Patient's question:
Which hospital in Beijing is best for checking chromosomes?Doctor's answer:
Disease Analysis:Hello, hope the following information is helpful to you:
Chromosome Introduction:
The following are the abbreviations and symbols for commonly used normal and abnormal chromosomes (ISCN 1978):
- A–G: A–G Karyotype
- 1–22: Autosome Number
- XY: Sex Chromosome
- /: Used to separate different cell lines in mosaicism
- +: When placed before the autosomal number or group symbol, it indicates an increase or loss of the entire chromosome; when placed after the chromosome structure or other symbols, it indicates an increase or decrease in chromosome length
- ?: Chromosome structure is unclear or questionable, should be placed before the karyotype or number
- : Indicates a break
- ∷: Breakage and reunion
- ;: Separates chromosomes and chromosome regions from several chromosome rearrangements
- →: From...to...
- ace: Acentric fragment
- ce: Centromere
- chi: Heteromorphic mosaicism
- ct: Chromatid
- del: Deletion
- der: Derivative chromosome
- dic: Dicentric
- dup: Duplication
- ed: Endoreduplication
- g: Gap
- h: Secondary constriction
- i: Isochromosome
- is: Insertion
- iv: Inversion
- ivis: Inversion insertion
- iv(p-q+)/iv(p+q-): Paracentric inversion
- mar: Marker chromosome
- mat: From mother
- mos: Mosaicism (homologous)
- P: Short arm of chromosome P
- pat: From father
- Ph'': Philadelphia chromosome
- q: Long arm of chromosome
- r: Ring chromosome
- rcp: Reciprocal translocation
- rea: Rearrangement
- rec: Recombinant chromosome
- rob: Robertsonian translocation
- s: Satellite
- sce: Sister chromatid exchange
- t: Translocation
- ta: Tandem translocation
- ter: Terminal
- pter: Terminal short arm
- qter: Terminal long arm
- tri: Trisomic chromosome
Normal Values:
- Male: 46XY
- Female: 46XX
Guidance:
1. Sex Chromosome Number and Morphological Abnormalities
(1) X Chromosome Deletion – Turner Syndrome (45X):
- 45X: 45 chromosomes, with only one X chromosome. Phenotype is female but with underdeveloped gonads, delayed or incomplete secondary sexual characteristics, short stature, low-set ears, high palate, small jaw, low posterior hairline, short neck, webbed neck, shield chest, wide intermammary distance, cubitus valgus, and possible mild intellectual defects. Some may have a karyotype of 45X/46XX mosaicism; X chromosome long arm deletion; X chromosome short arm deletion; X chromosome long and short arm deletion; ring X chromosome; X chromosome long arm isochromosome; and X chromosome translocation with autosomes, which may also show varying degrees of Turner syndrome.
(2) X Chromosome Polysomy (47XXX, 48XXXX, 49XXXXX, and their mosaics with normal chromosomes):
- Phenotype is mostly female, some with underdeveloped gonads, some with no obvious abnormalities, and some with fertility.
(3) Y Chromosome Polysomy and Abnormalities – Klinefelter Syndrome (47XXY):
- Patients are male, mostly tall, with small and firm testes, azoospermia, gynecomastia, feminine body type, sparse body hair, long arms and legs, and possible intellectual delays.
- 47XYY: Less common, patients are male, mostly tall, with behavioral problems, lower IQ, possible psychiatric and criminal behavior. A significant portion shows no clinical abnormalities.
(4) Intersex – True Intersex:
- Patients have both testicular and ovarian tissues. Their physical appearance, secondary sexual characteristics, and external genitalia resemble both males and females. Karyotypes are mostly 46XX, occasionally 46XY or 46XX/46XY/45X/46XY mosaicism.
- Testicular Feminization Syndrome: Patients appear as normal females but have XY chromosomes and testicular tissue. In XY gonadal dysgenesis, their gonads and secondary sexual characteristics are often underdeveloped like Turner syndrome.
2. Autosome Number and Morphological Abnormalities – Down Syndrome (Trisomy 21):
- Typical 21 trisomy has 47 chromosomes, with one extra 21st chromosome, the most common autosomal abnormality. Higher incidence in infants born to older mothers. Patients have significant intellectual disability, distinctive facial features, palm creases, and are prone to infections and leukemia. Most do not survive into adulthood.
- Translocations such as 21/21, 21/22, 21/14, and mosaics with 21 trisomy and normal karyotypes can also cause varying degrees of Down syndrome.
- Edwards Syndrome (Trisomy 18):
- Patients have 47 chromosomes, with one extra 18th chromosome. Incidence in newborns is about 1/4,500. Most die shortly after birth or during delivery. Multiple malformations are present.
- Patau Syndrome (Trisomy 13):
- Patients have 47 chromosomes, with one extra 13th chromosome from the D group. Incidence is about 4/100,000. Multiple malformations are present, mostly in miscarriages, premature infants, or infants who die shortly after birth.
- Other trisomies (e.g., trisomy 8, 9, 22) are rare and usually only observed in spontaneous abortions.
- Autosomal Deletions: Mostly lethal, rarely survive. 21 monosomy, 13 monosomy, and 22 monosomy cases are occasionally reported.
3. Autosomal Structural Abnormalities – Main Types:
- Deletions (partial or terminal), duplications, and various translocations.
(1) 5P- Syndrome (Cat Cry Syndrome):
- Due to a cat-like cry, also known as "cat cry syndrome." Partial deletion of the short arm of chromosome 5. Features include microcephaly, wide-set eyes, downslanting palpebral fissures, low-set ears, transverse palmar creases, and other malformations. About half of patients have congenital heart disease, intellectual disability, poor life expectancy, and often die early.
(2) 4P- Syndrome:
- Similar to 5P- syndrome but often more severe. May also present with hypospadias, cleft palate, severe mental and motor disorders, and seizures. Rare.
(3) 18P- Syndrome:
- Rare survivors.
(4) Chromosome Breakage Syndrome:
- Large numbers of chromosome breaks, often due to Fanconi syndrome and Bloom syndrome.
(5) Fragile X Syndrome:
- High frequency of chromosome breaks under pathological conditions, termed "fragile chromosomes." This is one such condition. Breaks or gaps are common at Xq27-28 in low-folate culture media. More common in males, with intellectual disability, social withdrawal, long face, large ears, large testes, large genitalia, and prominent jaw. Females have milder symptoms, with about 1/3 showing mild intellectual disability.
(6) Philadelphia Chromosome (Ph''):
- Named after its discovery in Philadelphia. A translocation where part of the long arm of chromosome 22 is attached to the long arm of chromosome 9. Seen in chronic myeloid leukemia (CML) and occasionally in other acute leukemias. The only chromosomal abnormality in malignant cells with a consistently recognized stable change.
Lifestyle Care:
- Couples with infertility or a history of habitual abortion should undergo chromosome testing or prenatal amniotic fluid chromosome analysis.
- Exposure to radiation can cause chromosomal damage, so monitoring chromosomes in individuals exposed to or receiving radiation is necessary.
- Certain substances can significantly induce chromosomal abnormalities, termed "mutagens."
- Teratogen testing and chromosome analysis (e.g., sister chromatid exchange) are essential.
- Chromosome analysis is also widely used in viral and tumor diagnosis and research.