Deletion syndrome (monosomy 1p36):
It is known to be one of the most widespread deletion mutations (structural mutation) and it is the most common terminal deletion syndrome observed in humans , occurs in one in every 5000 to 10000 live births , it is considered to be congenital genetic disorder caused by a genetic heterozygous deletion of the outermost band on the short arm (p) of chromosome (Heilstedt et al., 2008; Wiley ‐ Liss, 2007).
Clinical features:
The child with monosomy 1p36 is characterized by :
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- Moderate to sever mental retardation.
- Developmental delay.
- Impairment hearing and vision and absent speech.
- Craniofacial features such as microcephaly and the anterior fontanel is large (delayed closing)
- Seizure
- Delayed growth.
- Facial features such as flat nose, deep set eyes, pointed chain, straight eyebrows, long philtrum and mid-face hypoplasia.
- Hypoplasia.
- Obesity.
- Congenital heart defect (Heilstedt et al., 2008).
Complications of 1p36 deletion syndrome:
Other features of monosomy 1p36 are associated with behavioral problems including seizures, left ventricular non-compaction (LVNC), hypothyroidism, obesity and hyperphagia. The patients may also be suffering with type 2 diabetes mellitus with marked insulin resistance due to hyperinsulinism and decreased glucose metabolism. Other complication is their left-ventricular non-compaction (LVNC) due to congenital heart disease as we mention previously, cardiac abnormalities such as structural cardiac defects and dilated cardiomyopathy are common disease in patients with monosomy 1p36 (Thienpont et al., 2007; Stagi et al., 2014).
Methods for detection of 1p36 deletion syndrome:
First of all, observe the characteristics facial appearance of monosomy 1p36 including straight eyebrows, deeply set eyes, depressed nasal bridge, and also observe craniofacial such as microcephaly and late closing anterior fontanel and other characteristics, then we can use FISH to detect at least two subtelomeric region - specific probes, can also use methods such as quantitative PCR, long-range PCR, multiplex ligation - dependent probe amplification (MLPA) and chromosomal microarray (CMA) that includes this gene/chromosome segment (Battaglia, 2013).
Down syndrome (trisomy 21)
Is a genetic defect caused by a mistake in cell division during premature development of the fetus, it is one of the most common genetic causes of mental retardation, in most cases Down syndrome is not inherited, only about 3-4% of children with Down syndrome inherited it from either their mother or father. It is occur when chromosome 21 make three full or partial copies of itself rather than two copies. There are some risk factors that increase having baby with Down syndrome include:
- Advancing maternal age,
- One of the parents being carrier of the genetic translocation for Down syndrome,
- Having had one child with Down syndrome (American Family Physician , 2000).
Clinical features:
- Defect in development such as language skills impairment and specific impairment in speech.
- Mental retardation, intellectual disability, and learning difficulties.
- Short‐term memory and the verbal memory in childhood and infancy.
- Relative impairment in general movement skills (Fidler, 2005).
Complications of trisomy 21 (Down syndrome):
The children with Down syndrome are at high risk of suffering from multiple complications including, heart congenital defects, about 50% of the children with Down syndrome are born with some defects in their hearts. These heart problems can be fatal and may require prompt surgery in premature childhood. Gastrointestinal Tract (GIT) defects, may include abnormalities of the intestines, esophagus, and anus. the risks are increase as the patients can exposure to problems such as GI blockage, heartburn (GERD) or some digestive disorders. Immune disorders, they are have more tendency to develop autoimmune disease including cancers. Obesity, they are have greater tendency to become obese than normal people (Boseley et al., 2000).
Methods for detection of Down syndrome:
There are some methods that use during gestational months especially for women above 35 years old to detect and diagnose the likelihood of having baby with Down syndrome include blood test , this blood test measures the levels of the maternal serum concentrations known as human chorionic gonadotropin (HCG) and pregnancy-associated plasma protein-A (PAPP-A) were determined by microtiter-plate ELISA. Abnormal levels of HCG and PAPP-A may indicate a problem with the baby. Nuchal translucency test, an ultrasound is used to measure a specific area on the back of the fetus neck to examine if the fluids in this region are within the normal range or not (Tsai et al., 2001).
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