Genetics and genomics in neuropsychopharmacology: the impact on drug discovery and development.

Genomics, the complete tabulation of all the genes in an organism, has made a major impact on the organisation of fully-integrated pharmaceutical companies. Drug discovery begins with bioinformatic elucidation of a human sequence encoding a potential drug target, followed by cloning and expression of the gene in a format for high throughput screening. Target validation is aided by reference to homologous genes in subhuman species as well as production of transgenic animals. In contrast, the impact of genetics on neuropsychopharmacology has been modest. It is interesting to compare the experience of genetics in the two major clinical disciplines dealing with disorders of the nervous system. Neurology has been at the forefront of human genetics with over 600 disorders mapped, of which causative mutations have been assigned to about 200 Mendelian disorders, each individually rare. Psychiatric genetics has been based on two log fewer diagnoses use of which has only yielded complex segregation patterns, a plethora of weak associations and no gene assignments. In neither case has genetics resulted in the development of a novel therapeutic agent. However, by refinements in diagnosis and genetic technology the promise for the future is great, not only for drug discovery, but also for subsequent preclinical and clinical development.

Failure to confirm NOTCH4 association with schizophrenia in a large population-based sample from Scotland.

The NOTCH4 gene was recently reported to be associated with schizophrenia based on TDT analysis of 80 British trios. The strongest evidence for association derived from two microsatellites. We genotyped both loci in a large sample of unrelated Scottish schizophrenics and controls, but failed to replicate the reported association, finding instead that each putative schizophrenia-associated allele had a somewhat lower frequency in schizophrenics than in controls.

Novel drug development for amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) has become an increasingly attractive area for the pharmaceutical industry, the most experimentally tractable of the neurodegenerative diseases. Mechanisms underlying cell death in ALS are likely to be important in more common but more complex disorders. Riluzole, the only drug launched for treatment ALS is currently undergoing industrial trials for Alzheimer's, Parkinson's, Huntington disease, stroke and head injury. Other compounds in Phase III testing for ALS (mecamserin, xaliproden, gabapentin) are also in trials for other neurodegenerative disorders. Mechanisms of action of these advanced compounds are limited to glutamate antagonism, direct or indirect growth factor activity, as well as GABA agonism and interaction with calcium channels. A broader range of mechanisms is represented by compounds in Phase I trials: glutamate antagonism (dextramethorphan/p450 inhibitor; talampanel), growth factors (leukemia inhibiting factor; IL-1 receptor; encapsulated cells secreting CNTF) and antioxidants (TR500, a glutathione-repleting agent; recombinant superoxide dismutase; procysteine.) An even broader range of mechanisms is being explored in preclinical discovery programs. Recognition of the difficulties associated with delivery of protein therapeutics to the CNS has led to development of small molecules interacting either with neurotrophin receptors or with downstream intracellular signalling pathways. Other novel drug targets include caspaces, protein kinases and other molecules influencing apoptosis. High-throughput screens of large libraries of small molecules yield lead compounds that are subsequently optimized by chemists, screened for toxicity, and validated before a candidate is selected for clinical trials. The net is cast wide in early discovery efforts, only about 1% of which result in useful drugs at the end of a decade-long process. Successful discovery and development of novel drugs will increasingly depend on collaborative efforts between the academy and industry.

Perioperative intracranial hemorrhage in achondroplasia: a case report.

We report a case of a 35-year-old man with achondroplasia who previously had thoracolumbar decompressive laminectomies, who developed recurrence of spinal stenosis at the thoracolumbar junction. The patient underwent standard repeat thoracolumbar decompression, removal of a disc, and spinal fusion with instrumentation in the prone position. Postoperatively the patient was confused. Computed tomography (CT) revealed hemorrhages in both cerebellar hemispheres with surrounding edema and mild mass effect. These were interpreted as venous hemorrhages. Conservative therapy was successful. This is the first case report of perioperative venous intracranial hemorrhage in the context of spinal surgery for achondroplasia. Distinctive anatomic characteristics of achondroplasia, combined with several potentially modifiable aspects of his management, may have predisposed the patient to this complication.

Motor milestones in children with diastrophic dysplasia.

Diastrophic dysplasia (DD), an autosomal recessive skeletal dysplasia, results in short-limbed short stature, generalized joint dysplasia, and spinal, hand, foot, and ear deformities. Children with DD experience both growth and motor developmental delays. To quantify the motor developmental delays, data on motor milestone attainment and other important characteristics were collected by retrospective questionnaire on 25 individuals with DD. Means and standard deviations were calculated for time to motor milestone attainment and are presented with minimum, maximum, 25th, 50th, 75th, and 90th percentile values. Percentages of individuals who could perform daily living and recreational tasks were tabulated. The mean times to milestone attainment for children with DD are all significantly longer than published means for nonaffected children. Notably, children with DD roll over at 5.2 +/- 2.2 months, sit unsupported at 8.3 +/- 2.3 months, pull up to a stand at 13.5 +/- 5.8 months, and walk at 24.4 +/- 9.2 months. The data presented here should be useful as preliminary reference standards for motor milestone attainment in children with DD.

Reoperation for spinal restenosis in achondroplasia.

The characteristics of spinal restenosis in achondroplasia and its treatment are evaluated in this study. Radiologic and surgical findings were correlated to establish the causes of achondroplastic spinal restenosis and the benefits of its therapy. Eight patients (five men, three women) with spinal restenotic complications of achondroplasia were studied. The most common neurological sign of recurrent stenosis was impaired motor function. The mean interval between the most recent surgeries was 8.2 years (9.5 years for surgeries at the same levels). The most common causes of recurrent stenosis were facet hypertrophy and disk disease. The complications were a dural tear and cerebellar hemorrhage in one patient and transient neurological deterioration in another. One patient died after operation. Restenosis can occur many years after original decompression in the achondroplastic spine, and repeated operation can successfully lessen pain and neurological symptoms in most patients.

Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN): phenotypic analysis of a new skeletal dysplasia caused by a Lys650Met mutation in fibroblast growth factor receptor 3.

We previously discovered a novel missense mutation (Lys650Met) in the tyrosine kinase domain of the fibroblast growth factor receptor 3 (FGFR3) gene in four unrelated individuals with a condition we called "severe achondroplasia with developmental delay and acanthosis nigricans" (SADDAN) [Tavormina et al., 1999: Am. J. Hum. Genet. 64:722-731]. Here we present a more detailed clinical account of the SADDAN phenotype. The FGFR3 Lys650Met mutation results in severe disturbances in endochondral bone growth that approach and overlap those observed in thanatophoric dysplasia, type I. However, this mutation is most often compatible with survival into adulthood. Other unusual bone deformities, such as femoral bowing with reverse (i.e., posterior apex) tibial and fibular bowing and "ram's horn" bowing of the clavicle, are also seen in some patients. In addition to skeletal dysplasia, progressive acanthosis nigricans, and central nervous system structural anomalies, seizures and severe developmental delays are observed in surviving SADDAN patients. Despite its location within the same FGFR3 codon as the thanatophoric dysplasia type II mutation (Lys650Glu) and a similar effect on constitutive activation of the FGFR3 tyrosine kinase, the Lys650Met is not associated with cloverleaf skull or craniosynostosis.

Kearns-Sayre syndrome with features of Pearson's marrow-pancreas syndrome and a novel 2905-base pair mitochondrial DNA deletion.

Kearns-Sayre syndrome (KSS) and Pearson's marrow-pancreas syndrome (PMPS) are rare disorders caused by the same molecular defect, one of several deletion mutations in mitochondrial DNA (mtDNA). KSS is an encephalomyopathy with ophthalmoplegia, retinal degeneration, ataxia, and endocrine abnormalities. PMPS is a disorder of childhood characterized by refractory anemia, vacuolization of bone marrow cells, and exocrine pancreas dysfunction. Children with PMPS that have a mild phenotype, or are supported through bone marrow failure, often develop the encephalomyopathic features of KSS. The subject of numerous reports in the neuromuscular, genetic, and pediatric literature in recent years, very few cases of either disorder have ever been studied at autopsy. We report the results of our studies of a patient with clinically documented KSS who presented with renal dysfunction and was found to have a novel mtDNA deletion and degenerative changes in the central nervous system, retina, skeletal muscle, and pancreas.

Neurology and the skin.

As knowledge of pathophysiology grows, so does the refinement of diagnoses. Sometimes increased knowledge permits consolidation and unification. Unfortunately, at our present level of understanding, it usually demands proliferation of diagnostic categories. As tedious as this diagnostic splintering may seem, such is the price currently exacted of both the investigator and the clinician who seek to optimise management. Increased diagnostic refinement often requires inquiry into matters outside the bounds of one's specialty. Most often we turn to the radiologist or to the laboratory to narrow the differential diagnosis generated from the history and neurological examination. As we have shown, a useful intermediate step is extension of the physical examination to organs such as the skin, which are not the traditional preserve of the neurologist. That any text could confer the sophistication required for expert dermatological diagnosis is an unrealistic expectation. However, we hope that this review will encourage careful examination of the skin, hair, and nails by the neurological practitioner, with consideration of referral to a dermatologist when greater expertise is required.

Abnormal fatty acid metabolism in childhood spinal muscular atrophy.

Our previous experience with abnormal fatty acid metabolism in several children with spinal muscular atrophy (SMA) prompted evaluation of fatty acid metabolism in a larger cohort. Thirty-three infants with severe infantile SMA were shown to have a significantly increased ratio of dodecanoic to tetradecanoic acid in plasma compared with normal infants and 6 infants affected with equally debilitating, non-SMA denervating disorders. Seventeen children with milder forms of SMA had normal fatty acid profiles. In addition, all 5 infants with severe SMA evaluated in a fasting state developed a distinctive and marked dicarboxylic aciduria, including saturated, unsaturated, and 3-hydroxy forms, comparable in severity with the dicarboxylic aciduria of children with primary defects of mitochondrial fatty acid beta-oxidation. Nine children with chronic SMA and 23 control patients did not develop an abnormal dicarboxylic aciduria during fasting. No known disorder of fatty acid metabolism explains all of the abnormalities we find in SMA. Our data suggest, however, that the abnormalities are not a consequence of SMA-related immobility, systemic illness, muscle denervation, or muscle atrophy. These abnormalities in fatty acid metabolism may be caused by changes in cellular physiology related to the molecular defects of the SMA-pathogenic survival motor neuron gene or neighboring genes.

Sleep-disordered breathing in children with achondroplasia.

OBJECTIVE: Our objective was to characterize sleep-disordered breathing in 88 children with achondroplasia aged 1 month to 12.6 years. RESULTS: At the time of their initial polysomnography, five children had previously undergone tracheostomy, and seven children required supplemental oxygen. Initial polysomnography demonstrated a median obstructive apnea index of 0 (range, 0 to 19.2 apneas/hr). The median number of central apneas with desaturation per study was 0.5 (0 to 49), the median oxygen saturation nadir was 91% (50% to 99%), and the median peak end-tidal pCO2 was 47 mm Hg (36 to 87 mm Hg). Forty-two children (47.7%) had abnormal initial study results, usually caused by hypoxemia. Two children with severe obstructive sleep apnea eventually required continuous positive airway pressure therapy, and three additional children required tracheostomies. CONCLUSIONS: (1) Children with achondroplasia often have sleep-related respiratory disturbances, primarily hypoxemia. (2) The majority do not have significant obstructive or central apnea; however, a substantial minority are severely affected. (3) Tonsillectomy and adenoidectomy decreases the degree of upper airway obstruction in most but not all children with achondroplasia and obstructive sleep apnea. (4) Restrictive lung disease can present at a young age in children with achondroplasia.

Linkage of the locus for cerebral cavernous hemangiomas to human chromosome 7q in four families of Mexican-American descent.

OBJECTIVE: To determine with greater precision the map location of the locus associated with familial cavernous hemangiomas. BACKGROUND: Cavernous malformations of the brain are a significant cause of seizures, progressive or apoplectic neurologic deficit, and headache. Prevalence estimates from autopsy series vary from 0.39 to 0.9%. This disorder (OMIM #116860) can be inherited as an autosomal dominant trait with variable penetrance. Linkage to markers on the long arm of chromosome 7 was recently reported in separate reports in three apparently unrelated Hispanic kindreds as well as in two kindreds of non-Hispanic descent. DESIGN/METHODS: We examined clinically, by MRI scanning, and by pathologic examination of surgical specimens, members of four large Mexican-American families segregating cavernous hemangiomas of the brain. Linkage analysis was performed with use of blood specimens from morphologically proven cases. Two-point linkage analysis was performed with the MLINK program of the LINKAGE package. Multipoint analysis was performed between two markers and the disease locus with LINKMAP in the FASTLINKAGE package. Allele frequencies were set as described by the Genome Database (GDB). Maximum penetrance for the disease allele was set to 0.75. RESULTS: The highest lod score was observed for marker D7S652 with Zmax = 6.66 at theta(max) = 0.00. Multipoint LOD score analysis placed the disease locus in the 11 cM interval between markers D7S630 and D7S527 with Zmax = 9.19. Haplotype analysis is in agreement with the placement of the disease gene between D7S630 and D7S527 and further shows a minimal shared region within this interval, indicating a founder effect in the establishment of the mutation in these families. CONCLUSIONS: We confirmed the linkage of cavernous hemangioma to markers on the long arm of chromosome 7q, and the estimate of the map location has been refined to a region of shared haplotype between markers D7S630 and D7S527 in four Mexican-American families who may be descended from a common ancestor in Sonora County, Mexico.

Disorders of binocular control of eye movements in patients with cerebellar dysfunction.

Recent research has implicated the cerebellum in conjugate ocular motor control, including steady gaze-holding and accuracy of pursuit and saccades. Whether the cerebellum also has a role in the control of the alignment of the eyes during fixation and of the yoking of the eyes during movement i. less certain. We have studied binocular (disconjugate) ocular motor control in nine patients with cerebellar dysfunction and compared the results with those of normal subjects. Eye alignment during fixation and the yoking of the eyes during and immediately after saccades were quantified by recording the movements of both eyes using scleral search coils. Patients had disturbances of ocular alignment. All had an esophoria during monocular viewing and many an esotropia during binocular viewing, implying an increase in convergence tone. Most had a vertical misalignment that varied with horizontal eye position ('alternating skew deviation'). Patients showed conjugate dysmetria (saccade under- or overshoot and postsaccade drift) and disconjugate dysmetria (the eyes were poorly yoked during and immediately after saccades). Both the conjugate and disconjugate abnormalities were incommitant, i.e. they varied with orbital eye position. Correlations amongst the various abnormalities suggested that one part of the cerebellum, perhaps the dorsal vermis and the underlying posterior fastigial nucleus, controls the conjugate size of saccades and that another part of the cerebellum, perhaps the flocculus/paraflocculus, controls the yoking of the eyes during saccades and both the disconjugate and conjugate components of postsaccade drift.

Family study and segregation analysis of Tourette syndrome: evidence for a mixed model of inheritance.

To investigate the transmission of Tourette syndrome (TS) and associated disorders within families, complex segregation analysis was performed on family study data obtained from 53 independently ascertained children and adolescents with TS and their 154 first-degree relatives. The results suggest that the susceptibility for TS is conveyed by a major locus in combination with a multifactorial background. Other models of inheritance were definitively rejected, including strictly polygenic models, all single major locus models, and mixed models with dominant and recessive major loci. The frequency of the TS susceptibility allele was estimated to be .01. The major locus accounts for over half of the phenotypic variance for TS, whereas the multifactorial background accounts for approximately 40% of phenotypic variance. Penetrance estimates suggest that all individuals homozygous for the susceptibility allele at the major locus are affected, whereas only 2.2% of males and 0.3% of females heterozygous at the major locus are affected. Of individuals affected with TS, approximately 62% are heterozygous and approximately 38% are homozygous at the major locus. While none of the families had two parents affected with TS, 19% of families had two parents affected with the broader, phenotype, which includes TS, chronic tic disorder, or obsessive-compulsive disorder.

Respiration and growth defects in transmitochondrial cell lines carrying the 11778 mutation associated with Leber's hereditary optic neuropathy.

Mitochondrial DNA from two genetically unrelated patients carrying the mutation at position 11778 that causes Leber's hereditary optic neuropathy has been transferred with mitochondria into human mtDNA-less rho0206 cells. As analyzed in several transmitochondrial cell lines thus obtained, the mutation, which is in the gene encoding subunit ND4 of the respiratory chain NADH dehydrogenase (ND), did not affect the synthesis, size, or stability of ND4, nor its incorporation into the enzyme complex. However, NADH dehydrogenase-dependent respiration, as measured in digitonin-permeabilized cells, was specifically decreased by approximately 40% in cells carrying the mutation. This decrease, which was significant at the 99.99% confidence level, was correlated with a significantly reduced ability of the mutant cells to grow in a medium containing galactose instead of glucose, indicating a clear impairment in their oxidative phosphorylation capacity. On the contrary, no decrease in rotenone-sensitive NADH dehydrogenase activity, using a water-soluble ubiquinone analogue as electron acceptor, was detected in disrupted mitochondrial membranes. This is the first cellular model exhibiting in a foreign nuclear background mitochondrial DNA-linked biochemical defects underlying the optic neuropathy phenotype.

Reversibility of white matter changes and dementia after treatment of dural fistulas.

We describe two patients with dural fistulas who presented with dementia and diffuse white matter signal changes on MR that significantly improved after surgery. One patient had preoperative embolization.

Association between Ag1-CA alleles and severity of autosomal recessive proximal spinal muscular atrophy.

The gene for autosomal recessive proximal spinal muscular atrophy (SMA) has been mapped to an 850-kb interval on 5q11.2-q13.3, between the centromeric D5S823 and telomeric D5S557 markers. We report a new complex marker, Ag1-CA, that lies in this interval, whose primers produce one, two, or rarely three amplification-fragment-length variants (AFLVs) per allele. Class I chromosomes are those which amplify a single AFLV allele, and class II chromosomes are those which amplify an allele with two or three AFLVs. Ag1-CA shows highly significant allelic association with type I SMA in both the French Canadian (Hôpital Sainte-Justine [HSJ]) and American (Ohio State University [OSU]) populations (P < .0001). Significant association between the Ag1-CA genotype and disease severity was also observed. Type I patients were predominantly homozygous for class I chromosomes (P = .0003 OSU; P = .0012 HSJ), whereas the majority of type II patients were heterozygous for class I and II chromosomes (P = .0014 OSU; P = .001 HSJ). There was no significant difference in Ag1-CA genotype frequencies between type III patients (P = .5 OSU; P = .25 HSJ) and the paired normal chromosomes from both carrier parents. Our results indicate that Ag1-CA is the most closely linked marker to SMA and defines the critical candidate-gene region. Finally, we have proposed a model that should be taken into consideration when screening candidate SMA genes.