Developmental dysplasia of the hip caused by homozygous TRIM33 pathogenic variant affecting downstream BMP pathway.

BACKGROUND: Developmental dysplasia of the hip (DDH), formerly termed congenital dislocation of the hip, is the most common congenital disease of the musculoskeletal system in newborns. While familial predilection to DDH has been well documented, the molecular genetics/pathways of this common disorder are poorly understood. METHODS: Linkage analysis and whole exome sequencing; real-time PCR studies of skin fibroblasts. RESULTS: Consanguineous Bedouin kindred presented with DDH with apparent autosomal recessive heredity. Linkage analysis and whole exome sequencing delineated a single 3.2 Mbp disease-associated chromosome 1 locus (maximal multipoint Logarithm of the Odds score 2.3), containing a single homozygous variant with a relevant expression pattern: addition of threonine in TRIM33 (NM_015906.4); c.1648_1650dup. TRIM33 encodes a protein that acts both in the TGF-ß and the BMP pathways; however, it has been mostly studied regarding its function in the TGF-ß pathway. Since BMPs are known to act in bone formation, we focused on the BMP pathway, in which TRIM33 functions as a transcription factor, both an activator and repressor. Skin fibroblasts of two affected girls and a heterozygous TRIM33 variant carrier were assayed through reverse-transcription PCR for expression of genes known to be downstream of TRIM33 in the BMP pathway: fibroblasts of affected individuals showed significantly reduced expression of DLX5, significantly increased expression of BGLAP, increased expression of ALPL and no change in expression of RUNX2 or of TRIM33 itself. CONCLUSIONS: DDH can be caused by a biallelic variant in TRIM33, affecting the BMP pathway.

A POT1 Founder Variant Associated with Early Onset Recurrent Melanoma and Various Solid Malignancies.

POT1 (Protection of Telomeres 1) is a key component of the six-membered shelterin complex that plays a critical role in telomere protection and length regulation. Germline variants in the POT1 gene have been implicated in predisposition to cancer, primarily to melanoma and chronic lymphocytic leukemia (CLL). We report the identification of POT1 p.(I78T), previously ranked with conflicting interpretations of pathogenicity, as a founder pathogenic variant among Ashkenazi Jews (AJs) and describe its unique clinical landscape. A directed database search was conducted for individuals referred for genetic counselling from 2018 to 2023. Demographic, clinical, genetic, and pathological data were collected and analyzed. Eleven carriers, 25 to 67 years old, from ten apparently unrelated families were identified. Carriers had a total of 30 primary malignancies (range 1-6); nine carriers (82%) had recurrent melanoma between the ages of 25 and 63 years, three carriers (27%) had desmoid tumors, three (27%) had papillary thyroid cancer (PTC), and five women (63% of female carriers) had breast cancer between the ages of 44 and 67 years. Additional tumors included CLL; sarcomas; endocrine tumors; prostate, urinary, and colorectal cancers; and colonic polyps. A review of a local exome database yielded an allelic frequency of the variant of 0.06% among all ethnicities and of 0.25% in AJs. A shared haplotype was found in all carriers tested. POT1 p.(I78T) is a founder disease-causing variant associated with early-onset melanoma and additional various solid malignancies with a high tumor burden. We advocate testing for this variant in high-risk patients of AJ descent. The inclusion of POT1 in germline panels for various types of cancer is warranted.

Novel phenotype associated with homozygous likely pathogenic variant in the POP1 gene.

The biallelic variants of the POP1 gene are associated with the anauxetic dysplasia (AAD OMIM 607095), a rare skeletal dysplasia, characterized by prenatal rhizomelic shortening of limbs and generalized joint hypermobility. Affected individuals usually have normal neurodevelopmental milestones. Here we present three cases from the same family with likely pathogenic homozygous POP1 variant and a completely novel phenotype: a girl with global developmental delay and autism, microcephaly, peculiar dysmorphic features and multiple congenital anomalies. Two subsequent pregnancies were terminated due to multiple congenital malformations. Fetal DNA samples revealed the same homozygous variant in the POP1 gene. Expression of the RMRP was reduced in the proband compared with control and slightly reduced in both heterozygous parents, carriers for this variant. To our knowledge, this is the first report of this new phenotype, associated with a novel likely pathogenic variant in POP1. Our findings expand the phenotypic spectrum of POP1-related disorders.

A role of BPTF in viral oncogenicity delineated through studies of heritable Kaposi sarcoma.

Kaposi sarcoma (KS), caused by Herpesvirus-8 (HHV-8; KSHV), shows sporadic, endemic, and epidemic forms. While familial clustering of KS was previously recorded, the molecular basis of hereditary predilection to KS remains largely unknown. We demonstrate through genetic studies that a dominantly inherited missense mutation in BPTF segregates with a phenotype of classical KS in multiple immunocompetent individuals in two families. Using an rKSHV.219-infected CRISPR/cas9-model, we show that BPTFI2012T mutant cells exhibit higher latent-to-lytic ratio, decreased virion production, increased LANA staining, and latent phenotype in viral transcriptomics. RNA-sequencing demonstrated that KSHV infection dysregulated oncogenic-like response and P53 pathways, MAPK cascade, and blood vessel development pathways, consistent with KS. BPTFI2012T also enriched pathways of viral genome regulation and replication, immune response, and chemotaxis, including downregulation of IFI16, SHFL HLAs, TGFB1, and HSPA5, all previously associated with KSHV infection and tumorigenesis. Many of the differentially expressed genes are regulated by Rel-NF-κB, which regulates immune processes, cell survival, and proliferation and is pivotal to oncogenesis. We thus demonstrate BPTF mutation-mediated monogenic hereditary predilection of KSHV virus-induced oncogenesis, and suggest BPTF as a drug target.

[MULTIPLE CAFÉ-AU-LAIT MACULES AND INTERTRIGINOUS FRECKLING: BEYOND THE RASOPATHIES].

INTRODUCTION: Piebaldism is the dominantly inherited skin disorder clinically characterized by congenital stable and well circumscribed patches of leukoderma (depigmented skin) of ventral distribution, involving central forehead, frontal chest and abdomen and central portion of limbs, and by localized poliosis (white hair). Inherited or de novo mutations in proto-oncogene KIT, encoding the transmembrane tyrosine kinase receptor c-kit, underly the majority of piebaldism cases. Piebaldism is a disorder characterized by incomplete penetrance and variable expressivity.

De-novo "germline second hit" loss-of-heterozygosity RBP3 deletion mutation causing recessive high myopia.

Knudson's "two hit" hypothesis, mostly associated with cancer, relates to a primary heterozygous germline mutation complemented by a somatic mutation in the second allele. When the somatic "second hit" is a deletion mutation, the heterozygosity due to the first hit is lost ("loss of heterozygosity"). As the rate of germline mutations is almost two orders of magnitude lower than that of somatic mutations, de-novo germline mutations causing autosomal recessive diseases in carriers of inherited heterozygous mutations are not common. We delineate a case of high myopia presenting at infancy with mild diminution of retinal responses. Exome sequencing identified a paternally inherited apparently homozygous missense mutation in RBP3. Chromosomal microarrays delineated a de-novo germline heterozygous deletion encompassing RBP3, verified through revision of WES data. Thus, we demonstrate an inherited RBP3 missense mutation complemented by a de-novo germline RBP3 deletion, causing loss of heterozygosity of the inherited mutation. We describe a novel RBP3 missense mutation, report the first isolated RBP3 deletion, and demonstrate infantile high myopia as an initial presentation of RBP3 disease. Notably, we highlight de-novo germline deletion mutations causing "loss of heterozygosity" of inherited heterozygous mutations, culminating in autosomal recessive diseases, and discuss the scarce literature.

Looking for the skeleton in the closet-rare genetic diagnoses in patients with diabetes and skeletal manifestations.

AIMS: The precision medicine approach of tailoring treatment to the individual characteristics of each patient has been a great success in monogenic diabetes subtypes, highlighting the importance of accurate clinical and genetic diagnoses of the type of diabetes. We sought to describe three unique cases of childhood-onset diabetes in whom skeletal manifestations led to the revelation of a rare type of diabetes. METHODS : Case-scenarios and review of the literature. RESULTS: Case 1: A homozygous mutation in TRMT10A, a tRNA methyltransferase, was identified in a 15-year-old boy with new-onset diabetes, developmental delay, microcephaly, dysmorphism, short stature and central obesity. The progressive apoptosis of pancreatic beta cells required insulin replacement therapy, with increased demand due to an unfavorable body composition. Case 2: Congenital generalized lipodystrophy type 1 was suspected in an adolescent male with an acromegaloid facial appearance, muscular habitus, and diabetes who presented with a pathological fracture in a cystic bone lesion. A homozygous mutation in AGPAT2, an acyl transferase which mediates the formation of phospholipid precursors, was identified. Leptin replacement therapy initiation resulted in a remarkable improvement in clinical parameters. Case 3: A 12-year-old boy with progressive lower limb weakness and pain was diagnosed with diabetic ketoacidosis. Diffuse diaphyseal osteosclerosis compatible with the diagnosis of Camurati-Engelmann disease and a heterozygous mutation in TGFß1 were identified. Preservation of euglycemia by insulin replacement relieved pain, suggesting that the diabetic milieu may have augmented TGFß1 overexpression. CONCLUSION: Unraveling the precise genetic cause for the clinical manifestations led to the prediction of phenotypic manifestations, and enhanced the clinical outcomes.

Novel MTMR2 mutation causing severe Charcot-Marie-Tooth type 4B1 disease: a case report.

Mutations in myotubularin-related protein 2 (MTMR2) were shown to underlie Charcot-Marie-Tooth type 4B1 (CMT4B1) disease, a rare autosomal recessive demyelinating neuropathy, characterized by severe early-onset motor and sensory neuropathy. We describe three siblings of consanguineous kindred presenting with hypotonia, reduced muscle tone, action tremor, dysmetria, areflexia, and skeletal deformities, consistent with a diagnosis of CMT. Whole-exome sequencing identified a novel homozygous c.336_337 insertion mutation in MTMR2, resulting in a frameshift and putative truncated protein. In this concise report, we discuss the clinical presentation of this rare disease and support the limited number of observations regarding the pathogenesis of MTMR2-related neuropathies.

A homozygous missense variant of SUMF1 in the Bedouin population extends the clinical spectrum in ultrarare neonatal multiple sulfatase deficiency.

BACKGROUND: Multiple sulfatase deficiency (MSD, MIM #272200) is an ultrarare congenital disorder caused by SUMF1 mutation and often misdiagnosed due to its complex clinical presentation. Impeded by a lack of natural history, knowledge gained from individual case studies forms the source for a reliable diagnosis and consultation of patients and parents. METHODS: We collected clinical records as well as genetic and metabolic test results from two MSD patients. The functional properties of a novel SUMF1 variant were analyzed after expression in a cell culture model. RESULTS: We report on two MSD patients-the first neonatal type reported in Israel-both presenting with this most severe manifestation of MSD. Our patients showed uniform clinical symptoms with persistent pulmonary hypertension, hypotonia, and dysmorphism at birth. Both patients were homozygous for the same novel SUMF1 mutation (c.1043C>T, p.A348V). Functional analysis revealed that the SUMF1-encoded variant of formylglycine-generating enzyme is highly instable and lacks catalytic function. CONCLUSION: The obtained results confirm genotype-phenotype correlation in MSD, expand the spectrum of clinical presentation and are relevant for diagnosis including the extremely rare neonatal severe type of MSD.

SCAPER localizes to primary cilia and its mutation affects cilia length, causing Bardet-Biedl syndrome.

Studies of ciliopathies have served in elucidating much of our knowledge of structure and function of primary cilia. We report humans with Bardet-Biedl syndrome who display intellectual disability, retinitis pigmentosa, obesity, short stature and brachydactyly, stemming from a homozyogous truncation mutation in SCAPER, a gene previously associated with mitotic progression. Our findings, based on linkage analysis and exome sequencing studies of two remotely related large consanguineous families, are in line with recent reports of SCAPER variants associated with intellectual disability and retinitis pigmentosa. Using immuno-fluorescence and live cell imaging in NIH/3T3 fibroblasts and SH-SY5Y neuroblastoma cell lines over-expressing SCAPER, we demonstrate that both wild type and mutant SCAPER are expressed in primary cilia and co-localize with tubulin, forming bundles of microtubules. While wild type SCAPER was rarely localized along the ciliary axoneme and basal body, the aberrant protein remained sequestered to the cilia, mostly at the ciliary tip. Notably, longer cilia were demonstrated both in human affected fibroblasts compared to controls, as well as in NIH/3T3 cells transfected with mutant versus wildtype SCAPER. As SCAPER expression is known to peak at late G1 and S phase, overlapping the timing of ciliary resorption, our data suggest a possible role of SCAPER in ciliary dynamics and disassembly, also affecting microtubule-related mitotic progression. Thus, we outline a human ciliopathy syndrome and demonstrate that it is caused by a mutation in SCAPER, affecting primary cilia.

Mutations in the microtubule-associated protein MAP11 (C7orf43) cause microcephaly in humans and zebrafish.

Microtubule associated protein 11 (MAP11, previously termed C7orf43) encodes a highly conserved protein whose function is unknown. Through genome-wide linkage analysis combined with whole exome sequencing, we demonstrate that human autosomal recessive primary microcephaly is caused by a truncating mutation in MAP11. Moreover, homozygous MAP11-orthologue CRISPR/Cas9 knock-out zebrafish presented with microcephaly and decreased neuronal proliferation, recapitulating the human phenotype. We demonstrate that MAP11 is ubiquitously transcribed with high levels in brain and cerebellum. Immunofluorescence and co-immunoprecipitation studies in SH-SY5Y cells showed that MAP11 associates with mitotic spindles, co-localizing and physically associating with α-tubulin during mitosis. MAP11 expression precedes α-tubulin in gap formation of cell abscission at the midbody and is co-localized with PLK1, a key regulator of cytokinesis, at the edges of microtubule extensions of daughter cells post cytokinesis abscission, implicating a role in mitotic spindle dynamics and in regulation of cell abscission during cytokinesis. Finally, lentiviral-mediated silencing of MAP11 diminished SH-SY5Y cell viability, reducing proliferation rather than affecting apoptosis. Thus, MAP11 encodes a microtubule-associated protein that plays a role in spindle dynamics and cell division, in which mutations cause microcephaly in humans and zebrafish.

Malignant Peritoneal Mesothelioma in an Infant With Familial ATM Mutations.

Ataxia-telangiectasia (A-T), an autosomal recessive disorder characterized by progressive neurologic dysfunction, oculocutaneous telangiectasia, immunodeficiency, and cancer susceptibility, is caused by mutations in the ATM gene. A previous study of 4 A-T patients identified 2 rare homozygous missense mutations residing on the same allele of the ATM gene: c.1514T>C and c.1547T>C, which were shown to decrease ATM levels and increase T-cell acute lymphoblastic leukemia predisposition. We studied 5 patients from 2 consanguineous Bedouin families of the same tribe, presenting with A-T. Whole-exome sequencing data identified the 2 aforementioned mutations in ATM, which segregated within all family members as expected of autosomal recessive heredity. Interestingly, one individual was diagnosed with malignant peritoneal mesothelioma (MPM), an extremely rare neoplasm in pediatric patients. Here, we describe a case of a 4-month-old infant homozygous for the 2 ATM mutations, who developed MPM and died by the age of 2 years. To the best of our knowledge, this is the first case of peritoneal mesothelioma in an infant bearing ATM mutations, and one of the youngest pediatric mesotheliomas described. Thus, the risk of MPM might be considered in the follow-up of A-T patients, and ATM mutations sought in cases of early-onset MPM.

A novel homozygous SLC25A1 mutation with impaired mitochondrial complex V: Possible phenotypic expansion.

SLC25A1 mutations are associated with combined D,L-2-hydroxyglutaric aciduria (DL- 2HGA; OMIM #615182), characterized by muscular hypotonia, severe neurodevelopmental dysfunction and intractable seizures. SLC25A1 encodes the mitochondrial citrate carrier (CIC), which mediates efflux of the mitochondrial tricarboxylic acid (TCA) cycle intermediates citrate and isocitrate in exchange for cytosolic malate. Only a single family with an SLC25A1 mutation has been described in which mitochondrial respiratory chain dysfunction was documented, specifically in complex IV. Five infants of two consanguineous Bedouin families of the same tribe presented with small head circumference and neonatal-onset encephalopathy with severe muscular weakness, intractable seizures, respiratory distress, and lack of psychomotor development culminating in early death. Ventricular septal defects (VSD) were demonstrated in three patients. Blood and CSF lactate were elevated with normal levels of plasma amino acids and free carnitine and increased 2-OH-glutaric acid urinary exertion. EEG was compatible with white matter disorder. Brain MRI revealed ventriculomegaly, thin corpus callosum with increased lactate peak on spectroscopy. Mitochondrial complex V deficiency was demonstrated in skeletal muscle biopsy of one infant. Homozygosity mapping and sequencing ruled out homozygosity of affected individuals in all known complex V-associated genes. Whole exome sequencing identified a novel homozygous SLC25A1 c.713A>G (p.Asn238Ser) mutation, segregating as expected in the affected kindred and not found in 220 control alleles. Thus, SLC25A1 mutations might be associated with mitochondrial complex V deficiency and should be considered in the differential diagnosis of mitochondrial respiratory chain defects.

PAX7 mutation in a syndrome of failure to thrive, hypotonia, and global neurodevelopmental delay.

PAX7 encodes a transcription factor essential in neural crest formation, myogenesis, and pituitary lineage specification. Pax7 null mice fail to thrive and exhibit muscle weakness, dying within 3 weeks. We describe a human autosomal-recessive syndrome, with failure to thrive, severe global developmental delay, microcephaly, axial hypotonia, pyramidal signs, dystonic postures, seizures, irritability, and self-mutilation. Aside from low blood carnitine levels, biochemical and metabolic screen was normal, with growth hormone deficiency in one patient. Electromyography was normal, with no specific findings in brain MRI/MRS yet nondemonstrable neuropituitary, a finding of unclear significance. Muscle biopsy showed unaffected overall organization of muscle fibers, yet positive fetal alpha myosin staining, suggesting regeneration. Homozygosity mapping with whole-exome sequencing identified a single disease-associated mutation in PAX7, segregating as expected in the kindred with no homozygosity in 200 ethnically matched controls. Transfection experiments showed that the PAX7 splice-site mutation putatively causes nonsense-mediated mRNA decay affecting onlyPAX7 isoform 3. This isoform, expressed specifically in brain, skeletal muscle and testes, is the sole Pax7 variant normally found in mice. The human muscle phenotype is in line with that in conditional Pax7 null mutant mice, where initial aberrant histological findings resolve postnatally through muscle regeneration.

Mutations in ARMC9, which Encodes a Basal Body Protein, Cause Joubert Syndrome in Humans and Ciliopathy Phenotypes in Zebrafish.

Joubert syndrome (JS) is a recessive neurodevelopmental disorder characterized by hypotonia, ataxia, abnormal eye movements, and variable cognitive impairment. It is defined by a distinctive brain malformation known as the "molar tooth sign" on axial MRI. Subsets of affected individuals have malformations such as coloboma, polydactyly, and encephalocele, as well as progressive retinal dystrophy, fibrocystic kidney disease, and liver fibrosis. More than 35 genes have been associated with JS, but in a subset of families the genetic cause remains unknown. All of the gene products localize in and around the primary cilium, making JS a canonical ciliopathy. Ciliopathies are unified by their overlapping clinical features and underlying mechanisms involving ciliary dysfunction. In this work, we identify biallelic rare, predicted-deleterious ARMC9 variants (stop-gain, missense, splice-site, and single-exon deletion) in 11 individuals with JS from 8 families, accounting for approximately 1% of the disorder. The associated phenotypes range from isolated neurological involvement to JS with retinal dystrophy, additional brain abnormalities (e.g., heterotopia, Dandy-Walker malformation), pituitary insufficiency, and/or synpolydactyly. We show that ARMC9 localizes to the basal body of the cilium and is upregulated during ciliogenesis. Typical ciliopathy phenotypes (curved body shape, retinal dystrophy, coloboma, and decreased cilia) in a CRISPR/Cas9-engineered zebrafish mutant model provide additional support for ARMC9 as a ciliopathy-associated gene. Identifying ARMC9 mutations as a cause of JS takes us one step closer to a full genetic understanding of this important disorder and enables future functional work to define the central biological mechanisms underlying JS and other ciliopathies.

Progressive hereditary spastic paraplegia caused by a homozygous KY mutation.

Twelve individuals of consanguineous Bedouin kindred presented with autosomal recessive progressive spastic paraplegia evident as of age 0-24 months, with spasticity of lower limbs, hyperreflexia, toe walking and equinus deformity. Kyphoscolisois was evident in older patients. Most had atrophy of the lateral aspects of the tongue and few had intellectual disability. Nerve conduction velocity, electromyography and head and spinal cord magnetic resonance imaging were normal in tested subjects. Muscle biopsy showed occasional central nuclei and fiber size variability with small angular fibers. Genome-wide linkage analysis identified a 6.7Mbp disease-associated locus on chromosome 3q21.3-3q22.2 (LOD score 9.02; D3S1290). Whole-exome sequencing identified a single homozygous variant within this locus, c.51_52ins(28); p.(V18fs56*) in KY, segregating in the family as expected and not found in 190 Bedouin controls. High KY transcript levels were demonstrated in muscular organs with lower expression in the CNS. The phenotype is reminiscent of kyphoscoliosis seen in Ky null mice. Two recent studies done independently and parallel to ours describe somewhat similar phenotypes in one and two patients with KY mutations. KY encodes a tranglutaminase-like peptidase, which interacts with muscle cytoskeletal proteins and is part of a Z-band protein complex, suggesting the disease mechanism may resemble myofibrillar myopathy. However, the mixed myopathic-neurologic features caused by human and mouse Ky mutations are difficult to explain by loss of KY sarcomere stabilizing function alone. KY transcription in CNS tissues may imply that it also has a role in neuromotor function, in line with the irregularity of neuromuscular junction in Ky null mutant mice.

Novel GUCY2D mutation causes phenotypic variability of Leber congenital amaurosis in a large kindred.

BACKGROUND: Leber congenital amaurosis (LCA) is a severe retinal degenerative disease that manifests as blindness or poor vision in infancy. The purpose of this study was to clinically characterize and identify the cause of disease in a large inbred Bedouin Israeli tribe with LCA. METHODS: Thirty individuals of a single kindred, including eight affected with LCA, were recruited for this study. Patients' clinical data and electroretinography (ERG) findings were collected. Molecular analysis included homozygosity mapping with polymorphic markers and Sanger sequencing of candidate genes. RESULTS: Of the eight affected individuals of the kindred, nystagmus was documented in five subjects and keratoconus in three. Cataract was found in 5 of 16 eyes. Photopic and scotopic ERG performed in 5 patients were extinguished. All affected subjects were nearly blind, their visual acuity ranged between finger counting and uncertain light perception. Assuming autosomal recessive heredity of a founder mutation, studies using polymorphic markers excluded homozygosity of affected individuals at the genomic loci of all previously known genes associated with LCA, except GUCY2D. Sequencing of GUCY2D identified a novel missense mutation (c.2129C>T; p.Ala710Val) resulting in substitution of alanine by valine at position 710 within the protein kinase domain of the retina-specific enzyme guanylate cyclase 1 (GC1) encoded by GUCY2D. Molecular modeling implied that the mutation changes the conformation of the regulatory segment within the kinase styk-domain of GC1 and causes loss of its helical structure, likely inhibiting phosphorylation of threonine residue within this segment, which is needed to activate the catalytic domain of the protein. CONCLUSIONS: This is the first documentation of the p.Ala710Val mutation in GC1 and the second ever described mutation in its protein kinase domain. Our findings enlarge the scope of genetic variability of LCA, highlight the phenotypic heterogeneity found amongst individuals harboring an identical LCA mutation, and possibly provide hope for gene therapy in patients with this congenital blinding disease. As the Bedouin kindred studied originates from Saudi Arabia, the mutation found might be an ancient founder mutation in that large community.

CDC174, a novel component of the exon junction complex whose mutation underlies a syndrome of hypotonia and psychomotor developmental delay.

Siblings of non-consanguineous Jewish-Ethiopian ancestry presented with congenital axial hypotonia, weakness of the abducens nerve, psychomotor developmental delay with brain ventriculomegaly, variable thinning of corpus callosum and cardiac septal defects. Homozygosity mapping identified a single disease-associated locus of 3.5 Mb on chromosome 3. Studies of a Bedouin consanguineous kindred affected with a similar recessive phenotype identified a single disease-associated 18 Mb homozygosity locus encompassing the entire 3.5 Mb locus. Whole exome sequencing demonstrated only two homozygous mutations within a shared identical haplotype of 0.6 Mb, common to both Bedouin and Ethiopian affected individuals, suggesting an ancient common founder. Only one of the mutations segregated as expected in both kindreds and was not found in Bedouin and Jewish-Ethiopian controls: c.1404A>G, p.[*468Trpext*6] in CCDC174. We showed that CCDC174 is ubiquitous, restricted to the cell nucleus and co-localized with EIF4A3. In fact, yeast-two-hybrid assay demonstrated interaction of CCDC174 with EIF4A3, a component of exon junction complex. Knockdown of the CCDC174 ortholog in Xenopus laevis embryos resulted in poor neural fold closure at the neurula stage with later embryonic lethality. Knockdown embryos exhibited a sharp reduction in expression of n-tubulin, a marker for differentiating primary neurons, and of hindbrain markers krox20 and hoxb3. The Xenopus phenotype could be rescued by the human normal, yet not the mutant CCDC174 transcripts. Moreover, overexpression of mutant but not normal CCDC174 in neuroblastoma cells caused rapid apoptosis. In line with the hypotonia phenotype, the CCDC174 mutation caused depletion of RYR1 and marked myopathic changes in skeletal muscle of affected individuals.

A novel GLI3 mutation affecting the zinc finger domain leads to preaxial-postaxial polydactyly-syndactyly complex.

BACKGROUND: Polydactyly is a highly common congenital limb defect. Extra digits may appear as an isolated anomaly or as a part of a syndrome. Mutations in GLI3 have been shown to cause Greig cephalopolysyndactyly, Pallister-Hall syndrome and non-syndromic polydactyly. Genotype-phenotype correlation studies of GLI3 mutations suggest a model by which mutations in the zinc-finger domain (ZFD) of GLI3 likely lead to syndromic polydactyly. Here we describe a rare case of autosomal dominant heterozygous missense mutation in the ZFD of GLI3 leading to a variable polydactyly-syndactyly complex. CASE PRESENTATION: A large Jewish Moroccan family presented with apparently autosomal dominant heredity of bilateral thumb polydactyly in hands and feet combined with post-axial polydactyly type B or type A. Syndactyly was evident in most patients' hands and feet. Apart from head circumference beyond 90th percentile in some of the affected individuals, none had craniofacial dysmorphism. A novel GLI3 c.1802A > G (p.His601Arg) mutation was found in all affected individuals. CONCLUSION: We demonstrate that a mutation in the ZFD domain of GLI3 leads to phenotypic variability, including an isolated limb phenotype. Thus, the variability in phenotypes caused by mutations in this master developmental regulator is more profound than has been previously suggested.

Natural history and clinical manifestations of hyponatremia and hyperchlorhidrosis due to carbonic anhydrase XII deficiency.

INTRODUCTION: We identified patients of Bedouin origin with a mutation in carbonic anhydrase XII (CA XII) leading to hyponatremia due to excessive salt loss via sweat. METHODS: The medical records of patients were reviewed for clinical and laboratory data. RESULTS: A total of 11 subjects were identified; 7 symptomatic patients presented with hyponatremic dehydration in infancy. Screening of the entire kindred identified 4 asymptomatic individuals with elevated sweat chloride. All symptomatic patients had failure to thrive and moderate-severe hyponatremia (106-124 mmol·l(-1)); 6 had hypochloremia (79-94 mmol·l(-1)). All asymptomatic subjects had normal or near-normal serum sodium and chloride concentrations. Both symptomatic and asymptomatic subjects had normal renal functions and normal cortisol response on low-dose ACTH test. All symptomatic patients were treated by dietary salt, which prevents episodes of hyponatremic dehydration and promotes growth. At follow-up, the chief complaints remained heat intolerance, accumulation of salt precipitates on the face and hyperhidrosis. No evidence for chronic renal, respiratory, gastrointestinal or fertility abnormalities was found. CONCLUSION: Recognizing this newly described entity and differentiating it from cystic fibrosis and pseudohypoaldosteronism are important. Patients with CA XII mutations should be followed even after early childhood, especially in hot temperatures and intense physical activity.