Our results suggest that no consistent relationship exists between APOE genotype, plasma lipoproteins, and AD.

We compared anti-GM1 IgM antibody titers in patients with various neurologic diseases and in normal subjects. We found increased titers in patients with lower motor neuron disease, sensorimotor neuropathy, or motor neuropathy with or without multifocal conduction block. In patients with other diseases, titers are similar to those in normal individuals, suggesting that anti-GM1 antibody levels are not increased nonspecifically after neural injury or inflammatory diseases. Anti-GM1 antibodies in many of the patients occur as monoclonal gammopathies, predominantly of lambda light-chain type, but the antibodies are sometimes polyclonal with normal or increased serum IgM concentrations. Most of the anti-GM1 antibodies appear to react with the Gal(beta 1-3)GalNAc epitope which is shared with asialo-GM1 and GD1b, but in some patients the antibodies are more specific for GM1 and associated with motor neuropathy. Patients with motor or sensorimotor peripheral neuropathy or lower motor neuron disease should be tested for anti-GM1 antibodies or anti-Gal(beta 1-3)GalNAc antibodies, as therapeutic reduction in antibody concentrations was reported to result in clinical improvement in some patients.

The Gly206Ala mutation was found in 8 of 19 unrelated Caribbean Hispanic families with early-onset familial AD. This genetic change may be a prevalent cause of early-onset familial AD in the Caribbean Hispanic population.

Linkage to chromosome 12p for familial Alzheimer disease (AD) has been inconsistent. Using 35 markers near the centromere of chromosome 12, we investigated 79 Caribbean Hispanic families with AD. Two-point linkage analysis using affected sib pairs yielded LOD scores of 3.15 at D12S1623 and 1.43 at D12S1042. The LOD score at D12S1623 decreased to 1.62 in families with late-onset (age >65 years) AD (LOAD), but the LOD score at D12S1042 was unchanged. Among families negative for the apolipoprotein E (APOE-epsilon 4) allele, the LOD score for D12S1623 was lower (1.01), whereas that for D12S1042 increased to 1.73. Among families positive for the APOE-epsilon 4 allele, none of the LOD scores reached 1. Multipoint affected-relative-pair analysis showed peaks at D12S1623 (nonparametric linkage [NPL] score 1.52; P=.028) and near D12S1042, at D12S1057 (NPL score 1.57; P=.027). NPL scores for both D12S1623 and D12S1057 increased in families affected with LOAD, but, in APOE-epsilon 4-negative families, only scores for the region flanking D12S1623 remained elevated (NPL score 1.74; P=.013). This study of Caribbean Hispanics with familial AD extends and provides modest evidence of linkage to loci on chromosome 12p. Linkage varied by age at onset of AD and by the presence or absence of the APOE-epsilon 4 allele.

Both early-onset and late-onset familial AD occur in Caribbean Hispanics. In contrast to sporadic AD, late-onset familial AD among Caribbean Hispanics is strongly associated with APOE epsilon4. Future attempts to identify additional susceptibility genes should consider the effects of APOE epsilon4.