Clinicai And Genetic Analysis Of Patients With Kennedy’s Disease And Hereditary Spastic Paraplegia

Part I:Clinical and genetic analysis of patients with Kennedy’s diseaseBackgroundKennedy’s disease, also known as spinal and bulbar muscular atrophy (SBMA), is a hereditary neurodegenerative disease with X-linked recessive inheritance. Its prevalence is estimated about 1 in 40 000. The clinical manifestations are characterized by slowly progressive, symmetric or asymmetric weakness and atrophy in face, tongue, neck and proximal or distal limb muscles, occasionally with sensory disturbances. Tongue atrophy is particularly noticeable and fasciculations are apparent in most patients. There maybe have signs of incomplete androgen insensitivity syndrome, such as gynecomastia, elevated testosterone or progesterone, and reduced fertility. There may be mildly or severely elevated creatine kinase. Electromyography presents lower motor units damage, occasionally with abnormal sensory nerve conduction studies. Muscle biopsy shows neuropathic and accidentally myopathic alterations. Kennedy’s disease is caused by an expansion of the CAG triplet repeat in exon 1 of androgen receptor (AR) gene. Normal individuals will have repeat lengths between 14 and 32 CAGs,21 CAGs averagely, but the patients with Kennedy’s disease will have increased repeat length to between 40 and 55 CAGs,47 CAGs averagely. The disease will be diagnosed when the repeat length more than 40 CAGs. AR gene contains 8 exons and spans about 90kb. AR protein consists of 919 amino acids and is a member of steroid hormone receptors superfamily. Kennedy’s disease belongs to ployglutamine (poly-Q) disorders, which are caused by a CAG trinucleotide repeat expansion within the coding region of affected genes. This mutation results in an abnormally long polyQ tract within the respective proteins. The poly-Q expanded proteins show structural changes and functional abnormities and lead to the diseases eventually. The main molecular pathophysiology of Kennedy’s disease includes the following aspects. The trinucleotide (CAG) repeat expansion in AR gene causes an expanded polyglutamine in AR protein which shows an androgen-dependent toxic gain of function. Nuclear accumulation of the polyglutamine-expanded AR is the first step in the degeneration process of spinal and bulbar motor neuron. Abnormal post-translational modifications of AR protein, transcriptional dysregulation of related genes, axonal transport impairment, mitochondrial dysfunction, non-cell autonomous degeneration of motor neurons, abnormal endoplasmic reticulum stresss and activation of cell death pathways are all play important roles in the pathogenesis of Kennedy’s disease. These result in neuronal degeneration and dealth finally. An effective medical treatment does not yet exist for Kennedy’s disease. According the pathogenesis, androgen deprivation is a main therapeutic option and has been successfully performed on animal model. However, the clinical efficacy is not ideal.ObjectiveTo investigate the features of AR gene mutation and clinical manifestation in Kennedy’s disease and to lay a foundation for gene diagonosis and gain a greater understanding of the disease.MethodsThe CAG repeat length in exon 1 of AR gene were screened in the proband and his sister of family 1, the proband and his brother of family 2, and 1 sporadic case of family 3 by polymerase chain reaction and DNA direct sequencing. Retrospective analysis was made for the clinical manifestations and laboratory investigations of 5 patients who came from the above 2 SPG families and 1 sporadic case respectively. Correlation analysis between the numbers of CAG repeat of AR gene and the age of the disease onset was performed.ResultsThe genetic mode of the families was according to X-linked recessive inheritance. By mutation screening of the CAG trinucleotide repeat domain in exon 1 of AR gene, three different enlarged (CAG)n repeat domains were discovered in 2 Kennedy’s families and 1 sporadic case. The number of CAGs was 48 in patient â…¢4 of family 1. However, it was 22 in his healthy sister. Patient â…¢2 and his brother â…¢1 of family 2 had 43 CAG repeats. Patient â…¢2 of family 3 had 44 CAG repeats. So all 3 probands had a CAG repeat expansion which more than 40 repeats and were diagnosed as Kennedy’s disease definitely. Five affected individuals were examined in our study. They were patient â…¢2, patient â…¢4 and patient â…¢6 of family 1, patient â…¢2 of family 2, and the sporadic patient â…¡2 of family 3. All the patients were male and their average age was 55.80±12.97 years old. The mean±SD age of onset was 48.20±8.70 years. Dysarthria was observed a mean±SD of 5.33±1.53 years later. Dysphagia occurred after 11 years after the onset in 1 patient. The duration of the disease was a mean±SD of 7.60±5.32 years. The initial symptoms in all patients were weakness, atrophy and fasciculations in the limb and bulbar muscles, which were slowly progressive. Four patients had signs of androgen insensitivity, such as reduced fertility or gynaecomastia. All 5 patients demonstrated muscle atrophy and weakness of face, tongue, neck, trunk and upper and lower limbs in examination. Tongue atrophy was particularly noticeable and fasciculations were apparent in muscles. Muscle strength was 4 to 5 grades. Patient â…¢ 1 of family 2, aged 50 years, was mutation carriers, but he was asymptomatic and might be presymptomatic patients. Mild increased serum lactate dehydrogenase, creatine kinase, creatine kinase isoenzyme and hydroxybutyric dehydrogenase were detected in 2 patients. Testosterone levels were tested in 3 patients and slightly elevated only in 1 patient. Electrophysiological investigations showed compound muscle action potentials in median nerve and sensory nerve conduction velocity in sural nerve were moderately decreased in 1 patient respectively. Electromyogram showed extensive neurogenic abnormalities in 3 patients. Muscle magnetic resonance of right upper arm was performed on patient â…¡2 of family 3 demonstrated reduced muscular volumes and fatty infiltration, consistent with chronic atrophy. Correlation analysis of the numbers of CAG repeat of AR gene and the age of the disease onset was performed on 3 probands patients and the results showed negative correlation between them, but no linear correlation.ConclusionKennedy’s disease was featured by expansion of CAG repeat numbers in exon 1 of AR gene. The clinical manifestations of the disease are progressive weakness and atrophy in bulbar and spinal muscles in middle-aged men, occasionally demonstrating incomplete androgen insensitivity syndrome.Kennedy’s disease was featured by expansion of CAG repeat numbers in exon 1 of AR gene. The clinical manifestations of the disease are progressive weakness and atrophy in bulbar and spinal muscles in middle-aged men, occasionally demonstrating incomplete androgen insensitivity syndrome.Part II:Clinical and genetic analysis of patients with hereditary spastic paraplegiaBackgroundHereditary spastic paraplegia (HSP or SPG) is a group of inherited neurodegenerative disorders characterized by progressive spasticity and weakness of both lower extremities. Its prevalence is estimated about 1-10 in 100 000. According to the clinical manifestations, SPG is classified into two broad categories:pure HSP, only with predominant spastic paraplegia; and complicated SPG, with additional neurological abnormalities, such as intellectual disability, seizures, extrapramidal disturbances, ataxia, optic neuropathy, peripheral neuropathy, skin abnormalities and so on. Hereditary spastic paraplegia may be inherited as an autosomal dominant (AD), autosomal recessive (AR), or X-linked recessive (XR) form. AD transmission is observed in most SPG families. To date, there are over 70 SPG loci and more than 50 SPG genes. Mutations in spastin gene, which causes SPG4 genetype, are detected in approximately 40% of all SPG families. More than 400 spastin mutations are identified, mainly including missense, nonsense, splice site, insertion and deletion mutation, most of which are located in the AAA domain of spastin protein. Spastin gene contains 17 exons and spans about 110kb. Spastin protein consists of 616 amino acids and belongs to the AAA ATPase protein family. Degeneration and demyelination of bilateral corticospinal tract is the main pathological changes. Thoracic cord and lumbar cord are the most severely affected. Bilateral spinocerebellar tracts and fasiculus gracilis fibres also involved mostly. Marked neuronal losses are observed in Clarke’s column. The number of pyramidal cells in motor cortex is decreased occasionally. Complicated SPG may have other pathological changes, such as peripheral lesion, loss of hippocampal neurons and so on. There are several hypotheses about the pathogenesis of SPG. such as haploinsufficiency, dominant-negative effect, toxic gain-of-function effects of mutant spastin protein, or threshold-effect-model hypothesis. A variety of molecular abnormalities underlie the disease, including axonal transport disruption, mitochondrial dysfunction, primary myelin abnormality, abnormal protein degradation, disturbance in vesicle formation and membrane trafficking, et al. For SPG4, wild spastin protein associates with microtubules transiently by the N-terminal region of the protein and sever them to promote their disassembly. Their interaction is regulated through the ATPase activity of the AAA domain. Mutant spastin protein loses its ATPase function and binds to microtubules constitutively, leading to impairment of microtubule cell cytoskeleton in long axons. It may selectively disrupt anterograde axonal transport of mitochondria and membrane bound organelles. Mitochondria, microtubules. neurofilament and so on accumulate in axonal swelling. The axonal transport defects develop and lead to neuronal degeneration and death eventurally. To date, there is no an effective medical treatment for SPG.ObjectiveTo analyze the features of spastin gene mutation and investigate the characteristics of clinical manifestations in 2 autosomal dominant hereditary spastic paraplegia families and 1 spordic case.MethodsMutation analysis of the spastin gene was screened by polymerase chain reaction (PCR) combined with DNA direct sequencing in the probands and part of their relatives of two SPG families and 1 sporadic case. Retrospective analysis were made for the clinical information of 5 patients who came from the above 2 SPG families and 1 sporadic case, expecially the data of 2 patients of the family caused by spastin gene mutation.ResultsBy gene sequencing, a mutation c.1291Câ†'T in exon 10 of spastin gene was identified in the proband â…¢1 and his mother â…¡2 of family 1. The mutation might cause the codon CGA which encodes arginine at the site of 431 of spastin protein to turn into a premature termination codon TGA, thus leading to a truncated mRNA and a truncated spastin protein. So it was a nosense mutation. No spastin gene mutation was detected in familiy 2 and the sporadic patient. Five patients including 3 males and 2 femals came from two AD-SPG families and 1 spordic case. Their average age was 41.60±21.87years old. The mean±SD age of onset was 23.40±17.44 years. The duration of the disease was a mean±SD of 18.20± 13.94 years. The symptom that first appeared in these patients was a weakness and spasticity in lower limbs which slowly progressed in the subsequent years. Two of the patients reported urinary frequency. Hypermyotonia, hyperreflexia and bilateral Babinski sign in lower limbs were seen at examination. Some signs were observed, including patellar clonus in 1 patitent, ankle clonus in 3 patients, scissors gait in 4 patietns, and skeletal deformity such as clubfoot and cavus in 2 patients. In the family 1 which was caused by the spastin gene mutation c.1291Câ†'T, there were 2 patients including 1 male and 1 female. Their mean±SD age of onset was 42.00±2.83 years. The duration of the disease was a mean±SD of 15.00±12.73 years. Patient â…¡2 required a walking stick after 24 years of disease duration and she showed urinary frequency. Hyperreflexia, ankle clonus, scissors gait were seen at their examination. Patient â…¡2 presented clubfoot. Mild elevated blood sugar was detected in patient â…¢1. There were no specific changes in his brain and cervical vertebra magnetic resonance inspection and electromyogram.ConclusionThe c.1291Câ†'T mutation in spastin gene might cause autosomal dominant pure SPG with typical clinical manifestation. The patients had a later onset and mild symptoms and signs relatively.