Genetics Flashcards
Genetics of Beckwith Wiedemann syndrome
Genomic imprinting: 11p15.5, IGF2 gene, two copies from dad leading to over expression of IGF2
Genetics of Simpson-Golabi-Behmel (SGB)
Xq26.2
Loss of function variants in GPC3 (growth modulator proteoglycan) 
Symptoms of Sotos syndrome
Triad
- overgrowth (length >99% due to long limbs, macrocephaly, advanced bone age)
- characteristic facial features (frontal bossing, dolichocephaly, fronto-parietal balding, early erruption of teeth, high arched palate
- learning/intellectual disabilities, seizures
Can be confused with Marfan’s and fragile X
Genetics of Donahue syndrome
Mutation of insulin receptor gene on 16p13.2
Symptoms of Beckwith Wiedemann
Macrosomia Visceromegaly Neonatal hypoglycemia Omphalocele Ear creases and pits Hemihypertrophy
Symptoms of Simpson-Golabi-Behmel (SGB)
Increased wt/lt/ht Hypertelorism Broad upturned nose Macroglossia Supernumerary nipples Pectus excavatum Hypotonia Cleft lip or palate Can be confused with BWS
Genetics of Sotos syndrome
Autosomal dominant disorder
Mutations in the NSD1 gene on 5q35
Almost all de novo mutations
Symptoms of Donohue syndrome
Fasting hypoglycemia and hyperinsulinism with postprandial hyperglycemia
IUGR Reduced subcutaneous fat Distended abdomen Enlarged external genitalia and nipples (Large and lowset ears, prominent eyes, broad nasal tip, flared nares, thick lips and gingival hyperplasia)
Primary skeletal dysplasia
Mutated genes expressed in chondro-osseous tissue
Secondary skeletal dysplasia
Abnormalities of extraosseous factors with secondary effects on the skeletal system
Skeletal dysostoses
Malformations of bones as a result of an insult during organogenesis
COL1A
Osteogenesis imperfecta type 1-4
FGFR3
Thanatophoric dysplasia and achondroplasia
COL2A
Stickler syndrome
EVC1/2
Ellis-van Creveld syndrome
IFT80
Jeune syndrome
Disorders associated with advanced paternal age
Achondroplasia Apert syndrome Crouzon syndrome Neurofibromatosis I Osteogenesis imperfecta Pfeiffer syndrome Retinoblastoma Thanatophoric dysplasia
Deformation
Altered mechanical forces (extrinsic or intrinsic) on normal tissue
Ex: fetal akinesia sequence, Positional congenital hip subluxation
Malformation
Caused by abnormal tissue formation
Disruption
Breakdown of normal tissue caused by disruption of a normal developmental process
Ex: amniotic band sequence, Teratogen exposure
Dysplasia
Abnormal organization of cellular formation into tissue as a result of dysregulation
Syndrome
Pattern of many primary malformations as a result of one etiology
Legius syndrome
Café au lait spots
Axillary/inguinal freckling
Macrocephaly
Learning disabilities
Can be confused with NF1
AD, mutation in SPRED1 gene
Genetic defect in cartilage hair hypoplasia
Chromosome 9p13
RMRP
Symptoms of cartilage hair hypoplasia
Short-limbed dwarfism
Hypotrichosis
Hirschsprung’s
Severe combined immunodeficiency
Disorders with cataracts
Galactosemia Congenital hypoparathyroidism Fabry disease Lowe Syndrome (oculocerebrorenal) Congenital rubella
Genetic defect in galactosemia
GALT
Deficiency of galactose-1-phosphate uridyltransferase
Defect in Fabry disease
Mutation in GLA
X-linked deficiency a-galactosidase A
IEM that are not autosomal recessive
OTC deficiency
X-linked ALD
Hunters
Examples of amino and organic acid acidopathies
PKU Tyrosinemia MSUD Nonketotic hyperglycemia Propionic acidemia Methylmalonic acidemia
Phenylalanine hydroxylase
Defective enzyme in PKU
Urine organic acids with elevated succinylacetone
Tyrosinemia I
Fumarylacetoacetate hydrolase
Deficient enzyme in tyrosinemia type I
Symptoms of Tyrosinemia Type I
Hepatic failure, Fanconi syndrome
Branched chain ketoacid dehydrogenase
Enzyme defect in maple syrup urine disease
Symptoms of MSUD
Poor feeding, lethargy, coma, apnea
Cerebral edema = dreaded complication
Which amino acids are elevated in MSUD?
Leucine
Isoleucine
Valine
Glycine cleavage system
Defect = nonketotic hyperglycemia
Elevated CSF/plasma glycine ratio
Diagnostic for nonketotic hyperglycemia
Symptoms of nonketotic hyperglycemia
Seizures, myoclonus, hiccups
Propionyl CoA carboxylase
Defective enzyme in propionic acidemia
Symptoms of propionic acidemia
Lethargy, coma Anion gap metabolic acidosis Hyperammonemia Neutropenia, thrombocytopenia Hyperglycemia
Diagnosis of propionic acidemia
Elevated C3
Elevated glycine
Methylcitrate in urine
Treatment of propionic acidemia
Diet with decreased VOMITC
Carnitine
Treatment of nonketotic hyperglycemia
Hemodialysis
Benzoate (removes glycine)
Methylmalonyl CoA mutase
Enzyme deficient in methylmalonic acidemia
Symptoms of methylmalonic acidemia
Lethargy, coma Anion gap metabolic acidosis, hyperammonemia Neutropenia Thrombocytopenia Hyperglycemia
Diagnosis of methylmalonic acidemia
Elevated C3
Elevated urine methylmalonic acid
Elevated plasma glycine
Normal homocystine
B12 deficiency can cause elevated methylmalonic acid (maternal deficiency = baby positive for MMA on NBS)
Examples of urea cycle disorders
Ornithine transcarbamylase deficiency
Citrullinemia
Argininemia
Encephalopathy and hyperammonemia
Urea cycle defects
Increased orotic acid and decreased citrulline
OTC deficiency
Symptoms of OTC deficiency
After 48 hours
Poor feeding, grunting, lethargy, coma
Affected first born males usually die or are severely impaired
Treatment of OTC deficiency
Stabilize until liver transplant
Low protein diet
Ammonia scavenging drugs - phenylbutyrate, glycerol phenylbutyrate
Arginine
Argininosuccinate synthase 1
Enzyme defect in citrullinemia
Increased citrulline and decreased arginine
Citrullinemia
Symptoms of citrullinemia
Hyperammonemic crisis
Can have orotic acid elevations
Arginase
Enzyme defect in arginase deficiency (Argininemia)
Decreased urea and decreased ornithine
Arginase deficiency
Symptoms of arginase deficiency
Sometimes only spastic diplegia and delayed milestones
Can see hyperammonemia
Arginine levels high
Hyperammonemia with acidosis andelevated ketones
Organic acidemia
Hyperammonemia with acidosis andlow ketones
Fatty acid oxidation defect
Hyperammonemia with no acidosis
Urea cycle defects: Citrullinemia Argininemia Argininosuccinic aciduria OTC deficiency (elevated orotic acid) CPS deficiency (low orotic acid, trace citrulline)
Galactosemia associated with
E. coli sepsis/UTI, jaundice, urine reducing substances