Cri du chat syndrome is a kind of genetic disorder that occurs when a small part of chromosomal material is missing from a particular region on chromosome 5.
 

Overview of Cri du Chat Syndrome

In 1963, Dr. Jerome Lejeune first described Cri du chat syndrome. It is named for the cat-like cry made by the patients with this genetic disorder. In French, Cri du chat means “cry of the cat”. Or we can call this syndrome as “5p minus syndrome”. This is because there is small deletion of genetic material from the short “p” arm of chromosome 5 to cause this unusual genetic disorder.
 

Features of Cri du Chat Syndrome

There are many unusual features for the infants with Cri du chat syndrome.

i. Cat-like cry (the most classic feature)

ii. Unusual facial features

iii. Poor muscle tone (hypotonia)

iv. Small head size (microcephaly)

v. Mental retardation

vi. Low birth weight

vii. Slow growth

viii. Congenital heart defects

ix. Language difficulties

x. Delayed motor skill development

xi. Behavioral problems (childish)
 

Genetic Basis of Cri du Chat Syndrome

The high-pitched mewing cry during infancy is caused by defective development of the larynx (organ in the throat which produced voice). The deleted part of chromosome 5 is essential for normal development. As we all know, human have 46 chromosomes in every single cell of our body. At the same time, we should have two copies of chromosome 5. However, individuals with Cri du chat syndrome have lost a small part of chromosome 5. There is a small piece of material has been deleted from the “p” arm of one of the chromosome 5. On the other hand, the deleted chromosomal material consists of many important genes for normal development. Because of losing these essential genes, the larynx, brain and other parts of body cannot function normally. Generally, the deletion is sporadic (occurs irregularly).
 

Diagnosis of Cri du Chat Syndrome

Yet, the cat-like cry from children with Cri du chat syndrome will becomes less noticeable when they get older. Therefore, we can just identify and diagnose this syndrome if a child with younger age has this unusual mewing cry. Chromosome analysis or karyotyping can provide the definitive diagnosis of Cri du chat syndrome by staining the chromosome and examining them under a microscope. FISH (fluorescence in-situ hybridisation) is useful and effective to detect a small deletion in chromosome like Cri du chat syndrome.
 
Unfortunately, there is still no cure for this syndrome. Nevertheless, the medical experts can still provide the supportive care and development therapy to the patients to make the things better. Once the unusual features are under controlled, most of them can live normally.
 
In conclusion, although there is still no cure for Cri du chat syndrome, we can still lessen the symptoms by receiving the suitable therapy.
 
I have to apologise as I seldom to update this Cytogenetics and Cancer Research blog recently. I’m busying doing my final year project in University of Malaya. However, I will try my best to keep on updating the blog. Thanks!

Cri du Chat Syndrome – Human with Cat-like Cry is a post from: Cytogenetics and Cancer Research

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Angelman syndrome (AS) was first described by Dr. Harry Angelman, who is an English physician. He noticed that there are 3 children under his care with similar developmental problems. They looked very happy and tend to flap their hands when excited. Therefore, Dr. Harry Angelman described these children in his paper called “Puppet Children” as these children’s characteristics just like the puppet.
 
Angelman Syndrome is now a familiar genetic disorder to most clinical geneticists and child neurologists in Cytogenetics. It is a recognizable syndrome which related to mental retardation and infantile seizures. Unlike Prader-Willi syndrome that I described last week, individual with Angelman syndrome is because the loss of maternally inherited region 15q11 – q13 of chromosome 15. Simple to say, the AS individual does not inherit the region 15q11 – q13 of chromosome 15 from his/her mother but only from father.

 
The Angelman syndrome clinical diagnosis is heavily dependent on the combination of some common behaviour like excessive laughter, apparent happiness with tremulous movements and gait ataxia (lack of coordination of muscle movement). Usually, the normal prenatal and birth history do not provides any clues in diagnosis of AS in Cytogenetics. CT scans, laboratory tests of blood and urine are usually normal including metabolic screening. Consequently, it is difficult for the clinical experts to encounter the AS especially when the child is less than 12 months of age. It is because the tremulous movements, ataxia and severe lack of speech may not be apparent during that time.
 
There are many common features of Angelman syndrome.

i. Severe speech deficit (usually absent speech)
 
ii. Mental retardation
 
iii. Microcephaly (small head)
 
iv. Seizures (convulsions in which AS patient’s body shakes rapidly and uncontrollably)
 
v. Developmental delay
 
vi. Feeding problems
 
vii. Hypopigmentation (the loss of skin color)
 
viii. Frequently drooling
 
ix. Tend to put objects in mouth
 
The facial features general physical appearances are generally normal for the individual of Angelman syndrome. As the child with AS growing up, the correct diagnosis may become evident when speech is essentially absent and the attempts at walking are compromised because of sever ataxia. In addition, the seizures will occur more frequently after 1 year of age.
 
In conclusion, the individual of Angelman syndrome may be hyperexcitable with excessive laughing, grabbing and pulling to engage others. They are just like the ‘Angels’ who always bring happiness to people. Usually, the parents may be the first to suggest the possibility of Angelman syndrome. Thus, earlier detection of this genetic disorder may help the children to overcome the learning problem through the assessment from the clinical experts.
 

My ultimate hope is this Cytogenetics and Cancer Research blog can really help in increasing the awareness of people about the genetic disorders and cancer.

Angelman Syndrome – Angel-like Genetic Disorder is a post from: Cytogenetics and Cancer Research

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Cytogenetic abnormalities are what I have learnt during my internship in Hospital Kuala Lumpur. Today, I’m going to introduce Autosomal Aneuploidy in this Cytogenetics and Cancer Research blog.
 
In Cytogenetics, the term aneuploidy refers to cytogenetic abnormalities in which all or part of one or more chromosomes is added or deleted. Autosomal aneuploidy is the abnormality that does not involve the sex chromosomes. Sometimes, the abnormalities can be either numerical or structural. Normally we only have pair of chromosomes which are structurally similar. Other than that, it can be recognized as abnormal. Those cytogenetic abnormalities can be present only in some cells which we called mosaicism or in all cells.

Meiotic Nondisjunction Causes Autosomal Aneuploidy

The origin of autosomal aneuploidy is because of meiotic nondisjunction. The meiotic nondisjunction is random for all autosomes except for chromosome 21. Chromosome 21 has shown the highest frequency of autosomal aneuploidy.
 
According to cytogenetic studies, the incidence of autosomal aneuploidy in spontaneous abortuses (die before birth) is much higher than incidences in newborns. So, what is the case for aneuploidy actually observed in spontaneous abortuses or liveborns? All trisomies for all autosomes have been reported in spontaneous abortuses. The fetal only can survive if and only if the trisomies are in mosaic form. However, there are still many exceptions for the trisomies 13, 18 and 21. Some of the foetus still can survive even though the trisomies 13, 18 or 21 are in nonmosaic form.
 
Why the frequencies of trisomy for each chromosome might be similar at the time of conception but differ greatly among abortuses and liveborns especially for trisomy 21? It can be explained by the devastating effect of chromosomal imbalance. Most of the autosomal aneuploidies are very deleterious and lethal in the pre-embryonic stage. As a result, those abnormalities are unrecognized and, therefore, unstudied spontaneous abortions.
 
Furthermore, the lethality of a particular autosomal aneuploidy is related to the gene content of the particular chromosome. Aneuploidies for the gene rich chromosomes are less likely to survive. However, the less gene rich chromosomes like chromosome 13, 18 and 21 are more likely to survive to term.
 
Anyway, we will just focus on those observed in liveborns for the autosomal aneuploidy in Cytogenetics. I will talk more details about the monosomies and trisomies in my future post. Stay tuned!

Autosomal Aneuploidy – Cytogenetic Abnormalities is a post from: Cytogenetics and Cancer Research

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Down Syndrome is a popular topic in my Cytogenetics and Cancer Research blog now. I decide to write another post about the Down Syndrome to grab the attention from my readers. As I mentioned in my last post, Down Syndrome is caused by the non-disjunction of the chromosome during the meiosis. However, little is known about the causes for non-disjunction to occur as well as Down Syndrome in term of Cytogenetics. There are many hypotheses have been put forward to explain about the non-disjunction.
 

1. Enhanced Selective Miscarriage of Trisomy 21 Conceptions by Older Mothers

Analysis of the data shows that Trisomy 21 occurs in about 1 per 200 2000 of the births to mothers aged 18-24. The rate gradually increases in frequency to 1 per 300 births to mothers between 25 and 35. The rate continues to increase to 1 per 100 births to mothers at age 45 or older. Therefore, people start to come out with the hypothesis that is enhanced selective miscarriage of 21 trisomic conceptions by older mothers. This hypothesis claims that the increase of mother’s age is directly proportional to the enhanced selective miscarriage of trisomy 21. The non-disjunction seems to occur more frequently for older mother. During the meiosis, the older female’s gamete cell will miscarry two chromosome 21. Fertilization between this abnormal ovum with the sperm will cause the Down Syndrome.
 

 

2. Less Effectiveness for Oocyte Selection in Older Mothers

Another hypothesis is the decrease of effectiveness for oocyte selection in older mother. Oocyte selection is the process that determines which oocyte can enter the next stage of development. Only the normal oocyte will be selected and the abnormal oocyte will be eliminated. If the effectiveness of oocyte selection decrease because of the older age, the abnormal oocyte might be selected. This will cause the non-disjunction occur during the meiosis.
 

3. Sperm Aging Hypothesis

Some scientists raised up the sperm aging hypothesis claiming that the non-disjunction occurs because of the influence of sperm aging in male genital tract.
 

4. Chiasma Hormonal Hypothesis

Some scientists prove that there is an interaction between the hormonally governed rate of meiosis and the timing of chiasma terminalisation. The changing hormone levels during the menstrual cycle not only stimulate recommencement of meiosis in ovum, but also control the rate of meiosis through a limiting substance. The hormone levels and the length of the cycle will change with advancing age of the mother. Therefore the meiosis will slow down and chiasma frequencies decline. As we know, chiasmata is important for the meiotic chromosome bivalents to held together during meiosis. It will cause the premature separation during terminalisation. This can lead to Down Syndrome.
 

5. Consanguineous Parents Hypothesis

Some people said that the Down Syndrome is related to the consanguineous parents. Consanguineous parents are the parents who are blood-related.
 

In conclusion, there are many other hypotheses to explain about the causes of Down Syndrome. However, none of which was so far fully convincing. But what we need to aware of is the advancing age of woman. I will recommend you to have your child before 30 years old for woman to avoid from the risk of having Down Syndrome baby.
 

Do you have any knowledge about the cause of Down Syndrome? Share with us.

5 Hypotheses Causing Down Syndrome is a post from: Cytogenetics and Cancer Research

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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.

Have you seen any Down syndrome patient? Be patient with them.

Down Syndrome | Birth Defect with Trisomy 21 is a post from: Cytogenetics and Cancer Research

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