zoom RSS ほぼ全ての州で稀な遺伝性疾患の新生児スクリーニング/米国医療事情

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 本日発表されたMarch of Dimesレポートによれば、50州全てとコロンビア特別区で推奨された21種類以上の主要な病気の新生児スクリーニングが要求されている。中核となる病気は全てで29だが、多くは稀な病気だが障害を残したり死亡したりする代謝疾患である。全ての州でスクリーニングを必要とする規則や法律を持っているが、ペンシルベニアとウェストバージニアはまだこれから拡張する必要がある。

Screening for Rare Genetic Disorders Now Routine in Newborns
Published: February 18, 2009

When David Swift’s baby girl Giana was born at Santa Monica U.C.L.A. Medical Center six years ago, a nurse approached to ask if the baby could participate in a pilot program to screen newborns for dozens of rare genetic disorders. It involved little more than a heel prick blood test, but Mr. Swift, a 33-year-old first-time father, declined.

The nurse persisted, asking the question again and again, until Mr. Swift relented. And he’s been trying to find that nurse ever since, because the test, which identified an extremely rare metabolic condition in his newborn daughter, may have saved her life.

“Had we not been at that particular hospital, with that particular pilot program and that particular nurse...” he said, his voice trailing off. “It’s miraculous.”

A March of Dimes report released today says all 50 states and the District of Columbia now require newborn screening for 21 or more so-called core disorders recommended for testing. These core disorders, 29 in all, include many rare but potentially disabling or fatal metabolic disorders. Although all states have rules or laws requiring the screenings, Pennsylvania and West Virginia have yet to implement their expanded programs, according to the organization.

The increase represents a big change since 2000, when most states screened for only four conditions and testing practices varied widely from state to state, according to March of Dimes officials.

“It’s a milestone,” said Jennifer L. Howse, president of the March of Dimes, which advocated for expanded testing. Screening rates in newborns rose from 38 percent in 2005, when the organization began monitoring, to 96 percent by the end of 2008, she said. “That’s very, very dramatic.”

Twenty-four states do all of the tests, and seven do 28 of the 29 tests, she said. The tests include screens for phenylketonuria, or PKU, a potentially devastating illness that strikes about one in 25,000 newborns, and maple syrup urine disease, so-named for the infant’s sweet-smelling urine, which affects one in 100,000. More common ailments like sickle cell anemia, which affects one in 400 African-Americans, and cystic fibrosis and hearing loss, each of which affect one in 5,000 children, are screened for as well.

The American College of Medical Genetics developed the list of the 29 disorders recommended for testing. (A list of tests provided by each state can be found at the March of Dimes Web site).

Dr. Howse emphasized that the metabolic disorders on the list are rare but treatable, and “if they’re not detected and treated, they’re catastrophic and can lead to infant death.”

In most cases, she added, the babies look perfectly healthy.

New technology, specifically the advent of a technique called tandem mass spectrometry, provided the means to identify many conditions from just a tiny sample of blood, she said.

Mr. Swift’s daughter was found to suffer from a condition that makes her unable to break down leucine, an essential amino acid in protein. Only about 30 cases of the disorder have ever been documented and, undiagnosed, it could have led to mental or physical disability, or even death.

Instead, Giana was put on a modified diet with very little protein and takes a special protein formula free of leucine, Mr. Swift said.

“She is beautiful, healthy, precocious, 99th percentile height and weight, just wonderful,” Mr. Swift said. “That test saved her life.”
Recommended Newborn Screening Tests: 29 Disorders

The March of Dimes would like to see all babies in all states screened for the following 29 disorders, for which effective treatment is available. This recommendation is based on endorsement of a report by the American College of Medical Genetics (ACMG) urging screening for these disorders. The report was commissioned by the U.S. Health Resources and Services Administration.The 29 disorders can be grouped into five categories:

* Amino acid metabolism disorders
* Organic acid metabolism disorders
* Fatty acid oxidation disorders
* Hemoglobinopathies
* Others

Amino Acid Metabolism Disorders
This is a diverse group of disorders, with varying degrees of severity. Some affected individuals lack enzymes that are needed to break down the building blocks of protein called amino acids. Others have deficiencies in enzymes that help the body rid itself of the nitrogen incorporated in amino acid molecules. Toxic levels of amino acids or ammonia can build up in the body causing a variety of signs and symptoms, and even death.

PKU = Phenylketonuria
Incidence: greater than 1 in 25,000(1)

MSUD = Maple syrup urine disease
Incidence: less than 1 in 100,000(1)

HCY = Homocystinuria
Incidence: less than 1 in 100,000(1)

CIT = Citrullinemia
Incidence: less than 1 in 100,000(1)

ASA = Argininosuccinic acidemia
Incidence: less than 1 in 100,000(1)

TYR I = Tyrosinemia type I
Incidence: less than 1 in 100,000(1)

Organic Acid Metabolism Disorders
Each disease in this group of inherited disorders results from the loss of activity of an enzyme involved in the break down of amino acids, the building blocks of proteins, and other substances (lipids, sugars, steroids). When any of these chemicals is not properly broken down, toxic acids build up in the body. Without dietary treatment and prevention of acute episodes, these disorders can result in coma and death during the first month of life.

IVA = Isovaleric acidemia
Incidence: less than 1 in 100,000(1)

GA I = Glutaric acidemia type I
Incidence: greater than 1 in 75,000(1)

HMG = Hydroxymethylglutaric aciduria or HMG-CoA lyase deficiency or 3-OH 3-CH3 glutaric aciduria
Incidence: less than 1 in 100,000(1)

MCD = Multiple carboxylase deficiency
Incidence: less than 1 in 100,000(1)

MUT = Methylmalonic acidemia due to mutase deficiency
Incidence: greater than 1 in 75,000(1)

Cbl A,B = Methylmalonic acidemia cblA and cblB forms
Incidence: less than 1 in 100,000(1)

3MCC = 3-Methylcrotonyl-CoA carboxylase deficiency
Incidence: greater than 1 in 75,000(1)

PROP = Propionic acidemia
Incidence: greater than 1 in 75,000(1)

BKT = Beta-Ketothiolase deficiency
Incidence: less than 1 in 100,000(1)

Fatty Acid Oxidation Disorders
This group of disorders is characterized by inherited defects of enzymes needed to convert fat into energy. When the body runs out of glucose (sugar), it normally breaks down fat to support production of alternate fuels (ketones) in the liver. Because individuals with these disorders have a block in this pathway, their cells suffer an energy crisis when they run out of glucose. This is most likely to occur when an individual is ill or skips meals. Without treatment, the brain and many organs can be affected, sometimes progressing to coma and death.

MCAD = Medium-chain acyl-CoA dehydrogenase deficiency
Incidence: greater than 1 in 25,000(1)

VLCAD = Very long-chain acyl-CoA dehydrogenase deficiency
Incidence: greater than 1 in 75,000(1)

LCHAD = Long-chain 3-OH acyl-CoA dehydrogenase deficiency
Incidence: greater than 1 in 75,000(1)

TFP = Trifunctional protein deficiency
Incidence: less than 1 in 100,000(1)

CUD = Carnitine uptake defect
Incidence: less than 1 in 100,000(1)

These inherited diseases of red blood cells result in varying degrees of anemia (shortage of red blood cells), serious infections, pain episodes, and damage to vital organs. The symptoms are caused by abnormal kinds and/or amounts of hemoglobin, the main protein inside red blood cells that carries oxygen from the lungs and takes it to every part of the body. In the sickling disorders, an abnormal hemoglobin called HbS can cause some red blood cells to become stiff and abnormally shaped. The stiffer red blood cells can get stuck in tiny blood vessels, causing pain and sometimes organ damage. The severity of these disorders varies greatly from one person to the next.

Hb SS = Sickle cell anemia
Incidence: greater than 1 in 5,000(1); higher incidence among African-Americans (1 in 400)(2)

Hb S/C = Hb S/C disease
Incidence: greater than 1 in 25,000(1)

This mixed group of disorders includes some diseases that are inherited and others that are not genetic. This group of disorders varies greatly in severity, from mild to life-threatening.

CH = Congenital hypothyroidism
Incidence: greater than 1 in 5,000(1)

BIOT = Biotinidase deficiency
Incidence: greater than 1 in 75,000(1)

CAH = Congenital adrenal hyperplasia
Incidence: greater than 1 in 25,000(1)

GALT = Classical galactosemia
Incidence: greater than 1 in 50,000(1)

HEAR = Hearing loss
Incidence: greater than 1 in 5,000(1); up to 3-4 per 1,000 newborns(4)

CF = Cystic fibrosis
Incidence: greater than 1 in 5,000(1)

1. American College of Medical Genetics. Newborn Screening: Toward a Uniform Screening Panel and System. Final Report, March 8, 2005.

2. General Accounting Office. Newborn Screening: Characteristics of State Programs. Washington, DC: General Accounting Office, 2003. Publication GAO-03-449. Data from the National Newborn Screening and Genetics Resource Center.

3. American Academy of Pediatrics Section on Hematology/Oncology Committee on Genetics. Health Supervision for Children with Sickle Cell Disease, Pediatrics, volume 109, number 3, March 2002, pages 526-535.

4. National Center for Hearing Assessment and Management, Utah State University.

Additional References
National Library of Medicine Genetics Home Reference
Northwest Regional Newborn Screening Program, Portland, OR.

April 2006 (updated September 2006)


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