Homozygous Duplication in the CHRNE in a Family with Congenital Myasthenic Syndrome 4C: 18-Year Follow Up.

BACKGROUND AND OBJECTIVES: Congenital myasthenic syndromes (CMSs) are rare inherited diseases characterized by muscle weakness and fatigability on exertion resulting from defects in the neuromuscular junctions. Mutations in 32 genes have been reported as the underlying causes of CMS, with mutations in the cholinergic receptor nicotinic epsilon subunit (CHRNE) being the most common cause of the disease. Methodology and Materials: This study investigated a large consanguineous family with multiple individuals suffering from abnormal fatigue and muscle weakness in the ocular and limb regions. Moreover, the affected individuals were followed up for 18 years to observe the clinical course of the disease. RESULTS: High-quality exome sequencing followed by bidirectional Sanger sequencing revealed a homozygous duplication variant (NM_000080.4: c.1220-8_1227dup) in the splice acceptor site of exon 11 of the CHRNE gene. This variant is predicted to cause frameshift and premature termination (p.Cys410ProfsTer51). Both parents had heterozygous duplication variants with no clinical symptoms. The personalized treatment of the affected individuals resulted in a marked improvement in the clinical symptoms. More than 80% of the disease symptoms in the affected individuals subsided after the use of pyridostigmine and salbutamol (4 mg). CONCLUSIONS: This is the first report of long-term follow up of cases with homozygous insertion (c.1220-8_1227dup) in the CHRNE gene. Furthermore, this report expands the phenotypic symptoms associated with the CHRNE mutation.

A Current Landscape on Alport Syndrome Cases: Characterization, Therapy and Management Perspectives.

Alport syndrome (AS) is a rare genetic disorder categorized by the progressive loss of kidney function, sensorineural hearing loss and eye abnormalities. It occurs due to mutations in three genes that encode for the alpha chains of type IV collagen. Globally, the disease is classified based on the pattern of inheritance into X-linked AS (XLAS), which is caused by pathogenic variants in COL4A5, representing 80% of AS. Autosomal recessive AS (ARAS), caused by mutations in either COL4A3 or COL4A4, represents 15% of AS. Autosomal dominant AS (ADAS) is rare and has been recorded in 5% of all cases due to mutations in COL4A3 or COL4A4. This review provides updated knowledge about AS including its clinical and genetic characteristics in addition to available therapies that only slow the progression of the disease. It also focuses on reported cases in Saudi Arabia and their prevalence. Moreover, we shed light on advances in genetic technologies like gene editing using CRISPR/Cas9 technology, the need for an early diagnosis of AS and managing the progression of the disease. Eventually, we provide a few recommendations for disease management, particularly in regions like Saudi Arabia where consanguineous marriages increase the risk.

Clinical and genetic characterization of patients segregating variants in KPTN, MINPP1, NGLY1, AP4B1, and SON underlying neurodevelopmental disorders: Genetic and phenotypic expansion.

Neurodevelopmental disorders (NDDs) are heterogeneous genetic conditions of the central nervous system (CNS). Primary phenotypes of NDDs include epilepsy, loss of developmental skills, abnormal movements, muscle weakness, ocular anomalies, hearing problems, and macro- or microcephaly. NDDs occur due to variants in genes encoding proteins involved in the structure and function of CNS, thus interrupting its normal physiological role. In the study presented here, four consanguineous families (A-D), with members showing neurodevelopmental symptoms, were recruited for clinical and genetic characterization of the phenotypes. Clinical examinations, including Seguin Form Board Test (SFBT), Vineland Social Maturity Scale (VSMS), brain Magnetic Resonance Imaging (MRI), Electroencephalogram (EEG), Electromyography (EMG), Nerve Conduction Velocity (NCV), and Magnetic Resonance Spectroscopy, were employed to characterize the disease phenotypes. Whole exome sequencing (WES) followed by Sanger sequencing was employed to search for the genetic basis of the neurological symptoms observed in four families (A-D). Two of these families (A, B) were of Saudi Arabian origin, and two others (C, D) were of Pakistan origin. Two homozygous missense (KPTN: NM_007059.4:c.301T>G: NP_008990.2; p.(Phe101Val) and MINPP1:NM_001178118.2:c.1202G>A: NP_001171588.1; p.(Arg401Gln)) variants in families A and B, respectively, and two homozygous nonsense (NGLY1:NM_018297.3:c.1534_1541dup: NP_060767.2; p.(Ser515LysfsTer51) and AP4B1:NM_001253852:c.1668G>A: NP_001240781.1; p.(Trp556X)) variants in families C and D, respectively, were identified. Interestingly, additional heterozygous nonsense variant in SON: NM_138927.2: c.5753_5756del: NP_620305.3; p.(Val1918GlufsTer87) and a homozygous variant in FLG (FLG: NM_002016.2:c.7339C>T: NP_002007.1; p.(Arg2447X) were detected in families A and D, respectively. Further, we determined the deleteriousness of each variant through computational approaches. The present study expands the phenotypic and genetic spectrum of NDD-associated genes (KPTN, MINPP1, NGLY1, and AP4B1). Moreover, additional nonsense variants (SON: c.5753_5756del and FLG: c.7339C>T) identified in two families segregating with the phenotype might explain the phenotypic variability and severity in our patients.

Frameshift variant in MITF gene in a large family with Waardenburg syndrome type II and a co-segregation of a C2orf74 variant.

Waardenburg syndrome (WS) is a hereditary disorder affecting the auditory system and pigmentation of hair, eyes, and skin. Different variants of the disease exist with the involvement of mutation in six genes. The aim of the study is to identify the genetic defects underlying Waardenburg syndrome in a large family with multiple affected individuals. Here, in this study, we recruited a large family with eleven affected individuals segregating WS type 2. We performed whole genome SNP genotyping, whole exome sequencing and segregation analysis using Sanger approach. Whole genome SNP genotyping, whole exome sequencing followed by Sanger validation of variants of interest identified a novel single nucleotide deletion mutation (c.965delA) in the MITF gene. Moreover, a rare heterozygous, missense damaging variant (c.101T>G; p.Val34Gly) in the C2orf74 has also been identified. The C2orf74 is an uncharacterized gene present in the linked region detected by DominantMapper. Variants in MITF and C2orf74 follows autosomal dominant segregation with the phenotype, however, the variant in C2orf74 is incompletely penetrant. We proposed a digenic inheritance of variants as an underlying cause of WS2 in this family.