A gene for ataxic cerebral palsy maps to chromosome 9p12-q12

Clinical Characteristics Suggestive of a Genetic Cause in Cerebral Palsy: A Systematic Review

BACKGROUND

Cerebral palsy (CP) is a clinical diagnosis and was long categorized as an acquired disorder, but more and more genetic etiologies are being identified. This review aims to identify the clinical characteristics that are associated with genetic CP to aid clinicians in selecting candidates for genetic testing.

METHODS

The PubMed database was systematically searched to identify genes associated with CP. The clinical characteristics accompanying these genetic forms of CP were compared with published data of large CP populations resulting in the identification of potential indicators of genetic CP.

RESULLTS

Of 1930 articles retrieved, 134 were included. In these, 55 CP genes (described in two or more cases, n = 272) and 79 candidate genes (described in only one case) were reported. The most frequently CP-associated genes were PLP1 (21 cases), ARG1 (17 cases), and CTNNB1 (13 cases). Dyskinesia and the absence of spasticity were identified as strong potential indicators of genetic CP. Presence of intellectual disability, no preterm birth, and no unilateral distribution of symptoms were classified as moderate genetic indicators.

CONCLUSIONS

Genetic causes of CP are increasingly identified. The clinical characteristics associated with genetic CP can aid clinicians regarding to which individual with CP to offer genetic testing. The identified potential genetic indicators need to be validated in large CP cohorts but can provide the first step toward a diagnostic algorithm for genetic CP.

Genome-Wide Association Study Identifies Genetic Risk Factors for Spastic Cerebral Palsy

BACKGROUND

Although many clinical risk factors of spastic cerebral palsy (CP) have been identified, the genetic basis of spastic CP is largely unknown. Here, using whole-genome genetic information linked to a deidentified electronic health record (BioVU) with replication in the UK Biobank and FinnGen, we perform the first genome-wide association study (GWAS) for spastic CP.

OBJECTIVE

To define the genetic basis of spastic CP.

METHODS

Whole-genome data were obtained using the multi-ethnic genotyping array (MEGA) genotyping array capturing single-nucleotide polymorphisms (SNPs), minor allele frequency (MAF) > 0.01, and imputation quality score (r2) > 0.3, imputed based on the 1000 genomes phase 3 reference panel. Threshold for genome-wide significance was defined after Bonferroni correction for the total number of SNPs tested (P < 5.0 × 10-8). Replication analysis (defined as P < .05) was performed in the UK Biobank and FinnGen.

RESULTS

We identify 1 SNP (rs78686911) reaching genome-wide significance with spastic CP. Expression quantitative trait loci (eQTL) analysis suggests that rs78686911 decreases expression of GRIK4, a gene that encodes a high-affinity kainate glutamatergic receptor of largely unknown function. Replication analysis in the UK Biobank and FinnGen reveals additional SNPs in the GRIK4 loci associated with CP.

CONCLUSION

To our knowledge, we perform the first GWAS of spastic CP. Our study indicates that genetic variation contributes to CP risk.

Trunk Control in Children With Ataxic Cerebral Palsy

This study aimed to investigate the clinical characteristics of trunk control in children with ataxic cerebral palsy (CP). We included 15 children with ataxic CP with a mean age of 9.46 years (SD = 1.08 years, 5-17 years) and 15 healthy children with a mean age of 9.06 years (SD = 0.84 years, 5-13 years). While the small sample size and large age range used here were not ideal for generalizability, they were made necessary by the rarity of this clinical sample. We used the Gross Motor Function Classification System Expanded and Revised (GMFCS-E&R) to classify the children's functional levels, and we tested trunk control with the Trunk Control Measurement Scale (TCMS). We then used the Gross Motor Function Measurement-88 (GMFM-88) to assess their gross motor functions. We compared the total and subscale scores of the TCMS in healthy children and children with ataxic CP by using the Mann-Whitney U Test. We also analyzed differences between TCMS scores according to the children's GMFCS levels with the Mann-Whitney U Test and also compared TCMS scores with the GMFM-88 by means of Spearman correlation analysis. Spearman correlation analysis was used to compare the scores of the TCMS with the GMFM-88. Our results showed that healthy children showed significantly higher scores than children with ataxic CP in total and subscale scores of TCMS (p < .05).There was no significant difference between the TCMS scores in children of different GMFCS levels, but the GMFM-88B subscale was significantly correlated with the static sitting balance (r_ho = .568, p < .05) and dynamic sitting balance (r_ho = .547, p < .05) TCMS subscales and with the TCMS total score (r_ho = .590, p < .05). We concluded that trunk control, especially its dynamic aspects, was impaired in children with ataxic CP.

Profile of children with cerebral palsy spectrum disorder and a normal MRI study

OBJECTIVE

This study looks at what profile can be expected in children with cerebral palsy spectrum disorder (CP) and a normal MRI.

METHODS

The data were excerpted from the Canadian Cerebral Palsy Registry database. Only patients who had undergone MRI were included in the analysis. Neuroimaging classification was ascertained by university-based pediatric neuroradiologists and split into 2 categories: normal and abnormal MRIs. Six factors were then compared between those 2 groups: prematurity, perinatal adversity, presence of more than 1 comorbidity, CP subtype, bimanual dexterity (Manual Ability Classification System [MACS]), and gross motor function (Gross Motor Function Classification System [GMFCS]).

RESULTS

Participants with no perinatal adversity were 5.518 times more likely to have a normal MRI (p < 0.0001, 95% confidence interval [CI] 4.153-7.330). Furthermore, participants with dyskinetic, ataxic/hypotonic, and spastic diplegic forms of CP were 2.045 times more likely to have a normal MRI than those with hemiplegia, triplegia, and quadriplegia (p < 0.0001, 95% CI 1.506-2.778). No significant difference was found in prematurity, GMFCS levels, MACS levels, and the number of comorbidities.

CONCLUSIONS

Normal MRIs were associated with lack of perinatal adversity as well as with the dyskinetic, ataxic/hypotonic, and spastic diplegic CP subtypes. As MRI normality is not strongly associated with the severity of CP, continuous follow-up in children with normal imaging appears warranted. Further advanced imaging modalities, as well as strong consideration for metabolic and genetic testing, may provide additional insights into causal pathways in this population.

Cerebellar motor syndrome from children to the elderly

More than a century after the description of its cardinal components, the cerebellar motor syndrome (CMS) remains a cornerstone of daily clinical ataxiology, in both children and adults. Anatomically, motor cerebellum involves lobules I-V, VI, and VIII. CMS is typically associated with errors in the metrics of voluntary movements and a lack of coordination. Symptoms and motor signs consist of speech deficits, impairments of limb movements, and abnormalities of posture/gait. Ataxic dysarthria has a typical scanning (explosive with staccato) feature, voice has a nasal character, and speech is slurred. Cerebellar mutism is most common in children and occurs after resection of a large midline cerebellar tumor. Ataxia of limbs includes at various degrees dysmetria (hypermetria: overshoot, hypometria: undershoot), dysdiadochokinesia, cerebellar tremor (action tremor, postural tremor, kinetic tremor, some forms of orthostatic tremor), isometrataxia, disorders of muscle tone (both hypotonia and cerebellar fits), and impaired check and rebound. Handwriting is irregular and some patients exhibit megalographia. Cerebellar patients show an increased body sway with a broad-based stance (ataxia of stance). Gait is irregular and staggering. Delayed learning of complex motor skills may be a prominent feature in children. CMS is currently explained by the inability of the cerebellum to handle feedback signals during slow movements and to create, store, select, and update internal models during fast movements. The cerebellum is embedded in large-scale brain networks and is essential to perform accurate motor predictions related to body dynamics and environmental stimuli. Overall, the observations in children and adults exhibiting a CMS fit with the hypothesis that the cerebellum contains neural representations reproducing the dynamic properties of body, and generates and calibrates sensorimotor predictions. Therapies aiming at a reinforcement or restoration of internal models should be implemented to cancel CMS in cerebellar ataxias. The developmental trajectory of the cerebellum, the immature motor behavior in children, and the networks implicated in CMS need to be taken into account.

Cerebellar transcranial direct current stimulation in children with ataxic cerebral palsy: A sham-controlled, crossover, pilot study

OBJECTIVE

The aim of the present study was to analyze the use of anodal tDCS of the cerebellar region combined with treadmill training to improve balance and functional performance in children with ataxic cerebral palsy.

DESIGN

Single-blind, sham-controlled, crossover, pilot study.

SETTING

Rehabilitation center and research motion analysis laboratory.

PARTICIPANTS

Children (N = 6) with ataxic cerebral palsy and balance deficit.

MAIN OUTCOME MEASURES

Static balance (oscillations of the center of pressure), functional balance (Pediatric Balance Scale) and functional performance (Pediatric Evaluation of Disability Inventory) were evaluated.

RESULTS

Significant reductions occurred in oscillations of the center of pressure with eyes closed after active anodal tDCS only. The effects of treadmill training on functional balance and functional performance in mobility were maintained in the active tDCS group only.

CONCLUSION

These preliminary data support the notion that anodal tDCS of the cerebellar region combined with treadmill training improves balance in children with ataxic cerebral palsy.

Cerebral Palsy-Trends in Epidemiology and Recent Development in Prenatal Mechanisms of Disease, Treatment, and Prevention

Cerebral palsy (CP) is the most common motor disability in childhood. This syndrome is the manifestation of intrauterine pathologies, intrapartum complications, and the postnatal sequel, especially among preterm neonates. A double hit model theory is proposed suggesting that an intrauterine condition along with intrapartum or postnatal insult lead to the development of CP. Recent reports demonstrated that treatment during the process of preterm birth such as magnesium sulfate and postnatal modalities such as cooling may prevent or reduce the prevalence of this syndrome. Moreover, animal models demonstrated that postnatal treatment with anti-inflammatory drugs coupled with nanoparticles may affect the course of the disease in pups with neuroinflammation. This review will describe the changes in the epidemiology of this disease, the underlying prenatal mechanisms, and possible treatments that may reduce the prevalence of CP and alter the course of the disease.

Association of COL4A1 gene polymorphisms with cerebral palsy in a Chinese Han population

The basement membrane (BM) is an extracellular matrix associated with overlying cells and is important for proper tissue development, stability, and physiology. COL4A1 is the most abundant component of type IV collagen in the BM, and COL4A1 variants can present with variable phenotypes that might be related to cerebral palsy (CP). We postulated, therefore, that variations in the COL4A1 gene might play an important role in the etiology of CP. In this study, six single nucleotide polymorphisms (SNPs) in the COL4A1 gene were genotyped among 351 CP patients and 220 healthy controls from the Chinese Han population. Significant association was found for an association between CP and rs1961495 (allele: p = 0.008, odds ratio (OR) = 1.387, 95% confidence interval (CI) = 1.088-1.767) and rs1411040 (allele: p = 0.009, OR = 1.746, 95% CI = 1.148-2.656) SNPs of the COL4A1 gene. Multifactor dimensionality reduction analysis suggested that these SNPs had interactive effects on the risk of CP. This study is the first attempt to investigate the contribution of polymorphisms in the COL4A1 gene to the susceptibility of CP in a Chinese Han population. This study shows an association of the COL4A1 gene with CP and suggests a potential role of COL4A1 in the pathogenesis of CP.

The importance of de novo mutations for pediatric neurological disease--It is not all in utero or birth trauma

The advent of next generation sequencing (NGS, which consists of massively parallel sequencing to perform TGS (total genome sequencing) or WES (whole exome sequencing)) has abundantly discovered many causative mutations in patients with pediatric neurological disease. A surprisingly high number of these are de novo mutations which have not been inherited from either parent. For epilepsy, autism spectrum disorders, and neuromotor disorders, including cerebral palsy, initial estimates put the frequency of causative de novo mutations at about 15% and about 10% of these are somatic. There are some shared mutated genes between these three classes of disease. Studies of copy number variation by comparative genomic hybridization (CGH) proceded the NGS approaches but they also detect de novo variation which is especially important for ASDs. There are interesting differences between the mutated genes detected by CGS and NGS. In summary, de novo mutations cause a very significant proportion of pediatric neurological disease.

A diagnostic approach for cerebral palsy in the genomic era

An ongoing challenge in children presenting with motor delay/impairment early in life is to identify neurogenetic disorders with a clinical phenotype, which can be misdiagnosed as cerebral palsy (CP). To help distinguish patients in these two groups, conventional magnetic resonance imaging of the brain has been of great benefit in "unmasking" many of these genetic etiologies and has provided important clues to differential diagnosis in others. Recent advances in molecular genetics such as chromosomal microarray and next-generation sequencing have further revolutionized the understanding of etiology by more precisely classifying these disorders with a molecular cause. In this paper, we present a review of neurogenetic disorders masquerading as cerebral palsy evaluated at one institution. We have included representative case examples children presenting with dyskinetic, spastic, and ataxic phenotypes, with the intent to highlight the time-honored approach of using clinical tools of history and examination to focus the subsequent etiologic search with advanced neuroimaging modalities and molecular genetic tools. A precise diagnosis of these masqueraders and their differentiation from CP is important in terms of therapy, prognosis, and family counseling. In summary, this review serves as a continued call to remain vigilant for current and other to-be-discovered neurogenetic masqueraders of cerebral palsy, thereby optimizing care for patients and their families.

Gene sequences regulating the production of apoE and cerebral palsy of variable severity

BACKGROUND

The apoE protein is the most important lipid transporter in the brain and has also been shown to have several regulatory functions in the central nervous system. The production of apoE is regulated by a number of genes and increases under certain conditions such as cerebral injury in adults.

AIMS

Our aim was to study whether variations in genes regulating the expression of the APOE gene were associated with severity of cerebral palsy (CP).

METHODS

Children enrolled in the Cerebral Palsy Register of Norway (CPRN) were invited to participate in this cross-sectional study; 281 of the invited 703 children (40%) returned swabs with buccal cells collected by parents. Six genetic variations thought to affect the production of apoE were genotyped and correlated with clinical data recorded in the CPRN.

RESULTS

Compared with children carrying the GG allele, children with genotype GT or TT in a specific genetic variation (rs59007384 located in the nearby TOMM40 gene) had excess risk for worse fine motor function (Odds ratio (OR): 1.82; 95% Confidence interval (CI): 1.10-2.99; p = 0.019) and epilepsy (OR: 2.32; CI: 1.17-4.61; p = 0.016). There was no association between severity of CP and any of the other five genetic variations analyzed.

CONCLUSION

Our findings suggest that genetic variations in one of the sequences regulating the expression of APOE, may be associated with worse clinical outcome in children with cerebral palsy.

Rare copy number variation in cerebral palsy

Recent studies have established the role of rare copy number variants (CNVs) in several neurological disorders but the contribution of rare CNVs to cerebral palsy (CP) is not known. Fifty Caucasian families having children with CP were studied using two microarray designs. Potentially pathogenic, rare (<1% population frequency) CNVs were identified, and their frequency determined, by comparing the CNVs found in cases with 8329 adult controls with no known neurological disorders. Ten of the 50 cases (20%) had rare CNVs of potential relevance to CP; there were a total of 14 CNVs, which were observed in <0.1% (<8/8329) of the control population. Eight inherited from an unaffected mother: a 751-kb deletion including FSCB, a 1.5-Mb duplication of 7q21.13, a 534-kb duplication of 15q11.2, a 446-kb duplication including CTNND2, a 219-kb duplication including MCPH1, a 169-kb duplication of 22q13.33, a 64-kb duplication of MC2R, and a 135-bp exonic deletion of SLC06A1. Three inherited from an unaffected father: a 386-kb deletion of 12p12.2-p12.1, a 234-kb duplication of 10q26.13, and a 4-kb exonic deletion of COPS3. The inheritance was unknown for three CNVs: a 157-bp exonic deletion of ACOX1, a 693-kb duplication of 17q25.3, and a 265-kb duplication of DAAM1. This is the first systematic study of CNVs in CP, and although it did not identify de novo mutations, has shown inherited, rare CNVs involving potentially pathogenic genes and pathways requiring further investigation.

Normal imaging in patients with cerebral palsy: what does it tell us?

OBJECTIVE

To identify distinctive clinical features characterizing children with cerebral palsy (CP) and normal-appearing magnetic resonance imaging (MRI) findings.

STUDY DESIGN

Using a population-based CP registry, the Registre de la Paralysie Cérébrale au Québec (Quebec Cerebral Palsy Registry), various antenatal, perinatal, and postnatal predictor variables, as well as current phenotype, were compared in patients with normal-appearing MRI findings and those with abnormal MRI findings.

RESULTS

Of the 213 patients evaluated, 126 (60%) had MRI imaging results available and were included in our analysis. Of these 126 patients, 90 (71%; 51 males, 39 females) had abnormal findings and 36 (29%; 17 males and 19 females) had normal-appearing findings. Compared with other CP variants, normal-appearing MRI was more prevalent (P = .001) in dyskinetic CP (72.7%; 8 of 11) and less prevalent (P = .002) in spastic hemiplegic CP (10%; 4 of 40). There were no significant differences between the 2 groups (P > .05) in terms of the prevalence of perinatal or postnatal clinical features or clinical outcomes. Furthermore, 42% (15 of 36) of the children with normal-appearing MRI exhibited a high degree of functional disability (Gross Motor Functional Classification System IV-V), compared with 33% (30 of 90) with abnormal MRI.

CONCLUSION

No clinical features, except a higher prevalence of dyskinetic CP, was identified in the children with normal-appearing MRI. More refined imaging techniques may be needed to evaluate patients with normal-appearing MRI findings. Furthermore, genetic or functional, rather than gross structural lesions, may underlie the pathophysiology of CP in this cohort. Finally, the high proportion of substantial functional disability underscores the importance of continuous follow-up even in the absence of early structural abnormalities on imaging.

Study of Gene Expression Profiles and Biological Mechanism of Cerebral Palsy Using a Monozygotic Twin Pair

The gene expression profile of a normal-suffering monozygotic twin pair is investigated to explore biological mechanisms of spastic type cerebral palsy. Main works include following three aspects: First, a cDNA microarray test is carried out to get the differentially expressed genes of the patient with cerebral palsy compared to her monozygotic twin sister. Second, these differentially expressed genes are searched for their bioinformation within 4 biological databases: FatiGO, FatiGOPlus, KEGG, and SOURCE. Third, a set of special genes and gene families are screened out from the spastic type cerebral palsy patient. These biological analyses reveal that those genes for cell junction are mostly down-regulated, while those genes for metabolism are mostly up-regulated. The individual genes, gene family, and their associated biological functions can reflect the pathological and physiological characteristics of the cerebral palsy.

Linkage analysis in a large family from Pakistan with depression and a high incidence of consanguineous marriages

OBJECTIVES

A genome wide scan for linkage was performed in a five generation family with a high incidence of depression and high average coefficient of inbreeding ascertained in a rural area of Pakistan. The effect of inbreeding on linkage analysis in an extended pedigree is discussed.

METHODS

372 microsatellite markers were used in a genome wide linkage study. Inbreeding coefficients were measured by two methods using both genealogical and genotype data.

RESULTS

Of 111 family members with phenotypic information, 82 were diagnosed with recurrent major depression. Linkage analysis using the program Superlink online generated LOD scores of less than one at all loci. A model free analysis with SimWalk did not result in any significant linkage score. The mean inbreeding coefficient was 0.038 estimated from genealogical data and 0.02 estimated from the genotype data. These results did not differ significantly. The effects of inbreeding included a reduction in the polymorphism information content of markers and an overestimate of marker allele frequencies.

CONCLUSION

The analysis of very large families is computationally demanding. Problems encountered in this analysis, including loss of power due to reduced polymorphism information content and sensitivity of the LOD score method to estimates of allele frequencies, severely limited the chance of detecting linkage.

Genetics considerations in cerebral palsy

Cerebral palsy refers to a collective of neurologic conditions that share in common disorders of motor function and posture. Traditionally, and still today in many circles, the term is considered almost synonymous with brain injury. Multiple lines of evidence, however, point to the fact that cerebral palsy is rarely caused by problems with perinatal management. In fact, a mounting body of evidence points to strong genetic influences on the occurrence of cerebral palsy. Like most neurogenetic conditions, cerebral palsy exhibits complex inheritance. The best descriptor of the inheritance of cerebral palsy would be that of "multifactorial inheritance." This implies etiologic and genetic heterogeneity with complex interactions with multiple environmental influences. This article reviews known genetic influences on the origin of cerebral palsy. A proposed scheme for the genetic evaluation in identifying the etiology of cerebral palsy is provided.

Consanguineous marriages and their effects on common adult diseases: studies from an endogamous population

OBJECTIVES

The aim of the study was to determine the extent and nature of consanguinity in the Qatari population and its effects on common adult diseases.

SUBJECTS AND METHODS

The study was conducted in urban and semi-urban areas of Qatar between October 2004 and May 2005. The total sample of 1,050 married Qatari females 15 years of age and over were approached for study. The degree of consanguinity between each female and her spouse and the degree of consanguinity between their parents were recorded.

RESULTS

Of 1,050 married Qatari females who were approached, 876 agreed to participate in the study, giving an 83.4% response. The rate of consanguinity in the present generation was 51% (95% confidence interval = 47.7-54.4) with a coefficient of inbreeding of 0.023724. The consanguinity rate and coefficient of inbreeding in the current generation were significantly higher than the maternal rate (51.0 vs. 40.3%; p < 0.001; 0.023724 vs. 0.016410 maternal). All types of consanguineous marriages were higher in this generation, particularly first cousins (26.7 vs. 21.4% paternal and 23.1% maternal) and double first cousins (4.3 vs. 2.9% paternal and 0.8% maternal). The current generation of consanguineous parents had a slightly higher risk for most diseases: cancer, mental disorders, heart diseases, gastro-intestinal disorders, hypertension, hearing deficit and diabetes mellitus. All reported diseases were more frequent in consanguineous marriages.

CONCLUSION

The study showed that in a population with a high rate of consanguinity, there is a significant increase in the prevalence of common adult diseases like cancer, mental disorders, heart diseases, gastro-intestinal disorders, hypertension and hearing deficit.

Homozygosity for a missense mutation in the 67 kDa isoform of glutamate decarboxylase in a family with autosomal recessive spastic cerebral palsy: parallels with Stiff-Person Syndrome and other movement disorders

BACKGROUND

Cerebral palsy (CP) is an heterogeneous group of neurological disorders of movement and/or posture, with an estimated incidence of 1 in 1000 live births. Non-progressive forms of symmetrical, spastic CP have been identified, which show a Mendelian autosomal recessive pattern of inheritance. We recently described the mapping of a recessive spastic CP locus to a 5 cM chromosomal region located at 2q24-31.1, in rare consanguineous families.

METHODS

Here we present data that refine this locus to a 0.5 cM region, flanked by the microsatellite markers D2S2345 and D2S326. The minimal region contains the candidate gene GAD1, which encodes a glutamate decarboxylase isoform (GAD67), involved in conversion of the amino acid and excitatory neurotransmitter glutamate to the inhibitory neurotransmitter gamma-aminobutyric acid (GABA).

RESULTS

A novel amino acid mis-sense mutation in GAD67 was detected, which segregated with CP in affected individuals.

CONCLUSIONS

This result is interesting because auto-antibodies to GAD67 and the more widely studied GAD65 homologue encoded by the GAD2 gene, are described in patients with Stiff-Person Syndrome (SPS), epilepsy, cerebellar ataxia and Batten disease. Further investigation seems merited of the possibility that variation in the GAD1 sequence, potentially affecting glutamate/GABA ratios, may underlie this form of spastic CP, given the presence of anti-GAD antibodies in SPS and the recognised excitotoxicity of glutamate in various contexts.

Ataxias of childhood

BACKGROUND

This review examines the causes of ataxias in children. It is a relatively common manifestation of neurological diseases in children. The etiology of ataxia covers a broad range, from infections to rare hereditary metabolic diseases. A systematic approach is required to make the correct diagnosis.

REVIEW SUMMARY

The more common causes of ataxias in children are discussed in detail. The importance of recognizing potentially reversible conditions such as vitamin E deficiency and Refsum's disease is stressed. Recent advances in molecular genetics of some of the chronic ataxias are discussed. The importance of categorizing diseases based on the duration of symptoms and associated signs is discussed. Treatment options are mentioned.

CONCLUSION

Ataxia is a common mode of presentation of cerebellar, posterior column, and vestibular disease in children. Awareness of the spectrum of disease entities that cause ataxia in childhood may lead to better diagnosis.

Paternal factors and schizophrenia risk: de novo mutations and imprinting

There is a strong genetic component for schizophrenia risk, but it is unclear how the illness is maintained in the population given the significantly reduced fertility of those with the disorder. One possibility is that new mutations occur in schizophrenia vulnerability genes. If so, then those with schizophrenia may have older fathers, because advancing paternal age is the major source of new mutations in humans. This review describes several neurodevelopmental disorders that have been associated with de novo mutations in the paternal germ line and reviews data linking increased schizophrenia risk with older fathers. Several genetic mechanisms that could explain this association are proposed, including paternal germ line mutations, trinucleotide repeat expansions, and alterations in genetic imprinting in one or several genes involved in neurodevelopment. Animal models may be useful in exploring these and other explanations for the paternal age effect and they may provide a novel approach for gene identification. Finally, it is proposed that environmental exposures of the father, as well as those of the mother and developing fetus, may be relevant to the etiology of schizophrenia.