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hereditary spastic paraplegia ( hsp ) is a clinically and genetically heterogeneous group of neurodegenerative diseases that predominantly involves the lower extremities .
the essential features are insidiously progressive spastic leg weakness associated with corticospinal tract and dorsal column degeneration .
hsp is classified according to the mode of inheritance ( autosomal dominant , autosomal recessive , or x - linked ) , clinical symptoms ( " pure " or " complicated " ) , and specific gene locus ( " spg1 " through " spg17 " ) .
autosomal dominant hsp ( ad - hsp ) is the most prevalent mode and includes approximately 70% of cases .
approximately 40 - 45% of ad - hsp patients have pathogenic mutations in the spastin gene ( spg4 or spast gene ) , which causes predominantly " pure " hsp .
pure hsp is characterized by severe progressive spasticity limited to both legs , which is eventually accompanied by urinary urgency ( reported in up to 50% of cases in later disease stages ) and mildly impaired vibration sense resulting from " dying back " degeneration affecting axonal transport of the longest fibers that innervate the lower extremities .
pure hsp can be confused with other diseases involving the corticospinal tract and dorsal column .
therefore , clinicians should consider this when they encounter patients who do not show improvement in gait disturbance , although they receive appropriate treatment . here , we report the case of a patient who was initially misdiagnosed with subacute combined degeneration ( scd ) , but in fact had hsp with a novel spast mutation .
a 58-year - old man with gait disturbance came to our hospital on oct 30 , 2011 .
he was unable to regulate his steps by himself , and his acquaintances reported he walked with a slight limp .
the impaired gait began 3 years after he had undergone subtotal gastrectomy and chemotherapy for 6 months .
thereafter , he felt tingling sensations in the hands and feet and acquired gait difficulties .
he had quit smoking and drinking alcohol many years prior to his diagnosis . upon neurological examination ,
however , there was a severely decreased response to vibration in both big toes , particularly in the left .
the ankle jerk reflexes were bilaterally decreased , whereas the reflexes of other joints were normal .
thus , he had mixed neurological signs that involved the upper motor neuron and peripheral nerves .
considering his previous medical history , we investigated his brain , spinal cord , meninges , and peripheral nerve by using magnetic resonance imaging ( mri ) , cerebrospinal fluid ( csf ) analysis , blood tests , and electrodiagnostic studies .
notable results included the lower - normal limit of serum vitamin b12 ( 363 pg / ml ; reference range 200 - 1,000 pg / ml ) and generalized sensory dominant polyneuropathy with axonal involvement .
blood tests , including those for syphilis , hiv , diabetes , connective tissue disease , vasculitis , and renal and liver function , were normal .
mild small vessel disease and a small amount of chronic subdural hematoma were observed in the left cerebral convexity .
whole - spine mri revealed normal signal intensity in the cord , except for disc extrusion with mild cord indentation , which did not seem relevant to the exhibited neurological symptoms .
he was intramuscularly administered cyanocobalamin regularly for 6 months . however , there was no improvement in his condition .
after reconsidering his abnormal neurological signs and laboratory tests , we examined hsp mutations in his genomic dna . as a result , the spast mutation was detected from the gene sample of the proband ( fig .
the mutation , a novel splicing mutation , is c.870 + 1delg ( ivs5 ; heterozygote ) .
we compared this result with the mutation database ( http://hgmd.cf.ac.uk/ac/index.php ) , and there was no previous information of this polymorphism or mutation at this locus .
his 32-year - old son complained of subjective gait difficulty , even though there was no abnormality in his walking .
however , he showed hyper - reflexic knee jerks , ankle clonus , and bilateral extensor toe signs .
his 29-year - old daughter with an intellectual disability of unknown origin did not have any abnormalities upon examination .
the symptoms and signs of the patient and his son were different and are described in table 1 .
as described , we misdiagnosed this patient with scd , which is distinct from hsp , because of atypical neurological signs and previous medical history .
a genetic test revealed a novel splicing mutation in the spast gene that confirmed hsp .
genetically , hsp is classified according to the mode of inheritance and various gene loci . among the several autosomal dominant hsp loci ,
since the first mutation in the spast gene was identified in 1999 , at least 300 different pathogenic mutations have been detected .
spast is composed of 17 exons , encodes the spastin protein , and belongs to the atpases associated with various cellular activities ( aaa ) family . in the spast gene , the aaa domain in the c - terminal region ( amino acids 342 to 599 ) and the microtubule interacting and trafficking ( mit ) domain in the n - terminal region play important roles .
a large number of mutations are located in the aaa domain and are related with microtubule - severing and membrane - binding properties .
furthermore , the mit domain is involved in microtubule dynamics , such as intracellular organelle trafficking and endocytosis .
in korea , there are 4 previous reports of novel spast mutations : one report involved a large genetic study of spast and atl1 mutations among several families .
most mutations are located between exons 7 - 17 , in the aaa domain , and 1 mutation is located in intron 11 .
only one was a splicing mutation ; the others were missense mutations , in - frame deletions , and frame - shift mutations . unlike in our patient , the clinical manifestations in the patients in these reports typically corresponded to pure ad - hsp .
it is to be remained whether our hsp patient should be classified as having a rare " complicated " ad - hsp with a spast gene mutation or " pure " ad - hsp , combined with nutritional - deficiency peripheral neuropathy .
in conclusion , we report a novel splicing mutation , c.870 + 1delg ( ivs5 ) , in a korean family with autosomal dominant - inherited hsp . we confirmed the deletion of exon 5 by using rt - pcr and segregation of the spast gene among family members by direct sequencing .
autosomal dominant hereditary spastic paraplegia ( ad - hsp ) is due to mutations in the " spastin " gene ( spast gene ) encoding the aaa protein . 
 the main clinical features of " pure " hsp are progressive lower - limb spasticity with corticospinal tracts and dorsal column degeneration without peripheral neuropathy . here 
 we report the case of hsp with novel spast gene mutation that misdiagnosed with subacute combined degeneration initially . 
 a 58-year - old man with gait disturbance came to our hospital . 
 he was unable to regulate his steps by himself . 
 the impaired gait began 3 years after he had undergone subtotal gastrectomy and chemotherapy for 6 months . 
 thereafter , he started feeling tingling sensations in the hands and feet and acquired gait difficulties . 
 he denied having a family history of abnormal gait or developmental problem . 
 we diagnosed him with subacute combined degeneration on the evidence of history of gastrectomy , lower normal limit of vitamin b12 ( 363 pg / ml ) , apparent absence of vibration sensations and paresthesia in the feet . 
 he was intramuscularly administered cyanocobalamin regularly . however , there was no improvement in his condition . 
 we reconsidered his symptoms and signs , decided to examine the spast gene , which is the most common mutation in hsp . 
 the spast gene , c.870 + 1delg , heterozygote , splicing mutation is detected from the gene sample . 
 there was no previous information of this polymorphism or mutation at this locus . 
 we examined his two children , and the same mutation was founded in his son . 
 we report a patient of novel spast gene mutation with ad - hsp which is misdiagnosed with scd .