We have discovered that beta-III spectrin (SPTBN2) mutations cause spinocerebellar ataxia type 5 (SCA5) in an 11-generation American kindred descended from President Lincoln's grandparents and two additional families. Two families have separate in-frame deletions of 39 and 15 bp, and a third family has a mutation in the actin/ARP1 binding region. Beta-III spectrin is highly expressed in Purkinje cells and has been shown to stabilize the glutamate transporter EAAT4 at the surface of the plasma membrane. We found marked differences in EAAT4 and GluRdelta2 by protein blot and cell fractionation in SCA5 autopsy tissue. Cell culture studies demonstrate that wild-type but not mutant beta-III spectrin stabilizes EAAT4 at the plasma membrane. Spectrin mutations are a previously unknown cause of ataxia and neurodegenerative disease that affect membrane proteins involved in glutamate signaling.

Cognitive impairment was studied in distinct types of spinocerebellar ataxia (SCA): eleven SCA1, 14 SCA2, and 11 SCA3 individuals and 8 age- and IQ- matched controls. All were submitted to a neuropsychological test battery that comprised tests for IQ, attention, executive function, verbal and visuospatial memory. Executive dysfunction was prominent in SCA1 as compared with controls and all other SCA types. Mild deficits of verbal memory were present in SCA1, SCA2 and SCA3. The neuropathological pattern in different SCA types suggests that these cognitive deficits are not likely to be contingent upon cerebellar degeneration but to result from disruption of a cerebrocerebellar circuitry presumably at the pontine level.

The nosology and aetiology of sporadic adult-onset ataxia are poorly understood. The aim of the present study was to answer the following questions: (i) How many sporadic ataxia patients have a genetic cause? (ii) How many sporadic ataxia patients suffer from multiple system atrophy (MSA)? (iii) Is there a specific association between sporadic ataxia and serum anti-glutamic acid decarboxylase (GAD) or antigliadin antibodies? and (iv) What are the clinical features of patients with unexplained sporadic ataxia? The study was performed in 112 patients who met the following inclusion criteria: (i) progressive ataxia; (ii) onset after 20 years; (iii) informative and negative family history (no similar disorders in first- and second-degree relatives; parents older than 50 years); and (iv) no established symptomatic cause. Thirty-two patients (29%) met the clinical criteria of possible (7%) or probable (22%) MSA. The Friedreich's ataxia mutation was found in five patients (4%), the spinocerebellar ataxia (SCA) 2 mutation in one (1%), the SCA3 mutation in two (2%) and the SCA6 mutation in seven (6%). The disease remained unexplained in 65 patients (58%). We did not detect anti-GAD antibodies in any of our patients. Antigliadin antibodies were present in 14 patients, 10 patients with unexplained ataxia (15%) and 4 patients with an established diagnosis (9%). Patients with unexplained sporadic ataxia had a median disease onset of 56.0 years. Decreased vibration sense (62%), decreased or absent ankle reflexes (40%), increased ankle reflexes (39%), dysphagia (38%) and extensor plantar responses and/or spasticity (34%) were the most frequent extracerebellar symptoms. Compared with MSA, disease progression was significantly slower.

A novel neurological syndrome has recently been described to be associated with an expanded polyglutamine domain. The expansion results from partial duplication within the TATA-binding protein (TBP). By investigation of 604 sporadic and familial cases with various forms of neurological syndromes and 157 unaffected individuals, we found repeat expansions in the TBP in four patients of two families with autosomal dominant inheritance of ataxia, dystonia, and intellectual decline. Two different genotypes for the repetitive sequence could be demonstrated which led to elongated polyglutamine stretches between 50 and 55 residues, whereas normal alleles with 27 to a maximum of 44 glutamine residues were found in this study. The expansion to 50 or more glutamine residues results in a pathological phenotype and confirms the report of a new polyglutamine disease.

Oculocutaneous albinism (OCA) is caused by a deficiency of melanin synthesis and characterized by generalized hypopigmentation of skin, hair, and eyes. Due to the hypopigmentation of the retinal pigment epithelium, OCA is usually associated with congenital visual impairment, in addition to an increased risk of skin cancer. OCA is a genetically heterogeneous disease with distinct types resulting from mutations in different genes involved in the pathway which results in pigmentation. OCA1 is associated with mutations in the TYR gene encoding tyrosinase. OCA2 results from mutations in the P gene encoding the P protein and is the most common form of OCA. OCA3, also known as rufous/red albinism, is caused by mutations in the TYRP1 gene, which encodes the tyrosinase-related protein 1. Recently, OCA4 was described as a new form of OCA in a single patient with a splice site mutation in the MATP gene (or AIM1), the human ortholog of the murine underwhite gene. The similarity of MATP to transporter proteins suggests its involvement in transport functions, although its actual substrate is still unclear. We screened 176 German patients with albinism for mutations within the MATP gene and identified five individuals with OCA4. In this first report on West European patients, we describe 10 so far unpublished mutations, as well as two intronic variations, in addition to two known polymorphisms.