PGD: Pre-implantation Genetic Diagnosis
Embryo biopsy is the more practical method for pre-implantation genetic diagnosis. The biopsy can be performed at one of the following stages:
Cleavage-stage Embryos This is usually performed on day 3 embryos (i.e. 3 days after oocyte retrieval) which have normally reached the 6 to 10 cell stage. Under the inverted microscope used for micromanipulation the embryo is held by gentle suction from one side using the holding pipette. On the opposite side of the embryo, a hole is made in the zona pellucida either mechanically using a fine-glass knife or by applying acid Tyrode’s solution locally using a fine pipette. A fine-bore glass pipette can then be pushed through the hole and one or two blastomeres aspirated.
Blastocyst Stage Embryos Here the biopsy is taken on day 5 or 6 (i.e. 5 or 6 days after oocyte retrieval). At this stage, the embryo has reached the blastocyst stage. The advantages of this technique is that more cells may be used for biopsy. In this technique, 3 to 5 cells are usually aspirated after drilling a hole in the zona pellucida using acid Tyrode’s solution. These cells are taken from the trophectoderm at the anembryonic pole away from the inner cell mass which will develop into the fetus.
Embryo biopsy is the more practical method for pre-implantation genetic diagnosis. The biopsy can be performed at one of the following stages:
Cleavage-stage Embryos This is usually performed on day 3 embryos (i.e. 3 days after oocyte retrieval) which have normally reached the 6 to 10 cell stage. Under the inverted microscope used for micromanipulation the embryo is held by gentle suction from one side using the holding pipette. On the opposite side of the embryo, a hole is made in the zona pellucida either mechanically using a fine-glass knife or by applying acid Tyrode’s solution locally using a fine pipette. A fine-bore glass pipette can then be pushed through the hole and one or two blastomeres aspirated.
Blastocyst Stage Embryos Here the biopsy is taken on day 5 or 6 (i.e. 5 or 6 days after oocyte retrieval). At this stage, the embryo has reached the blastocyst stage. The advantages of this technique is that more cells may be used for biopsy. In this technique, 3 to 5 cells are usually aspirated after drilling a hole in the zona pellucida using acid Tyrode’s solution. These cells are taken from the trophectoderm at the anembryonic pole away from the inner cell mass which will develop into the fetus.
DiGeorge Syndrome – 22q11.2 deletion syndrome
DiGeorge syndrome caused by deletion – missing part of chromosome 22 ; known more accurately by broader term – 22q11.2 deletion syndrome. Medical sequel of the syndrome include heart defects, cleft palate, poor immune system function, low level of calcium in blood with its consequences, delayed development with emotional and behavioral problems.
Number and severity of symptoms vary. Signs and symptoms of DiGeorge syndrome (22q11.2 deletion syndrome) can vary in type and severity, depending on what body systems are affected and how severe the defects are
Each person has two copies of chromosome 22, one inherited from each parent. If a person has DiGeorge syndrome (22q11.2 deletion syndrome), one copy of chromosome 22 is missing a segment that includes an estimated 30 to 40 genes. Many of these genes haven't been clearly identified and aren't well-understood. The region of chromosome 22 that's deleted is known as 22q11.2.
Patients with 22q11.2 DS usually have characteristic facial features. Common ones include the following (see the images below):
DiGeorge syndrome caused by deletion – missing part of chromosome 22 ; known more accurately by broader term – 22q11.2 deletion syndrome. Medical sequel of the syndrome include heart defects, cleft palate, poor immune system function, low level of calcium in blood with its consequences, delayed development with emotional and behavioral problems.
Number and severity of symptoms vary. Signs and symptoms of DiGeorge syndrome (22q11.2 deletion syndrome) can vary in type and severity, depending on what body systems are affected and how severe the defects are
Each person has two copies of chromosome 22, one inherited from each parent. If a person has DiGeorge syndrome (22q11.2 deletion syndrome), one copy of chromosome 22 is missing a segment that includes an estimated 30 to 40 genes. Many of these genes haven't been clearly identified and aren't well-understood. The region of chromosome 22 that's deleted is known as 22q11.2.
Patients with 22q11.2 DS usually have characteristic facial features. Common ones include the following (see the images below):
- Retrognathia or micrognathia
- Long face
- High and broad nasal bridge
- Narrow palpebral fissures
- Small teeth
- Asymmetrical crying face
- Downturned mouth
- Short philtrum
- Low-set, malformed ears
- Hypertelorism
- Dimple on the tip of the nose