7 - Developmental Delays in infancy and Early Childhood Flashcards
(183 cards)
1
Q
What is developmental delay?
A
A condition where a child’s overall development progresses more slowly than normal, affecting areas such as motor skills, learning, language, or behavior.
2
Q
What are inborn errors of metabolism (IEMs)?
A
Disorders caused by a single gene defect resulting in the accumulation of enzyme substrate due to a metabolic obstruction or deficiency of a reaction product.
3
Q
What percentage of children with unexplained intellectual disability (ID) do inborn errors of metabolism account for?
A
<5%
4
Q
List the types of IEMs based on their classification.
A
- Defects in the metabolism of energy sources (carbohydrates, protein, lipids)
- Dysfunction in pathways within cellular organelles (lysosome, peroxisome, mitochondria)
5
Q
What is intellectual disability (ID)?
A
A neurodevelopmental disorder characterized by significant limitations in both intellectual functioning and adaptive behavior.
6
Q
What is the APGAR score?
A
A score to assess an infant’s well-being immediately after birth based on Appearance, Pulse, Grimace, Activity, and Respiration.
7
Q
What is hypotonia?
A
Diminished resistance to passive movement of muscles, often resulting in soft floppy muscles.
8
Q
What are primitive reflexes?
A
Muscular reactions to stimuli observed in the first few months of life; persistence may signal developmental delay.
9
Q
What are the common laboratory tests for diagnosing IEMs?
A
- Complete blood count
- Blood gases
- Electrolytes
- Calcium and magnesium
- Glucose
- Lactate
- Ammonia
- Liver enzymes
- Prothrombin time
- Acylcarnitine profile
- Levels of copper, ceruloplasmin, carnitine, homocysteine, and amino acids
- Urine analysis plus organic acids
10
Q
True or False: All IEMs manifest early in life.
A
False
11
Q
What is the significance of detecting IEMs early?
A
Early detection is essential to improve outcomes, prevent adverse disease manifestations, and reduce burden on affected individuals and their families.
12
Q
What are the symptoms that might indicate an IEM?
A
Symptoms reflect the affected metabolic pathway and may include distinctive features such as unusual urine color or odor.
13
Q
What is phenylketonuria (PKU)?
A
A genetic disorder caused by a deficiency of the phenylalanine hydroxylase enzyme, leading to elevated phenylalanine levels.
14
Q
What are the consequences of untreated PKU?
A
Severe intellectual impairment, eczema, seizure activity, and self-abusive behavior.
15
Q
Fill in the blank: The high phenylalanine and low tyrosine levels in a child suggest a diagnosis of _______.
A
PKU
16
Q
What is the biochemical basis of neurological dysfunction in PKU?
A
Excessive phenylalanine is toxic to the myelin sheath and decreases the biosynthesis of dopamine, epinephrine, and norepinephrine.
17
Q
What dietary management is required for individuals with PKU?
A
Strict dietary restriction of phenylalanine to prevent neurological damage.
18
Q
What is the relationship between maternal phenylalanine levels and fetal development?
A
Elevated maternal phenylalanine levels can result in serious teratogenic damage in utero, leading to microcephaly and cardiac abnormalities.
19
Q
What are the key clinical presentations of PKU?
A
- Peculiar ‘mousy odor’ in urine
- Fair complexion, hair, and eyes
- Developmental delays
20
Q
What is the role of genetic testing in diagnosing PKU?
A
It confirms the diagnosis of phenylalanine hydroxylase deficiency.
21
Q
What is the standard of care for newborn infants regarding phenylketonuria?
A
Mandatory screening of all newborn infants is the standard of care.
22
Q
What dietary considerations must PAH-deficient expectant mothers take into account?
A
PAH-deficient expectant mothers must judiciously restrict dietary phenylalanine before and during pregnancy to avoid teratogenic damage.
23
Q
What is the biochemical basis of phenylketonuria?
A
Phenylketonuria falls into the aminoacidopathies category of IEMs due to defective metabolism of amino acids, leading to symptoms such as hyperactivity, intellectual disability, developmental delay, vomiting, and seizures.
24
Q
What are the two metabolic fates of amino acids?
A
Amino acids have two fates: incorporation into protein and conversion to various biomolecules.
25
List the nine essential amino acids that humans cannot synthesize.
* Phenylalanine
* Valine
* Tryptophan
* Threonine
* Isoleucine
* Methionine
* Histidine
* Leucine
* Lysine
26
What are conditionally essential amino acids?
Conditionally essential amino acids can be synthesized from an essential amino acid and include cysteine, glutamine, glycine, proline, and tyrosine.
27
What is the role of phenylalanine hydroxylase in tyrosine metabolism?
Phenylalanine hydroxylase synthesizes tyrosine from phenylalanine using tetrahydrobiopterin as a cofactor.
28
What are the consequences of a defect in tyrosine metabolism?
Defects in tyrosine metabolism can lead to accumulation of phenylalanine and its toxic metabolites, resulting in neurological damage.
29
What is hyperphenylalaninemia, and what causes it?
Hyperphenylalaninemia may arise from deficiencies in either phenylalanine hydroxylase or dihydropteridine reductase (DHPR).
30
How does the accumulation of phenylalanine affect cognitive function?
Accumulation of phenylalanine leads to depletion of tyrosine, neural tissue α-ketoglutarate, and other large neutral amino acids, impairing protein and neurotransmitter synthesis.
31
What is the recommended treatment for phenylketonuria?
A strict dietary regimen is required to control phenylalanine intake, using a special formula lacking phenylalanine and a small amount of natural protein.
32
What is the historical significance of Ivar Asbörn Følling in relation to phenylketonuria?
Ivar Asbörn Følling isolated phenylpyruvate from the urine of children with intellectual impairment, marking a milestone in understanding metabolic disorders.
33
What is betaine's role in homocysteine metabolism?
Betaine provides an alternate remethylation pathway for homocysteine, lowering serum concentration and its deleterious effects.
34
Define ectopia lentis.
Ectopia lentis refers to lens dislocation, typically upward in Marfan syndrome and downward in homocystinuria.
35
What is homocystinuria?
Homocystinuria is characterized by elevated levels of homocysteine in the urine due to deficiencies in specific enzymes.
36
What is the difference between homocystinuria and homocysteinemia?
Homocystinuria involves elevated homocysteine in urine, while homocysteinemia involves elevated homocysteine in blood and may exist without homocystinuria.
37
What is the Marfanoid appearance?
Marfanoid appearance includes features such as tall stature, long limbs, high arched palate, and scoliosis.
38
What is the role of methylenetetrahydrofolate reductase (MTHFR)?
MTHFR is necessary for converting 5,10 methylenetetrahydrofolate to 5-methyltetrahydrofolate, affecting serum homocysteine levels.
39
What clinical findings are associated with the 7-year-old boy's condition?
The boy presents with generalized seizure, stupor, disorientation, papilledema, high arched palate, pectus excavatum, and Marfanoid features.
40
What diagnostic imaging was performed for the 7-year-old boy?
An emergent CT angiogram of the head was requested.
41
What was the diagnosis for the 7-year-old boy experiencing seizure?
A working diagnosis of homocystinuria was established.
42
What are the three metabolic cycles involved in methionine metabolism?
The folate cycle, methionine cycle, and transsulfuration pathway.
43
What are the dual fates of methionine?
Protein synthesis and catabolism to sulfur-containing compounds
## Footnote
These compounds include S-adenosylmethionine (SAM), S-adenosyl-L-homocysteine (SAH), homocysteine (Hcy), cystathionine, and cysteine.
44
Name the three interdependent pathways involved in the metabolism of homocysteine.
* Folate cycle
* Methionine cycle
* Transsulfuration pathway
45
What enzymes are deficient in the accumulation of homocysteine?
* Cystathionine beta synthase (CBS)
* Methylenetetrahydrofolate reductase (MTHFR)
* Methionine synthase (MS)
46
What vitamins are required for the enzymes involved in the metabolism of homocysteine?
* Folate (B7)
* Riboflavin (B2)
* Cobalamin (B12)
* Pyridoxal phosphate (B6)
47
What is the primary methyl donor for methylation reactions in the body?
S-adenosylmethionine (SAM)
## Footnote
SAM is involved in more than 35 methylation reactions in the human body.
48
What is the role of methionine synthase in the metabolism of homocysteine?
It remethylates homocysteine back to methionine using methyl-cobalamin as a cofactor.
49
What does the transsulfuration pathway produce from homocysteine?
Cysteine
## Footnote
This pathway condenses homocysteine with serine to form cystathionine, which is then converted to cysteine.
50
What are the clinical consequences of cystathionine beta-synthase (CBS) deficiency?
* Homocystinuria
* Neurological injury
* Vascular disease
* Phenotypic abnormalities resembling Marfan syndrome
51
What are common causes of elevated homocysteine levels?
* Deficiencies in vitamin B12
* Deficiencies in vitamin B6
* Deficiencies in folate
* Inborn errors of homocysteine remethylation
* Renal insufficiency
* Medications
52
How does hyperhomocysteinemia differ from homocystinuria?
Hyperhomocysteinemia indicates high homocysteine levels in the blood, while homocystinuria is a specific condition characterized by the presence of homocysteine in urine.
53
What are the symptoms of homocystinuria?
* Developmental delays
* Marfan-like phenotypic features
* Recurrent thrombosis
54
What is the relationship between cysteine and methionine?
Cysteine is a conditionally essential amino acid derived from the essential amino acid methionine.
55
What is the clinical presentation of a newborn with a metabolic disorder?
Symptoms may include vomiting, lethargy, poor feeding, and neurological deficits.
56
What is the role of carboxylases in metabolism?
Carboxylases remove CO2 from the carboxyl group of alpha amino keto acids and utilize biotin as a cofactor.
57
What does a prolonged QT interval indicate in a neonate?
It may indicate underlying metabolic disturbances or cardiac issues.
58
What is the significance of a strongly positive ketone bodies test in a neonate?
It suggests a state of ketosis, often associated with metabolic disorders.
59
What is the first step in the clinical management of a neonate with suspected metabolic acidosis?
Stabilization with intravenous fluids containing glucose and addressing the acid-base imbalance.
60
What laboratory findings are indicative of metabolic acidosis in a neonate?
Hypoglycemia, hyperammonemia, and possibly elevated anion gap.
61
What is the importance of ruling out sepsis in a newborn with metabolic symptoms?
Sepsis can present with overlapping symptoms and must be differentiated from inborn errors of metabolism.
62
What dietary modifications might be necessary for managing elevated homocysteine levels?
A low methionine diet.
63
Which enzyme is involved in the conversion of propionyl CoA to methylmalonyl CoA?
Propionyl CoA carboxylase.
64
What is the risk of untreated high homocysteine levels?
Increased risk of stroke and vascular disease.
65
What is the significance of elevated ammonia levels in a neonate?
Elevated ammonia levels could suggest a urea cycle disorder, typically appearing shortly after birth with rapid deterioration in mental status (encephalopathy)
## Footnote
However, in urea cycle disorders, blood urea nitrogen (BUN) is expected to be low.
66
What are the common symptoms seen in inborn errors of metabolism (IEMs)?
Hypoglycemia, acidosis, and elevated ammonia levels
## Footnote
These symptoms can indicate a metabolic disorder in neonates.
67
How can glycogen storage diseases be differentiated from other metabolic disorders?
Glycogen storage diseases often present with hypoglycemia but not with hyperammonemia, thus can be ruled out from the differential diagnosis.
68
What is the role of gas chromatographic/mass spectrographic analysis in diagnosing metabolic disorders?
It is used to analyze urine for organic and amino acids, helping to confirm diagnoses like propionic aciduria.
69
What are the characteristic findings in urine for propionic aciduria?
Positive for 3-hydroxypropionate, methylcitrate, tiglylglycine, propionylglycine, ketone bodies, and lactic acid.
70
What is the confirmatory test for propionic aciduria?
Determination of decreased activity of propionyl CoA carboxylase (PCC) in fibroblasts or identification of mutations in the PCCA or PCCB genes.
71
What are organic acidurias?
A group of disorders characterized by increased excretion of nonamino organic acids in urine.
72
List the five groups of organic acidurias.
* Branched-chain organic acidemias
* Fatty acid oxidation defects
* Multiple carboxylase deficiencies
* Glutaric acidurias
* Disorders of energy metabolism
73
What is the metabolic consequence of defective beta-oxidation in mitochondria?
Accumulation of acyl-CoA molecules leading to the formation of acylcarnitines.
74
What amino acids are associated with propionyl CoA metabolism?
Isoleucine, valine, methionine, and threonine.
75
What enzyme converts propionyl CoA to methylmalonyl CoA?
Propionyl CoA carboxylase.
76
What vitamin is essential for the enzyme methylmalonyl CoA mutase?
Vitamin B12.
77
What are the symptoms of multiple carboxylase deficiencies (MCD)?
* Feeding difficulties
* Breathing difficulties
* Lethargy
* Seizures
* Skin rash
* Alopecia
* Developmental delay
78
What is the treatment approach for propionic acidemia?
A low protein diet with supplementation of biotin and carnitine.
79
What are the clinical features of propionic acidemia?
Typically presents shortly after birth with vomiting and rapid deterioration in mental status.
80
True or False: Hyperglycinemia arises due to the inhibition of a glycine cleavage enzyme in the liver.
True.
81
What is the relationship between oxidative phosphorylation and the urea cycle?
The urea cycle requires ATP generated in mitochondria by oxidative phosphorylation.
82
Fill in the blank: Propionic acidemia is due to a deficiency of ______.
propionyl CoA carboxylase.
83
What is the primary condition of the 1-month-old girl admitted to the hospital?
Failure to thrive and hypotonia
84
What were the significant dysmorphic features observed in the infant?
* Large fontanels
* High forehead
* Epicanthic folds
* Deformed earlobes
* Camptodactyly of the third, fourth, and fifth fingers
85
What laboratory findings were normal for the infant?
* Blood sugar
* Complete blood count (CBC)
* Urea and electrolytes (U/E)
* Calcium
* Magnesium
* Total serum bilirubin
* Creatine kinase
* Lactate
* Ammonia
86
What were the elevated liver transaminases for the infant?
* AST = 255 (Normal range = 7-55 units/L)
* ALT = 111 (Normal range = 7-55 units/L)
87
What does TORCH screening test for?
Infectious diseases: toxoplasmosis, rubella, cytomegalovirus, herpes simplex virus
88
What is camptodactyly?
A rare genetic or acquired condition where a finger or fingers is fixed in a bent position at the middle joint
89
What is neuronal migration?
The process during embryonic development where neurons travel to locate in the proper location for correct function
90
What are peroxisomes?
Organelles with a single membrane that contain over 50 enzymes for various oxidation reactions
91
What are PEX genes?
16 genes that direct the normal assembly of peroxisomes; defects cause peroxisome biogenesis disorders
92
What are plasmalogens?
Unique membrane glycerophospholipids found in the brain, myelin sheath, heart, bones, and eye
93
What is transferrin isoelectric focusing used for?
Screening tool to determine congenital disorders of glycosylation
94
What do urine organic acids screening detect?
* Propionic acid
* Isovaleric acid
* Methylmalonic acid
* Fatty acid oxidation defects
* Maple syrup urine disorder
* Tyrosinemia
95
What is the initial clinical impression of the neonatologist?
A metabolic or chromosomal aberration
96
What laboratory tests are used to rule out infections?
TORCH screen
97
What is Zellweger syndrome?
The most severe peroxisomal disorder with complete absence of peroxisomes
98
What are common clinical findings in Zellweger spectrum disorder?
* Hypotonia
* Poor feeding
* Distinctive facies
* Brain malformations
* Seizures
* Renal cysts
* Hepatosplenomegaly
* Cholestasis
* Hepatic dysfunction
99
What is the key enzyme in alpha-oxidation?
Phytanoyl-CoA hydroxylase
100
What is the most common peroxisomal disorder?
X-linked adrenoleukodystrophy (X-ALD)
101
What does beta-oxidation of fatty acids in peroxisomes oxidize?
Very long-chain fatty acids (VLCFA) to medium-chain fatty acids
102
What is Refsum disease?
A disorder caused by deficiency of phytanoyl-CoA hydroxylase leading to accumulation of phytanic acid
103
What are the two classifications of peroxisomal disorders?
* Peroxisomal biogenesis disorders (PBDs)
* Single enzyme defects
104
What is the role of peroxisomes in detoxification?
Detoxification of various toxic molecules including alcohol through peroxidation reactions
105
What are the major biochemical pathways in peroxisomes?
* Beta-oxidation of fatty acids
* Alpha-oxidation of fatty acids
* Biosynthesis of bile acids
* Biosynthesis of plasmalogen
106
What is the significance of elevated C26:0 and C26:1 ratios in fatty acid analysis?
Consistent with a defect in peroxisomal fatty acid metabolism
107
What is the outcome for the child in this case?
Died at 8 months
108
What is the purpose of genetic counseling in this case?
Assistance with further family planning
109
What is the role of PEX gene analysis in diagnosing peroxisomal spectrum disorder?
Aids in establishing a diagnosis of peroxisomal spectrum disorder.
110
What are the two main causes of peroxisomal disorders?
Single gene defect or biogenesis disorder.
111
What is the most common peroxisomal disorder?
Zellweger syndrome.
112
What are common symptoms presented by a child with hypotonia and developmental regression?
* Progressive muscular weakness
* Difficulty with feedings
* Listlessness
* Inability to sit without support
* Rarely rolling over.
113
What does consanguinity refer to?
Blood relationship between individuals.
114
What is dysostosis multiplex an indicator of?
Lysosomal storage diseases caused by mucopolysaccharide accumulation.
115
What are gangliosides?
Sugar-lipid components of neural membranes involved in transmission of impulses.
116
What are acroparesthesias?
Burning or tingling as well as numbness in the extremities.
117
What does HEXA stand for?
HEXA is an abbreviation for the HEX gene that codes for the alpha subunit hexosaminidase A.
118
What is the function of lysosomes?
Degradation of various cellular macromolecular waste products.
119
What does hypotonia in utero indicate?
An ominous sign that must be investigated.
120
What is the pathophysiology of lysosomal storage disorders (LSDs)?
Accumulation of various cellular metabolites in the lysosome leading to progressive disorders.
121
How are lysosomal proteins targeted to the lysosome?
Via a mannose 6-phosphate-dependent (M6P) pathway.
122
What enzyme deficiency is responsible for I-cell disease?
N-acetylglucosamine-1-phosphotransferase.
123
What are the substrates of lysosomal enzymes?
* Sphingolipids
* Mucopolysaccharides
* Glycogen.
124
What are sphingolipidoses?
Lysosomal lipid storage diseases that typically affect neuronal function.
125
What causes Niemann-Pick disease?
Deficiency in sphingomyelinase leading to sphingomyelin buildup.
126
What are the symptoms of type A Niemann-Pick disease?
* Severe neurological damage
* Liver enlargement
* Premature death.
127
What is Gaucher disease caused by?
Deficiency in beta-glucocerebrosidase leading to glucosylceramide accumulation.
128
What are the clinical features of Gaucher disease?
* Bone marrow involvement
* Macrophage dysfunction.
129
What is the significance of the cherry-red spot in ophthalmological examination?
Noted in several lysosomal storage diseases including Tay-Sachs and Niemann-Pick.
130
True or False: Lysosomal storage disorders can be caused by mutations in any of the various acid hydrolases.
True.
131
Fill in the blank: The degradation pathway of sphingomyelin is achieved by _______ and ceramidase.
sphingomyelinase.
132
What is the common pathway for the breakdown of sphingolipids?
Deficiencies in enzymes lead to accumulation of compounds toxic to tissues.
133
What is Gaucher disease?
An autosomal recessive disease caused by a deficiency in beta-glucocerebrosidase leading to accumulation of glucosylceramide in macrophages.
134
What is the significance of lysosomes in Gaucher disease?
Lysosomes are critical for macrophage function, which involves engulfing and digesting cellular debris.
135
What are the main organs affected by Gaucher disease?
* Bone marrow
* Liver
* Lungs
* Spleen
* Brain
136
What are the characteristic symptoms of Gaucher disease?
* Enlarged liver
* Massive splenomegaly
* Diffuse lymphadenopathy
* Pancytopenia
137
What is the appearance of Gaucher cells?
They have a characteristic 'crumpled up' or tissue paper appearance due to lipid accumulation.
138
How is Gaucher disease diagnosed?
By measuring glucocerebrosidase activity in peripheral leukocytes and histology revealing Gaucher cells.
139
What is the treatment for Gaucher disease?
Intravenous recombinant glucocerebrosidase.
140
What causes Metachromatic Leukodystrophy?
A deficiency in arylsulfatase leading to accumulation of cerebroside sulfate.
141
What are common symptoms of Metachromatic Leukodystrophy?
* Ataxia
* Peripheral neuropathy
* Dementia
142
What is the inheritance pattern of Fabry Disease?
X-linked recessive.
143
What enzyme is deficient in Fabry Disease?
Alpha-galactosidase A.
144
What are the progressive symptoms of Fabry Disease?
* Acroparesthesias
* Full body pain
* Renal failure
* Cardiomyopathy
* Hypertension
* Severe fatigue
145
What unique skin findings are associated with Fabry Disease?
* Angiokeratomas
* Anhidrosis or hyperhidrosis
146
What is the hallmark feature of Krabbe Disease?
Myelin loss and the presence of globoid bodies in white matter.
147
What enzyme deficiency leads to Krabbe Disease?
Lysosomal β-galactocerebrosidase.
148
What are the initial symptoms of Tay-Sachs Disease?
Progressive motor and neurological impairment in infants.
149
What enzyme deficiency is responsible for Tay-Sachs Disease?
Beta-hexosaminidase A.
150
Which population has a higher prevalence of Tay-Sachs Disease?
Ashkenazi Jewish population.
151
What is a common clinical finding in Tay-Sachs Disease?
A 'cherry-red spot' on eye examination.
152
What are glycosaminoglycans more commonly known as?
Mucopolysaccharides.
153
What is the structure of glycosaminoglycans?
Linear polymers composed of repeating disaccharide subunits.
154
How are glycosaminoglycans synthesized?
By sequential addition of alternating acidic and amino sugars.
155
What are the six types of glycosaminoglycans?
* Hyaluronic acid
* Chondroitin sulfate
* Heparan sulfate
* Dermatan sulfate
* Keratan sulfate
* Heparin
156
What characterizes Mucopolysaccharidoses (MPS)?
Accumulation of glycosaminoglycans due to deficiency of lysosomal hydrolases.
157
What is the genetic inheritance of Hunter syndrome?
X-linked recessive.
158
What defect causes Hurler syndrome?
Defect in alpha-L-iduronidase.
159
What are the key features of Hurler syndrome?
* Coarsening of facial features
* Corneal clouding
* Hepatosplenomegaly
160
What is the main feature of Sanfilippo syndrome?
Deficiency in heparan sulfate–degrading enzymes.
161
What enzyme deficiency causes Pompe disease?
Acid alpha-glucosidase.
162
What differentiates Pompe disease from other glycogen storage disorders?
It does not lead to hypoglycemia.
163
What are the symptoms of Pompe disease?
* Cardiomegaly
* Hypotonia
* Hepatomegaly
164
What treatment is available for Pompe disease?
Approved enzyme therapy.
165
True or False: There is an effective treatment for Tay-Sachs disease.
False
166
Fill in the blank: Lysosomal storage disease describes a family of disorders characterized by _______.
[chromosomal abnormalities resulting in enzymatic defects]
167
What is the clinical presentation of lysosomal storage diseases often related to?
The organ where the toxic metabolite accumulates.
168
What is the likely working diagnosis for a 10-day-old infant with lethargy, feeding difficulties, decreased muscle tone, hepatomegaly, acidosis, hypoglycemia, and elevated serum ammonia levels?
C. Propionic acidemia
## Footnote
The symptoms and laboratory findings support a diagnosis of propionic acidemia.
169
What substrate accumulates in a 6-year-old boy with bone pain, hepatomegaly, and a bone marrow aspirate showing macrophages with a wrinkled tissue paper appearance?
C. Sphingomyelin
## Footnote
This presentation is characteristic of Gaucher disease.
170
In a 2-year-old girl with phenylketonuria, what should be measured next in the plasma?
C. Tyrosine
## Footnote
Tyrosine becomes essential in patients with phenylketonuria due to the deficiency in phenylalanine hydroxylase.
171
What enzyme is likely deficient in a 7-day-old infant with poor feeding, lethargy, vomiting, and elevated levels of 3-carbon glycine?
C. Propionyl-CoA carboxylase
## Footnote
The symptoms and lab results indicate propionic acidemia.
172
What disease is indicated by a one-month-old infant with hypotonia, failure to thrive, dysmorphic features, and elevated levels of 26-carbon fatty acids?
B. Zellweger syndrome
## Footnote
This condition is characterized by peroxisomal biogenesis defects.
173
What is the least likely intervention to improve the outcome in a 4-year-old with developmental delay and elevated serum methionine?
C. Biotin
## Footnote
Biotin is not involved in homocysteine metabolism.
174
What is the enzyme deficiency in Tay-Sachs disease?
Hexosaminidase A
## Footnote
Tay-Sachs is characterized by neurodegeneration and cherry-red spots on the macula.
175
What is the likely diagnosis for a patient with homocystinuria presenting with thrombotic events due to elevated homocysteine?
Homocystinuria
## Footnote
This condition is associated with increased risk of vascular events.
176
What condition is associated with a deficiency in glucocerebrosidase and presents with bone pain and hepatosplenomegaly?
Gaucher disease
## Footnote
Gaucher disease is a lysosomal storage disorder.
177
What distinguishes Zellweger syndrome from X-linked adrenoleukodystrophy in terms of fatty acid accumulation?
Zellweger syndrome shows elevated phytanic and pristanic acids
## Footnote
In Zellweger syndrome, VLCFA levels are also elevated.
178
What are the symptoms of propionic acidemia?
* Poor feeding
* Lethargy
* Vomiting
* Elevated 3-carbon glycine levels
## Footnote
These symptoms result from propionyl-CoA carboxylase deficiency.
179
What is the role of biotin in metabolism?
Biotin is a cofactor for the ABC carboxylases, which include acetyl CoA carboxylase, propionyl CoA carboxylase, 3-methylcrotonyl CoA carboxylase, and pyruvate carboxylase.
## Footnote
Biotin is not involved in homocysteine metabolism.
180
Which vitamin plays an important role in homocysteine metabolism?
Vitamin B6
## Footnote
It is a cofactor for cystathionine beta synthase and cystathionase.
181
What is the function of vitamin B12 in homocysteine metabolism?
Vitamin B12 is a cofactor for methionine synthase, which catalyzes the conversion of homocysteine to methionine.
## Footnote
This process is crucial for maintaining normal homocysteine levels.
182
What is the role of betaine in metabolism?
Betaine is important for the folate-independent recycling of homocysteine to methionine.
## Footnote
This recycling helps regulate homocysteine levels.
183
True or False: Biotin is involved in homocysteine metabolism.
False
## Footnote
Biotin functions primarily as a cofactor for carboxylases.
