Presentation of Rare Phenotypes Associated with the FKBP10 Gene.

Pathogenic variants in the FKBP10 gene lead to a spectrum of rare autosomal recessive phenotypes, including osteogenesis imperfecta (OI) Type XI, Bruck syndrome Type I (BS I), and the congenital arthrogryposis-like phenotype (AG), each with variable clinical manifestations that are crucial for diagnosis. This study analyzed the clinical-genetic characteristics of patients with these conditions, focusing on both known and newly identified FKBP10 variants. We examined data from 15 patients, presenting symptoms of OI and joint contractures. Diagnostic methods included genealogical analysis, clinical assessments, radiography, whole exome sequencing, and direct automated Sanger sequencing. We diagnosed 15 patients with phenotypes due to biallelic FKBP10 variants-4 with OI Type XI, 10 with BS I, and 1 with the AG-like phenotype-demonstrating polymorphism in disease severity. Ten pathogenic FKBP10 variants were identified, including three novel ones, c.1373C>T (p.Pro458Leu), c.21del (p.Pro7fs), and c.831_832insCG (p.Gly278Argfs), and a recurrent variant, c.831dup (p.Gly278Argfs). Variant c.1490G>A (p.Trp497Ter) was found in two unrelated patients, causing OI XI in one and BS I in the other. Additionally, two unrelated patients with BS I and epidermolysis bullosa shared identical homozygous FKBP10 and KRT14 variants. This observation illustrates the diversity of FKBP10-related pathology and the importance of considering the full spectrum of phenotypes in clinical diagnostics.

ECEL1 related distal arthrogryposis 5D in an Indian cohort-Report of recognizable musculoskeletal phenotype and a possible founder variant.

Distal arthrogryposis type 5D (DA5D) is clinically characterized by knee extension contractures, distal joint contractures, clubfoot, micrognathia, ptosis, and scoliosis. We report nine affected individuals from eight unrelated Indian families with DA5D. Although the overall musculoskeletal phenotype is not very distinct from other distal arthrogryposis, the presence of fixed knee extension contractures with or without scoliosis could be an important early pointer to DA5D. We also report a possible founder variant in ECEL1 along with four novel variants and further expand the genotypic spectrum of DA5D.

New insights into the clinical and molecular spectrum of the MADD-related neurodevelopmental disorder.

Biallelic pathogenic variants in MADD lead to a very rare neurodevelopmental disorder which is phenotypically pleiotropic grossly ranging from severe neonatal hypotonia, failure to thrive, multiple organ dysfunction, and early lethality to a similar but milder phenotype with better survival. Here, we report 5 patients from 3 unrelated Egyptian families in whom 4 patients showed the severe end of the spectrum displaying neonatal respiratory distress, hypotonia and chronic diarrhea while one patient presented with the mild form displaying moderate intellectual disability and myopathy. In addition, we observed distal arthrogryposis and nonspecific structural brain anomalies in all our patients. Interestingly, cerebellar and brainstem hypoplasia were noted in one patient. Whole exome sequencing identified three novel homozygous variants in the MADD gene: two likely pathogenic [c.4321delC p.(Gln1441ArgfsTer46) and c.2620 C > T p.(Arg874Ter)] and one variant of uncertain significance (c.4307 G > A, p.Arg1436Gln). The variants segregated with the disease in all available family members. Our findings confirm that arthrogryposis, genital, cardiac and structural brain anomalies are manifestations of MADD which expand the spectrum of MADD-related neurodevelopmental disorder. Moreover, they further highlight the convergence of MADD variants on different organ systems leading to complex phenotypes.

Subcellular localisation of truncated MAGEL2 proteins: insight into the molecular pathology of Schaaf-Yang syndrome.

Schaaf-Yang syndrome (SYS) is an ultra-rare neurodevelopmental disorder caused by truncating mutations in MAGEL2 Heterologous expression of wild-type (WT) or a truncated (p.Gln638*) C-terminal HA-tagged MAGEL2 revealed a shift from a primarily cytoplasmic to a more nuclear localisation for the truncated protein variant. We now extend this analysis to six additional SYS mutations on a N-terminal FLAG-tagged MAGEL2. Our results replicate and extend our previous findings, showing that all the truncated MAGEL2 proteins consistently display a predominant nuclear localisation, irrespective of the C-terminal or N-terminal position and the chemistry of the tag. The variants associated with arthrogryposis multiplex congenita display a more pronounced nuclear retention phenotype, suggesting a correlation between clinical severity and the degree of nuclear mislocalisation. These results point to a neomorphic effect of truncated MAGEL2, which might contribute to the pathogenesis of SYS.

Clinical and molecular characteristics of 26 fetuses with lethal multiple congenital contractures.

Multiple congenital contractures (MCC) due to fetal akinesia manifest across a broad spectrum of diseases, ranging from mild distal arthrogryposis to lethal fetal akinesia deformation sequence. We hereby present a series of 26 fetuses displaying severe MCC phenotypes from 18 families and describe detailed prenatal ultrasound findings, postmortem clinical evaluations, and genetic investigations. Most common prenatal findings were abnormal facial profile (65%), central nervous system abnormalities (62%), polyhydramnios (50%), increased nuchal translucency (50%), and fetal hydrops (35%). Postmortem examinations unveiled additional anomalies including facial dysmorphisms, dysplastic skeletal changes, ichthyosis, multiple pterygia, and myopathy, allowing preliminary diagnosis of particular Mendelian disorders in multiple patients. Evaluation of the parents revealed maternal grip myotonia in one family. By exome sequencing and targeted testing, we identified causative variants in ACTC1, CHST14, COG6, DMPK, DOK7, HSPG2, KLHL7, KLHL40, KIAA1109, NEB, PSAT1, RAPSN, USP14, and WASHC5 in 15 families, and one patient with a plausible diagnosis associated with biallelic NEB variants. Three patients received a dual diagnosis. Pathogenic alterations in newly discovered genes or in previously known genes recently linked to new MCC phenotypes were observed in 44% of the cohort. Our results provide new insights into the clinical and molecular landscape of lethal MCC phenotypes.

Severe neuromuscular forms of glycogen storage disease type IV: Histological, clinical, biochemical, and molecular findings in a large French case series.

Glycogen storage disease type IV (GSD IV), also called Andersen disease, or amylopectinosis, is a highly heterogeneous autosomal recessive disorder caused by a glycogen branching enzyme (GBE, 1,4-alpha-glucan branching enzyme) deficiency secondary to pathogenic variants on GBE1 gene. The incidence is evaluated to 1:600 000 to 1:800 000 of live births. GBE deficiency leads to an excessive deposition of structurally abnormal, amylopectin-like glycogen in affected tissues (liver, skeletal muscle, heart, nervous system, etc.). Diagnosis is often guided by histological findings and confirmed by GBE activity deficiency and molecular studies. Severe neuromuscular forms of GSD IV are very rare and of disastrous prognosis. Identification and characterization of these forms are important for genetic counseling for further pregnancies. Here we describe clinical, histological, enzymatic, and molecular findings of 10 cases from 8 families, the largest case series reported so far, of severe neuromuscular forms of GSD IV along with a literature review. Main antenatal features are: fetal akinesia deformation sequence or arthrogryposis/joint contractures often associated with muscle atrophy, decreased fetal movement, cystic hygroma, and/or hydrops fetalis. If pregnancy is carried to term, the main clinical features observed at birth are severe hypotonia and/or muscle atrophy, with the need for mechanical ventilation, cardiomyopathy, retrognathism, and arthrogryposis. All our patients were stillborn or died within 1 month of life. In addition, we identified five novel GBE1 variants.

Mutation In Fkbp10 Gene Cause Bruck Syndrome 1 (Brks1) In A Pakistani Family Of Pashtun Origin.

BACKGROUND: Bruck syndrome or BRKS1 is an extremely rare condition characterized by the onset of fractures in infancy, joint contractures, short stature, severe limb deformity, and progressive scoliosis. Less than fifty cases of BRKS1 have been reported so far. Here, we report Bruck syndrome 1 in two siblings who belong to a consanguineous Pashtun family living in Karachi. Our first case is a seven years old boy who presented with recurrent fractures, lower limb deformity, and unable to walk. He had markedly reduced bone mineral density (BMD) and a normal bone profile. The other sibling presented at one week of age with arthrogryposis multiplex congenita, post-axial polydactyly of both feet and spontaneous fracture of the right proximal femur. Genetic testing of our cases was performed in which genomic DNA was enriched for targeted regions using the hybridization-based protocol, and DNA sequencing was done using Illumina technology; both cases were found homozygous for pathogenic variant c.344G>A (p.Arg115Gln) in FKBP10 gene leading to the diagnosis of BRKS1. FKBP10 gene mutation has been reported earlier in association with BRKS1, but in our case report, we have reported the first case of BRKS1, particularly in the Pakistani population of Pashtun ethnicity. We have reported post-axial polydactyly of both feet and spina bifida for the first time in association with FKBP10 mutation. In addition, the skeletal survey of patients with BRKS 1 is elaborated in detail in this report.

Bi-allelic loss-of-function variants in KIF21A cause severe fetal akinesia with arthrogryposis multiplex.

BACKGROUND: Fetal akinesia (FA) results in variable clinical presentations and has been associated with more than 166 different disease loci. However, the underlying molecular cause remains unclear in many individuals. We aimed to further define the set of genes involved. METHODS: We performed in-depth clinical characterisation and exome sequencing on a cohort of 23 FA index cases sharing arthrogryposis as a common feature. RESULTS: We identified likely pathogenic or pathogenic variants in 12 different established disease genes explaining the disease phenotype in 13 index cases and report 12 novel variants. In the unsolved families, a search for recessive-type variants affecting the same gene was performed; and in five affected fetuses of two unrelated families, a homozygous loss-of-function variant in the kinesin family member 21A gene (KIF21A) was found. CONCLUSION: Our study underlines the broad locus heterogeneity of FA with well-established and atypical genotype-phenotype associations. We describe KIF21A as a new factor implicated in the pathogenesis of severe neurogenic FA sequence with arthrogryposis of multiple joints, pulmonary hypoplasia and facial dysmorphisms. This hypothesis is further corroborated by a recent report on overlapping phenotypes observed in Kif21a null piglets.

A lethal and rare cause of arthrogryposis: Glyt1 encephalopathy.

Glycine encephalopathy with normal serum glycine (MIM #617301), also known as GLYT1 encephalopathy, is an extremely rare disorder caused by biallelic variants in SLC6A9 and characterised by facial dysmorphic features, skeletal findings including contractures, knee hyperextension, and joint dislocations and seizures. To date, only ten patients from five families have been reported and only two of them could survive until childhood. In this study, we report on a consanguineous Turkish couple with a history of six pregnancies with three habitual abortions and three postpartum exitus. While in three pregnancies the babies were born prematurely at 32nd gestational week by emergency ceserean section due to hydrops and fetal distress, the other pregnancy was medically terminated at 16th gestational week due to absent fetal heart activity. The product of all these three pregnancies exhibited similar phenotype including short neck, thoracic kyphosis, hypertrichosis, joint contractures and dislocations, hypertonia, knee hyperextension and facial dysmorphic features. Trio exome sequencing was performed prenatally during the last pregnancy and a novel VUS variant in SLC6A9 and a likely pathogenic variant in MTOR gene were detected. DNA isolation was performed from frozen muscle and adrenal tissue of previously autopsied fetuses with similar clinical features, and the same variants were confirmed in both of them. Our data suggest that SLC6A9 and MTOR variants may be responsible for this extremely lethal phenotype in this family.

PIEZO2-related distal arthrogryposis type 5: Longitudinal follow-up of a three-generation family broadens phenotypic spectrum, complications, and health surveillance recommendations for this patient group.

Arthrogryposis is a heterogenous condition with a wide variety of etiological causes. It has been subdivided clinically based on the presence of additional features. Dominant gain of function (GoF) pathogenic variants in PIEZO2 have been associated with several forms of arthrogryposis. Previous reports have focused on diagnosis and clinical features. We report a three-generation family with four affected individuals with a known pathogenic GoF change p.(Glu2727del) in PIEZO2. All family members presented at birth with distal arthrogryposis and ophthalmoplegia but have varied in their subsequent clinical course with differences in mobility and joint restriction. In the longer term, other features have presented including dysphagia, back pain and spinal stenosis-like symptoms, raised intraocular pressure, and progressive restrictive lung disease. As far as we know, this is the first report detailing the longitudinal follow-up of a three-generation family which highlights potential long-term complications in patients with PIEZO2-related arthrogryposis. We present this family to demonstrate the importance of long-term follow-up for the clinical management of this group of patients.

Phenotypic spectrum and genomics of undiagnosed arthrogryposis multiplex congenita.

BACKGROUND: Arthrogryposis multiplex congenita (AMC) is characterised by congenital joint contractures in two or more body areas. AMC exhibits wide phenotypic and genetic heterogeneity. Our goals were to improve the genetic diagnosis rates of AMC, to evaluate the added value of whole exome sequencing (WES) compared with targeted exome sequencing (TES) and to identify new genes in 315 unrelated undiagnosed AMC families. METHODS: Several genomic approaches were used including genetic mapping of disease loci in multiplex or consanguineous families, TES then WES. Sanger sequencing was performed to identify or validate variants. RESULTS: We achieved disease gene identification in 52.7% of AMC index patients including nine recently identified genes (CNTNAP1, MAGEL2, ADGRG6, ADCY6, GLDN, LGI4, LMOD3, UNC50 and SCN1A). Moreover, we identified pathogenic variants in ASXL3 and STAC3 expanding the phenotypes associated with these genes. The most frequent cause of AMC was a primary involvement of skeletal muscle (40%) followed by brain (22%). The most frequent mode of inheritance is autosomal recessive (66.3% of patients). In sporadic patients born to non-consanguineous parents (n=60), de novo dominant autosomal or X linked variants were observed in 30 of them (50%). CONCLUSION: New genes recently identified in AMC represent 21% of causing genes in our cohort. A high proportion of de novo variants were observed indicating that this mechanism plays a prominent part in this developmental disease. Our data showed the added value of WES when compared with TES due to the larger clinical spectrum of some disease genes than initially described and the identification of novel genes.

Models of Distal Arthrogryposis and Lethal Congenital Contracture Syndrome.

Distal arthrogryposis and lethal congenital contracture syndromes describe a broad group of disorders that share congenital limb contractures in common. While skeletal muscle sarcomeric genes comprise many of the first genes identified for Distal Arthrogyposis, other mechanisms of disease have been demonstrated, including key effects on peripheral nerve function. While Distal Arthrogryposis and Lethal Congenital Contracture Syndromes display superficial similarities in phenotype, the underlying mechanisms for these conditions are diverse but overlapping. In this review, we discuss the important insights gained into these human genetic diseases resulting from in vitro molecular studies and in vivo models in fruit fly, zebrafish, and mice.

Homozygous variant in MADD, encoding a Rab guanine nucleotide exchange factor, results in pleiotropic effects and a multisystemic disorder.

Rab proteins coordinate inter-organellar vesicle-mediated transport, facilitating intracellular communication, protein recycling, and signaling processes. Dysfunction of Rab proteins or their direct interactors leads to a wide range of diseases with diverse manifestations. We describe seven individuals from four consanguineous Arab Muslim families with an infantile-lethal syndrome, including failure to thrive (FTT), chronic diarrhea, neonatal respiratory distress, variable pituitary dysfunction, and distal arthrogryposis. Exome sequencing analysis in the independent families, followed by an internal gene-matching process using a local exome database, identified a homozygous splice-site variant in MADD (c.2816 + 1 G > A) on a common haplotype. The variant segregated with the disease in all available family members. Determination of cDNA sequence verified single exon skipping, resulting in an out-of-frame deletion. MADD encodes a Rab guanine nucleotide exchange factor (GEF), which activates RAB3 and RAB27A/27B and is thus a crucial regulator of neuromuscular junctions and endocrine secretory granule release. Moreover, MADD protects cells from caspase-mediated TNF-α-induced apoptosis. The combined roles of MADD and its downstream effectors correlate with the phenotypic spectrum of disease, and call for additional studies to confirm the pathogenic mechanism and to investigate possible therapeutic avenues through modulation of TNF-α signaling.

The mystery of monozygotic twinning II: What can monozygotic twinning tell us about Amyoplasia from a review of the various mechanisms and types of monozygotic twinning?

Monozygotic (MZ) twins ("identical twins") are essentially unique to human beings. Why and how they arise is not known. This article reviews the possible different types of MZ twinning recognized in the previous article on twins and arthrogryposis. There appear to be at least three subgroups of MZ twinning: spontaneous, familial, and those related to artificial reproductive technologies. Each is likely to have different etiologies and different secondary findings. Spontaneous MZ twinning may relate to "overripe ova." Amyoplasia, a specific nongenetic form of arthrogryposis, appears to occur in spontaneous MZ twinning and may be related to twin-twin transfusion.

The mystery of monozygotic twinning I: What can Amyoplasia tell us about monozygotic twinning and the possible role of twin-twin transfusion?

Amyoplasia is a very specific, nongenetic clinically recognizable form of arthrogryposis, representing about one-third of individuals with arthrogryposis surviving the newborn period. There is a markedly increased number of individuals with Amyoplasia who are one of monozygotic (MZ) twins, with the other twin being normal. Thus, it would appear that Amyoplasia is definitely associated with and may be caused by an MZ twinning event. The twin-twin transfusion seen in MZ twins could play an etiologic role in producing Amyoplasia. In this article, Amyoplasia twinning is compared to twinning in other forms of arthrogryposis. The accompanying paper examines various types of MZ twinning (Hall, 2021). Amyoplasia is primarily associated with spontaneous MZ twinning.

Deformations associated with arthrogryposis.

Fetal movement is essential to normal human development. If the fetus does not move for whatever reason, then multiple organs and organ systems develop secondary and tertiary effects not normally present. Most of these are deformations with secondary structural damage.

Fetal early motor neuron disruption and prenatal molecular diagnosis in a severe BICD2-opathy.

BICD2 (BICD Cargo Adaptor 2, MIM*609797) mutations are associated with severe prenatal-onset forms of spinal muscular atrophy, lower extremity-predominant 2B (SMALED2B MIM 618291) or milder forms with childhood-onset (SMALED2A MIM 615290). Etiopathogenesis is not fully clarified and a wide spectrum of phenotypic presentations is reported, ranging from extreme prenatal forms with adverse outcome, to slow progressive late-onset forms. We report a fetus at 22 gestational weeks with evidence of Arthrogryposis Multiplex Congenita on ultrasound, presenting with fixed extended lower limbs and flexed upper limbs, bilateral clubfoot and absent fetal movements. A trio-based prenatal Exome Sequencing was performed, disclosing a de novo heterozygous pathogenic in frame deletion (NM_015250.3: c.1636_1638delAAT; p.Asn546del) in BICD2. After pregnancy termination, quantitative analysis on NeuN immunostained spinal cord sections of the ventral horns, revealed that neuronal density was markedly reduced compared to the one of an age-matched normal fetus and an age-matched type-I Spinal Muscular Atrophy sample, used as a comparative model. The present case, the first prenatally diagnosed and neuropathologically characterized, showed an early motor neuron loss in SMALED2B, providing further insight into the pathological basis of BICD2-opathies.

New evidence for secondary axonal degeneration in demyelinating neuropathies.

Development of peripheral nervous system (PNS) myelin involves a coordinated series of events between growing axons and the Schwann cell (SC) progenitors that will eventually ensheath them. Myelin sheaths have evolved out of necessity to maintain rapid impulse propagation while accounting for body space constraints. However, myelinating SCs perform additional critical functions that are required to preserve axonal integrity including mitigating energy consumption by establishing the nodal architecture, regulating axon caliber by organizing axonal cytoskeleton networks, providing trophic and potentially metabolic support, possibly supplying genetic translation materials and protecting axons from toxic insults. The intermediate steps between the loss of these functions and the initiation of axon degeneration are unknown but the importance of these processes provides insightful clues. Prevalent demyelinating diseases of the PNS include the inherited neuropathies Charcot-Marie-Tooth Disease, Type 1 (CMT1) and Hereditary Neuropathy with Liability to Pressure Palsies (HNPP) and the inflammatory diseases Acute Inflammatory Demyelinating Polyneuropathy (AIDP) and Chronic Inflammatory Demyelinating Polyneuropathy (CIDP). Secondary axon degeneration is a common feature of demyelinating neuropathies and this process is often correlated with clinical deficits and long-lasting disability in patients. There is abundant electrophysiological and histological evidence for secondary axon degeneration in patients and rodent models of PNS demyelinating diseases. Fully understanding the involvement of secondary axon degeneration in these diseases is essential for expanding our knowledge of disease pathogenesis and prognosis, which will be essential for developing novel therapeutic strategies.

GLYT1 encephalopathy: Further delineation of disease phenotype and discussion of pathophysiological mechanisms.

GLYT1 encephalopathy is a form of glycine encephalopathy caused by disturbance of glycine transport. The phenotypic spectrum of the disease has not yet been completely described, as only four unrelated families with the disorder have been reported to date. Common features of affected patients include neonatal hypotonia, respiratory failure, encephalopathy, myoclonic jerks, dysmorphic features, and musculoeskeletal anomalies. All reported affected patients harbor biallelic genetic variants in SLC6A9. SNP array together with Sanger sequencing were performed in a newborn with arthrogryposis and severe neurological impairment. The novel genetic variant c.997delC in SLC6A9 was detected in homozygous state in the patient. At protein level, the predicted change is p.(Arg333Alafs*3), which most probably results in a loss of protein function. The variant cosegregated with the disease in the family. A subsequent pregnancy with ultrasound anomalies was also affected. The proband presented the core phenotypic features of GLYT1 encephalopathy, but also a burst suppression pattern on the electroencephalogram, a clinical feature not previously associated with the disorder. Our results suggest that the appearance of this pattern correlates with higher cerebrospinal fluid glycine levels and cerebrospinal fluid/plasma glycine ratios. A detailed discussion on the possible pathophysiological mechanisms of the disorder is also provided.

COFS type 3 in an Indian family with antenatally detected arthrogryposis.

Fetal akinesia and contractures can be caused by mutations in various genes that lead to overlapping phenotypes with contractures, rocker bottom feet, cerebellar hypoplasia, ventriculomegaly, growth retardation, pulmonary hypoplasia, cystic hygroma and cleft palate in various combinations. Cerebro-oculo-facio-skeletal (COFS) syndrome is a condition resulting from defects in DNA repair pathway, and genes involved include ERCC1 (COFS), ERCC2 (XPD), ERCC5(XPG), and ERCC6 (CSB). It is a severe disorder presenting in fetal or neonatal period with microcephaly, arthrogryposis, prominent nose, and kyphoscoliosis, and leads to early death in childhood. We report a baby with antenatally identified arthrogryposis in which the homozygous pathogenic variant in exon 8 was identified in ERCC5 gene, by targeted next generation sequencing. This was predicted to cause premature chain termination in the protein. ERCC5 gene is mainly implicated in xeroderma pigmentosum, sometimes in COFS syndrome.