Homocarnosinosis: A historical update and findings in the SPG11 gene

OBJECTIVES

A family with homocarnosinosis was reported in the literature in 1976. Three affected siblings had spastic paraplegia, retinitis pigmentosa, mental retardation, and cerebrospinal fluid (CSF) homocarnosine concentrations 20 times higher than in controls. Based on the clinical findings and new genetic techniques, we have been able to establish a precise genetic diagnosis.

METHOD

The medical records were re-evaluated, and genetic analyses were performed post-mortem in this original family. SNP array-based whole genome homozygosity mapping and Sanger sequencing of the SPG11 gene were performed. Seven additional Norwegian SPG11 patients and their disease-causing variants and clinical findings were evaluated. Homocarnosine levels in CSF were measured in four of these seven patients.

RESULTS

A homozygous pathogenic splice-site variant in the SPG11 gene, c.2316 + 1G>A, was found. The clinical findings in the original family correlate with the heterogeneous SPG11 phenotype. The same variant was found in seven other Norwegian SPG11 patients, unrelated to the original family, either as homozygous or compound heterozygous constellation. Normal homocarnosine levels were found in the CSF of all unrelated SPG11 patients.

CONCLUSIONS

A re-evaluation of the clinical symptoms and findings in the original family correlates with the SPG11 phenotype. The increased levels of homocarnosine do not seem to be a biomarker for SPG11 in our patients. Homocarnosinosis is still a biochemical aberration with unknown clinical significance.

A founder mutation p.H701P identified as a major cause of SPG7 in Norway

BACKGROUND AND PURPOSE

SPG7 is one of the most common forms of autosomal recessive hereditary spastic paraplegia. The phenotype has been shown to be heterogeneous, varying from a complex spastic ataxia to pure spastic paraplegia or pure ataxia. The aim of this study was to clinically and genetically characterize patients with SPG7 in Norway.

METHODS

Six Norwegian families with a clinical diagnosis of hereditary spastic paraplegia were diagnosed with SPG7 through Sanger sequencing and whole-exome sequencing. Haplotypes were established to identify a possible founder mutation. All patients were thoroughly examined and the clinical and molecular findings are described.

RESULTS

The core phenotype was spastic paraparesis with ataxia, bladder disturbances and progressive external ophthalmoplegia. The variant p.H701P was identified in homozygous state in one family and in compound heterozygous state in three families. Haplotype analysis of seven surrounding single nucleotide polymorphisms supports that this variant resides on a founder haplotype. Four of the families were compound heterozygous for the previously well-described p.A510V variant.

CONCLUSION

SPG7 is a common subgroup of hereditary spinocerebellar disorders in Norway. The broad phenotype in the Norwegian SPG7 population illustrates the challenges with the traditional dichotomous classification of hereditary spinocerebellar disorders into hereditary spastic paraplegia or hereditary ataxia. A Norwegian founder mutation p.H701P was identified in four out of six families, making it a major cause of SPG7 in Norway.

Clinical and genetic studies in a family with a novel mutation in the sepiapterin reductase gene

OBJECTIVES

Sepiapterin reductase deficiency is a rare, but treatable inherited disorder of tetrahydrobiopterin and neurotransmitter metabolism. This disorder is most probably underdiagnosed. To date, only 44 cases have been described in the literature. We present the clinical and genetic investigations in a family with a complex movement disorder.

MATERIALS AND METHODS

We examined two affected sisters and three healthy family members. The cerebrospinal fluid was analyzed for neurotransmitter and pterins, and the sepiapterin reductase gene (SPR) was sequenced.

RESULTS

The sisters had a complex movement disorders with dystonia and diurnal fluctuations. Both had oculogyric crises, and the older sister also hypersomnia. Both sisters had raised prolactin levels twice above the reference level. One sister had a dramatic response to levodopa, the other responded, but developed dyskinesia despite low doses. Both patients improved dramatically over time with levodopa (2.3 and 1.5 mg/kg/day). Very low levels of homovanillic acid and 5-hydroxyindoleacetic acid and increased levels of sepiapterin and dihydrobiopterin were measured in the cerebrospinal fluid before treatment. DNA analyses revealed a novel homozygous mutation in exon 2 in the SPR gene, c.364A>G/p.(Tyr123Cys), located in a highly conserved region in the gene. Both parents and the healthy sister were carriers for the same mutation.

CONCLUSIONS

A new homozygous mutation in the SPR gene was found in two sisters with dopa-responsive dystonia. This important and treatable neurotransmitter disorder must be considered in patients with a complex movement disorder with diurnal fluctuations with or without intellectual impairment. Patients with these symptoms should undergo levodopa trial, cerebrospinal fluid investigations, and genetic analyses.

SCA14 in Norway, two families with autosomal dominant cerebellar ataxia and a novel mutation in the PRKCG gene

OBJECTIVES

Despite a similar prevalence of autosomal dominant cerebellar ataxia (ADCA) in Norway compared to other European countries, less than 10% of the families are explained by the CAG trinucleotide expansions. We wanted to find the occurence of SCA14 in the dominant ataxia population and describe the phenotype.

METHODS

We screened a large dominant cerebellar ataxia cohort for mutations in the PRKCG gene. Patients were evaluated according to a standard clinical protocol for ataxia patients.

RESULTS

A novel mutation was found in two families, a C to A transversion altering Histidine to a Glutamine at codon 139, located in a highly concerved region in the gene. It completely co-segregated with the affected family members and was not seen in 576 control chromosomes. Genetic analysis revealed common alleles at three microsatellite markers between these two families suggesting a shared ancestral chromosome. Affected subjects displayed a mild, slowly progressive cerebellar syndrome that included gait and limb ataxia and saccadic pursuit and head tremor in one. Age at onset ranged from 10 to 45 years.

CONCLUSIONS

These are the first families with SCA14 reported from Scandinavia and a new mutation in the PRKCG gene. The occurrence in the Norwegian dominant ataxia cohort is 3.5%.

Ataxia with oculomotor apraxia type 2: clinical, biological and genotype/phenotype correlation study of a cohort of 90 patients

Ataxia with oculomotor apraxia type 2 (AOA2) is an autosomal recessive disease due to mutations in the senataxin gene, causing progressive cerebellar ataxia with peripheral neuropathy, cerebellar atrophy, occasional oculomotor apraxia and elevated alpha-feto-protein (AFP) serum level. We compiled a series of 67 previously reported and 58 novel ataxic patients who underwent senataxin gene sequencing because of suspected AOA2. An AOA2 diagnosis was established for 90 patients, originating from 15 countries worldwide, and 25 new senataxin gene mutations were found. In patients with AOA2, median AFP serum level was 31.0 microg/l at diagnosis, which was higher than the median AFP level of AOA2 negative patients: 13.8 microg/l, P = 0.0004; itself higher than the normal level (3.4 microg/l, range from 0.5 to 17.2 microg/l) because elevated AFP was one of the possible selection criteria. Polyneuropathy was found in 97.5% of AOA2 patients, cerebellar atrophy in 96%, occasional oculomotor apraxia in 51%, pyramidal signs in 20.5%, head tremor in 14%, dystonia in 13.5%, strabismus in 12.3% and chorea in 9.5%. No patient was lacking both peripheral neuropathy and cerebellar atrophy. The age at onset and presence of occasional oculomotor apraxia were negatively correlated to the progression rate of the disease (P = 0.03 and P = 0.009, respectively), whereas strabismus was positively correlated to the progression rate (P = 0.03). An increased AFP level as well as cerebellar atrophy seem to be stable in the course of the disease and to occur mostly at or before the onset of the disease. One of the two patients with a normal AFP level at diagnosis had high AFP levels 4 years later, while the other had borderline levels. The probability of missing AOA2 diagnosis, in case of sequencing senataxin gene only in non-Friedreich ataxia non-ataxia-telangiectasia ataxic patients with AFP level > or =7 microg/l, is 0.23% and the probability for a non-Friedreich ataxia non-ataxia-telangiectasia ataxic patient to be affected with AOA2 with AFP levels > or =7 microg/l is 46%. Therefore, selection of patients with an AFP level above 7 microg/l for senataxin gene sequencing is a good strategy for AOA2 diagnosis. Pyramidal signs and dystonia were more frequent and disease was less severe with missense mutations in the helicase domain of senataxin gene than with missense mutations out of helicase domain and deletion and nonsense mutations (P = 0.001, P = 0.008 and P = 0.01, respectively). The lack of pyramidal signs in most patients may be explained by masking due to severe motor neuropathy.

Ataxia with vitamin E deficiency in southeast Norway, case report

BACKGROUND

Ataxia with vitamin E deficiency (AVED) is a rare cause of hereditary ataxia in north European countries with unknown prevalence. Few cases are reported from these countries.

METHODS

Through a systematic population based study of hereditary ataxia in southeast Norway subjects were classified and investigated.

AIMS

To report a subject with ataxia due to vitamin E deficiency in Norway.

RESULTS

One patient with AVED was identified. The subject was a 45 years old woman with progressive ataxia from preschool age. When she was 12 years old Friedreich's ataxia was diagnosed after neurological examination. At the age of 45 re-evaluation and re-examination was performed and genetic analysis of the Frataxin gene was negative. At that time she had truncal and extremities ataxia, titubation of the head, pes cavus, inverted plantar response, loss of proprioceptive and vibration sense and a severe sensory neuropathy. Vitamin E in serum was undetectable and genetic analysis detected a compound heterozygous mutation, p.A120T and p.R134X, in the alpha-tocopherol transport protein gene on chromosome 8q13.

DISCUSSION

Vitamin E should always be assessed in progressive ataxia of genetic or unexplained causes and especially with a Friedreich's ataxia-like phenotype since treatment is available.

CONCLUSION

AVED is rare in Norway, but exists, and we here report the first genetically confirmed subject with ataxia due to vitamin E deficiency in Norway.

Cerebellar ataxia in the eastern and southern parts of Norway

INTRODUCTION

The relative frequencies of different ataxias vary among different ethnic and geographic groups. The aim of this study was to examine patients with cerebellar ataxia and find the occurrence of autosomal dominant and recessive cerebellar ataxias in the population of the southern and eastern parts of Norway and estimate its prevalence.

MATERIALS AND METHODS

Probands were systematically tested for spinocerebellar ataxia 1, 2, 3, 6 and Friedreich's ataxia. A total of 94 patients with ataxia were assessed.

RESULTS

We registered 60 patients from 39 unrelated families with hereditary ataxias. One family with SCA2 (two patients), one family with Friedreich's ataxia (two patients), two patients heterozygote for Friedreich's ataxia and one metabolic ataxia were identified.

CONCLUSIONS

We have few Friedreich's ataxia and SCA 1,2,3 and 6 in our population. Prevalence in Oslo County was estimated at 2.2/100,000 for autosomal recessive and 3.0/100,000 for autosomal dominant ataxia, respectively.