Genetic control of the eighth component of complement.

Using isoelectric focusing in polyacrylamide gel and a hemolytic assay for development of patterns, extensive, structural polymorphism in human C8 has been delineated. Two alleles, C8A and C8B, have been identified in orientals, with gene frequencies of 0.655 and 0.345. In blacks, what appears to be a third common allele was found, so that frequencies were 0.692, 0.259, and 0.049 for C8A, C8B, and C8A1. In whites, C8A1 was rare with a frequency of 0.003, and frequencies for C8A and C8B were 0.649 and 0.349. Inheritance was autosomal codominant in family studies and the distribution of types in random unrelated populations fit the Hardy-Weinberg equilibrium in all groups. C8 allotypes have been determined for two previously studied families, each with a homozygous C8-deficient propositus. This study suggests that C8 deficiency is a silent or null allele of the C8 structural locus, and that half normal levels of C8 cannot be used as a single criterion for the establishment of heterozygous C8 deficiency. C8 allotypes, as well as 18 other autosomal markers, were also determined for 24 families. The C8 structural locus is not closely linked to these markers, including the human histocompatibility loci complex.

Autism and genetics. A decade of research.

The last ten years of research on the genetics of infantile autism were critically reviewed. Epidemiologic findings have shown that autism is a rare disorder with a prevalence of two to five per 10,000, a male-female ratio of 3:1, and an association with mental retardation (66% to 75% of autistic subjects have full-scale IQ scores [70]). Autism is familial, as reflected in an empiric sibling recurrence risk of 3% and pooled monozygotic and dizygotic concordance rates of 64% and 9%, respectively, which are much greater than the population prevalence of 0.02% to 0.05%. Genetic heterogeneity is pronounced with potential genetic subgroups, including autosomal recessive inheritance, X-linked inheritance, and sporadic chromosomal anomalies. Studies of subclinical markers in autism have elucidated potential markers at various levels of phenotypic expression from the DNA to the behavioral level. Linkage and cytogenetic studies point to two chromosome regions as putative markers, 9q34 and Xq27. Results of family studies support a putative biochemical marker, low levels of plasma dopamine-beta-hydroxylase, and a putative cognitive marker, ie, normal visuospatial but low verbal functioning, in autism. The frequency of minor physical anomalies and presence or absence of mental retardation are two dimensions of the physical and behavioral phenotype that may demark etiologically distinct subgroups. Genetic heterogeneity is offered as one explanation of the observed sex difference in the prevalence of autism. Directions for potentially fruitful research should be considered.

Linkage studies of bipolar disorder: methodologic and analytic issues. Report of MacArthur Foundation Workshop on Linkage and Clinical Features in Affective Disorders.

To review the findings of the linkage studies of affective disorders, a workshop, "Linkage and Clinical Features in Affective Disorders," was organized by the MacArthur Foundation Mental Health Research Network I on the Psychobiology of Depression meeting in Alexandria, Va, April 13 to 15, 1989. The major goals of the workshop for affective disorders were to explore the relationship between genetic and clinical heterogeneity, to identify major impediments to linkage studies, and to develop recommendations for the application of standardized methods of conducting linkage studies. The participants in the conference presented detailed demographic and clinical data from most of the published linkage studies of affective disorders. No systematic correspondence between genetic and clinical subtypes of bipolar disorder pedigrees was evident. The major problems hampering the linkage analyses of psychiatric disorders that were identified follow: (1) the major psychiatric disorders--the affective disorders in particular--constituting complex human disorders; (2) the lack of valid definitions of affective disorders; (3) comorbidity between the affective disorders with other disorders; (4) nonrandom mating; (5) a cohort effect, with younger birth cohorts exhibiting higher rates of affective disorders; and (6) the lack of replication of current linkage studies. The recommendations that were made for linkage study designs that incorporate some of the complexities of the affective disorders are reported.

Dopamine genes and ADHD.

Family, twin, and adoption studies have documented a strong genetic basis for ADHD/HKD, but these studies do not identify specific genes linked to the disorder. Molecular genetic studies can identify allelic variations of specific genes that are functionally associated with ADHD/HKD, and dopamine genes have been the initial candidates based on the site of action of the stimulants drugs, which for a half century have provided the primary pharmacological treatment for ADHD/HKD. Two candidate dopamine genes have been investigated and reported to be associated with ADHD/HKD: the dopamine transporter (DAT1) gene [Cook et al., American Journal of Human Genetics 1995;56:993-998, Gill et al., Molecular Psychiatry 1997;2:311-313] and the dopamine receptor D4 (DRD4) gene [LaHoste et al., Molecular Psychiatry 1996;1:121-124: Smalley et al., 1998;3:427-430; Swanson et al., Molecular Psychiatry 1998;3:38-41]. Speculative hypotheses [Swanson and Castellanos, NIH Consensus Development Conference: Diagnosis and Treatment of Attention Deficit Hyperactivity Disorder, November 1998. p. 37-42] have suggested that specific alleles of these dopamine genes may alter dopamine transmission in the neural networks implicated in ADHD/HKD (e.g. that the 10-repeat allele of the DAT1 gene may be associated with hyperactive re-uptake of dopamine or that the 7-repeat allele of the DRD4 gene may be associated with a subsensitive postsynaptic receptor). These and other variants of the dopamine hypothesis of ADHD will be discussed.

Evidence for heritability of biogenic amine levels in the cerebrospinal fluid of rhesus monkeys.

Susceptibility to several human psychopathological disorders is under partial genetic influence, and many of these disorders have biological correlates that may form part of the basis of this vulnerability. In humans, alterations in cerebrospinal fluid (CSF) metabolite levels of the amine transmitters norepinephrine, dopamine, and serotonin have been associated with several forms of psychopathology, and altered levels of these metabolites have been found in healthy probands with a familial history of such illnesses. We report evidence for heritability of CSF levels of biogenic amine measures in rhesus monkeys, Macaca mulatta. In a pilot study of 54 monkeys with known pedigrees, significant differences among sire families were found for CSF levels of norepinephrine (p = 0.04), homovanillic acid (p = 0.02), and 5-hydroxyindoleacetic acid (p = 0.04). These data indicate that variation in bioaminergic measures is associated with pedigree, and that model systems incorporating both genetic and environmental factors can contribute to the understanding of the function of aminergic systems implicated in vulnerability to psychopathology.

Evidence for autosomal recessive inheritance in 46 families with multiple incidences of autism.

The authors ascertained 46 families with multiple incidences of autism (41 with two and five with three autistic probands). Classical segregation analyses revealed a maximum likelihood estimate of the segregation ratio of p = 0.19 +/- 0.07. This is not significantly less than 0.25, the expected value for autosomal recessive inheritance. However, it is significantly less than 0.50, the expected value for autosomal dominant inheritance. The polygenic threshold model was tested and rejected over a full range of values of heritability and ascertainment probability for these families. These results are most consistent with the hypothesis of autosomal recessive inheritance in this subset of 46 families with multiple incidences of autism.

Tests for genetic heterogeneity among 18 families with Alzheimer's disease.

Two tests for genetic heterogeneity within the framework of linkage analysis were performed among 18 caucasian families with Alzheimer's disease, for each of 27 phenotypic markers. Both tests were performed twice, first assuming that individuals with Down's syndrome were also "affected" with Alzheimer's disease, and second assuming that they were not. No statistically significant heterogeneity was found under either test, regardless of the affected status assumption. However, trends in the data were consistent with heterogeneous etiology between families with both Alzheimer's disease and Down's syndrome versus families with Alzheimer's disease only. The trends were stronger when the Down's syndrome members were considered affected, and were most striking for linkage with the MNSs locus.

Physostigmine in familial ataxias.

Physostigmine was given to 12 patients with various spincerebellar degenerations, and neurologic examinations were recorded on video tapes and assessed on a semiquantitative scale. Forty minutes after a single dose, the scores improved by 35.7 +/- 4.7 percent (means +/- SEM). Eight patients were then studied over sequential 3-month periods by a randomized double-blind trial of physostigmine versus placebo. With physostigmine, scores were 33.9 +/- 8.3 percent better than before treatment or with placebo. Further investigations of cholinergic drugs seem warranted in patients with these diseases.

Genetic linkage studies in Alzheimer's disease.

We studied 18 families with Alzheimer's disease in family members, under the assumption that the disease is due to a single gene with an autosomal dominant form of inheritance. There was no evidence of linkage of Alzheimer's disease with any of 27 phenotypic gene markers analyzed, but close linkage for the Rh and MNS blood group loci was excluded.

The autosomal dominant form of "pure" familial spastic paraplegia: clinical findings and linkage analysis of a large pedigree.

We studied 33 affected members in a family with autosomal dominant "pure" familial spastic paraplegia (FSP). Symptoms began in the fourth or fifth decade, expression varied, and progression was slow. We excluded close linkage to the HLA locus (distal end of short arm of chromosome 6); C8 alpha-gamma locus (proximal end of short arm of chromosome 1); PGM1 (middle region of short arm of chromosome 1); and P blood group (location unknown). Although there was no statistically significant linkage between FSP and any of the other markers, lod scores were positive with loci for GC (vitamin D binding globulin) located on chromosome 4 (4q11-q13) and Rh located on chromosome 1 (1p34-p36).

Genetics of essential hypertension.

Blood pressure is a complex quantitative trait that is determined by multiple environmental and genetic factors. Although some simple Mendelian forms of high blood pressure have been described, essential hypertension is characterized by a complex mode of inheritance. Based on recent advances in molecular biology and statistical genetics, it has become feasible to search for chromosome regions that may contain genes contributing to the pathogenesis of hypertension in humans. For example, recent linkage and association studies have raised the possibility that a blood pressure regulatory locus may exist in or near the angiotensinogen gene on chromosome 1. Detailed genetic experiments in animal models of hypertension may help to guide further clinical studies and lead to an improved understanding of gene action in the pathogenesis of essential hypertension.

A new locus for autosomal dominant cataract on chromosome 12q13.

PURPOSE: To map the gene for autosomal dominant cataracts (ADC) in an American white family of European descent. METHODS: Ophthalmic examinations and linkage analyses using a variety of polymorphisms were performed; two-point lod scores calculated. RESULTS: Affected individuals (14 studied) exhibited variable expressivity of embryonal nuclear opacities based on morphology, location within the lens, and density. This ADC locus to 12q13 was mapped on the basis of statistically significantly positive lod scores and no recombinations (theta(m) = theta(f) = 0) with markers D12S368, D12S270, D12S96, D12S359, D12S1586, D12S312, D12S1632, D12S90, and D12S83; assuming full penetrance, a maximum lod score of 4.73 was calculated between the disease locus and D12S90. CONCLUSIONS: The disease in this family represents the first ADC locus on chromosome 12; major intrinsic protein of lens fiber (MIP) is a candidate gene.

A new betaA1-crystallin splice junction mutation in autosomal dominant cataract.

PURPOSE: To map the locus for autosomal dominant cataracts (ADCs) in a Brazilian family using candidate gene linkage analyses, describe the clinical variability, and identify potential mutations in the human betaA1-crystallin gene (CRYBA1), a candidate gene identified through linkage studies demonstrating cosegregation with markers on chromosome 17. METHODS: Members of a Brazilian family with ADC were studied. Clinical examinations and linkage analyses with polymerase chain reaction (PCR) polymorphisms of 22 anonymous markers and 2 within the neurofibromatosis type 1 gene were performed; two-point lod scores were calculated. DNA sequences of all 6 exons and 12 exon-intron boundaries of the betaA1-crystallin gene, a proximal candidate gene mapped to 17q11.1-q12 in one unaffected and two affected individuals, were screened and new variants assessed for cosegregation with the disease. RESULTS: Affected individuals exhibited variable expressivity of pulverulent opacities in the embryonal nucleus and sutures; star-shaped, shieldlike, or radial opacities in the posterior embryonal nucleus; and/or midcortical opacities. All known loci for ADC in this family on chromosomes 1 and 13 were excluded. A positive lod score on chromosome 17 was calculated. This ADC locus was mapped to two potential regions on the long arm with an intervening recombination. The only known candidate gene in these regions was betaA1-crystallin. Three previously unreported single nucleotide variants were found in this gene, one in the donor splice junction site of intron C. This variant was found in all affected members and is presumed to be the causative mutation. CONCLUSIONS: An ADC locus was mapped in a Brazilian family with variable expressivity to either 17q23.1-23.2 or 17q11.1-12 based on linkage analyses. Analyses of DNA sequences of the betaA1-crystallin gene in this family revealed three new variants, one of which is within a donor splice junction and cosegregates with affected members.

HLA haplotypes, polysomnography, and pedigrees in a case series of patients with narcolepsy.

An ongoing study of the genetics of narcolepsy ascertains families through a case series of narcoleptic probands using diagnostic criteria consisting of 1) clinical history of excessive somnolence, 2) a mean sleep latency on the multiple sleep latency test (MSLT) of less than 7.9 minutes, 3) the rapid eye movement (REM) sleep-related symptom of cataplexy, 4) nocturnal polysomnography ruling out sleep apnea syndrome, and 5) two or more transitions to REM sleep on the MSLT. All probands and first-degree relatives received clinical and laboratory evaluations as well as human leukocyte antigen (HLA) typing. Demographic characteristics of the 32 probands are as follows: 17 males and 15 females; mean age was 42.1 years (range 13-70 years). The polysomnographic data confirmed daytime sleepiness and increased tendency for REM sleep for the 32 probands. Nocturnal polysomnographic results are as follows: sleep latency, 3.2 minutes; total sleep time, 442 minutes. MSLT results are as follows: sleep latency, 3.1 minutes; REM latency, 6.9 minutes; number of REM periods, 3.2. HLA typing revealed the presence of the HLA haplotypes, DRB1*15 and DQB1*0602, in 21 narcoleptic probands, with two African-Americans having the DQB1*0602 but not the DRB1*15 allele. Among the 57 relatives of the 32 probands, 1/31 females and 7/26 males were found to be affected with narcolepsy (p < 0.02), which suggests a higher diagnostic rate in male relatives. The 21 probands who were positive for the DRB1*15 and DQB1*0602 haplotypes did not differ from the 10 probands who were negative for these alleles in terms of their nocturnal sleep parameters, MSLT findings, or clinical presentation. Three families with multiple individuals affected with narcolepsy are presented. Two families have more than one affected individual who does not have the high-risk HLA haplotype. In one of these families, the disease is segregating independently of any HLA haplotype. In the third family, there is cosegregation with HLA DRB1*15 and DQB1*0602. One family contains a pair of DNA-confirmed, monozygotic twins with narcolepsy who are discordant for cataplexy and have the HLA DR14(Dw9)/DQB1*0503 and DR4(Dw4)/DQB1*0302 haplotypes.

A goodness-of-fit test for the polygenic threshold model: application to pyloric stenosis.

A new test of goodness of fit for the polygenic threshold model is proposed. This test, when applied to disorders showing different incidence rates in males and females, is designed to account for ascertainment in more detail than previously done by other investigators. This is accomplished by computing the expected distribution of nuclear families with more than one affected sib conditioned on several family-dependent variables, including whether each family was ascertained via only affected boys or via at least one affected girl. A direct measure of the probability of observing a data set is thereby derived. The test, when applied to data on pyloric stenosis, exposes the critical nature of the ascertainment procedures. Different levels of statistical significance are obtained when mode of ascertainment is taken into account than when the mode of ascertainment is ignored.

A goodness-of-fit test for the polygenic threshold model: application to multiple sclerosis.

Recently it has been suggested that multiple sclerosis may be a multifactorial disorder. We found in British Columbia 364 families (sibship size greater than or equal to 2) in which at least on sibling was diagnosed as having "clinically definite" multiple sclerosis. The data were tested for goodness-of-fit to the multifactorial model using an analysis that considers various parameters including ascertainment probability heritability, and sex-dependent prevalence rates. The results suggest that multiple sclerosis does not fit the multifactorial model. As an alternative genetic model we propose that a major gene could be responsible for at least a portion of the cases of multiple sclerosis.

Genetic analysis of cleft lip with or without cleft palate in Danish kindreds.

The present study population consists of 2,532 families ascertained through non-syndromic cleft lip with or without cleft palate (CL +/- P) surgical probands born in Denmark between 1941 and 1971. Three samples were derived for analyses of the trait "clefted (CL +/- P) or not." Sample 1 consists of the 26 largest multigenerational families with four or more affected members. Both samples 2-MG and 2-N consist of nuclear families with at least two children and at least one proband among the children. Sample 2-MG contains 846 nuclear families derived from the kindreds with three or more generations. Sample 2-N contains a further 1,181 kindreds with only two generations, nuclear family information available. Four methods of analysis were used: 1) Pedigree analysis was performed on each of the multigenerational kindreds of Sample 1. Results were consistent with autosomal recessive inheritance in eight families and codominant inheritance in three families. These simple genetic hypotheses could not be distinguished in the remaining 15 families. 2) The goodness-of-fit of the multifactorial threshold (MF/T) model was tested in Samples 2-MG and 2-N. The MF/T model was rejected in both samples. 3) Classical segregation analysis was performed on Samples 2-MG and 2-N. Results were consistent with a possible recessive major gene for CL +/- P in Sample 2-MG, but not in Sample 2-N, and with significant admixture of sporadic cases in both samples. 4) Complex segregation analysis under the mixed model was performed on Samples 2-MG and 2-N. In Sample 2-MG, results were consistent with either the general mixed model or with an hypothesis of no major gene. In Sample 2-N, four hypotheses were equally likely: the mixed model with no polygenic component, the mixed model with the major gene component, the mixed model with no sib environmental correlation, and major gene alone. Three conclusions may be drawn: 1) The data provide no support for the MF/T model. 2) The data are consistent with the possibility of a major gene in a portion of the kindreds. 3) The data provide evidence for genetic heterogeneity for CL +/- P.

Analysis of a 1-megabase deletion in 15q22-q23 in an autistic patient: identification of candidate genes for autism and of homologous DNA segments in 15q22-q23 and 15q11-q13.

We have identified a one megabase deletion in the 15q22-15q23 region in a patient with autism, developmental delay, and mild dysmorphism. Genes that map within the deletion region and genes that are interrupted or rearranged at the deletion breakpoints are candidate genes for autism. Fluroescence in situ hybridization studies in this patient revealed that part or all of the PML gene is absent from one chromosome 15 and a BAC clone containing the D15S124 gene locus hybridizes to only one chromosome 15. BAC clones containing the PTPN9, and SLP-1[hUNC24] genes showed markedly reduced hybridization in the 15q22-q23 region on one chromosome 15 in the patient. These BACs also hybridize to the 15q11-q13 region in close proximity to SNRPN and HERC2, and in this region there is equal intensity of signal on the normal and on the deleted chromosome. There are previous reports of deletions and duplications of the 15q11-q13 region in patients with autism. Our patient represents the first report of a 15q22-q23 deletion. Hybridization of the PTPN9 and Slp-1 Bac clones to the 15q11-q13 and the 15q22-q23 regions of chromosome 15 may be due to the presence of PTPN9 or SLP-1 gene sequences or to the presence of other gene sequences or to non-coding homologous DNA sequences. The PTPN9 gene encodes a non-receptor protein tyrosine phosphatase. The Slp-1 [hUNC24] gene is expressed mainly in the brain. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:765-770, 2000.

Confirmation of linkage between juvenile myoclonic epilepsy locus and the HLA region of chromosome 6.

Juvenile myoclonic epilepsy (JME) is a generalized, non-progressive epilepsy characterized by an adolescent onset of sudden, involuntary myoclonic jerks. Greenberg et al. (American Journal of Medical Genetics 31:185-192, 1988b; Cytogenetics and Cell Genetics 51:1008, 1989b) reported tight linkage of a JME locus to the HLA region of chromosome 6p. We confirm this linkage assignment, although at a larger recombination fraction than previously reported. Twenty-three, mostly nuclear, families were ascertained through a JME proband. The affected status of relatives of the probands was assigned by 4 different clinical criteria, and separate analyses were done assuming an autosomal dominant model with 90% penetrance and an autosomal recessive model with full penetrance. A linear age-of-onset correction with maximum penetrance at age 20 years was incorporated into the analyses. The maximum lod score obtained was 3.11 at (-)m = 0.001, (-)f = 0.20, assuming autosomal dominant inheritance and using the second definition of the disease phenotype. There was strong support for linkage using the other phenotype definitions and the autosomal dominant model, although the lod scores did not exceed 3.0. There was also support for linkage of a JME locus to this region under the autosomal recessive model, although the results varied depending upon the definition of the disease phenotype. There was no significant evidence for linkage heterogeneity.