Case Report: A Case Report and Literature Review of 3p Deletion Syndrome

Objective: The aim of the present study is to explore the clinical and genetic characteristics of 3p deletion syndrome to improve clinicians' understanding of the disease.Methods: The clinical manifestations, process of diagnosis and treatment, and genetic characteristics of an individual case of 3p deletion syndrome were analyzed. CNKI, Wanfang Data, and the Biomedical Literature Database (PubMed) were searched. The search time limit, using “3p deletion syndrome” and “BRPF1” as keywords, was from the creation of the database up to June 2020. Related data were reviewed.Results: The proband was a male child with general developmental and intellectual disabilities, special facial features and congenital heart disease. The child was the parents' first pregnancy and first born. Gene microarray analysis showed a 10.095 Mb deletion in the 3p26.3-p25.3 region, resulting in a heterozygous mutation of the BRPF1 gene; thus, the patient was diagnosed with 3p deletion syndrome. At the time of diagnosis, the child was 1 year of age and was responding to comprehensive rehabilitation training. A total of 29 well-documented cases were found in the literature, of which 19 cases had an onset within 1 year of birth, and mainly manifested with mental and motor development disabilities and abnormal facial features, with different gene deletions, depending on the size and location of the 3p deletion.Conclusion: The genetic test results of the child in this study indicated a heterozygous deletion of the BRPF1 gene on the short arm of chromosome 3, which was a unique feature of this study, since it was rarely mentioned in other reports of 3p deletion syndrome. The clinical phenotype of this syndrome is complex as it can include intellectual and motor development backwardness, low muscle tone, certain abnormal facial features (low hairline, bilateral ptosis, widely spaced eyes, a forward nose, left ear auricle deformity, a high-arched palate, a small jaw), and the deformation of systems such as the gastrointestinal tract and the urinary tract malformation or symptoms of epilepsy. As clinical manifestations can be relatively mild, the syndrome is easy to miss or misdiagnose. Clinical workers need to be aware of this disease when they find that children have special features, such as stunted growth, low muscle tone or ptosis, and it needs to be diagnosed through genetic testing. Most children are able to develop certain social skills after rehabilitation treatment.

Cell Adhesion Molecules Involved in Neurodevelopmental Pathways Implicated in 3p-Deletion Syndrome and Autism Spectrum Disorder

Autism spectrum disorder (ASD) is characterized by impaired social interaction, language delay and repetitive or restrictive behaviors. With increasing prevalence, ASD is currently estimated to affect 0.5–2.0% of the global population. However, its etiology remains unclear due to high genetic and phenotypic heterogeneity. Copy number variations (CNVs) are implicated in several forms of syndromic ASD and have been demonstrated to contribute toward ASD development by altering gene dosage and expression. Increasing evidence points toward the p-arm of chromosome 3 (chromosome 3p) as an ASD risk locus. Deletions occurring at chromosome 3p result in 3p-deletion syndrome (Del3p), a rare genetic disorder characterized by developmental delay, intellectual disability, facial dysmorphisms and often, ASD or ASD-associated behaviors. Therefore, we hypothesize that overlapping molecular mechanisms underlie the pathogenesis of Del3p and ASD. To investigate which genes encoded in chromosome 3p could contribute toward Del3p and ASD, we performed a comprehensive literature review and collated reports investigating the phenotypes of individuals with chromosome 3p CNVs. We observe that high frequencies of CNVs occur in the 3p26.3 region, the terminal cytoband of chromosome 3p. This suggests that CNVs disrupting genes encoded within the 3p26.3 region are likely to contribute toward the neurodevelopmental phenotypes observed in individuals affected by Del3p. The 3p26.3 region contains three consecutive genes encoding closely related neuronal immunoglobulin cell adhesion molecules (IgCAMs): Close Homolog of L1 (CHL1), Contactin-6 (CNTN6), and Contactin-4 (CNTN4). CNVs disrupting these neuronal IgCAMs may contribute toward ASD phenotypes as they have been associated with key roles in neurodevelopment. CHL1, CNTN6, and CNTN4 have been observed to promote neurogenesis and neuronal survival, and regulate neuritogenesis and synaptic function. Furthermore, there is evidence that these neuronal IgCAMs possess overlapping interactomes and participate in common signaling pathways regulating axon guidance. Notably, mouse models deficient for these neuronal IgCAMs do not display strong deficits in axonal migration or behavioral phenotypes, which is in contrast to the pronounced defects in neuritogenesis and axon guidance observed in vitro. This suggests that when CHL1, CNTN6, or CNTN4 function is disrupted by CNVs, other neuronal IgCAMs may suppress behavioral phenotypes by compensating for the loss of function.

Chromosome r(3)(p25.3q29) in a Patient with Developmental Delay and Congenital Heart Defects: A Case Report and a Brief Literature Review

Ring chromosome 3, r(3), is an extremely rare cytogenetic abnormality with clinical heterogeneity and only 12 cases reported in the literature. Here, we report a 1-year-old girl presenting distinctive facial features, developmental delay, and congenital heart defects with r(3) and a ∼10-Mb deletion of chromosome 3pterp25.3 (61,891-9,979,408) involving 42 known genes which was detected using G-banding karyotyping and CytoScan 750K-Array. The breakpoints in r(3) were mapped at 3p25.3 and 3q29. We also analyzed the available information on the clinical features of the reported cases with r(3) and 3p deletion syndrome in order to provide more valuable information of genotype-phenotype correlations. To our knowledge, this is the largest detected fragment described in r(3) cases and the second r(3) study using whole-genome microarray.