Moyra Smith

Autism and Tuberous Sclerosis

Autism is a behavior disorder with genetic influences indicated from twin and family studies and from the cooccurrence of autism with known genetic disorders. Tuberous sclerosis complex (TSC) is a known genetic disorder with behavioral manifestations including autism. A literature review of these two disorders substantiates a significant association of autism and TSC with 17–58% of TSC subjects manifesting autism and 0.4–3% of autistic subjects having TSC. In initial data collected on 13 TSC probands and 14 autistic probands in our family study of autism and TSC, we identified 7 TSC subjects with autism. The seven TSC autistic probands are similar to non-TSC autistic probands on the Social and Communication domains of the Autism Diagnostic Inventory (ADI) (Le Couteur et al., 1989), but show fewer Repetitive Rituals. There are more male TSC probands with autism than female, despite an equal sex ratio among TSC probands. The TSC probands with autism have significantly more seizures and mental retardation than those without autism; however, the extent and etiology of associations require further study. Our preliminary findings suggest that a fruitful approach for delineating genetic influences in autism may come from further investigation of possible mechanisms underlying the association of autism and TSC.

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.

Mutations in the gene encoding 3β-hydroxysteroid-Δ8,Δ7-isomerase cause X-linked dominant Conradi-Hunermann syndrome

X-linked dominant Conradi-Hünermann syndrome (CDPX2; MIM 302960) is one of a group of disorders with aberrant punctate calcification in cartilage, or chondrodysplasia punctata (CDP). This is most prominent around the vertebral column, pelvis and long bones in CPDX2. Additionally, CDPX2 patients may have asymmetric rhizomesomelia, sectorial cataracts, patchy alopecia, ichthyosis and atrophoderma. The phenotype in CDPX2 females ranges from stillborn to mildly affected individuals identified in adulthood. CDPX2 is presumed lethal in males, although a few affected males have been reported,. We found increased 8(9)-cholestenol and 8-dehydrocholesterol in tissue samples from seven female probands with CDPX2 ( ref. 4). This pattern of accumulated cholesterol intermediates suggested a deficiency of 3β-hydroxysteroid-Δ8,Δ 7-isomerase (sterol-Δ8-isomerase), which catalyses an intermediate step in the conversion of lanosterol to cholesterol. A candidate gene encoding a sterol-Δ8-isomerase ( EBP) has been identified and mapped to Xp11.22–p11.23 (Refs 5,6). Using SSCP analysis and sequencing of genomic DNA, we found EBP mutations in all probands. We confirmed the functional significance of two missense alleles by expressing them in a sterol-Δ8-isomerase-deficient yeast strain. Our results indicate that defects in sterol-Δ8-isomerase cause CDPX2 and suggest a role for sterols in bone development.

REPORT OF THE DIAGNOSTIC-CRITERIA COMMITTEE OF THE NATIONAL-TUBEROUS-SCLEROSIS-ASSOCIATION

Special Article Criteria: Tuberous Sclerosis Complex Diagnostic Editorial Note: This issue of the Journal of Child Neu- carries the consensus report of the the Diagnostic Criteria Committee of the National Tuberous Sclerosis Associa- tion. Reliable diagnostic criteria for tuberous sclerosis complex are important for a number of reasons. If we are to identify specific gene markers for tuberous sclerosis, it is essential that we accurately identify those patients with definite tuberous sclerosis and not include in our research individuals whose diagnosis is open to question. Debates about the validity of a gene marker should not fall on the issue of the accuracy of the diagnosis of tuberous sclerosis in those patients in whom a marker is first identified. Likewise, clinically useful laboratory tests for tuberous sclerosis complex based on these markers can not be developed rology without a carefully screened homogeneous population of patients with tuberous sclerosis. Eventually these same concerns will arise in conjunction with therapeutic issues. Thus, it is only through the use of a well-defined patient population that we can hope to develop the tools for the diagnosis, evaluation, therapy related to tuberous sclerosis. and The National Tuberous Sclerosis Association now sponsors and supports tuberous sclerosis clinics in 11 medical centers around the country. Tuberous sclerosis clinics are ideal sites at which to collect patients with tuberous sclerosis and investigate the combinations and constellations of stigmata of tuberous scle- rosis. The clinics provide an ideal opportunity to test many of the assumptions in the tuberous sclerosis diagnostic criteria, then to improve the criteria. The availability of large numbers of tuber- Report of the Diagnostic sclerosis patients and a uniform system of diagnosis and clas- sification should in turn promote research and eventually therapy. Thus, the development of uniform diagnostic criteria for tuberous sclerosis promotes better use of the tuberous sclerosis clinics for research. Any attempt to arrive at a consensus stimulates debate about the validity and veracity of cherished assumptions which have not before been submitted to critical scrutiny. Debate often draws attention to the emperor’s new clothes and recognition of his true form. Over the last 12 months, committee members real- ous ized that we do not have a consensus on what tuberous sclerosis really looks like. The disease is extremely variable from patient to patient, and there are few data on the general incidence of many of the stigmata of tuberous sclerosis. We are unsure how many of the phenomena are necessary or sufficient for the diagnosis of tu- berous sclerosis. This debate forced the committee to make some assumptions about the specificity of lesions, assumptions which will need to be tested during the next decade. Are facial angiofi- bromas, subependymal giant cell astrocytomas, or ungual fibro- mas pathognomonic of tuberous sclerosis? Hypomelanotic macules, cysts, and seizures seem to be less reliable witnesses of tuberous sclerosis than the former group. The committee intends these criteria to be adaptable, susceptible to modification as data are collected by empiricism. It is our fervent wish that the criteria for the diagnosis of tuberous sclerosis will metamorphose into a stable support for molecular diagnosis and treatment of tuberous sclerosis complex.-Robert M. Shuman, MD Criteria Committee of the National Tuberous Sclerosis Association E.S. Roach, MD; Moyra Smith, MD, PhD; Peter Huttenlocher, MD; Mohandes Bhat, DDS; Deborah Alcorn, MD; Louise Hawley, PhD uberous sclerosis complex is a genetic disor- Tder with protean clinical manifestations. Since there is presently no reliable molecular marker for tuberous sclerosis, we must rely on clinical diag- nostic criteria, especially for patients with atypical features or subtle forms of the disorder. Accurate di- agnosis underpins the clinical approach to individ- ual tuberous sclerosis patients, influences the From the University of Texas Southwestern Medical School (Dr Roach), Dallas, TX, the University of California (Dr Smith), Irvine, CA, the University of Chicago (Dr Huttenlocher), Chicago, IL, the National Institute of Dental Research (Dr Bhat), Bethesda, MD, Stanford University (Dr Alcorn), Stanford, CA, and the Uni- versity of Minnesota (Dr Hawley), Minneapolis, MN. Address correspondence to Dr E.S. Roach, University of Texas Southwestern Medical School, Department of 5323 Harry Hines Blvd, Dallas, TX 75235. Neurology, estimated recurrence risk figures provided to fami- lies in the course of genetic counseling, and affects the validity of the results of clinical and basic re- search on tuberous sclerosis. The need for accurate diagnosis in research is critical; even if a definite di- agnosis can not be established, it would be helpful to estimate the probability that an individual family member is affected. Unfortunately, there are few population-based studies of the various clinical fea- tures of tuberous sclerosis, and it is not always pos- sible to establish a firm diagnosis on clinical grounds alone. A definitive diagnosis of tuberous sclerosis is easy when many features of the disorder are present. However, fined to clinical since findings, present day criteria it is are con- impossible to absolutely Downloaded from jcn.sagepub.com at UNIV CALIFORNIA IRVINE on March 23, 2015

Genetics of human alcohol and aldehyde dehydrogenases

During the past 5 years considerable progress has been made in the elucidation of the biochemical genetics of human alcohol dehydrogenases (ADH) and human aldehyde dehydrogenases (ALDH). In particular, progress has been made in determining the number of gene loci coding for these enzymes and the tissue distribution of the enzymes. In addition, a number of allelic variants of specific forms of alcohol and aldehyde dehydrogenases have been described. Studies have been done on different population groups to determine the frequencies of some of these variants. The relationship of the presence of variant forms of alcohol and aldehyde dehydrogenases to altered alcohol tolerance has been investigated. Efficient procedures for purifying alcohol and aldehyde dehydrogenases have been defined. As a result, detailed studies on the kinetics of separated isozymes and amino acid sequence determinations have been possible. To date, complete amino acid sequence data have been obtained for three ADH isozymes and one ALDH isozyme, while partial amino acid sequence data have been published on a second ALDH isozyme. Antibodies to specific forms of aldehyde dehydrogenase have been used to determine the nature of the genetic variation in mitochondrial ALDH.

High prevalence of rare dopamine receptor D4 alleles in children diagnosed with attention-deficit hyperactivity disorder

Associations have been reported of the 7-repeat (7R) allele of the human dopamine receptor D4 (DRD4) gene with both the personality trait of novelty seeking and attention-deficit/hyperactivity disorder (ADHD). The increased prevalence of the 7R allele in ADHD probands is consistent with the common variant–common disorder hypothesis, which proposes that the high frequency of many complex genetic disorders is related to common DNA variants. Recently, based on the unusual DNA sequence organization and strong linkage disequilibrium surrounding the DRD4 7R allele, we proposed that this allele originated as a rare mutational event, which nevertheless increased to high prevalence in human populations by positive selection. We have now determined, by DNA resequencing of 250 DRD4 alleles obtained from 132 ADHD probands, that most ADHD 7R alleles are of the conserved haplotype found in our previous 600 allele worldwide DNA sample. Interestingly, however, half of the 24 haplotypes uncovered in ADHD probands were novel (not one of the 56 haplotypes found in our prior population studies). Over 10 percent of the ADHD probands had these novel haplotypes, most of which were 7R allele derived. The probability that this high incidence of novel alleles occurred by chance in our ADHD sample is much less than 0.0001. These results suggest that allelic heterogeneity at the DRD4 locus may also contribute to the observed association with ADHD.

Mitochondrial Dysfunction in Autistic Patients with 15q Inverted Duplication

Two autistic children with a chromosome 15q11‐q13 inverted duplication are presented. Both had uneventful perinatal courses, normal electroencephalogram and magnetic resonance imaging scans, moderate motor delay, lethargy, severe hypotonia, and modest lactic acidosis. Both had muscle mitochondrial enzyme assays that showed a pronounced mitochondrial hyperproliferation and a partial respiratory chain block most parsimoniously placed at the level of complex III, suggesting candidate gene loci for autism within the critical region may affect pathways influencing mitochondrial function. Ann Neurol 2003;53:801–804

Mutations in the gene encoding 3 beta-hydroxysteroid-delta 8, delta 7-isomerase cause X-linked dominant Conradi-Hunermann syndrome

X-linked dominant Conradi-Hünermann syndrome (CDPX2; MIM 302960) is one of a group of disorders with aberrant punctate calcification in cartilage, or chondrodysplasia punctata (CDP). This is most prominent around the vertebral column, pelvis and long bones in CPDX2. Additionally, CDPX2 patients may have asymmetric rhizomesomelia, sectorial cataracts, patchy alopecia, ichthyosis and atrophoderma. The phenotype in CDPX2 females ranges from stillborn to mildly affected individuals identified in adulthood. CDPX2 is presumed lethal in males, although a few affected males have been reported,. We found increased 8(9)-cholestenol and 8-dehydrocholesterol in tissue samples from seven female probands with CDPX2 ( ref. 4). This pattern of accumulated cholesterol intermediates suggested a deficiency of 3β-hydroxysteroid-Δ8,Δ 7-isomerase (sterol-Δ8-isomerase), which catalyses an intermediate step in the conversion of lanosterol to cholesterol. A candidate gene encoding a sterol-Δ8-isomerase ( EBP) has been identified and mapped to Xp11.22–p11.23 (Refs 5,6). Using SSCP analysis and sequencing of genomic DNA, we found EBP mutations in all probands. We confirmed the functional significance of two missense alleles by expressing them in a sterol-Δ8-isomerase-deficient yeast strain. Our results indicate that defects in sterol-Δ8-isomerase cause CDPX2 and suggest a role for sterols in bone development.

Mapping of a gene determining tuberous sclerosis to human chromosome 11q1411q23

Tuberous sclerosis (TSC) is a dominantly inherited disorder characterized by hamartomas and hamartias in one or more organs, most often in skin, brain, and kidneys. Analysis of the basic genetic defect in tuberous sclerosis would be greatly expedited by definitive determination of the chromosomal location of the TSC gene or genes. We have carried out genetic linkage studies in 15 TSC families, using 34 polymorphic markers including protein markers and DNA markers. Pairwise lod scores were calculated using LIPED, and multipoint analyses were carried out using MENDEL. In the pairwise linkage analysis, using a penetrance value of 90%, a significant positive lod score was obtained with MCT128.1 (D11S144), 11q22-11q23, Zmax 3.26 at theta = 0.08. The tyrosinase probe TYR (11q14-11q22) gave a maximum lod score of 2.88 at theta = 0. In the multipoint analyses the most likely order is (TYR,TSC)-MCT128.1-HHH172. Homogeneity analysis was carried out using the USERM9 subprogram of MENDEL, which conducts the admixture test of C. Smith (1963, Ann. Hum. Genet. 27: 175-182). This test provided no evidence for genetic heterogeneity (that is, non-11-linked families) in this data set.

Regional assignment of the gene for human liver/bone/kidney alkaline phosphatase to chromosome 1p36.1-p34.

We have used three different methods to map the human liver/bone/kidney alkaline phosphatase (ALPL) locus: (1) Southern blot analysis of DNA derived from a panel of human-rodent somatic cell hybrids; (2) in situ hybridization to human chromosomes; and (3) genetic linkage analysis. Our results indicate that the ALPL locus maps to human chromosome bands 1p36.1-p34 and is genetically linked to the Rh (maximum lod score of 15.66 at a recombination value of 0.10) and fucosidase A (maximum lod score of 8.24 at a recombination value of 0.02) loci. These results, combined with restriction fragment length polymorphisms identified by ALPL DNA probes, provide a useful marker for gene mapping studies involving the short arm of chromosome 1. In addition, our results help to elucidate further the structure and evolution of the human alkaline phosphatase multigene enzyme family.