HLA-DR4 as a risk allele for autism acting in mothers of probands possibly during pregnancy.

OBJECTIVES: To test whether HLA-DR4 acts in the mother, possibly during pregnancy, to contribute to the phenotype of autistic disorder in her fetus. DESIGN: Transmission disequilibrium testing in case mothers and maternal grandparents. SETTING: Previous studies have consistently shown increased frequency of HLA-DR4 in probands with autism and their mothers, but not their fathers. However, this has been documented only in case-control studies and not by a more direct study design to determine whether HLA-DR4 acts in mothers during pregnancy to contribute to autism in their affected offspring. PARTICIPANTS: We genotyped for HLA-DR alleles in members of 31 families with parents and maternal grandparents. Probands with autism were tested using the Autism Diagnostic Observation Schedule-Western Psychological Services and Autism Diagnostic Interview, Revised. There was 80% power to detect an odds ratio of 3.6. Participants were all families from New Jersey and were similar in number to earlier studies of autism and HLA-DR4. OUTCOME MEASURES: Analysis was by standard transmission disequilibrium testing. As a secondary test we examined the possibility of maternal imprinting. RESULTS: Significant transmission disequilibrium for HLA-DR4 was seen (odds ratio, 4.67; 95% confidence interval, 1.34-16.24; P = .008) for transmissions from maternal grandparents to mothers of probands, supporting a role for HLA-DR4 as an autism risk factor acting in mothers during pregnancy. Transmission disequilibrium was not seen for HLA-DR4 transmissions from parents to probands or from mothers to probands. CONCLUSIONS: The HLA-DR4 gene may act in mothers of children with autism during pregnancy to contribute to autism in their offspring. Further studies are required to confirm these findings.

Incomplete penetrance of susceptibility genes for MHC-determined immunoglobulin deficiencies in monozygotic twins discordant for type 1 diabetes.

Incomplete intrinsic penetrance is the failure of some genetically susceptible individuals (e.g., monozygotic twins of those who have a trait) to exhibit that trait. For the first time, we examine penetrance of susceptibility genes for multiple MHC gene-determined traits in the same subjects. Serum levels of IgA, IgD, IgG3, but not IgG4, in 50 pairs of monozygotic twins discordant for type 1 diabetes (T1D) correlated more closely in the twins than in random paired controls. The frequencies of subjects deficient in IgA (6%), IgD (33%) and IgG4 (12%), but not in IgG3, were higher in the twins than in controls. We postulate that this was because the MHC haplotypes (and possible non-MHC genes) that predispose to T1D also carry susceptibility genes for certain immunoglobulin deficiencies. Immunoglobulin deficiencies were not associated with T1D. Pairwise concordance for the deficiencies in the twins was 50% for IgA, 57% for IgD and 50% for IgG4. There were no significant associations among the specific immunoglobulin deficiencies except that all IgA-deficient subjects had IgD deficiency. Thus, intrinsic penetrance is a random process independently affecting different MHC susceptibility genes. Because multiple different external triggers would be required to explain the results, differential environmental determinants appear unlikely.

Immunoglobulin deficiencies and susceptibility to infection among homozygotes and heterozygotes for C2 deficiency.

About 25% of C2-deficient homozygotes have increased susceptibility to severe bacterial infections. C2-deficient homozygotes had significantly lower serum levels of IgG2, IgG4, IgD, and Factor B, significantly higher levels of IgA and IgG3 and levels of IgG1 and IgM similar to controls. Type 1 (28 bp deletion in C2 exon 6 on the [HLA-B18, S042, DR2] haplotype or its fragments) and type II (non-type I) C2-deficient patients with increased susceptibility to bacterial infection had significantly lower mean levels of IgG4 (p < 0.04) and IgA (p < 0.01) than those without infections (who had a higher than normal mean IgA level) but similar mean levels of other immunoglobulins and Factor B. Of 13 C2-deficient homozygotes with infections, 85% had IgG4 deficiency, compared with 64% of 25 without infections. IgD deficiency was equally extraordinarily common among infection-prone (50%) and noninfection-prone (70%) homozygous type I C2-deficient patients. IgD deficiency was also common (35%) among 31 type I C2-deficient heterozygotes (with normal or type II haplotypes), but was not found in 5 type II C2-deficient heterozygotes or 1 homozygote. Thus, C2 deficiency itself is associated with many abnormalities in serum immunoglobulin levels, some of which, such as in IgG4 and IgA, may contribute to increased susceptibility to infection. In contrast, IgD deficiency appears not to contribute to increased infections and appears to be a dominant trait determined by a gene or genes on the extended major histocompatibility complex (MHC) haplotype [HLA-B 18, S042, DR2] (but probably not on type II C2-deficient haplotypes) similar to those previously identified on [HLA-B8, SC01, DR3] and [HLA-B18, F1C30, DR3].