Evolution of genetic and genomic features unique to the human lineage.

Given the unprecedented tools that are now available for rapidly comparing genomes, the identification and study of genetic and genomic changes that are unique to our species have accelerated, and we are entering a golden age of human evolutionary genomics. Here we provide an overview of these efforts, highlighting important recent discoveries, examples of the different types of human-specific genomic and genetic changes identified, and salient trends, such as the localization of evolutionary adaptive changes to complex loci that are highly enriched for disease associations. Finally, we discuss the remaining challenges, such as the incomplete nature of current genome sequence assemblies and difficulties in linking human-specific genomic changes to human-specific phenotypic traits.

DUF1220 dosage is linearly associated with increasing severity of the three primary symptoms of autism.

One of the three most frequently documented copy number variations associated with autism spectrum disorder (ASD) is a 1q21.1 duplication that encompasses sequences encoding DUF1220 protein domains, the dosage of which we previously implicated in increased human brain size. Further, individuals with ASD frequently display accelerated brain growth and a larger brain size that is also associated with increased symptom severity. Given these findings, we investigated the relationship between DUF1220 copy number and ASD severity, and here show that in individuals with ASD (n = 170), the copy number (dosage) of DUF1220 subtype CON1 is highly variable, ranging from 56 to 88 copies following a Gaussian distribution. More remarkably, in individuals with ASD CON1 copy number is also linearly associated, in a dose-response manner, with increased severity of each of the three primary symptoms of ASD: social deficits (p = 0.021), communicative impairments (p = 0.030), and repetitive behaviors (p = 0.047). These data indicate that DUF1220 protein domain (CON1) dosage has an ASD-wide effect and, as such, is likely to be a key component of a major pathway underlying ASD severity. Finally, these findings, by implicating the dosage of a previously unexamined, copy number polymorphic and brain evolution-related gene coding sequence in ASD severity, provide an important new direction for further research into the genetic factors underlying ASD.

DUF1220 copy number is linearly associated with increased cognitive function as measured by total IQ and mathematical aptitude scores.

DUF1220 protein domains exhibit the greatest human lineage-specific copy number expansion of any protein-coding sequence in the genome, and variation in DUF1220 copy number has been linked to both brain size in humans and brain evolution among primates. Given these findings, we examined associations between DUF1220 subtypes CON1 and CON2 and cognitive aptitude. We identified a linear association between CON2 copy number and cognitive function in two independent populations of European descent. In North American males, an increase in CON2 copy number corresponded with an increase in WISC IQ (R (2) = 0.13, p = 0.02), which may be driven by males aged 6-11 (R (2) = 0.42, p = 0.003). We utilized ddPCR in a subset as a confirmatory measurement. This group had 26-33 copies of CON2 with a mean of 29, and each copy increase of CON2 was associated with a 3.3-point increase in WISC IQ (R (2) = 0.22, p = 0.045). In individuals from New Zealand, an increase in CON2 copy number was associated with an increase in math aptitude ability (R (2) = 0.10 p = 0.018). These were not confounded by brain size. To our knowledge, this is the first study to report a replicated association between copy number of a gene coding sequence and cognitive aptitude. Remarkably, dosage variations involving DUF1220 sequences have now been linked to human brain expansion, autism severity and cognitive aptitude, suggesting that such processes may be genetically and mechanistically inter-related. The findings presented here warrant expanded investigations in larger, well-characterized cohorts.

Finished sequence and assembly of the DUF1220-rich 1q21 region using a haploid human genome.

BACKGROUND: Although the reference human genome sequence was declared finished in 2003, some regions of the genome remain incomplete due to their complex architecture. One such region, 1q21.1-q21.2, is of increasing interest due to its relevance to human disease and evolution. Elucidation of the exact variants behind these associations has been hampered by the repetitive nature of the region and its incomplete assembly. This region also contains 238 of the 270 human DUF1220 protein domains, which are implicated in human brain evolution and neurodevelopment. Additionally, examinations of this protein domain have been challenging due to the incomplete 1q21 build. To address these problems, a single-haplotype hydatidiform mole BAC library (CHORI-17) was used to produce the first complete sequence of the 1q21.1-q21.2 region. RESULTS: We found and addressed several inaccuracies in the GRCh37sequence of the 1q21 region on large and small scales, including genomic rearrangements and inversions, and incorrect gene copy number estimates and assemblies. The DUF1220-encoding NBPF genes required the most corrections, with 3 genes removed, 2 genes reassigned to the 1p11.2 region, 8 genes requiring assembly corrections for DUF1220 domains (~91 DUF1220 domains were misassigned), and multiple instances of nucleotide changes that reassigned the domain to a different DUF1220 subtype. These corrections resulted in an overall increase in DUF1220 copy number, yielding a haploid total of 289 copies. Approximately 20 of these new DUF1220 copies were the result of a segmental duplication from 1q21.2 to 1p11.2 that included two NBPF genes. Interestingly, this duplication may have been the catalyst for the evolutionarily important human lineage-specific chromosome 1 pericentric inversion. CONCLUSIONS: Through the hydatidiform mole genome sequencing effort, the 1q21.1-q21.2 region is complete and misassemblies involving inter- and intra-region duplications have been resolved. The availability of this single haploid sequence path will aid in the investigation of many genetic diseases linked to 1q21, including several associated with DUF1220 copy number variations. Finally, the corrected sequence identified a recent segmental duplication that added 20 additional DUF1220 copies to the human genome, and may have facilitated the chromosome 1 pericentric inversion that is among the most notable human-specific genomic landmarks.

Suicides in urban and rural counties in the United States, 2006-2008.

BACKGROUND: Suicide rates are higher in rural areas. It has been hypothesized that inadequate access to care may play a role, but studies examining individual decedent characteristics are lacking. AIMS: We sought to characterize the demographic, socioeconomic, and mental health features of individual suicide decedents by urban-rural residence status. METHOD: We analyzed suicides in 16 states using 2006-2008 data from the National Violent Death Reporting System and examined associations between decedent residence type and suicide variables with separate logistic regressions adjusted for age, sex, race, and ethnicity. RESULTS: Of 17,504 analyzed suicides, 78% were in urban, 15% in rural adjacent, and 8% in rural nonadjacent locations. Rural decedents were less likely than urban decedents to have a mental health diagnosis or mental health care, although the prevalence of depressed moods appeared similar. Most suicides were by firearm, and rural decedents were more likely than urban decedents to have used a firearm. CONCLUSION: Rural decedents were less likely to be receiving mental health care and more likely to use firearms to commit suicide. A better understanding of geographic patterns of suicide may aid prevention efforts.

Seasonal variation in suicidal behavior with prescription opioid medication.

BACKGROUND: Suicide attempts by self-poisoning utilizing prescription opioids account for more than half of prescription drug abuse and misuse emergency calls received by poison centers. Additionally seasonal suicidal behavior using other means is a commonly replicated finding. We hypothesized seasonal behavior would exist in individuals using opioid medication as a suicide means, and that this pattern would change at different latitudes in the United States. METHODS: We used a harmonic regression strategy to investigate sinusoidal seasonal variations of suicidal behavior utilizing prescription opioids, and to contrast changes in seasonal behavior by latitude within the United States. Further, we investigated associations between suicide frequency utilizing opioid medication and frequency of dispensed opioid prescriptions. RESULTS: Seasonal patterns were identified; overall, all harmonic terms were significant (p<0.05). Interaction terms of harmonic by latitude and harmonic by gender also were significant (p<0.05). After stratification, females had significant harmonic terms at all latitudes. A changing peak time period with latitude also was observed, such that the peak appeared later at more southern latitudes. Additionally, increased dispensed prescriptions rates per population were associated with increased suicidal behavior utilizing prescription opioids. LIMITATIONS: This study has limitations due to its ecological nature and to missing data that may inform our understanding of suicide risk factors, such as marital status and socio-economic status. CONCLUSION: Suicidal behavior with prescription opioids follows a seasonal pattern that changes with latitude within the United States. Further, increased accessibility may contribute to increased suicidal attempt rates utilizing prescription opioids.