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Genetic Eval of MR

Developmental Delay used for children under 5, descriptive term, used until valud IQ can be measured
Mental Retardation Significant sub-average intellectual behavior and deficits in adaptive behavior
Etiology a specific diagnosis that can be translated into useful clinical information for the family, including providing information about prognosis, recurrence risks, and preferred moes of therapy
Diagnostic yield The percentage of time an etiology can be determined utilizing a specific evaluation test or scheme
Expanded phenotype The full range of phenotypes seen with changes in a specific locus (gene), often initially a gene chance associated with a specific sydnrome
Rett Syndrome 1/10,000-1/15,00; Clinical phenotype of progressive autistiform disorder, exclusively in girls (X-Linked dominant with male lethality), severely imparised expressive language, loss of puprose hand skills, repitive hand movements, truncal ataxia, seizures,
Rett Syndrome gene Gene= MECP2, Xp28
Phenotype of MECP-2 mutations male Encephalopathy (static or progressive) may have peculiar silver-grey hair, Angelman, MR
Epidemiology... Incidence Mental Retardation, males 4 times as common as females; neurodevelopmental disabilities
Reported emperic recurrence risks for MR One child affected, negative family history ~5%
If the affected child with MR is male, ... Brother 5-15%, sister 3-5%, all 2-10%
If the affect child with MR is female... Brother 4-10%, Sister 5-8%, and all have a 3-5%
Inheritance of MR is.. polygenic/oligogenic
Polygenic inheritance IQ dispalys all of the traits of polygenic inheritance... distributed in a normative manner; close relationship to parental IQs, quantitative trait, no sexual dimorphism
By definition, what % of the general population has an IQ in the MR Range? 2.5% (SD)
FISH commonly used to determine if portion of chromosome is deleted.
MR Syndromes with Available FISH testing Williams, Angelman, PW, Smith-Magenis, DiGeorge/VCFS, Miller-Dieker
Subtelomeric FISH Panel 40 individual FISH tests specific for subtelomeric regions (does not have 46 probes for acrocentric chromosomes)
Subtelomeric rearragements familial implications Dependent on parental studies, 90% de novo, 10% positive in one parent
Genome microarray Human Whole Genome Array, Large insert clones (BACs), Clones are arrayed in duplicate
CGH Panels can be customized and are constantly evolving, has likely a 15-20% positive rate for MR
Gene Sequencing FISH tests are very helpful in identifying duplication or deletions of specific loci, won't detect small changes, point mutations etc., often the only method to make a diagnosis is to sequence the gene; but that is very expensive and time consuming
Automated mutation screening WAVE show few to no false negatives...
Epidiomiology of MR Male: Female ratio of 4:1, one explanation is X-linked
Sample MRX gene panel ARX, DLG3, FACL4, FTSK1, JARID1c, PQBP1, TM4SF2,ZNF41
Tiered/Step-wise evaluations are based upon... 1. Expected diagnostic yield, 2. Invasiveness of testing 3. Potential of intervention 4. Overall practicality of obtaining tests
Step 1 in Evaluation Clinical Hx (prenatal, perinatal, postnatal including development, growth and behavior)
Step 2 in Eval Family Hx (parental IQs, developmental abnormalities, psychiatric problems, birth defects, pregnancy loss, and other genetic problems)
Step 3 in Eval Physical Examination (growth parameters, including head; major and minor anomalies and malformations, neurologic examination)
Importance of the dysmorphology eval Establishes the diagnosis (62%), contributes to the diagnosis (79%)
What can be a significant aid in reaching a diagnosis? A characteristic personality and behavioral pattern/behavioral phenotype
Behavioral phenotypes Cognitive levels, static versus progressive, autistiform, disordered sleep, speech and language characteristics, self injurious/aggressive behaviors, associated neurosensory conditions
How many of all diagnoses can be made by history and physical examination alone? 1/3rd to 1/2
After the physical eval, what comes next? Referral for ophthalmologic, audiologic, and/or psychometric testing
Neuropsychologic testing Provides information beyond the simple "IQ" testing; gives information about processes, not just outcomes; non-verbal testing component; can't be performed until mid-childhood, positive predictive value for long term neurodevelopmental potential
What comes after referrals in the eval? Diagnostic testing
Karyotypes... (high resolution) Should be done in ALL developmentally delayed individuals without a recognized cause,
Reported diagnostic yield of karyotypes 9-36%
Pigmentary changes -Embryological association of skin and CNS (neuroectoderm), individuals with neurologic disorders and pigmentary abnormalities should have a fibroblast karyotype if the lymphocytic karyotype is normal; biopsy can be from any site +unselected patch of skin
Subtelomere/CGH studies 1. All patients with MR, 10-15% yield as a single test
Molecular testing Non-syndrome MR (Fragile X, MECP-2), XLMR panel is FH indicates, selected tests based on H&P
Fragile X Syndrome: Diagnostic testing -Recommended for all patients with MR, Diagnostic yield of 2%, reported range of 0-20%, regional uneven distribution (?)
Cranial Imaging 30-96% of those with MR have CNS structural abnormalities detectable by imaging
Cranial Imaging leads to an etiology in what % of patients? 4
Abnormal head size and neurological findings increased the likelihood of... detecting abnormalities
Dr. Schaefer says to do cranial imaging on... all patients without a diagnosis
Metabolic testing Yield only 1% or less; only if clinical indicators; targeted testing, not screening; check newborn screening!
Identifiable causes of MR Chromosome abnormalities 25-30%; UNKNOWN 30-50%
Diagnoses increase by how much with return visits for repeat history and physical examination? 5 to 20%
What happens when the brain malfunctions? 1. Cognition (MR), 2. CP (Motor dysfunction) 3. Movement DOs (HD, Ataxias) 4. Paraximsomal events (seizures- episodic discharge), 5. Autism- behavioral problems
Created by: KChatham
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