Birth seasonality in Prader-Willi syndrome

Established and Novel Mechanisms Leading to de novo Genomic Rearrangements in the Human Germline

During gametogenesis, the human genome can acquire various de novo rearrangements. Most constitutional genomic rearrangements are created through 1 of the 4 well-known mechanisms, i.e., nonallelic homologous recombination, erroneous repair after double-strand DNA breaks, replication errors, and retrotransposition. However, recent studies have identified 2 types of extremely complex rearrangements that cannot be simply explained by these mechanisms. The first type consists of chaotic structural changes in 1 or a few chromosomes that result from “chromoanagenesis (an umbrella term that covers chromothripsis, chromoanasynthesis, and chromoplexy).” The other type is large independent rearrangements in multiple chromosomes indicative of “transient multifocal genomic crisis.” Germline chromoanagenesis (chromothripsis) likely occurs predominantly during spermatogenesis or postzygotic embryogenesis, while multifocal genomic crisis appears to be limited to a specific time window during oogenesis and early embryogenesis or during spermatogenesis. This review article introduces the current understanding of the molecular basis of de novo rearrangements in the germline.

Frequency of Common Copy-Number Variations at 15q11.2q13 in Sperm of Healthy Men

The genomic region at 15q11.2q13 represents a hotspot for copy-number variations (CNVs) due to nonallelic homologous recombination. Previous studies have suggested that the development of 15q11.2q13 deletions in sperm may be affected by seasonal factors because patients with Prader-Willi syndrome resulting from 15q11.2q13 deletions on paternally derived chromosomes showed autumn-dominant birth seasonality. The present study aimed to determine the frequency of 15q11.2q13 CNVs in sperm of healthy men and clarify the effects of various environmental factors, i.e., age, smoking status, alcohol intake, and season, on the frequency. Thirty volunteers were asked to provide semen samples and clinical information once in each season of a year. The rates of 15q11.2q13 CNVs were examined using 2-color FISH. The results were statistically analyzed using a generalized estimating equation with negative binomial distribution and a log link function. Consequently, informative data were obtained from 83 samples of 26 individuals. The rates of deletions and duplications ranged from 0.04 to 0.48% and from 0.08 to 0.30%, respectively. The rates were not correlated with the age, smoking status, or alcohol intake. Sperm produced in winter showed 1.2 to 1.4-fold high rates for both deletions and duplications as compared with sperm produced in the other seasons; however, there was no significant difference. These results demonstrate high and variable CNV rates at 15q11.2q13 in sperm of healthy men. These CNVs appear to occur independent of the age, smoking status, or alcohol intake, while the effect of season remains inconclusive. Our results merit further validation.

Birth seasonality studies in a large Prader-Willi syndrome cohort

Prader‐Willi syndrome (PWS) is generally due to sporadic paternal deletions of the chromosome 15q11‐q13 region followed by maternal disomy 15. Advanced maternal age is more commonly seen in those with maternal disomy 15. Environmental factors (e.g., drug use, occupational chemical exposure, infectious agents, and irradiation) could account for chromosome changes. Previous evidence of differences in male and female gametogenesis could suggest an environmental role in the causation of the paternal 15q11‐q13 deletion seen in PWS. Certain occupations such as hydrocarbon‐exposing occupations (e.g., landscaping, farming, and painting) and viral exposure (e.g., human coronavirus 229E causing upper respiratory infections in adults with an incorporation site in the human genome at chromosome 15q11) can be seasonal in nature and contribute to chromosome damage. To assess, we reviewed birth seasonality data in a large cohort of individuals with PWS recruited nationally (N = 355) but no significant differences were seen by month between those with the 15q11‐q13 deletion compared with maternal disomy 15 when analyzing quarterly seasonal patterns. Although early evidence supported birth seasonality differences in PWS, a larger number of individuals in our recent study using advanced genetic testing methods did not find this observation.

Birth seasonality in Korean Prader-Willi syndrome with chromosome 15 microdeletion

PURPOSE

Prader-Willi syndrome (PWS) is a well-known genetic disorder, and microdeletion on chromosome 15 is the most common causal mechanism. Several previous studies have suggested that various environmental factors might be related to the pathogenesis of microdeletion in PWS. In this study, we investigated birth seasonality in Korean PWS.

METHODS

A total of 211 PWS patients born from 1980 to 2014 were diagnosed by methylation polymerase chain reaction at Samsung Medical Center. Of the 211 patients, 138 were born from 2000-2013. Among them, the 74 patients of a deletion group and the 22 patients of a maternal uniparental disomy (UPD) group were compared with general populations born from 2000 using the Walter and Elwood method and cosinor analysis.

RESULTS

There was no statistical significance in seasonal variation in births of the total 211 patients with PWS (χ(2)=7.2522, P=0.2982). However, a significant difference was found in the monthly variation between PWS with the deletion group and the at-risk general population (P<0.05). In the cosinor model, the peak month of birth for PWS patients in the deletion group was January, while the nadir occurred in July, with statistical significance (amplitude=0.23, phase=1.2, low point=7.2). The UPD group showed the peak birth month in spring; however, this result was not statistically significant (χ(2)=3.39, P=0.1836).

CONCLUSION

Correlation with birth seasonality was identified in a deletion group of Korean PWS patients. Further studies are required to identify the mechanism related to seasonal effects of environmental factors on microdeletion on chromosome 15.

Season of birth: issues, approaches and findings for autism

Rates of birth in the general population show seasonal fluctuations for reasons that are ill understood. Variations from these general population patterns have been reported for several psychiatric conditions and used as the basis for aetiological hypotheses. In this paper, the evidence for alterations in the expected seasonal fluctuation in birth dates of autistic people is evaluated. A national sample of 1435 autistic individuals and a clinic sample of 196 subjects are compared to general population figures and to 121 sibling controls. Compared with the general population, the national sample showed significant deviations from the expected rate of birth by month. In the clinic sample, differences from the anticipated monthly pattern were only evident when this sample was compared to the sibling controls. A variety of models for seasonal trends, including year quarters, temperature and sine wave forms, were fitted to these variations but no consistent picture emerged.

The speech and language characteristics of children with Prader-Willi syndrome

Prader-Willi syndrome was initially identified in 1956. Since then, a majority of the literature pertaining to Prader-Willi has focused on the medical and genetic aspects of the syndrome. There has been limited information available regarding the speech and language abilities of children with Prader-Willi. This study investigated the communicative development of 18 children with the syndrome, ranging in age from 8:8 to 17:1. A number of evaluative procedures were used to evaluate the subjects' spontaneous speech, articulation, and receptive and expressive language abilities, as well as their voice, fluency, oral mechanisms, hearing, and their developmental histories. A variety of communicative deficiencies were found in the children's speech, language, voice, and fluency.

Restriction fragment length polymorphisms within proximal 15q and their use in molecular cytogenetics and the Prader-Willi syndrome

Restriction fragment length polymorphisms (RFLPs) are described in detail for 6 DNA probes (D15S9-13, D15S18) that localize to the proximal long arm of human chromosome 15 (15q11-15q13: this report and Tantravahi et al., Am. J. Med. Genet. 33:78-87. Multiple RFLPs are detected by the probe that identifies locus D15S13, and these RFLPs are shown by genomic mapping to result from a nearby insertion or deletion of 1.8 kilobases (kb) of DNA. This set of RFLPs detected by proximal 15q probes can be used for studies on the Prader-Willi syndrome (PWS) and on mentally retarded individuals with a supernumerary inv dup(15) chromosome. Five of the polymorphic loci (D15S9-13) map to the region implicated in the cause of the PWS (15q11.2-15q12). Each of 4 families tested with these probes, as well as an additional "PWS-like" patient, was informative by RFLP analysis. The two PWS deletions studied, which occurred de novo, were inherited from the chromosome 15 provided by the father. By contrast, the 2 inv dup(15) chromosomes analyzed were of maternal origin. The use of RFLPs can also simplify the molecular determination of copy number in chromosomal aneuploidy, as exemplified by analysis of individuals with the PWS and a deletion, patients with an inv dup(15), and one patient with a more complex rearrangement involving chromosome 15. Our studies demonstrate the application of DNA probes for both molecular cytogenetic studies on this chromosome region and the development of diagnostic molecular markers to aid early clinical diagnosis of the PWS.

Alcoholism: theoretical consideration of season of birth and geographic latitude

Several neurological and immune phenomena associated with cerebral laterality also show an atypical season of birth pattern. Alcoholism is also associated with cerebral laterality. In this pilot study (n = 292), 66% of right-handed alcoholic men were born during the summer and fall (expected 52%, p less than 0.001). This finding suggests that at high latitude more right-handed men would become alcoholic because seasonal effects usually intensify with increasing latitude. In addition, in our sample of alcoholic men, left-handedness was associated with having an alcoholic father or with being first-born. Together, these findings suggest that the prevalence of alcoholism should increase with increasing latitude, and that the frequency in alcoholic men of being left-handed, first-born or having an alcoholic father should decrease with increasing latitude. The available literature tends to substantiate these correlations, but more systematic studies of season of birth and correlations with latitude in alcoholism are required.