Pathogenic TNNI1 variants disrupt sarcomere contractility resulting in hypo- and hypercontractile muscle disease.

Troponin I (TnI) regulates thin filament activation and muscle contraction. Two isoforms, TnI-fast (TNNI2) and TnI-slow (TNNI1), are predominantly expressed in fast- and slow-twitch myofibers, respectively. TNNI2 variants are a rare cause of arthrogryposis, whereas TNNI1 variants have not been conclusively established to cause skeletal myopathy. We identified recessive loss-of-function TNNI1 variants as well as dominant gain-of-function TNNI1 variants as a cause of muscle disease, each with distinct physiological consequences and disease mechanisms. We identified three families with biallelic TNNI1 variants (F1: p.R14H/c.190-9G>A, F2 and F3: homozygous p.R14C), resulting in loss of function, manifesting with early-onset progressive muscle weakness and rod formation on histology. We also identified two families with a dominantly acting heterozygous TNNI1 variant (F4: p.R174Q and F5: p.K176del), resulting in gain of function, manifesting with muscle cramping, myalgias, and rod formation in F5. In zebrafish, TnI proteins with either of the missense variants (p.R14H; p.R174Q) incorporated into thin filaments. Molecular dynamics simulations suggested that the loss-of-function p.R14H variant decouples TnI from TnC, which was supported by functional studies showing a reduced force response of sarcomeres to submaximal [Ca2+] in patient myofibers. This contractile deficit could be reversed by a slow skeletal muscle troponin activator. In contrast, patient myofibers with the gain-of-function p.R174Q variant showed an increased force to submaximal [Ca2+], which was reversed by the small-molecule drug mavacamten. Our findings demonstrated that TNNI1 variants can cause muscle disease with variant-specific pathomechanisms, manifesting as either a hypo- or a hypercontractile phenotype, suggesting rational therapeutic strategies for each mechanism.

A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.

Otofaciocervical syndrome (OTFCS) is a rare genetic disorder of both autosomal recessive and autosomal dominant patterns of inheritance. It is caused by biallelic or monoallelic mutations in PAX1 or EYA1 genes, respectively. Here, we report an OTFCS2 female patient of 1st consanguineous healthy parents. She manifested facial dysmorphism, hearing loss, intellectual disability (ID), and delayed language development (DLD) as the main clinical phenotype. The novel homozygous variant c.1212dup (p.Gly405Argfs*51) in the PAX1 gene was identified by whole exome sequencing (WES), and family segregation confirmed the heterozygous status of the mutation in the parents using the Sanger sequencing. The study recorded a novel PAX1 variant representing the sixth report of OTFCS2 worldwide and the first Egyptian study expanding the geographic area where the disorder was confined.

Clinical and molecular study of Egyptian patients with Treacher Collins syndrome.

Treacher Collins syndrome (TCS) is a rare disorder of craniofacial development following different patterns of inheritance. To date, mutations in four genes ( TCOF1, POLR1D, POLR1C , and POLR1B ) have been found to cause the condition. The molecular defect remains unidentified in a significant proportion of patients. In the current study, whole exome sequencing including analysis of copy number variants was applied for genetic testing of eight Egyptian patients with typical TCS phenotype, representing the first molecular analysis of TCS patients in Egypt as well as in Arab countries. Five heterozygous frameshift mutations were reported, including four variants in the TCOF1 gene (c.3676_3694delinsCTCTGG, c.3984_3985delGA, c.4366_4369delGAAA, and c.3388delC) and one variant in the POLR1D gene (c.60dupA). Four variants were novel extending the disease mutation spectrum. In three affected individuals, no variants of interest were identified in genes associated with TCS or clinically overlapping conditions. Additionally, no relevant variant was detected in genes encoding other subunits of RNA polymerase (pol) I. Molecular analysis is important to provide accurate genetic counseling. It would also contribute to reduced disease incidence. Further studies should be designed to investigate other possible etiologies when no pathogenic variants were revealed in either of the known genes.

Mutation analysis reveals novel and known mutations in SAG gene in first two Egyptian families with Oguchi disease.

BACKGROUND: Oguchi disease is a rare type of congenital stationary night blindness associated with an abnormal fundus appearance. It is inherited in an autosomal recessive manner where two types exist according to the gene affected; type 1 associated with S-antigen (SAG) gene mutations and type 2 associated with rhodopsin kinase (GRK1) gene mutations. PURPOSE: The aim of this work was to describe the clinical and genetic findings of the first two reported families of Oguchi disease in Egypt and African region. METHODS: Four members of two consanguineous Egyptian families with history of night blindness since childhood underwent complete ophthalmological examination, standard automated static perimetry, fundus color photography, fundus autofluorescence (FAF), fundus fluorescein angiography (FFA) in light-adapted state and spectral-domain optical coherence tomography (SD-OCT) of both the macula and the optic nerve head as well as central corneal thickness with repeated fundus photography following prolonged dark adaptation. Mutation screening of 7 coding exons of GRK1 gene and 15 coding exons of SAG gene as well as some flanking regions were performed using Sanger sequencing technique. The variants were tested for pathogenicity using different in silico functional analysis tools. RESULTS: The clinical examination and investigations confirmed Oguchi disease phenotype. One patient showed p.R193* (c.577C > T) which is a previously reported SAG gene mutation in a homozygous form. The other three patients from a different family showed (c.649-1 G > C), a novel canonical splice site SAG gene mutation in a homozygous form. CONCLUSION: The identification of the novel canonical splice site SAG gene variant in three members of the same family with clinically confirmed Oguchi disease reinforces its pathogenicity. A fourth patient from another family carried a previously reported mutation in the same gene. SAG gene variants may be the underlying genetic cause for Oguchi disease in Egypt. Our findings have expanded the spectrum of Oguchi disease-associated mutations in SAG gene and may serve as a basis for genetic diagnosis for Oguchi disease.

Potential Value of miR-23a for Discriminating Neuromyelitis Optica Spectrum Disorder from Multiple Sclerosis.

BACKGROUND: Until now, no laboratory test or test set can guarantee the diagnosis of multiple sclerosis (MS) at early disease stages, and the disease symptoms may interfere with many other disease conditions. Analyzing the expression of circulating miRNAs may provide a useful approach for early and differential MS diagnosis. The main objective is assessment of the potential of serum miR-23a, miR-155, and miR-572 to differentiate between MS and other neuroinflammatory diseases. METHODS: Serum miRNAs were obtained from 37 MS patients and 25 healthy age-matched controls, along with patients with neuromyelitis optica spectrum disorder (NMOSD) [n = 13] and neuropsychiatric systemic lupus erythematosus (NPSLE) [n = 10]. miRNA expression levels were analyzed using real-time polymerase chain reaction (PCR) and pairwise comparisons were made to reveal the diagnostic/distinguishing potential of the analyzed miRNAs. RESULTS: In the study cohort, the three investigated miRNAs failed to display significant dysregulation in MS patients. However, they could significantly discriminate patients with NMOSD and NPSLE [median (IQR): 8.1 (6.1-9.2) and 8.8 (7.9-9.7) for miR-23a, 7.5 (5.3-8.3) and 8.0 (7.5-9.5) for miR-155 and 6.9 (5.0-8.8) and 6.4 (5.3-8.8) for miR-572 in NMOSD and NPSLE, respectively] from healthy subjects [median (IQR): 3.4 (1.5-4.3), 3.1 (1.1-5.6) and 3.5 (1.7-5.6) for miR-23a, miR-155 and miR-572, respectively], with area under the curve (AUC) ≤0.8. Remarkably, miR-23a has been emerging as a prospective biomarker for differentiation of MS from NMOSD as well as NPSLE (AUC<0.9). The miRNA combined use contributed to enhanced diagnostic and discriminatory performance in the study groups. CONCLUSION: Certain miRNA expression levels would contribute to discriminating MS from other neuroinflammatory diseases.

Assessment of the most common CYP21A2 point mutations in a cohort of congenital adrenal hyperplasia patients from Egypt.

Objectives Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency (21-OHD) is a common autosomal recessive disorder caused by defects in the CYP21A2 gene. We aimed to determine the prevalence of the most commonly reported mutations among 21-OHD Egyptian patients and correlate genotype with phenotype. Methods Molecular analysis of the CYP21A2 gene was performed for the detection of the six most common point mutations (p.P30L, p.I172N, p.V281L, p.Q318X, the splice site mutation Int2 [IVS2-13A/C>G], and the cluster of three mutations [p.I236N, p.V237E, and p.M239K] designed as CL6). Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was performed on 47 unrelated Egyptian 21α-OH deficiency patients and their available parents to detect the presence of the six most common point mutations. Results Screening for the six most common point mutations in CYP21A2 gene, revealed mutations in 87.2% (82/94) of the studied alleles corresponding to 47 Egyptian patients. The most common mutation among the studied cases was IVS2-13C/A>G that was found to be presented in a frequency of 46.8% (44/94). The genotype/phenotype correlations related to null, A, and B groups were with PPV of 100, 55.5, and 83.3%, respectively. Conclusions The described method diagnosed CAH in 80.8% of the studied patients. Good correlation between genotype and phenotype in salt wasting and simple virilizing forms is determined, whereas little concordance is seen in nonclassical one. Furthermore, studying the carrier frequency of 21-OHD among the normal population is of great importance.