin presenting features of EDSS1. Using whole exome sequencing, we found a recurrent nonsense mutation (NM_030916: c.181C > T, p.(Gln61 ∗)) in the NECTIN4 gene. The variant segregated perfectly with the disorder within the family. The candidate variant was absent in 50 in-house exomes pertaining to other disorders from the same population. In addition to the previously reported clinical phenotype, an upper lip cleft was found in one of the affected members as a novel phenotype that is not reported by previous studies in EDSS1 patients. Therefore, the study presented here, which was conducted on the Kashmiri population, is the first to document a NECTIN4 mutation associated with the upper lip cleft as a novel phenotype. This finding broadens the molecular and phenotypic spectrum of EDSS1.

A novel homozygous nonsense mutation in NECTIN4 gene in a Pakistani family with ectodermal dysplasia syndactyly syndrome 1

BACKGROUND

Ectodermal dysplasia syndactyly syndrome 1 (EDSS1) is a rare hereditary disorder characterized by defects in teeth, hair, and nails in association with a fusion of the digits. Genetically, the disease phenotypes are caused by homozygous and compound heterozygous variants in NECTIN4 gene.

OBJECTIVE

The main objective of the study was to identify the pathogenic sequence variant(s) for family screening and identification of carriers.

METHODS

In the present study, the authors have investigated a large consanguineous family of Pakistani origin segregating autosomal recessive EDSS1. All the coding exons of the NECTIN4 gene were directly sequenced using gene-specific primers.

RESULTS

The affected individuals presented the classical EDSS1 clinical features including sparse hair, hypoplastic nails with thick flat discolored nail plates, peg-shaped, conical, and widely spaced teeth with enamel hypoplasia, proximal cutaneous syndactyly of fingers and toes. Sequence analysis of the coding region of the NECTIN4 identified a novel nonsense variant [c.163C>T; p.(Arg55*)] in exon-2 of the gene. Computational analysis of protein structure revealed that the variant induced premature termination at Arg55 located in Ig-like V-loop region leading to loss of Ig-C2 type domains and transmembrane region, and most likely Nectin-4 function will be lost.

STUDY LIMITATION

Gene expression studies are absent that would have strengthened the findings of computational analysis.

CONCLUSION

The present study expanded the phenotypic and mutation spectrum of the NECTIN4 gene. Further, the study would assist in carrier testing and prenatal diagnosis of the affected families.

Same Gene, Different Story (a Case Report of Congenital Long QT Syndrome Subtype 8 With a Novel Mutation)

Long QT syndrome (LQTS) 8 is a rare inherited channelopathy caused by CACNA1C gene mutations that affects calcium channels, and when combined with congenital heart defects, musculoskeletal defects, and neurodevelopmental defects, it is referred to as Timothy syndrome. A female patient, aged 17 years, presented with a witnessed episode of syncope secondary to ventricular fibrillation that was successfully cardioverted. Electrocardiogram showed sinus bradycardia 52/min, normal axis, and a QTc of 626 ms. In the hospital, she had another episode of asystole and Torsade de pointes and underwent successful cardiopulmonary resuscitation. Echocardiogram showed severely reduced left ventricular systolic function from postcardiac arrest myocardial dysfunction and no congenital heart defects. Long QT genetic test detected a missense mutation in the CACNA1C gene (NM_199460.3, variant c.2573G>A, p Arg858His, heterozygous, autosomal dominant), resulting in replacement of arginine with histidine at position 858(R858H), leading to the gain of function in the L-type calcium channel. Given the absence of congenital cardiac defects, musculoskeletal deformities, or neurodevelopmental delay a final diagnosis of LQTS subtype 8 was made. A cardioverter defibrillator was implanted. In conclusion, our case highlights the importance of genetic testing in the diagnosis of LQTS. Some CACNA1C mutations, such as R858H described here, cause LQTS without the extracardiac manifestations observed in classic Timothy syndrome and should be included in the genetic testing for LQTS. To the best of our knowledge, our case is the first one from United States with the R585H mutation. Three cases with similar mutations have been reported from Japan and one from New Zealand.

FREM2-related Fraser syndrome with popliteal pterygium and structural central nervous system anomalies

Fraser syndrome (FS) is a rare multiple malformation disorder characterized by cryptophthalmos, characteristic craniofacial dysmorphism, cutaneous syndactyly, malformations of the respiratory and urinary tract, and anogenital anomalies. Although the characteristic presentation of FS can be detected prenatally, oligohydramnios often challenges the clinical diagnosis. Here we report on the atypical prenatal and postmortem findings of a fetus with FS caused by a novel homozygous frameshift variant in FREM2. Our study highlights the variable manifestations of the FS and expands the clinical spectrum to include popliteal pterygium and structural central nervous system anomalies.

A novel variant in AFF3 underlying isolated syndactyly

Isolated syndactyly is a common limb malformation with limited known genetic etiology. We used exome sequencing to discover a novel heterozygous missense variant c.2915G > C: p.Arg972Pro in AFF3 on chromosome 2q11.2 in a family with isolated syndactyly in hands and feet. AFF3 belongs to a family of nuclear transcription activating factors and is involved in limb dorsoventral patterning. The variant Arg972Pro is located near the C terminus, a region that is yet to be associated with human disorders. Functional studies did not show a difference in the stability or subcellular localization of the mutant and wild type proteins. Instead, overexpression in zebrafish embryos suggests that Arg972Pro is a loss-of-function allele. These results suggest that variants in the C terminus of AFF3 may cause a phenotype distinct from previously characterized AFF3 variants.

The identification of a novel CCNQ gene tail extension variant contributing to syndactyly, telecanthus and anogenital and renal malformations syndrome

The "toe syndactyly, telecanthus and anogenital and renal malformations" (STAR) syndrome is a rare X-linked dominant inherited kidney ciliopathy caused by CCNQ gene mutations. Here, we investigated the genotype and phenotype in the first two twin sisters with a novel tail extension CCNQ variant in Asia. Genetic variants of the pedigree were screened using whole-exome sequence analysis and validated by direct Sanger sequencing. The genetic function was investigated through cultured cells and zebrafish embryos transfected with mutant. The proband is suffered from end-stage renal disease, telecanthus, scoliosis, anal atresia, bilateral hydronephrosis pyeloureter dilation and hearing loss, while her twin sister had milder phenotypes. A novel heterozygous variant c.502_518delinsA (p.Val168SerfsTer173) in CCNQ gene was identified in the twins and their asymptomatic mosaic mother. The concurrent deletion of 17 bases and insertion of one base variant led to the loss of 5 amino acids, subsequently caused a 96 more amino acids tail extension delaying the appearance of stop codon. The loss-of-function variant of CCNQ not only led to the impaired expression of cyclin M but also increased the binding affinity of CDK10-cyclin M complex, which is different from the previous study. The research expanded the genotypic and phenotypic spectrum of STAR syndrome.

Triphalangeal thump, thumb duplication, and syndactyly: The first case report in the literature

RATIONALE

Triphalangeal thumb (TPT) is a rare congenital malformation where the thumb has three phalanges instead of two. Syndactyly is a condition in which children are born with fused or webbed fingers. The combination of TPT, Syndactyly, and thumb duplication is extremely rare, especially when these deformities are combined in one hand.

PATIENT CONCERNS

Hand abnormalities and polydactyl have been reported in a 1-year-old boy.

DIAGNOSIS

A clinical examination reveals two thumb duplications, finger fusion (Syndactyly), and a thumb with three phalanges (TPT). The diagnosis was based on clinical findings and an X-ray image of the hand.

INTERVENTIONS

The Z-plasty method was used to remove the adhesion between the thumb and forefinger, as well as the removal of the medial and distal phalanx of the thumb's medial tip.

OUTCOMES

The patient was followed for 2 months and found him in good health. To authors' knowledge, we described an unusual case from Syria, considered the first in medical history.

LESSONS LEARNED

General and plastic surgeons should be aware about this unusual mix of the three abnormalities. The family history must also be carefully investigated to explore the occurrence of hereditary illnesses.

Hyperinsulinemic Hypoglycemia Associated with a CaV1.2 Variant with Mixed Gain- and Loss-of-Function Effects

The voltage-dependent L-type calcium channel isoform CaV1.2 is critically involved in many physiological processes, e.g., in cardiac action potential formation, electromechanical coupling and regulation of insulin secretion by beta cells. Gain-of-function mutations in the calcium voltage-gated channel subunit alpha 1 C (CACNA1C) gene, encoding the CaV1.2 α1-subunit, cause Timothy syndrome (TS), a multisystemic disorder that includes autism spectrum disorders and long QT (LQT) syndrome. Strikingly, TS patients frequently suffer from hypoglycemia of yet unproven origin. Using next-generation sequencing, we identified a novel heterozygous CACNA1C mutation in a patient with congenital hyperinsulinism (CHI) and associated hypoglycemic episodes. We characterized the electrophysiological phenotype of the mutated channel using voltage-clamp recordings and in silico action potential modeling experiments. The identified CaV1.2L566P mutation causes a mixed electrophysiological phenotype of gain- and loss-of-function effects. In silico action potential modeling supports that this mixed electrophysiological phenotype leads to a tissue-specific impact on beta cells compared to cardiomyocytes. Thus, CACNA1C variants may be associated with non-syndromic hyperinsulinemic hypoglycemia without long-QT syndrome, explained by very specific electrophysiological properties of the mutated channel. We discuss different biochemical characteristics and clinical impacts of hypoglycemia in the context of CACNA1C variants and show that these may be associated with significant morbidity for Timothy Syndrome patients. Our findings underline that the potential of hypoglycemia warrants careful attention in patients with CACNA1C variants, and such variants should be included in the differential diagnosis of non-syndromic congenital hyperinsulinism.

Recent Advances in Syndactyly: Basis, Current Status and Future Perspectives

A comprehensive summary of recent knowledge in syndactyly (SD) is important for understanding the genetic etiology of SD and disease management. Thus, this review article provides background information on SD, as well as insights into phenotypic and genetic heterogeneity, newly identified gene mutations in various SD types, the role of HOXD13 in limb deformities, and recently introduced modern surgical techniques for SD. This article also proposes a procedure for genetic analysis to obtain a clearer genotype-phenotype correlation for SD in the future. We briefly describe the classification of non-syndromic SD based on variable phenotypes to explain different phenotypic features and mutations in the various genes responsible for the pathogenesis of different types of SD. We describe how different types of mutation in HOXD13 cause various types of SD, and how a mutation in HOXD13 could affect its interaction with other genes, which may be one of the reasons behind the differential phenotypes and incomplete penetrance. Furthermore, we also discuss some recently introduced modern surgical techniques, such as free skin grafting, improved flap techniques, and dermal fat grafting in combination with the Z-method incision, which have been successfully practiced clinically with no post-operative complications.

Deletion of the last two exons of FGF10 in a family with LADD syndrome and pulmonary acinar hypoplasia

Pulmonary acinar hypoplasia (PAH) and lacrimo-auriculo-dento-digital (LADD) syndrome have both been associated with loss-of-function variants in, or deletions of FGF10. Here we report a multi-generational family with seven members manifesting varying features of LADD syndrome, with one individual dying in early infancy of PAH. Whole genome sequencing in one family member identified a 12,158 bp deletion on chromosome 5p12 that removes two of the three exons of FGF10. Allele-specific PCR demonstrated that all affected family members, including the individual with PAH, carried the 12 kb deletion. We conclude the deletion is pathogenic and expands the mutational spectrum of FGF10 variants in LADD syndrome. The common mechanism underlying the variable clinical features of LADD syndrome is defective terminal branching of salivary and lacrimal glands and pulmonary acini, regulated by the TBX4-FGF10-FGFR2 pathway. The variable phenotypic expressivity of FGF10 haploinsufficiency from relatively benign to lethal is likely due to variation at other genetic loci.

A Novel Mutation in a Gene Causes Sclerosteosis in a Family of Mediterranean Origin

Background and Objectives: Sclerostin is an SOST gene product that inhibits osteoblast activity and prevents excessive bone formation by antagonizing the Wnt signaling pathway. Sclerosteosis has been linked to loss of function mutations in the SOST gene. It is a rare autosomal recessive disorder characterized by craniotubular hyperostosis and can lead to fatal cerebellar herniation. Our aim is to describe the clinical and radiological features and the new underlying SOST mutation in a patient with sclerosteosis. Case: A 25-year-old female who was referred to the endocrine clinic for suspected excess growth hormone. The patient complained of headaches, progressive blurred vision, hearing disturbances, increased size of feet, proptosis, and protrusion of the chin. She had normal antenatal history except for syndactyly. Images showed diffuse osseous thickening and high bone mineral density. Biochemical and hormonal tests were normal. Due to progressive compressive optic neuropathy, optic nerve fenestration with decompression hemicraniotomy was performed. Sclerosteosis was suspected due to the predominant craniotubular hyperostosis with syndactyly. Using peripheral leucocyte DNA, genomic sequencing of the SOST gene was performed. This identified a novel deletion homozygous mutation in the SOST gene (c.387delG, p.Asp131ThrfsTer116) which disrupts sclerostin function, causing sclerosteosis. Conclusions: Discovery of the molecular basis of sclerosteosis represents an important advance in the diagnosis and management of this fatal disease.

[Apert syndrome or acrocephalosyndactilia type I]

Apert syndrome, or acrocephalosyndactilia type I, is a rare genetic disorder caused by mutations in the FGFR2 gene and characterized by craniosynostosis, craniofacial dysmorphia and symmetrical syndactyly of the hands and feet. The estimated prevalence of this syndrome is 10 to 15.5 cases per 1,000,000 live births. This syndrome presents significant clinical variability and its early diagnosis is essential. We report an isolated case of Apert syndrome, diagnosed during follow-up of a biamniotic bichorium twin pregnancy.

Ectodermal Dysplasia-Syndactyly Syndrome with Toe-Only Minimal Syndactyly Due to a Novel Mutation in NECTIN4: A Case Report and Literature Review

Ectodermal dysplasia-syndactyly syndrome 1 (EDSS1) is characterized by cutaneous syndactyly of the toes and fingers and abnormalities of the hair and teeth, variably associated with nail dystrophy and palmoplantar keratoderma (PPK). EDSS1 is caused by biallelic mutations in the NECTIN4 gene, encoding the adherens junction component nectin-4. Nine EDSS1 cases have been described to date. We report a 5.5-year-old female child affected with EDSS1 due to the novel homozygous frameshift mutation c.1150delC (p.Gln384ArgfsTer7) in the NECTIN4 gene. The patient presents brittle scalp hair, sparse eyebrows and eyelashes, widely spaced conical teeth and dental agenesis, as well as toenail dystrophy and mild PPK. She has minimal proximal syndactyly limited to toes 2-3, which makes the phenotype of our patient peculiar as the overt involvement of both fingers and toes is typical of EDSS1. All previously described mutations are located in the nectin-4 extracellular portion, whereas p.Gln384ArgfsTer7 occurs within the cytoplasmic domain of the protein. This mutation is predicted to affect the interaction with afadin, suggesting that impaired afadin activation is sufficient to determine EDSS1. Our case, which represents the first report of a NECTIN4 mutation with toe-only minimal syndactyly, expands the phenotypic and molecular spectrum of EDSS1.

Lethal Cenani Lenz syndrome in two consecutive pregnancies: Further extension of phenotype from Maldives

Cenani Lenz syndrome is a rare autosomal recessive disorder associated with variable degree of limb malformations, dysmorphism, and renal agenesis. It is caused due to pathogenic variants in the LRP4 gene, which plays an important role in limb and renal development. Mutations in the APC gene have also been occasionally associated with CLS. The phenotypic spectrum ranges from mild to very severe perinatal lethal type depending on the type of variant. We report a pathogenic variant, c.2710 del T (p.Trp904GlyfsTer5) in theLRP4 gene, in a fetus with lethal Cenani Lenz syndrome with antenatal presentation of tetraphocomelia and symmetrical involvement of hands and feet.