PolyQ Repeat Expansions in ATXN2 Associated with ALS Are CAA Interrupted Repeats

Amyotrophic lateral sclerosis (ALS) is a devastating, rapidly progressive disease leading to paralysis and death. Recently, intermediate length polyglutamine (polyQ) repeats of 27–33 in ATAXIN-2 (ATXN2), encoding the ATXN2 protein, were found to increase risk for ALS. In ATXN2, polyQ expansions of ≥34, which are pure CAG repeat expansions, cause spinocerebellar ataxia type 2. However, similar length expansions that are interrupted with other codons, can present atypically with parkinsonism, suggesting that configuration of the repeat sequence plays an important role in disease manifestation in ATXN2 polyQ expansion diseases. Here we determined whether the expansions in ATXN2 associated with ALS were pure or interrupted CAG repeats, and defined single nucleotide polymorphisms (SNPs) rs695871 and rs695872 in exon 1 of the gene, to assess haplotype association. We found that the expanded repeat alleles of 40 ALS patients and 9 long-repeat length controls were all interrupted, bearing 1–3 CAA codons within the CAG repeat. 21/21 expanded ALS chromosomes with 3CAA interruptions arose from one haplotype (GT), while 18/19 expanded ALS chromosomes with <3CAA interruptions arose from a different haplotype (CC). Moreover, age of disease onset was significantly earlier in patients bearing 3 interruptions vs fewer, and was distinct between haplotypes. These results indicate that CAG repeat expansions in ATXN2 associated with ALS are uniformly interrupted repeats and that the nature of the repeat sequence and haplotype, as well as length of polyQ repeat, may play a role in the neurological effect conferred by expansions in ATXN2

A mouse monoclonal antibody detecting the allospecificity HLA-A3

Balb/c mice were immunized with a human B-lymphoblastoid cell line typed HLA-A3, B7. The splenocytes of the immunized mice were fused with a murine myeloma. Supernatants of the cultures were screened against the immunizing cell line in fluorochromasia. Positive cultures were expanded and cloned. One of the clones, X 15.4, was expanded and brought to ascites in Balb/c mice. Monoclonality of the antibody X 15.4, which belongs to the class IgM and immunoprecipites a molecule of 44000 daltons, was demonstrated by isoelectric focusing. By complement dependent citotoxicity the ascites only reacted with the lymphocytes of all HLA-A3 individuals from a panel of 146 donors, showing no crossreactions. X 15.4 appears to be one of the very rare xenomonoclonal antibodies suitable for HLA typing

Instability of a premutation allele in homozygous patients with myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is caused by the expansion of an unstable CTG repeat in the DMPK gene on chromosome 19q13.3. We present two siblings with DM1 who each inherited a premutation allele, (CTG)43, stably transmitted from the mother and a full-mutation allele, either (CTG)500 or (CTG)180, derived from a paternal protomutation allele, (CTG)52. Small-pool polymerase chain reaction analysis showed that the (CTG)52 repeat allele was relatively stable in somatic tissues but was highly unstable in the male germline and extremely biased toward further expansion, consistent with the high levels of anticipation observed in DM1 families. The (CTG)43 allele showed subtle somatic instability in the mother, with maximum additions of two repeats and deletions of one repeat. Conversely, in the younger affected siblings the (CTG)43 allele showed a high degree of somatic instability (approximately 70% mutation load), resulting in deletions reverting to the high end of the normal range (down to [CTG]33) and additions up to the proto-mutation range (up to [CTG]64). The difference in the somatic stability of the (CTG)43 allele between the mother and her offspring suggests that interallelic interactions or other mechanisms in trans regulate the stability of the (CTG)43 premutation allele

How genetics affects the brain to produce higher-level dysfunctions in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multisystemic disorder dominated by muscular impairment and brain dysfunctions. Although brain damage has previously been demonstrated in DM1, its associations with the genetics and clinical/neuropsychological features of the disease are controversial. This study assessed the differential role of gray matter (GM) and white matter (WM) damage in determining higher-level dysfunctions in DM1. Ten patients with genetically confirmed DM1 and 16 healthy How genetics affects the brain to produce higher-level dysfunctions in myotonic dystrophy type 1matched controls entered the study. The patients underwent a neuropsychological assessment and quantification of CTG triplet expansion. All the subjects underwent MR scanning at 3T, with studies including T1-weighted volumes and diffusion-weighted images. Voxel-based morphometry and tractbased spatial statistics were used for unbiased quantification of regional GM atrophy and WM integrity. The DM1 patients showed widespread involvement of both tissues. The extent of the damage correlated with CTG triplet expansion and cognition. This study supports the idea that genetic abnormalities in DM1mainly target the WM, but GM involvement is also crucial in determining the clinical characteristics of DM1