The proximal 15q11-13 chromosome region contains five breakpoints (BP1-BP5). Chromosomal rearrangements such as duplications, microdeletions are common changes in this region. The well known microdeletion syndromes related to this region are the Prader-Willi (PWS) and Angelman syndromes (AS), depending on the parental origin of the deleted allele . The severity of the symptoms depends on the size of the deleted region. BP1-BP2 region is composed of approximately 500 kb and contains four evolutionarily conserved, non-imprinted genes. The microdeletion of this smaller region has recently been considered as a separate entity, the 15q11.2 microdeletion syndrome. The main phenotypic attributes of this microdeletion syndrome are as follows: developmental delay, idiopathic generalized epilepsy, behavioural abnormalities, motor apraxia and dysmorphic features.
Since in some cases these rearrangements/microdeletions can be inherited from unaffected parents, while the majority of patients suffer from serious symptoms, the pathogenicity of 15q11.2 microdeletion remains unclear. Incomplete penetrance, high variability of expression, genetic and epigenetic changes provoked by environmental events may lead to these differences, but further investigations are needed to clarify the perfect genotype-phenotype correlations. Herein, we report a male patient with BP1-BP2 microdeletion associated AS symptoms and his mother with the same genetic rearrangement but without any clinical symptom. By analysis of genotype-phenotype correlation of the family presented here we try to find the explanation of this variance. As the symptoms of the boy are the same as characteristic of the AS, we concern the mechanisms presumably can cause AS or Angelman-like syndromes.