Overlapping phenotypes in complex spastic paraplegias SPG11, SPG15, SPG35 and SPG48.
Hereditary spastic paraplegias are a heterogeneous group of neurodegenerative disorders, clinically classified in pure and complex forms. Genetically, more than 70 different forms of spastic paraplegias have been characterized. A subgroup of complicate recessive forms has been distinguished for the presence of thin corpus callosum and white matter lesions at brain imaging. This group includes several genetic entities, but most of the cases are caused by mutations in the KIAA1840 (SPG11) and ZFYVE26 genes (SPG15). We studied a cohort of 61 consecutive patients with complicated spastic paraplegias, presenting at least one of the following features: mental retardation, thin corpus callosum and/or white matter lesions. DNA samples were screened for mutations in the SPG11/KIAA1840, SPG15/ZFYVE26, SPG21/ACP33, SPG35/FA2H, SPG48/AP5Z1 and SPG54/DDHD2 genes by direct sequencing. Sequence variants were found in 30 of 61 cases: 16 patients carried SPG11/KIAA1840 gene variants (26.2%), nine patients carried SPG15/ZFYVE26 variants (14.8%), three patients SPG35/FA2H (5%), and two patients carried SPG48/AP5Z1 gene variants (3%). Mean age at onset was similar in patients with SPG11 and with SPG15 (range 11-36), and the phenotype was mostly indistinguishable. Extrapyramidal signs were observed only in patients with SPG15, and epilepsy in three subjects with SPG11. Motor axonal neuropathy was found in 60% of cases with SPG11 and 70% of cases with SPG15. Subjects with SPG35 had intellectual impairment, spastic paraplegia, thin corpus callosum, white matter hyperintensities, and cerebellar atrophy. Two families had a late-onset presentation, and none had signs of brain iron accumulation. The patients with SPG48 were a 5-year-old child, homozygous for a missense SPG48/AP5Z1 variant, and a 51-year-old female, carrying two different nonsense variants. Both patients had intellectual deficits, thin corpus callosum and white matter lesions. None of the cases in our cohort carried mutations in the SPG21/ACP33 and SPG54/DDH2H genes. Our study confirms that the phenotype of patients with SPG11 and with SPG15 is homogeneous, whereas cases with SPG35 and with SPG48 cases present overlapping features, and a broader clinical spectrum. The large group of non-diagnosed subjects (51%) suggests further genetic heterogeneity. The observation of common clinical features in association with defects in different causative genes, suggest a general vulnerability of the corticospinal tract axons to a wide spectrum of cellular alterations.
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Viviana
V
Pensato
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Barbara
B
Castellotti
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Cinzia
C
Gellera
2 Clinic of Central and Peripheral Degenerative Neuropathies Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Davide
D
Pareyson
3 Clinical Neurophysiology Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Claudia
C
Ciano
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Lorenzo
L
Nanetti
2 Clinic of Central and Peripheral Degenerative Neuropathies Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Ettore
E
Salsano
2 Clinic of Central and Peripheral Degenerative Neuropathies Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Giuseppe
G
Piscosquito
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Elisa
E
Sarto
4 Molecular Neuro-Oncology Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Marica
M
Eoli
5 Paediatric Neurology Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Isabella
I
Moroni
6 Movement Disorders Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Paola
P
Soliveri
7 Neuro-Oncology Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Elena
E
Lamperti
8 Neuroradiology Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Luisa
L
Chiapparini
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Daniela
D
Di Bella
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy.
Franco
F
Taroni
1 Genetics of Neurodegenerative and Metabolic Diseases Unit, IRCCS-Fondazione Istituto Neurologico Carlo Besta, via Celoria 11, 20133 Milan, Italy mariotti.c@istituto-besta.it.
Caterina
C
Mariotti
D000293:Adolescent; D000328:Adult; D001921:Brain / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics; D002648:Child; D002675:Child, Preschool; D005260:Female; D014644:Genetic Variation / Q000235:genetics*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics; D010641:Phenotype; D011506:Proteins / Q000145:classification / Q000235:genetics*; D012720:Severity of Illness Index; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics* / Q000503:physiopathology*; D055815:Young Adult
D002352:Carrier Proteins; D011506:Proteins; C520412:SPG11 protein, human; C528699:ZFYVE26 protein, human; D006899:Mixed Function Oxygenases; C019081:fatty acid alpha-hydroxylase
corpus callosum; corticospinal; hereditary spastic paraplegia; molecular genetics; neurodegenerative disorders