Familial 15q11.2 Micro deletions are not Fully Penetrant in Two Cases with Hereditary Spastic Paraplegia and Dysmorphic Features

Hereditary Spastic Paraplegias (HSP) is heterogenic neurodegenerative disorders with progressive spasticity of the lower limbs as a prominent feature. Spastic paraplegia type 6 (SPG6) is an autosomal dominant form of the disorder caused by point mutations in the NIPA1 gene on chromosome 15q11.2. The microdeletions within the region 15q11.2 and spanning the four genes TUBGCP5, CYFIP1, NIPA2, and NIPA1 were previously reported in several different syndromes, including mental retardation, and/or developmental delay with hypotonia. Furthermore, these genes were associated with several congenital abnormalities, including autism, developmental delay, motor, and language disturbances, behavioural problems, and Idiopathic General Epilepsies (IGE), suggesting the existence of a new microdeletion syndrome. Our index cases, in whom the microdeletion 15q11.2 was detected, suffer from spastic paraplegia, but neither cognitive impairment nor behavioural problems were observed in them and other tested relatives. We considered several interpretations of the 15q11.2 microdeletion’s phenotypic significance, including polymorphism, the pleiotropic effect of the microdeletion, and the influence of other modifiers. Specifying the exact range of the microdeletion 15q11.2 in patients with diverse clinical presentation is essential. Though the clinical implications of the microdeletion 15q11.2 remain unclear, our study contributes by extending the phenotypic variability of the subjects carrying this micro rearrangement.