Thalassemia: Causes, Symptoms, Diagnosis, and Treatment
Karyotyping For Chromosomal Abnormalities
In order to maximize the diagnostic information obtained from a chromosome preparation, images of the individual chromosomes are arranged into a standardized format known as a karyotype, or more precisely, a karyogram (Figure 1a-c). According to international conventions, human autosomes, or non-sex chromosomes, are numbered from 1 to 22, in descending order by size, with the exceptions of chromosomes 21 and 22, the former actually being the smallest autosome. The sex chromosomes are generally placed at the end of a karyogram.
Within a karyogram, chromosomes are aligned along a horizontal axis shared by their centromeres. Individual chromosomes are always depicted with their short p arms—p for "petite," the French word for "small"—at the top, and their long q arms—q for "queue"—at the bottom. Centromere placement can also be used to identify the gross morphology, or shape, of chromosomes. For example, metacentric chromosomes, such as chromosomes 1, 3, and 16, have p and q arms of nearly equal lengths. Submetacentric chromosomes, such as chromosomes 2, 6, and 10, have centromeres slightly displaced from the center. Acrocentric chromosomes, such as chromosomes 14, 15, and 21, have centromeres located near their ends.
Arranging chromosomes into a karyogram can simplify the identification of any abnormalities. Note that the banding patterns between the two chromosome copies, or homologues, of any autosome are nearly identical. Some subtle differences between the homologues of a given chromosome can be attributed to natural structural variability among individuals. Occasionally, technical artifacts associated with the processing of chromosomes will also generate apparent differences between the two homologues, but these artifacts can be identified by analyzing 15–20 metaphase spreads from one individual. It is highly unlikely that the same technical artifact would occur repeatedly in a given specimen.
Using FISH To Detect Chromosomal Abnormalities In Interphase Nuclei.
Using FISH to detect chromosomal abnormalities in interphase nuclei.
(a) The duplication of a small portion of chromosome 17 that causes Charcot-Marie-Tooth syndrome is evident from the appearance of three, rather than two, red signals in this nucleus. The green spots mark a sequence outside the duplication. (b) The translocation that creates a fusion of the BCR (on chromosome 22) and ABL (on chromosome 9) genes in the Philadelphia chromosome is evident from the close juxtaposition of one pair of green and red signals. These signals were generated using FISH probes for sequences located near these two genes, respectively. Der(22) is the Philadelphia chromosome. Only the relevant portions of the normal and abnormal chromosomes are shown in the diagram below each panel.
Cytogeneticists can now go "FISH-ing" for chromosomal abnormalities, which are deletions and duplications that can cause disease. How exactly does FISH work?
Developmental Disorders And Delays
About 1 in 54 children will receive a diagnosis of autism. With treatment and support, many grow to lead full, meaningful lives, but early detection and diagnosis is considered essential so that parents can start to provide the attention and services children need. The developmental disorder affects information processing and can significantly affect social and communication skills. But the symptoms and their intensity vary widely from person to person, which is why the condition is generally referred to as Autism Spectrum Disorder.
Symptoms are usually detectable by age two, and are found in males four times more often than in females. While the number of children diagnosed with autism has risen sharply in recent years, there is some debate over whether the incidence is increasing, diagnosis is improving, or if the broader definition of the autism spectrum now simply covers a wider range of individuals
There is no cure for autism, and some in the community of autistic families believe it does not need one, but is instead an example of human neurodiversity. Still, for many on the lower-functioning end of the autism spectrum, therapies can be crucial for alleviating symptoms and stress.
For more, see Autism.
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