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The Smiths had just given birth to their second child and were eagerly waiting to take the newborn home. At that moment, their obstetrician walked into the hospital room with some news about their daughter’s newborn screening tests. The physician told them that the state’s mandatory newborn screening test had detected an abnormally high level of phenylalanine in their daughter’s blood. The Smiths asked if this was just a fleeting effect, like newborn jaundice, that would “go away” in a few days. When they were told that that was unlikely, they were even more confused. The pregnancy had progressed without any complications, and their daughter was born looking perfectly “normal.” Mrs. Smith even had a normal amniocentesis early in the pregnancy. The physician asked a genetic counselor to come to their room to explain their daughter’s newly diagnosed condition. The counselor began her discussion with the Smiths by taking a family history from each of them. She explained that phenylketonuria (PKU) is a genetic condition that results when an individual inherits an altered gene from each parent. The counselor wanted to make this point early in the session in case either parent attempted to cast blame for their daughter’s condition. She explained that PKU is characterized by an increased concentration of phenvlalanine in blood and urine and that intellectual disability can be part of this condition if it is not treated at an early age. To prevent the development of intellectual disability, after early diagnosis, dietary therapy must begin before the child is 30 days old. The newborn needs to follow a special diet in which the bulk of protein in the infant’s formula is replaced by an artificial amino acid mixture low in phenylalanine. The child must stay on this diet indefinitely for it to be maximally effective. PKU is one of several diseases known as the hyperphenylal-aninemias, which occur with a frequency of 1 in 10,000 births. Classic PKU accounts for two-thirds of these cases. PKU is an autosomal recessive disorder that is distributed widely among whites and Asians but is rare in blacks. Heterozygous carriers do not show symptoms but may have slightly increased phenylalanine concentrations. If untreated, children with classic PKU can experience progressive intellectual disability, seizures, and hyperactivity. EEG abnormalities; mousy odor of the skin, hair, and urine; a tendency to have light-colored skin; and eczema complete the clinical picture. Why did amniocentesis fail to detect PKU? What disorders can amniocentesis detect?

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Human Heredity: Principles and Iss...

11th Edition
Michael Cummings
Publisher: Cengage Learning
ISBN: 9781305251052

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BuyFindarrow_forward

Human Heredity: Principles and Iss...

11th Edition
Michael Cummings
Publisher: Cengage Learning
ISBN: 9781305251052
Chapter 3, Problem 1CS
Textbook Problem
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The Smiths had just given birth to their second child and were eagerly waiting to take the newborn home. At that moment, their obstetrician walked into the hospital room with some news about their daughter’s newborn screening tests. The physician told them that the state’s mandatory newborn screening test had detected an abnormally high level of phenylalanine in their daughter’s blood. The Smiths asked if this was just a fleeting effect, like newborn jaundice, that would “go away” in a few days. When they were told that that was unlikely, they were even more confused. The pregnancy had progressed without any complications, and their daughter was born looking perfectly “normal.” Mrs. Smith even had a normal amniocentesis early in the pregnancy. The physician asked a genetic counselor to come to their room to explain their daughter’s newly diagnosed condition.

The counselor began her discussion with the Smiths by taking a family history from each of them. She explained that phenylketonuria (PKU) is a genetic condition that results when an individual inherits an altered gene from each parent. The counselor wanted to make this point early in the session in case either parent attempted to cast blame for their daughter’s condition. She explained that PKU is characterized by an increased concentration of phenvlalanine in blood and urine and that intellectual disability can be part of this condition if it is not treated at an early age.

To prevent the development of intellectual disability, after early diagnosis, dietary therapy must begin before the child is 30 days old. The newborn needs to follow a special diet in which the bulk of protein in the infant’s formula is replaced by an artificial amino acid mixture low in phenylalanine. The child must stay on this diet indefinitely for it to be maximally effective.

PKU is one of several diseases known as the hyperphenylal-aninemias, which occur with a frequency of 1 in 10,000 births. Classic PKU accounts for two-thirds of these cases. PKU is an autosomal recessive disorder that is distributed widely among whites and Asians but is rare in blacks. Heterozygous carriers do not show symptoms but may have slightly increased phenylalanine concentrations. If untreated, children with classic PKU can experience progressive intellectual disability, seizures, and hyperactivity. EEG abnormalities; mousy odor of the skin, hair, and urine; a tendency to have light-colored skin; and eczema complete the clinical picture.

Why did amniocentesis fail to detect PKU? What disorders can amniocentesis detect?

Summary Introduction

To determine: The reason for the inability to detect PKU in amniocentesis.

Introduction: The given case study describes a couple who have given birth to a second child and are informed about their newborn daughter’s genetic screening tests. The genetic tests indicated abnormally high levels of amino acid phenylalanine in the blood. Phenylketonuria (PKU) also known as hyperphenylalaninemia. This occurs 1 in every 10,000 births. It is an autosomal recessive disorder implying that both the alleles of the patient are affected. When untreated, it can lead to intellectual disability, seizures, and hyperactivity.

Explanation of Solution

The disease PKU is caused due to the abnormal metabolism of the amino acid phenylalanine which is not identified during amniocentesis. This procedure can detect any abnormality in the genes of the fetus. The presence of extra or absence of the chromosomes or their genes can be detected using amniocentesis. However, in PKU, the chromosomes are intact. The genetic composition for the nucleotides coding for amino acid alone has been changed. This is not identified using this method.

Thus, the disease PKU could not be detected in amniocentesis as the disease results in alteration of amino acid balance and not in the chromosomal pattern.

Summary Introduction

To determine: The disorders detected by amniocentesis.

Introduction: Phenylketonuria is a recessive disorder that mainly affects the Caucasian and the Asian populations. This disease is marked by increased levels of phenylalanine in the blood. It can result in intellectual disability and other physiological problems.

Explanation of Solution

Amniocentesis can detect various disorders that are marked by chromosomal abnormalities like increase or decrease in the number of part of chromosomes. This detection can be used to make an informed decision about the developmental needs of the fetus, and the required genetic screening and treatment.

The most common diseases detected by amniocentesis are Down syndrome or Trisomy of 21, neural tube defects, cystic fibrosis, Turner syndrome, Klinefelter syndrome, trisomy of 18, and many more.

Thus, the diseases detected by amniocentesis are the ones that alter the chromosomal number in an individual.

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