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Background Hypotonia occurs as a result of neurological dysfunction in the brain, brainstem, spinal cord, motor neurons, anterior horn cells, peripheral nerves, and muscles. Although the genotype-phenotype correlation can be established in 15 to 30% of patients, it is difficult to obtain a correlation in most cases. Aims This study was aimed to investigate the genetic etiology in cases of peripheral hypotonia that could not be diagnosed using conventional methods. Methods A total of 18 pediatric patients with peripheral hypotonia were included. They were referred to our genetic disorders diagnosis center from the Pediatric Neurology Department with a prediagnosis of hypotonia. A custom designed multigene panel, including ACTA1 , CCDC78 , DYNC1H1 , GARS , RYR1 , COL6A1 , COL6A2 , COL6A3 , FKRP , FKTN , IGHMBP2 , LMNA , LAMA2 , LARGE1 , MTM1 , NEM , POMGnT1 , POMT1 , POMT2 , and SEPN1 , was used for genetic analysis using next-generation sequencing (NGS). Results In our study, we found 13 variants including pathogenic (two variants in LAMA2) and likely pathogenic variants (three variants in RYR1 and POMGnT1) and variants of uncertain clinical significance (eight variants in RYR1, COL6A3, COL6A2, POMGnT1 and POMT1) in 11 (61%) out of 18 patients. In one of our patients, a homozygous, likely pathogenic c.1649G > A, p.(Ser550Asn) variant was defined in the POMGnT1 gene which was associated with a muscle-eye-brain disease phenotype. Conclusion The contribution of an in-house designed gene panel in the etiology of peripheral hypotonia with a clinical diagnosis was 5.5%. An important contribution with the clinical diagnosis can be made using the targeted multigene panels in larger samples.
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INTRODUCTION: Hypotonia is a common presentation that child neurologists encounter daily. The hypotonic neonate represents a diagnostic challenge as a lesion at any level in the neuro-axis may cause hypotonia. In this paper, we study the diagnostic yield of investigations commonly used as part of a hypotonia work-up. METHODS: A 12-year retrospective cohort study was conducted at a tertiary care center in Saudi Arabia from 2007 to 2018. Final diagnoses, clinical presentations, laboratory tests, imaging and genetic studies were reviewed from the patient's electronic health records. RESULTS: 164 patients were identified as fitting the inclusion criteria of the study. 50% had central hypotonia, 18% peripheral hypotonia and 32% mixed hypotonia. Molecular testing was performed for 82% (74) of patients. 65 Microarray studies were done; 27% abnormal and 9% diagnostic. 55 gene panels were done; 58% abnormal and 30% diagnostic. 53 single-gene tests were done; 57% abnormal and 40% diagnostic. 61 whole exome sequences were done; 72% positive and 59% diagnostic. 126 MRIs were reviewed; 56% abnormal and 33% contributed to the diagnosis. CONCLUSION: Molecular genetic testing is our recommended next step in the diagnosis of patients with hypotonia after careful phenotyping. Neuroimaging is helpful to guide further costly workup of patients with hypotonia.