It is quite a long time I do not write about the genetic disorder in term of Cytogenetics. This time I would like to introduce the Down Syndrome, the most common genetic disorder in cytogenetic level.
Down syndrome is a common genetic chromosomal syndrome among the population in the world. It is about 1 in 800 liveborns in the population with Down syndrome. This syndrome starts to be described by a physician named John Langdon Down who published an article in 1866. He stated that there are some children with common characteristics but distinct from other children with mental retardation. He described this syndrome as “Mongoloids”. He used this unfortunate name just because of those children looked like people from Mongolia. The “Mongoloids” was dropped from scientific use since 1960s to stop the ethic insult.
In cytogenetics, about 95% of all patients with Down syndrome have a 47, +21 karyotype. Among these cases there is a small group with familial translocation involving a chromosome 21 and another chromosome with balanced rearrangement. There are some very rare instances of direct transmission of the additional 21 from a Down syndrome mother or father to a Down syndrome child. This is a kind of birth defect syndrome just like Trisomy X and Mosaicism. There are many hypotheses explain how the Down Syndrome occur.
Down syndrome patient looks almost alike to each other. We can simply identify the Down syndrome patient by just looking to their physical outlook. However, a confident clinical diagnosis might be difficult early after birth, especially in prematures. Some of the useful diagnostic signs are brachycephaly (flat-head), small ears, Brushfield spots (brown spots on the periphery of the iris) and low iliac and acetabular index in pelvic radiographs. Congenital malformations are frequent in Down syndrome patients too. Thyroid dysfunction is also significantly associated with Down syndrome and might be the cause for developmental delay. Mentally retardation is the most common feature among the Down syndrome patients.
Generally, female menarche occurs at normal time and pregnancies are common among the Down syndrome patients. However, there is hypogenitalism and hypogonadism among the male patients. Therefore, the male with Down syndrome usually is infertile.
In conclusion, Down syndrome patients need to be taken care as there are various specific problems throughout their life. I will write more about the guideline for optimal medical care on these Down syndrome patients later.