Symptoms associated with mutations in the 15q11.2 region include dysmorphic features (including microcephaly), developmental delays (particularly speech delay), neurological and behavioral issues (e.g. ADD/ADHD, tantrums, OCD, sleep issues), seizures, gait or coordination problems, hypotonia, and intellectual disability. (Burnside et al. 2011 and references therein, pubmed:21359847.)

Nine unrelated patients that did not have Prader-Willi or Angelman syndrome were found to have a heterozygous 340-kb microdeletion between BP1 and BP2 on chromosome 15q11. Eight had overlapping and variable features, including general, speech, or motor developmental delay, and abnormal behavior such as autism spectrum disorder, obsessive-compulsive disorder, attention deficit-hyperactivity disorder, and happy demeanor. Many patients had dyspraxia, and 2 had seizures. Dysmorphic features were present in some patients and included plagiocephaly, broad forehead, hypertelorism, dysmorphic ears, cleft palate, and slender fingers. (Doornbos et al. 2009, pubmed:19328872.) [from MIM:615656, 2019.10.29]

Deletions spanning a four-gene region on chromosome 15 (BP1-BP2 at 15q11.2), present at a population frequency of approximately 1 in 500, are associated with increased risk for multiple neurodevelopmental disorders (NDDs). (Woo et al. 2019 and references therein, FBrf0243072.)

The proximal 15q region includes five regions of segmental duplications or low copy repeats (designated by breakpoints [BPs]), which result in increased susceptibility to genomic rearrangements. These five regions are termed BP1 through BP5. The Prader-Willi/Angelman critical region (PWACR) lies between BP2 and BP3. [Gene Reviews, 15q Duplication Syndrome and Related Disorders; 2021.01.10]

The deleted region spans approximately 300 to 500 kb between breakpoints 1 (BP1) and 2 (BP2) of the Prader-Willi (PWS; MIM:176270)/Angelman syndrome (AS; MIM:105830) critical region. The deletion region between BP1 and BP2 contains 4 genes that are not imprinted: TUBGCP5 (MIM:608147), NIPA1 (MIM:608145), NIPA2 (MIM:608146), and CYFIP1 (MIM:606322). [from MIM:615656, 2019.10.29]

Altered CYFIP1 dosage perturbs neuronal morphology, synaptic excitation, and brain patterning and function. Importantly, alterations in white matter architecture and functional connectivity, similar to those observed in humans with BP1-BP2 deletions, were observed in mice and rats heterozygous for a mutation in Cyfip1. (Woo et al. 2019 and references therein, FBrf0243072.)

Structural magnetic resonance imaging found that the 15q11.2(BP1-BP2) deletion affects brain structure in a pattern consistent with both that observed during first-episode psychosis in schizophrenia and that of structural correlates in dyslexia. For both gray and white matter, 15q11.2(BP1-BP2) duplication carriers always showed reciprocal changes in exactly the same regions altered in deletion carriers, demonstrating allele dose-dependent effects of CNVs on the structure of the human brain. (Stefansson et al. 2014, pubmed:24352232.)