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What is Tetrasomy 18p and explain in detail?
Tetrasomy 18p is a genetic condition that is caused by the presence of an isochromosome composed of two copies of the short arm of chromosome 18 in addition to the two normal copies of the chromosome. It is characterized by multiple medical and developmental concerns.

Signs and symptoms
Tetrasomy 18p causes a wide range of medical and developmental problems.

Congenital anomalies
Cardiac anomalies are the most common congenital malformation in individuals with tetrasomy 18p.  However, there is no pathognomatic heart defect associated with the condition.  Patent ductus arteriosus is the most common defect.  Septal defects (ventricular septal defects and atrial septal defects) are also common, as are patent foramina ovalia.  Other cardiac anomalies include mitral valve regurgitation,  mitral valve prolapse, bicuspid pulmonary valve, hypoplastic transverse aortic arch, tricuspid valve regurgitation, right ventricular hypertrophy, and pulmonic stenosis.
In males, cryptorchidism is common.  Abnormal genitalia in females is not a common feature.  Renal abnormalities have been reported in a minority of patients.  Horseshoe kidney and bladder diverticuli have been reported.  Other abdominal malformations, including pyloric stenosis and hernias, have also been reported, though they are present in only a minority of patients.Orthopedic anomalies also occur relatively frequently, with hip dysplasia being the most common orthopedic issue.  Clubfoot and rocker bottom feet have also been reported.Myelomeningocele is another known feature associated with tetrasomy 18p.

Neonatal complications
Neonatal complications (apart from congenital anomalies) are common.  In a paper published in 2010, 41 of 42 individuals had some type medical problem in the first days of life, the most common being feeding difficulties.  Respiratory difficulty and jaundice are also relatively frequent.

ENT
Recurrent otitis media is common, and many patients required the placement of PE tubes.  Small ear canals are also fairly common, but not as much as in 18q-.

Gastrointestinal
The most common gastrointestinal abnormality is chronic constipation, though gastrointestinal reflux was also common.

Endocrine
Growth hormone deficiency is present in about 20% of people with tetrasomy 18p.

Neurologic
Hypotonia and/or hypertonia are present in nearly all individuals with tetrasomy 18p.  Approximately 25% have a seizure disorder.

Growth
Short stature is common, with ~50% being at or below the 25th centile and 20% being at or below the 3rd centile