• Hemma Summan

Part One: Guthrie Test

What is PKU and biopterin deficiency?

Phenylketonuria (PKU) is an autosomal recessive disease; it is an extremely common inborn defect of amino acid metabolism. Insufficiency of the enzyme phenylalanine hydroxylase (PAH) prejudices the body’s capability to metabolise phenylalanine: consequently accumulation of phenylalanine in tissues, plasma and urine is characterised resulting in hyperphenylalaninaemia (HPA). Over 500 genetic mutations in the PAH gene on chromosome 12 have been recognised in people who have the disease; resulting is single amino acid mutations. The inherited disease is diagnosed by newborn screening, as screening is mandatory for newborns in the UK. If high phenylalanine levels are identified treatment and management should be started; including advised nutritional restriction of phenylalanine. A low –protein diet should be achieved, and amino acid supplements may be prescribed to ensure irreversible mental retardation is avoided. Deficiency of melanin is a common symptom of PKU; therefore fair skin and hair are common symptoms as a result, in addition to eczema and light sensitivity. Long term management of PKU can be achieved by using the drug sapropterin to degrade phenylalanine and in-turn benefit metabolic control, tolerance to dietary phenylalanine and quality of life. (Georgianne L Arnold, 2013).

Here is a flow diagram showing phenylalanine metabolism in PKU:

Phenylalanine Phenylpyruvate

Phe hydroxylase

Tyrosine

MelaninThyroid Hormones (Hypothyroidism)

Homogentisic AcidAlkaptans

HGA Oxidase Deficiency

Further Metabolism

Figure 1. Flow chart representing the consequences of PKU on metabolism.

Biopterin is a coenzyme; it is an oxidized degradation product of tetrahydrobiopterin (BH4). A decreased level of urinary biopterin is associated with accumulated phenylalanine serum concentrations in HPA. This is caused by a shortage of BH4, the mandatory cofactor for phenylalanine hydroxylase; or deficiency of 6-pyruvoyl-tetrahydropterin synthase (PTPS) activity, the second enzyme in the biosynthetic pathway for BH4. (Dr. Friedrich Trefz, 2012). Biopterin deficient cases have been associated with Alzheimer’s disease, Parkinson’s disease, rabies and dystonia. Rabies virus in particular has the ability to modify neurotransmission, through occupancy of cellular receptors or alterations of ion channels, inevitably leading to loss of BH4. (Willoughby RE, 2009).

Part Two: Screening process for mucopolysaccharidoses (MPS)

Part Three: Lactase deficiency

Which is the lactase deficient specimen and why?

Gut P sample had lactase deficiency

Gut O sample did not have lactase deficiency.

Blank row a number 1 no glucose in it representing a person whos blood has an average amount of glucose

Standard 2 has loads of glucose

Upper n higer limits

Sample o closer to blank vblood doesn’t have much glucose

Sample p is closer to the standard not lactose deficient does have glucose

Part 4: TLC Inherited Disease

Identify the three urines and briefly describe

1. the condition of histidinaemia and

Histidinaemia is an inherited autosomal recessive disorder. It is associated with deficiency of the enzyme histidine due to mutations in the HAL gene, which is essential for the metabolism of histidine (amino acid). Accumulation of histidine is prevalent in blood concentrations; resulting in excessive amounts to be excreted via micturition, along with imidazole pyruvic acid, and other imidazole metabolism products. The disease is asymptomatic and is considered a benign disorder. However previous studies related this disease to a variety of developmental symptoms including learning difficulties and mental retardation, it was later discovered this was untrue, as infants tested positive for histidinaemia did not present such symptoms.

2. clinical conditions in which chromatography of hydroxyproline might be useful.

Hydroxyproline is a postsynthetic derivative of proline that is frequently used to estimate the collagen or gelatin content of tissue; this can be achieved using high pressure liquid chromatography (HPLC). Hydroxyproline is not only found in collagen, it is also found is elastin in mammals. Diseases such as neoplastic, inflammatory, renal or bone disease to endocrine and autoimmune disorders are affected by collagen turnover; consequently raising serum and urine hydroxyproline. In addition Collagen is the key structural protein of the acellular matrix of the lung; therefore hydroxyproline quantification may be useful for evaluating tissue fibrosis/ collagen deposition. Advancements in quantification of hydroxyproline are now available such as BioVision’s Hydroxyproline Colorimetric Assay Kit: It is a convenient and easy to use method; however it only detects hydroxyproline in the ranges of 0.1-2 μg. (BioVision, 2014).

HPLC can be used to seperate and quantify hydroxyproline in calvarial cultures, which can be a successful technique in monitoring variations in bone matrix degradation that are associated with sarcoma, Rheumatoid Arthritis, Morbus Paget, acromegaly and osteoporosis. Additionally Bone density and calcium levels are affected by hyperparathyroidism, therefore hydroxyproline measurements may be useful in diagnosig and monitoring the condition.

Part 5: MSUD

What characteristic smell do you associate with this MSUD?

Maple Syrup Urine Disease is related with the maple syrup odor to urine, which can also be described as a burnt sugar smell due to accumulation of plasma isoleucine.

Describe briefly why keto-acids are present in MSUD?

MSUD is an autosomal recessive inherited metabolic disorder; it is caused by lack of branched-chain alpha-keto acid dehydrogenase complex (BCKDC). BCKDC has an important role in catalysing the decarboxylation of the alpha-keto acids of leucine, isoleucine, and valine to their individual branched-chain acyl-CoAs. These are further metabolised to produce acetyl-CoA, acetoacetate, and succinyl-CoA. Build-up of keto- acids can contribute to encephalopathy and progressive neurodegeneration if undiagnosed and untreated in infants. Therefore prompt diagnosis is extremely important and immediate change in the diet will inhibit any symptoms from occurring; and children will develop without intellectual impairment. As a result MSUD is involved with newborn screening problems; to ensure children are not at risk of this detrimental inborn error. (Olaf A Bodamer, 2012).

References

Willoughby RE. (2009). Tetrahydrobiopterin deficiency in human rabies. Journal of Inherited Metabolic Disease . 32 (1), 65-72.

BioVision Incorporated . (2014). Hydroxyproline Colorimetric Assay Kit. Available: http://www.biovision.com/hydroxyproline-colorimetric-assay-kit-4386.html. Last accessed 21/03/2014.

Dr. Friedrich Trefz. (2012). Biopterin. Available: http://www.metagene.de/program/l.prg?id_l=1362. Last accessed 21/03/2014.

Olaf A Bodamer. (2012). Maple Syrup Urine Disease . Available: http://emedicine.medscape.com/article/946234-overview. Last accessed 21/03/2014.

Georgianne L Arnold. (2013). Phenylketonuria. Available: http://emedicine.medscape.com/article/947781-overview. Last accessed 21/03/2014.

Langrock T. (2012). Analysis of hydoxyproline in Collagen Hydrolysates . Methods in Molecular Biology. 828 (1), 271-280.