Association of genes within the major histocompatibility complex with attention deficit hyperactivity disorder.

The objective was to determine whether a relationship exists among the complement C4B gene, a DR region gene and attention deficit hyperactivity disorder (ADHD). Thirty-one subjects with ADHD, their mothers, all but 5 of their fathers, and 90 normal subjects living in northern Utah were studied. DR and C4B typing were performed by serologic HLA typing techniques and the DNA methods PCR-RFLP. The alleles of 2 genes, the null allele of the C4B gene and the beta 1 allele of the DR gene, encode for products involved in immune function and regulation. Each of these alleles was found to be significantly associated with ADHD. Moreover, approximately 55% of the ADHD subjects carried both of these alleles on 1 of their chromosomes, compared to only 8% of normal controls. Genes related to the immune system may be associated with development of the symptoms of ADHD.

Strong association of the third hypervariable region of HLA-DR beta 1 with autism.

We reported that the major histocompatibility complex (MHC) including the null allele of the C4B gene and the extended haplotype B44-C30-DR4 is associated with autism. We report now that the third hypervariable region (HVR-3) of certain DR beta 1 alleles have very strong association with autism. The HVR-3 of DR beta 1* 0401 or the shared HVR-3 alleles DR beta 1* 0404 and DR beta 1* 0404 and DR *0101, was expressed on extended haplotypes in 23 of 50 (46%) autistic subjects as compared to only 6 of 79 (7.5%) normal subjects. Another HVR-3 sequence, the DR beta 1* 0701 allele, was carried on extended haplotypes in 16 (32.0%) of the autistic subjects as compared to 8 (10.1%) of the normal subjects.

Immunogenetic studies in autism and related disorders.

The major histocompatibility complex comprises a number of genes that control the function and regulation of the immune system. One of these genes, the C4B gene, encodes a product that is involved in eliminating pathogens such as viruses and bacteria from the body. We previously reported that a deficient form of the C4B gene, termed the C4B null allele (no C4B protein produced) had an increased frequently in autism. In this study we attempted to confirm the increased incidence of the C4B null allele in autism and investigated the presence of a C4B null allele in two other childhood disorders, attention-deficit hyperactivity disorder and dyslexia (reading disability). In addition, we explored the relationship of autism to the DR beta 1 gene, a gene located close to the C4B in autism. We confirmed the finding of an increased frequency of the C4B null allele in autism and found that the related disorders also had an increased frequency of this null allele. In addition, two alleles of the DR beta 1 gene also had significantly increased representation in the autistic subjects.

Is decreased blood plasma concentration of the complement C4B protein associated with attention-deficit hyperactivity disorder?

OBJECTIVE: The complement system is a group of blood proteins that play an important role in defending against viral and bacterial infections. The objective of this investigation was to study the plasma levels of the C4B protein in attention-deficit hyperactivity disorder (ADHD) in an attempt to associate infections with the development of some cases of this disorder. METHOD: C4B plasma protein levels were studied using an enzyme-linked immunosorbent assay in a group of 23 subjects meeting DSM-III-R criteria for ADHD and a similar number of age- and sex-matched controls. Also studied were parents of the ADHD subjects. RESULTS: C4B plasma levels (157.0 micrograms/mL) in the ADHD subjects were significantly (p < .01) lower than those (239.3 micrograms/mL) in the normal age-matched subjects. Mothers of the ADHD subjects also had significantly lower C4B values compared with mothers of normal children. On the other hand, C4B values in the fathers were not significantly altered. CONCLUSIONS: Decreased C4B levels in ADHD, if replicated, may represent an important marker for ADHD (or a subgroup of ADHD). It also seems plausible that C4B levels are an important etiological factor for ADHD.

Increased frequency of the extended or ancestral haplotype B44-SC30-DR4 in autism.

Autism likely results from several different etiologies or a combination of pathological mechanisms. Recent studies suggest that this disorder may be associated with immune abnormalities, pathogen-autoimmune processes and perhaps the major histocompatibility complex (MHC). In a preliminary study we found that 22 autistic subjects had an increased frequency of the extended or ancestral MHC haplotype B44-SC30-DR4. The current study attempted to confirm this observation by studying 23 additional randomly chosen autistic subjects, most of their parents and 64 unrelated normal subjects. In agreement with earlier findings B44-SC30-DR4 was associated with autism. In combining the data from the original and current studies, B44-SC30-DR4 or a substantial fragment of this extended haplotype was represented in 40% of the autistic subjects and/or their mothers as compared to about 2% of the unrelated subjects. It is concluded that one or more genes of the MHC is (are) involved in the development of some cases of autism.

Antibodies to myelin basic protein in children with autistic behavior.

Based on a possible pathological relationship of autoimmunity to autism, antibodies reactive with myelin basic protein (anti-MBP) were investigated in the sera of autistic children. Using a screening serum dilution of 1:400 in the protein-immunoblotting technique, approximately 58% (19 of 33) sera of autistic children (< or = 10 years of age) were found to be positive for anti-MBP. This result in autistics was significantly (p < or = .0001) different from the controls (8 of 88 or only 9% positive), which included age-matched children with normal health, idiopathic mental retardation (MR) and Down syndrome (DS), and normal adults of 20 to 40 years of age. Since autism is a syndrome of unknown etiology, it is possible that anti-MBP antibodies are associated with the development of autistic behavior.

Possible association of the extended MHC haplotype B44-SC30-DR4 with autism.

We previously reported that the complement C4B null allele appears to be associated with infantile autism. Since the C4B null allele is known to be part of the extended or ancestral haplotype [B44-SC30-DR4], we investigated the incidence of [B44-SC30-DR4] in 21 autistic children and their parents. This extended haplotype was increased by almost six-fold in the autistic subjects as compared with healthy controls. Moreover, the total number of extended haplotypes expressed on chromosomes of autistic subjects was significantly increased as compared with those expressed on chromosomes of healthy subjects. We conclude that a gene related to, or included in, the extended major histocompatibility complex may be associated with autism.

Changes of soluble interleukin-2, interleukin-2 receptor, T8 antigen, and interleukin-1 in the serum of autistic children.

Immune abnormalities in autistic children led us to study for indirect evidence of immune activation as measured by the serum analysis of soluble interleukin-2 (sIL-2), interleukin-2 receptor (sIL-2R), T8 antigen (sT8), and interleukin-1 (sIL-1). The serum concentration of these soluble antigens was quantitated by enzyme-linked immunosorbent assays. The concentration of sIL-2 and sT8, but not of sIL-2R and sIL-1, antigens was significantly (P less than 0.05) increased in the sera of autistic children over that in the control healthy children or children with mental retardation (non-Down's syndrome). This finding indirectly indicates that the activation of a subpopulation of T cells occurs in some children with autism.

Increased frequency of the null allele at the complement C4b locus in autism.

Associations between C4 deficiency and autoimmune disorders have been found over the past several years. Since autism has several autoimmune features, the frequencies of null (no protein produced) alleles at the C4A and C4B loci were studied in 19 subjects with autism and their family members. The autistic subjects and their mothers had significantly increased phenotypic frequencies of the C4B null allele (58% in both the autistic subjects and mothers, compared with 27% in control subjects). The siblings of the autistic subjects also had an increased frequency of the C4B null allele, but this increase was not significant. The fathers had normal frequencies of this null allele. All family members had normal frequencies of the C4A null allele, all normal C4A and C4B alleles and all BF and C2 alleles.

Detection of maternal antibodies in infantile autism.

Maternal antibodies reactive with antigenic proteins expressed on the cell surface of paternal lymphocytes can be detected in couples with histories of more than one miscarriage or stillbirth. It is possible, but not proven, that these antibodies also react with tissues of the fetus and result in fetal death. Since many mothers of autistic children have a history of pregnancy disorder, antibodies were studied in 11 mothers of autistic children who were 6 years of age or younger. Six of the mothers had antibodies that reacted with lymphocytes of the autistic child. Five of these six mothers had a history of pregnancy disorder. Since antigens expressed on lymphocytes are found on cells of the central nervous system and, perhaps, other tissues of the developing embryo, it is suggested that aberrant maternal immunity may be associated with the development of some cases of infantile autism.

CD4+ helper T cell depression in autism.

CD4+ (helper) T cells are a heterogenous population of lymphocytes including at least two distinct subpopulations. To investigate the possibility that immune abnormalities in some subjects with autism may involve abnormal distributions of CD4+ and/or CD8+ cells, (suppressor) T cells, peripheral blood lymphocytes of 25 autistic subjects were characterized with monoclonal antibodies and flow cytometry. The autistic subjects had a significantly lower percentage and number of CD4+ cells, a lower number of T cells (CD2+ cells) and B cells (CD20+ cells), and a lower percentage and number of total lymphocytes than siblings and normal subjects. The level of blood values for female subjects appeared lower than those for males as compared to normal subjects of the same sex. These results suggest that a decrease in CD4+ cells is associated with autism.

Deficiency of suppressor-inducer (CD4+CD45RA+) T cells in autism.

CD4+ cells are a heterogenous population of lymphocytes including at least two distinct subpopulations: CD45RA+ cells, inducers of suppressor T cells and CDw29+ cells, inducers of helper function for antibody production. To investigate the possibility that immune abnormalities in autism may involve abnormal distribution of these helper subpopulations, monoclonal antibodies were used in flow cytometric analysis to characterize peripheral blood lymphocytes of 36 subjects with autism. The autistic subjects as compared to a group of 35 healthy age-matched subjects had a significantly reduced number of lymphocytes, a decreased number of CD2+ T cells and reduced numbers of CD4+ and CD4+CD45RA+ lymphocytes. The numbers of B (CD20+) cells, suppressor T (CD8+) cells, inducers of helper function (CD4+CDw29+) and natural killer (CD56+) cells were not altered in the autistic subjects. Our results suggest that an alteration in the suppressor-inducer T-cell subset is associated with autism.