A 20-year Clinical and Genetic Neuromuscular Cohort Analysis in Lebanon: An International Effort.

BACKGROUND: Clinical and molecular data on the occurrence and frequency of inherited neuromuscular disorders (NMD) in the Lebanese population is scarce. OBJECTIVE: This study aims to provide a retrospective overview of hereditary NMDs based on our clinical consultations in Lebanon. METHODS: Clinical and molecular data of patients referred to a multi-disciplinary consultation for neuromuscular disorders over a 20-year period (1999-2019) was reviewed. RESULTS: A total of 506 patients were diagnosed with 62 different disorders encompassing 10 classes of NMDs. 103 variants in 49 genes were identified. In this cohort, 81.4% of patients were diagnosed with motor neuron diseases and muscular dystrophies, with almost half of these described with spinal muscular atrophy (SMA) (40.3% of patients). We estimate a high SMA incidence of 1 in 7,500 births in Lebanon. Duchenne and Becker muscular dystrophy were the second most frequently diagnosed NMDs (17% of patients). These disorders were associated with the highest number of variants (39) identified in this study. A highly heterogeneous presentation of Limb Girdle Muscular Dystrophy and Charcot-Marie-Tooth disease was notably identified. The least common disorders (5.5% of patients) involved congenital, metabolic, and mitochondrial myopathies, congenital myasthenic syndromes, and myotonic dystrophies. A review of the literature for selected NMDs in Lebanon is provided. CONCLUSIONS: Our study indicates a high prevalence and underreporting of heterogeneous forms of NMDs in Lebanon- a major challenge with many novel NMD treatments in the pipeline. This report calls for a regional NMD patient registry.

Homozygous deletion of exons 2-7 within TGFB3 gene in a child with severe Loeys-Dietz syndrome and Marfan-like features.

We describe a patient with palatal abnormalities-cleft palate and bifid uvula; distinctive facial features-long and triangular face, large ears and nose, thin lips and dental crowding; musculoskeletal abnormalities-severe scoliosis, joint laxity, long digits, flat feet, decreased muscle mass, and diminished muscle strength; and cardiac features-a dilatated ascending aorta at the level of Valsalva sinuses and a patent foramen ovale. Sequence analysis and deletion/duplication testing for a panel of genes involved in connective tissue disorders revealed the presence of a novel homozygous deletion of exons 2-7 in TGFB3 gene. Heterozygous pathogenic mutations in TGFB3 have been associated with Loeys-Dietz syndrome 5 (LDS5) and Arrhythmogenic Right Ventricular Dysplasia type 1. Here, we report the first case of a homozygous TGFB3 variant associated with a severe LDS5 and Marfan-like presentation.

COQ8A and MED25 Mutations in a Child with Intellectual Disability, Microcephaly, Seizures, and Spastic Ataxia: Synergistic Effect of Digenic Variants?

We report on a girl, born to first-cousin Lebanese parents, with severe intellectual disability, congenital hip luxation, cardiac malformation, short stature, facial dysmorphic features including microcephaly, sparse hair, bilateral epicanthal folds, ataxia, seizures, and elevated lactate and pyruvate levels in serum. Whole exome sequencing was carried out on the patient's DNA. Potentially causal homozygous variants in the MED25 (p.Ile173Thr) and COQ8A (p.Arg512Trp) genes were found. The potential pathogenicity of these variants, and the possibility that the 2 variants could synergistically act to produce the phenotype reported, is discussed.

A novel EXT2 mutation in a consanguineous family with severe developmental delay, microcephaly, seizures, feeding difficulties, and osteopenia extends the phenotypic spectrum of autosomal recessive EXT2-related syndrome (AREXT2).

We report a consanguineous family where 2 boys presented with developmental delay, hypotonia, microcephaly, seizures, gastro-intestinal abnormalities, osteopenia, and neurological regression. Whole exome sequencing performed in one of the boys revealed the presence of a novel homozygous missense variant in the EXT2 gene: c.11C > T (p.Ser4Leu). Segregation analysis by Sanger sequencing confirmed homozygous by descent autosomal recessive transmission of this mutation. Another family was previously reported with homozygous mutations in this gene in four siblings affected with a nearly similar clinical condition (Farhan et al., 2015). We discuss the similarities and differences between the two syndromes and propose AREXT2 as a new acronym for EXT2-related diseases.