Table 2.

L1 Syndrome: Comparison of Phenotypes in Male Probands by Select Features

FeatureL1 Phenotype
HSASMASA syndrome,
incl SPG1
X-linked complicated
CC agenesis
Hydrocephalus w/or w/o stenosis
of aqueduct of Sylvius
100%Variable dilation of
the 3rd ventricle
CC agenesis/hypogenesis +
+ in some100%
Intellectual disability SevereMild to moderateMild to moderate
Delayed speech +++
Spasticity of legs ++Variable
Adducted thumbs 50%<50%<50%

CC = corpus callosum; HSAS = X-linked hydrocephalus with stenosis of aqueduct of Sylvius; MASA = mental retardation [intellectual disability], aphasia [delayed speech], spastic paraplegia [shuffling gait], adducted thumbs; SPG1 = X-linked complicated hereditary spastic paraplegia type 1

From: L1 Syndrome

Cover of GeneReviews®
GeneReviews® [Internet].
Adam MP, Feldman J, Mirzaa GM, et al., editors.
Seattle (WA): University of Washington, Seattle; 1993-2024.
Copyright © 1993-2024, University of Washington, Seattle. GeneReviews is a registered trademark of the University of Washington, Seattle. All rights reserved.

GeneReviews® chapters are owned by the University of Washington. Permission is hereby granted to reproduce, distribute, and translate copies of content materials for noncommercial research purposes only, provided that (i) credit for source ( and copyright (© 1993-2024 University of Washington) are included with each copy; (ii) a link to the original material is provided whenever the material is published elsewhere on the Web; and (iii) reproducers, distributors, and/or translators comply with the GeneReviews® Copyright Notice and Usage Disclaimer. No further modifications are allowed. For clarity, excerpts of GeneReviews chapters for use in lab reports and clinic notes are a permitted use.

For more information, see the GeneReviews® Copyright Notice and Usage Disclaimer.

For questions regarding permissions or whether a specified use is allowed, contact: ude.wu@tssamda.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.