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✅ Summary: What is Genomic Imprinting?
(Based on the case of a 17-month-old male with Silver-Russell Syndrome)
🧬 Definition of Genomic Imprinting
Genomic imprinting is an epigenetic process that results in genes being expressed in a parent-of-origin-specific manner.
Key characteristics:
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Only one allele of the gene (either maternal or paternal) is expressed, while the other is silenced.
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Silencing is controlled through DNA methylation and histone modification.
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This imprinting occurs during gamete formation and is maintained throughout embryonic development.
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It does not alter the DNA sequence, so it’s not Mendelian inheritance.
🔍 Why It Matters in Medicine
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Imprinted genes regulate growth, metabolism, and development.
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Disruption in imprinting can lead to serious genetic syndromes, often involving:
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Growth abnormalities
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Metabolic dysfunction
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Developmental delays
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👶 Silver-Russell Syndrome (SRS) and Imprinting
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SRS is a rare condition marked by:
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Small for gestational age
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Postnatal growth failure
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Feeding difficulties
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Facial features: triangular face, protruding forehead, downturned mouth, ear anomalies
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Body asymmetry
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Genetic causes of SRS often involve abnormal imprinting on:
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Chromosome 11p15 (maternal transmission)
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Chromosome 7 (maternal uniparental disomy)
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📚 Examples of Human Imprinting Disorders
| Disorder | Affected Chromosome | Key Features |
|---|---|---|
| Angelman syndrome | Chr 15q11-q13 | Severe developmental delay, happy demeanor |
| Prader-Willi syndrome | Chr 15q11-q13 | Hypotonia, hyperphagia, obesity, intellectual delay |
| Beckwith-Wiedemann syndrome | Chr 11p15 | Overgrowth, macroglossia, abdominal wall defects |
| Silver-Russell syndrome | Chr 7 or 11p15 | Growth restriction, feeding problems |
| Temple syndrome | Chr 14q32 | Short stature, precocious puberty |
| Others | Various | See full list above |
💡 Clinical Pearl
Even though many imprinting disorders are sporadic, their diagnosis can significantly affect clinical management and genetic counseling. Understanding imprinting helps guide care, prognosis, and discussions around recurrence risk.
Would you like a visual diagram showing how imprinting works in SRS vs other syndromes (like Prader-Willi or Angelman)?
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