1 medical history
Child, male, 8 years old, from Hunan, 2065438+September 2004? Mental retardation, language retardation, short stature and facial dysplasia? Come to our hospital for treatment.
The baby was born at 39+ 1 week, with a birth weight of 2920g. No history of birth asphyxia.
The child's motor development is normal, he looks up at 3 months, sits alone at 7 months, 12 months, and walks alone at 2 years old. At the age of 8, the child's height 103.3 cm, sitting height 60.0 cm and weight 16.45 kg.
The child is mentally retarded and can't speak.
Deny the family history of birth defects, the history of toxic and radiation exposure, and the history of drugs, and deny that relatives have a history of genetic diseases.
2 physical examination
The child's forehead is flat, hairline is high, middle and low ears are short. The development of secondary sexual characteristics is characterized by beard stage I, armpit hair stage I, pubic hair stage I, external genitalia stage I, bilateral testicles less than 1 ml, and no nocturnal emission.
3. Auxiliary inspection
The leaf bone age was 5.3 years old, and the R series score was 135.
Growth hormone drug provocation test suggests complete growth hormone deficiency.
Brain MRI showed nothing unusual.
The electrocardiogram in the outer hospital is normal.
Tandem mass spectrometry (chromatography) showed no obvious abnormality in screening common genetic and metabolic diseases.
After diagnosis and treatment.
After the family members of the children knew and signed the informed consent form, genetic testing was carried out.
① Cytogenetic detection
Methods: The peripheral blood of children and their parents was collected and inoculated in the culture medium containing phytohemagglutinin for culture. Chromosomes were prepared by routine operation and G banding was performed. Karyotypes with more than 400 bands were selected for analysis. See "20 13 International Nomenclature System for Human Cytogenetics (ISCN)" for karyotype description.
Results: G banding karyotype analysis showed that the karyotype of the child was 46. XY，t(4； 15)(p 14； q 26. 1)； The results of G-banding karyotype analysis of the mother and father of the child are normal, indicating that the child is a new chromosome 4 and 15 translocation, as shown in figure 1.
Figure 1 G-banding Karyotype Analysis of Children's Peripheral Blood
Arrow: 4p end and 15q end translocation.
② Single nucleotide polymorphism (SNP) detection on chip.
Methods: 2 ml of venous blood from children was anticoagulated with EDTA to extract the whole genome DNA from peripheral blood. Cyto Scan 750K SNP-Array (containing about 200,000 SNPs and 550,000 CNV probes) provided by Affymetrix Company of the United States was used to detect the copy number variation of the whole gene. Take 250 ng complete genomic DNA and carry out the experiment according to the standard detection process: Nsp I digestion, linker ligation, polymerase chain reaction amplification, product purification, fragmentation, labeling and hybridization. Affymetrix Fluids Stations 450dx is used for washing, Affymetrix 7G scanner is used for scanning, and the scanning signal is analyzed by Affymetrix CHAS software.
Results: The results of children's high-density SNP-ARR chip were ARR [Hg19] 4q13./q13.3 (63,042,514-74,655,455. 1, deleted at 4q13.1q13.3, has about 1 1.6 Mb, and the parents' test results are normal.
③ Fish detection
Methods: The specific probe RP11111019 (CHR 4: 67586902-67781. Specific probe RP11-350c22 (CHR 4: 57716-216840, 153 kb, red signal), Specific probe RP11-159a22 (CHR15:185524560-65560 green signal), specific probe RP11-. The cell suspension cultured from children's peripheral blood lymphocytes was made into sections and the sections were pretreated. The probe and chromosome were denatured, hybridized, washed and DAPI stained according to the steps in the reagent instructions, and the hybridization signal was observed under the fluorescence microscope.
Results: In the middle childhood, the probe FISH results showed that 1 chromosome 4q119 lacked the probe RP 1 1-65448. In addition, the probe of chromosome 4RP11-350c22 (4p16.3) was translocated to the end of the long arm of chromosome 15, and the derived chromosomes115 were formed. At the same time, the FISH results also verified that the 4q 13.2 deletion chromosome and the derivative chromosome 4 are the same chromosome, as shown in Figure 2.
Fig. 2 FISH analysis results of children's mid-term probe
A:
Green: 4q35. 1 area-specific probe;
Brown: 4q 13.2 area-specific probe;
Arrows show that chromosome 4 and corresponding fragments are missing normal chromosomes respectively.
B:
Green: 15q26.3 region-specific probe;
Brown: 4q 13.2 area-specific probe;
Red: 4p 16.3 region-specific probe;
1 chromosome 4p 16.3 lacks probe signal and translocates to the end of 15 chromosome.
5 Final diagnosis
4q13.1-13.3 microdeletions.
6 discussion
The incidence of mental retardation in the population is about 3%, and genetic factors account for about 40%, of which chromosomal abnormalities and monogenic diseases account for 25% and 10% respectively. Chromosome abnormalities can be detected by traditional karyotype analysis and microarray analysis techniques. Chromosome abnormality can detect fragment abnormalities above 5 ~ 10 MB; However, it is limited by the inspector's experience, the quality of metaphase chromosomes and the structure of abnormal fragments themselves. In this study, the deletion fragment size of 4q13.1-13.3 in children was 1 1.6 Mb, which was not found during detection. The reason is that the patient has a chromosome translocation. The first thing that comes to mind is that the translocation chromosome interrupts the gene, which leads to the phenotype abnormality of the patient. In addition, the length of chromosome 4 is 190 Mb, which is easily overlooked when the deep band of 4q 13 narrows. Microarray analysis technology can analyze the whole genome and submicroscopic structural abnormalities. At present, this technology can explain nearly 30% of mental retardation. 20 10 American medical genetics association recommended chromosome chip as the first-line detection method for patients with mental retardation and growth retardation, which was also confirmed by the author's research. This study further emphasizes the importance of chromosome chip detection for such patients.
There are few reports about the long arm deletion of chromosome 4, and the incidence is about1110,000. The deletion from q33 to the end of chromosome is more common, while the deletion in 4q13.1-kloc-0/3.2 region is even rarer. In the reported cases of deletion of the middle part of the long arm of chromosome 4, breakpoints are easy to appear at 4q 13. 1 3.2 and 4q 13.3, but as far as I know, there is no 4q13./kloc-0 at present. Although the missing areas of reported cases are different, the clinical manifestations are certain * * *. The clinical phenotypes of the syndrome in the decrypted database include mental retardation, facial deformity, nasal collapse, low ear, gastroesophageal reflux and so on. Some scholars have made great progress in studying the relationship between some genes in the long arm of chromosome 4 and diseases. EPHA5 receptor plays an important role in individual development. COOPER et al. have shown that EPHA5 interacts with its ligand to regulate axonal interaction of dopaminergic system by preventing and promoting the release of dopamine neurons in striatum. GERLAI and other studies show that the expression level of tubulin in hippocampus of adult mice is down-regulated after EphA5 activation, which indicates that EphA5 and its ligands play an important role in the formation of axons and dendrites in the central nervous system.
In this paper, it is considered that patients have the common characteristics of 4q deletion syndrome, and also have the characteristics of incomplete deficiency of growth hormone and delayed development of secondary sexual characteristics. The author searched 49 genes in the microdeletion region of patient 4q13.1-13.3, and found that the following genes were related to the phenotype of the patient. The gonadotropin-releasing hormone receptor gene encodes 1 gonadotropin-releasing hormone receptor, which is highly expressed in gonads, lymphocytes, thymus, ovary and prostate. The mutation of this gene can lead to partial or total loss of gonadotropin-releasing hormone function, resulting in hypogonadism (MIM:146110) or azoospermia (MIM:228300). MUC7 encodes salivary gland mucin, which is mainly expressed in bronchi and salivary glands. Muc7 plays an immune barrier role by promoting oral bacteria clearance, and also has the function of assisting chewing, pronunciation and swallowing. The remaining ubiquitin-activating enzyme 6, synaptic binding protein 14 and UGT2B gene family (UGT2B 17, UGT2B 15, UGT2B 10, UGT2B7, ugt2b1/,and ugt2b1.
In this paper, the author reported the loss of heterozygosity in 1 case 4q13.13.3 with 4p 14 and 15q26. 1 balanced chromosome translocation with mental retardation. Although the author can't completely rule out the influence of gene interruption at chromosome break on children's phenotype, the patient has a microdeletion of 1 1.6 Mb in the 4Q 13.3 region, but his parents have no such deletion. There are as many as 49 genes in this region in the online human Mendelian genetic database, and many genes are obviously related to the phenotype of patients. Therefore, the single dose deficiency caused by 4q13.1-4q13.3 microdeletion is more likely to be the phenotypic cause of children. However, due to the few reported cases, it is necessary to further clarify the key areas of the syndrome and the relationship between its source and phenotype, and more cases need to be accumulated and analyzed. SNP-array technology can detect chromosome aberration at submicroscopic level with high resolution, so it has great advantages in chromosome microdeletion/microduplication detection, and has become an important means to detect unexplained mental retardation and dysplasia. Moreover, because this technique accurately locates the chromosome break point, it is beneficial to the study of the relationship between genotype and phenotype.