Dentofacial manifestations in a child with Jalili syndrome.

Jalili syndrome (JS) (MIM#217080) is a rare autosomal recessive disorder with oculo-dental malformations. The clinical phenotype is characterized by the presence of Cone-Rod Dystrophy (CRD) and Amelogenesis Imperfecta (AI). Genetic mechanism entails a mutation in the CNNM4, a metal transporter gene located on Chromosome 2q11.2. A high fluoride concentration in groundwater has also been identified as an epigenetic factor in this syndrome. JS draws the attention of dentists due to its distinct oral manifestations. To the best of our knowledge, this is the first genetically confirmed pediatric case report from the Indian subcontinent emphasizing the clinical and radiographic features of this condition and its management in a 6-year-old child.

Dimerization of the CNNM extracellular domain.

Cystathionine- ß $$ \beta $$ -synthase (CBS)-pair domain divalent metal cation transport mediators (CNNMs) are an evolutionarily conserved family of magnesium transporters. They mediate magnesium homeostasis directly by transport of Mg2+ ions and indirectly by regulation of the transient receptor potential ion channel subfamily M member 7 (TRPM7). Here, we report the crystal structure of the extracellular domain of tapeworm CNNM4. The domain forms a dimer of immunoglobulin-like (Ig-like) folds with electron density observed for three glycosylation sites. Analytical ultracentrifugation confirms that mutations in the extracellular domain of human CNNM4 prevent its dimerization. An analogous mutation in mouse CNNM2 impairs its activity in a cellular assay of Mg2+ transport.

New insights into the structure and function of CNNM proteins.

Magnesium (Mg2+ ) is the most abundant divalent cation in cells and plays key roles in almost all biological processes. CBS-pair domain divalent metal cation transport mediators (CNNMs) are a newly characterized class of Mg2+ transporters present throughout biology. Originally discovered in bacteria, there are four CNNM proteins in humans, which are involved in divalent cation transport, genetic diseases, and cancer. Eukaryotic CNNMs are composed of four domains: an extracellular domain, a transmembrane domain, a cystathionine-ß-synthase (CBS)-pair domain, and a cyclic nucleotide-binding homology domain. The transmembrane and CBS-pair core are the defining features of CNNM proteins with over 20 000 protein sequences known from over 8000 species. Here, we review the structural and functional studies of eukaryotic and prokaryotic CNNMs that underlie our understanding of their regulation and mechanism of ion transport. Recent structures of prokaryotic CNNMs confirm the transmembrane domain mediates ion transport with the CBS-pair domain likely playing a regulatory role through binding divalent cations. Studies of mammalian CNNMs have identified new binding partners. These advances are driving progress in understanding this deeply conserved and widespread family of ion transporters.

Novel homozygous nonsynonymous variant of CNNM4 gene in a Chinese family with Jalili syndrome.

BACKGROUND: Jalili syndrome (JS) is a rare autosomal-recessive inherited disorder characterized by cone-rod dystrophy and amelogenesis imperfecta. It is often misdiagnosed in clinical practice due to its heterogeneity and rarity. METHODS: Two JS patients from a consanguineous family were included in this study. Detailed ophthalmic examinations were performed. Oral photography was taken. The DNA sample of the proband was sequenced using the customized capture panel, which includes 338 retinal disease genes. Sanger sequencing was performed for validation and segregation. RESULTS: The patients had poor vision, photophobia, and nystagmus from childhood. Fundus examination revealed diffused chorioretinal atrophy with a prominent macular coloboma. OCT showed a deep staphyloma, severely reduced retinal thickness, retinoschisis, loss of photoreceptor layer, and retinal pigment epithelium in the macular region. Amelogenesis imperfecta, dental decay, staining, irregular shapes, and loss of teeth were present. Next-generation sequencing combined with Sanger validation identified a novel homozygous nonsynonymous variant c.598T>C (p.S200P) in CNNM4 gene (NM_020184.3). CONCLUSIONS: We described the clinical features of a Chinese family with JS and identified a novel disease-causing mutation. Our findings broadened the phenotypes and mutation spectrums of JS in Chinese population, as well as are helpful in the diagnosis of this rare disease.

Cone pathway dysfunction in Jalili syndrome due to a novel familial variant of CNNM4 revealed by pupillometry and electrophysiologic investigations.

PURPOSE: To evaluate retinal function in a family presenting with Jalili syndrome due to a previously unreported variant in CNNM4. METHODS: A family of three sisters with a novel CNNM4 variant, c.482 T > C p.(Leu161Pro), and ten visually normal, age-similar controls participated in this study. The subjects underwent detailed dental examinations and comprehensive ophthalmological examinations that included color vision testing, retinal imaging, and electroretinography. Full-field light- and dark-adapted luminance thresholds were obtained, in addition to light- and dark-adapted measures of the pupillary light reflex (PLR; pupil constriction elicited by a flash of light) across a range of stimulus luminance. RESULTS: Clinical findings of cone dysfunction and amelogenesis imperfecta were observed, consistent with Jalili syndrome. Light-adapted ERGs were non-detectable in CNNM4 subjects, whereas dark-adapted ERGs were generally normal. Full-field luminance thresholds were normal under dark-adapted conditions and were elevated, but measurable, under light-adapted conditions. The CNNM4 subjects had large PLRs under dark-adapted conditions and responses near the lower limit of normal, or slightly subnormal, under light-adapted conditions. CONCLUSION: CNNM4 variants can result in Jalili syndrome with cone dystrophy and generally preserved rod function. The PLR may be a useful measure for evaluating cone function in these individuals, as robust cone-mediated PLRs were recordable despite non-detectable light-adapted ERGs.

Expanding the genotypic spectrum of Jalili syndrome: Novel CNNM4 variants and uniparental isodisomy in a north American patient cohort.

Jalili syndrome is a rare multisystem disorder with the most prominent features consisting of cone-rod dystrophy and amelogenesis imperfecta. Few cases have been reported in the Americas. Here we describe a case series of patients with Jalili syndrome examined at the National Eye Institute's Ophthalmic Genetics clinic between 2016 and 2018. Three unrelated sporadic cases were systematically evaluated for ocular phenotype and determined to have cone-rod dystrophy with bull's eye maculopathy, photophobia, and nystagmus. All patients had amelogenesis imperfecta. Two of these patients had Guatemalan ancestry and the same novel homozygous CNNM4 variant (p.Arg236Trp c.706C > T) without evidence of consanguinity. This variant met likely pathogenic criteria by the American College of Medical Genetics guidelines. An additional patient had a homozygous deleterious variant in CNNM4 (c.279delC p.Phe93Leufs*31), which resulted from paternal uniparental isodisomy for chromosome 2p22-2q37. This individual had additional syndromic features including developmental delay and spastic diplegia, likely related to mutations at other loci. Our work highlights the genotypic variability of Jalili syndrome and expands the genotypic spectrum of this condition by describing the first series of patients seen in the United States.

Mg2+-ATP Sensing in CNNM, a Putative Magnesium Transporter.

The family of cystathionine-ß-synthase (CBS)-pair domain divalent metal cation transport mediators (CNNMs) is composed of four integral membrane proteins associated with Mg2+ transport. Structurally, CNNMs contain large cytosolic regions composed of a CBS-pair and a cyclic nucleotide-binding homology (CNBH) domain. How these regulate Mg2+ transport activity is unknown. Here, we determined the crystal structures of cytosolic fragments in two conformations: Mg2+-ATP-analog bound and ligand free. The structures reveal open and closed conformations with functionally important contacts not observed in structures of the individual domains. We also identified a second Mg2+-binding region in the CBS-pair domain and a different dimerization interface for the CNBH domain. Analytical ultracentrifugation and isothermal titration calorimetry experiments revealed a tight correlation between Mg2+-ATP binding and protein dimerization. Mutations that blocked either function prevented cellular Mg2+ efflux activity. The results suggest Mg2+ efflux is regulated by conformational changes associated with Mg2+-ATP binding to CNNM CBS-pair domains.

A novel pathogenic missense variant in CNNM4 underlying Jalili syndrome: Insights from molecular dynamics simulations.

BACKGROUND: Jalili syndrome (JS) is a rare cone-rod dystrophy (CRD) associated with amelogenesis imperfecta (AI). The first clinical presentation of JS patients was published in 1988 by Jalili and Smith. Pathogenic mutations in the Cyclin and CBS Domain Divalent Metal Cation Transport Mediator 4 (CNNM4) magnesium transporter protein have been reported as the leading cause of this anomaly. METHODS: In the present study, a clinical and genetic investigation was performed in a consanguineous family of Pakistani origin, showing characteristic features of JS. Sanger sequencing was successfully used to identify the causative variant in CNNM4. Molecular dynamics (MD) simulations were performed to study the effect of amino acid change over CNNM4 protein. RESULTS: Sequence analysis of CNNM4 revealed a novel missense variant (c.1220G>T, p.Arg407Leu) in exon-1 encoding cystathionine-ß-synthase (CBS) domain. To comprehend the mutational consequences in the structure, the mutant p.Arg407Leu was modeled together with a previously reported variant (c.1484C>T, p.Thr495Ile) in the same domain. Additionally, docking analysis deciphered the binding mode of the adenosine triphosphate (ATP) cofactor. Furthermore, 60ns MD simulations were carried out on wild type (p.Arg407/p.Thr495) and mutants (p.Arg407Leu/p.Thr495Ile) to understand the structural and energetic changes in protein structure and its dynamic behavior. An evident conformational shift of ATP in the binding site was observed in simulated mutants disrupting the native ATP-binding mode. CONCLUSION: The novel identified variant in CNNM4 is the first report from the Pakistani population. Overall, the study is valuable and may give a novel insight into metal transport in visual function and biomineralization.

Current Structural Knowledge on the CNNM Family of Magnesium Transport Mediators.

The cyclin and cystathionine ß-synthase (CBS) domain magnesium transport mediators, CNNMs, are key players in maintaining the homeostasis of magnesium in different organs. The human family includes four members, whose impaired activity causes diseases such as Jalili Syndrome or Familial Hypomagnesemia, but is also linked to neuropathologic disorders, altered blood pressure, and infertility. Recent findings demonstrated that CNNMs are associated with the highly oncogenic phosphatases of the regenerating liver to promote tumor growth and metastasis, which has attracted renewed focus on their potential exploitation as targets for cancer treatment. However, the exact function of CNNMs remains unclear and is subject to debate, proposed as either direct transporters, sensors, or homeostatic factors. This review gathers the current structural knowledge on the CNNM family, highlighting similarities and differences with the closely related structural partners such as the bacterial Mg2+/Co2+ efflux protein CorC and the Mg2+ channel MgtE.

Features, genetics and their correlation in Jalili syndrome: a systematic review.

Jalili syndrome is a rare genetic disorder first identified by Jalili in Gaza. Amelogenesis imperfecta and cone-rode dystrophy are simultaneously seen in Jalili syndrome patients as the main and primary manifestations. Molecular analysis has revealed that the CNNM4 gene is responsible for this rare syndrome. Jalili syndrome has been observed in many countries around the world, especially in the Middle East and North Africa. In the current scoping systematic review we searched electronic databases to find studies related to Jalili syndrome. In this review we summarise the reported clinical symptoms, CNNM4 gene and protein structure, CNNM4 mutations, attempts to reach a genotype-phenotype correlation, the functional role of CNNM4 mutations, and epidemiological aspects of Jalili syndrome. In addition, we have analysed the reported mutations in mutation effect prediction databases in order to gain a better understanding of the mutation's outcomes.

Report of two unrelated families with Jalili syndrome and a novel nonsense heterozygous mutation in CNNM4 gene.

Jalili syndrome (JS) is an autosomal recessive disease characterized by a combination of cone-rode retinal dytrophy (CRD) and amelogenesis imperfect (AI). Mutations in cyclin and CBS domain divalent metal cation transport mediator 4 (CNNM4) gene cause JS. Here we described 2 families (3 members) affected by JS. In the first family, JS was caused by the homozygous p.Leu324Pro (c.971T > C) missense mutation and the affected patient developed both CRD and AI. In the second family, a specific combination of a compound heterozygous mutation was found - the p.Leu324Pro (c.971T > C) missense transition and the novel p.Tyr581* (c.1743C > G) nonsense mutation. The proband showed CRD and AI, but her father just developed eye alterations. Together, these findings suggest that the p.Leu324Pro mutation in homozygosis induces a complete phenotype with both CRD and AI, but in heterozygosis and in composition with the novel p.Tyr581* nonsense mutation in CNNM4 promotes variable clinical expressivity, particularly with lack of dental phenotypes. These different phenotypes could be explained by deletions affecting the proband's homologous allele, epistasia or interactions with environmental factors leading to residual activity of protein.

Identification of a mutation in CNNM4 by whole exome sequencing in an Amish family and functional link between CNNM4 and IQCB1.

We investigated an Amish family in which three siblings presented with an early-onset childhood retinal dystrophy inherited in an autosomal recessive fashion. Genome-wide linkage analysis identified significant linkage to marker D2S2216 on 2q11 with a two-point LOD score of 1.95 and a multi-point LOD score of 3.76. Whole exome sequencing was then performed for the three affected individuals and identified a homozygous nonsense mutation (c.C1813T, p.R605X) in the cyclin and CBS domain divalent metal cation transport mediator 4 (CNNM4) gene located within the 2p14-2q14 Jalili syndrome locus. The initial assessment and collection of the family were performed before the clinical delineation of Jalili syndrome. Another assessment was made after the discovery of the responsible gene and the dental abnormalities characteristic of Jalili syndrome were retrospectively identified. The p.R605X mutation represents the first probable founder mutation of Jalili syndrome identified in the Amish community. The molecular mechanism underlying Jalili syndrome is unknown. Here we show that CNNM4 interacts with IQCB1, which causes Leber congenital amaurosis (LCA) when mutated. A truncated CNNM4 protein starting at R605 significantly increased the rate of apoptosis, and significantly increased the interaction between CNNM4 and IQCB1. Mutation p.R605X may cause Jalili syndrome by a nonsense-mediated decay mechanism, affecting the function of IQCB1 and apoptosis, or both. Our data, for the first time, functionally link Jalili syndrome gene CNNM4 to LCA gene IQCB1, providing important insights into the molecular pathogenic mechanism of retinal dystrophy in Jalili syndrome.

Co-occurrence of Jalili syndrome and muscular overgrowth.

Jalili syndrome is a rare disorder inherited in an autosomal recessive pattern manifesting as a combination of cone-rod dystrophy including progressive loss of visual acuity, color blindness, photophobia, and amelogenesis imperfecta with hypoplastic, immature, or hypocalcified dental enamel. It is caused by mutations in CNNM4, which encodes the ancient conserved domain protein 4. Here we report three brothers with Jalili syndrome and muscle overgrowth of the legs. Myopathic changes were found in needle electromyography. Mutational analysis showed in all three brothers a novel likely pathogenic homozygous missense substitution in exon 1 (c.1076T>C, p.(Leu359Pro)) of CNNM4. Both parents were carriers for the variant. In order to exclude other causative variants that could modify the patients' phenotype we performed exome sequencing and MLPA analysis of the DMD gene in Patient 1. These analyses did not identify any additional variants. Our results expand the mutational spectrum associated with Jalili syndrome and suggest that mild myopathy with muscle overgrowth of the legs could be a newly identified manifestation of the disorder.

Novel splice site mutation in CNNM4 gene in a family with Jalili syndrome.

Jalili syndrome is a rare autosomal recessive genetic disease characterized by the association of amelogenesis imperfecta and cone-rod retinal dystrophy. This syndrome is caused by mutations in the CNNM4 gene. Different types of CNNM4 mutations have been reported; missense, nonsense, large deletions, single base insertion, and duplication. We used Sanger sequencing to analyze a large consanguineous family with three siblings affected with Jalili syndrome, suspected clinically after dental and ophthalmological examination. These patients are carrying a novel homozygous mutation in the splice site acceptor of intron 3 (c.1682-1G > C) in the CNNM4 gene. We compare the findings of the present family to those from literature, in order to further delineate Jalili syndrome.

A new familial case of Jalili syndrome caused by a novel mutation in CNNM4.

Jalili syndrome (JS) is a rare autosomal recessive disorder characterized by the combination of cone-rod dystrophy (CRD) and amelogenesis imperfecta. To date, 18 families with JS have been reported, 16 of which were found to have a mutation in CNNM4. We describe three siblings with clinical features of JS with a homozygous missense mutation in exon 4 of CNNM4, c.1781A>G (p.N594S). They demonstrated phenotypic variability in terms of ocular and dental findings. Although fundus examination and optical coherence tomography results were normal, the electroretinogram was compatible with CRD, supporting the diagnosis of JS. The dental phenotype severity also varied among the siblings.