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Mohamed FE, Al Sorkhy M, Ghattas MA, Al-Zaabi N, Al-Shamsi A, Almansoori TM, Al-Gazali L, Al-Dirbashi OY, Al-Jasmi F, Ali BR. A Novel Homozygous Missense Variant in the NAGA Gene with Extreme Intrafamilial Phenotypic Heterogeneity. J Mol Neurosci 2019; 70:45-55. [PMID: 31468281 DOI: 10.1007/s12031-019-01398-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2019] [Accepted: 08/14/2019] [Indexed: 02/05/2023]
Abstract
Schindler disease is a rare autosomal recessive lysosomal storage disorder caused by a deficiency in alpha-N-acetylgalactosaminidase (α-NAGA) activity due to defects in the NAGA gene. Accumulation of the enzyme's substrates results in clinically heterogeneous symptoms ranging from asymptomatic individuals to individuals with severe neurological manifestations. Here, a 5-year-old Emirati male born to consanguineous parents presented with congenital microcephaly and severe neurological manifestations. Whole genome sequencing revealed a homozygous missense variant (c.838C>A; p.L280I) in the NAGA gene. The allele is a reported SNP in the ExAC database with a 0.0007497 allele frequency. The proband's asymptomatic sister and cousin carry the same genotype in a homozygous state as revealed from the family screening. Due to the extreme intrafamilial heterogeneity of the disease as seen in previously reported cases, we performed further analyses to establish the pathogenicity of this variant. Both the proband and his sister showed abnormal urine oligosaccharide patterns, which is consistent with the diagnosis of Schindler disease. The α-NAGA activity was significantly reduced in the proband and his sister with 5.9% and 12.1% of the mean normal activity, respectively. Despite the activity loss, p.L280I α-NAGA processing and trafficking were not affected. However, protein molecular dynamic simulation analysis revealed that this amino acid substitution is likely to affect the enzyme's natural dynamics and hinders its ability to bind to the active site. Functional analysis confirmed the pathogenicity of the identified missense variant and the diagnosis of Schindler disease. Extreme intrafamilial clinical heterogeneity of the disease necessitates further studies for proper genetic counseling and management.
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Affiliation(s)
- Fedah E Mohamed
- Department of Pathology, College of Medicine and Health Sciences, United Arab Emirates University, P.O. Box: 17666, Al Ain, United Arab Emirates
| | - Mohammad Al Sorkhy
- College of Pharmacy, Al Ain University of Science and Technology, Al Ain, United Arab Emirates
| | - Mohammad A Ghattas
- College of Pharmacy, Al Ain University of Science and Technology, Al Ain, United Arab Emirates
| | - Nuha Al-Zaabi
- Department of Paediatrics, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates.,Department of Paediatrics, Tawam Hospital, Al Ain, United Arab Emirates
| | - Aisha Al-Shamsi
- Department of Paediatrics, Tawam Hospital, Al Ain, United Arab Emirates
| | - Taleb M Almansoori
- Department of Radiology, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates
| | - Lihadh Al-Gazali
- Department of Paediatrics, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates
| | - Osama Y Al-Dirbashi
- Department of Paediatrics, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates
| | - Fatma Al-Jasmi
- Department of Paediatrics, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, United Arab Emirates. .,Department of Paediatrics, Tawam Hospital, Al Ain, United Arab Emirates.
| | - Bassam R Ali
- Department of Pathology, College of Medicine and Health Sciences, United Arab Emirates University, P.O. Box: 17666, Al Ain, United Arab Emirates.
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