Chromosome 15q24 microdeletion syndrome

Chromosome 15q24 microdeletion syndrome is a recently described rare microdeletion syndrome that has been reported in 19 individuals. It is characterized by growth retardation, intellectual disability, and distinct facial features including long face with high anterior hairline, hypertelorism, epicanthal folds, downslanting palpebral fissures, sparse and broad medial eyebrows, broad and/or depressed nasal bridge, small mouth, long smooth philtrum, and full lower lip. Other common findings include skeletal and digital abnormalities, genital abnormalities in males, hypotonia, behavior problems, recurrent infections, and eye problems. Other less frequent findings include hearing loss, growth hormone deficiency, hernias, and obesity. Congenital malformations, while rare, can be severe and include structural brain anomalies, cardiovascular malformations, congenital diaphragmatic hernia, intestinal atresia, imperforate anus, and myelomeningocele. Karyotypes are typically normal, and the deletions were detected in these individuals by array comparative genomic hybridization (aCGH). The deletions range in size from 1.7-6.1 Mb and usually result from nonallelic homologous recombination (NAHR) between paralogous low-copy repeats (LCRs). The majority of 15q24 deletions have breakpoints that localize to one of five LCR clusters labeled LCR15q24A, -B, -C, -D, and -E. The smallest region of overlap (SRO) spans a 1.2 Mb region between LCR15q24B to LCR15q24C. There are several candidate genes within the SRO, including CYP11A1, SEMA7A, CPLX3, ARID3B, STRA6, SIN3A and CSK, that may predispose to many of the clinical features observed in individuals with 15q24 deletion syndrome. The deletion occurred as a de novo event in all of the individuals when parents were available for testing. Parental aCGH and/or FISH studies are recommended to provide accurate genetic counseling and guidance regarding prognosis, recurrence risk, and reproductive options. Management involves a multi-disciplinary approach to care with the primary care physician and clinical geneticist playing a crucial role in providing appropriate screening, surveillance, and care for individuals with this syndrome. At the time of diagnosis, individuals should receive baseline echocardiograms, audiologic, ophthalmologic, and developmental assessments. Growth and feeding should be closely monitored. Other specialists that may be involved in the care of individuals with 15q24 deletion syndrome include immunology, endocrine, orthopedics, neurology, and urology. Chromosome 15q24 microdeletion syndrome should be differentiated from other genetic syndromes, particularly velo-cardio-facial syndrome (22q11.2 deletion syndrome), Prader-Willi syndrome, and Noonan syndrome. These conditions share some phenotypic similarity to 15q24 deletion syndrome yet have characteristic features specific to each of them that allows the clinician to distinguish between them. Molecular genetic testing and/or aCGH will be able to diagnose these conditions in the majority of individuals.