Why is alkaptonuria recessive

Lack of the enzyme phenylalanine hydroxylase is due to the the abnormal autosomal recessive gene on chromosome In children, symptoms are mental retardation, decrease pigmentation of hair and skin and eczema.

The heterozygous individuals are normal but carriers. It occurs in about 1 in births among Europeans. Albinism is characterized by the lack of dark pigment melanin in the skin, hair and iris. Caused by the absence of thyrosinase which is necessary for the synthesis of the pigment melanin from dihydroxyphenylalanine. The gene for albinism a does not produce the enzyme tyrosinase, but its normal allele A does. Thus, only homozygous individuals aa is affected. Homozyous children show degeneration of central nervous system due to accumulation of a fatty substance Sphingolipid in nerve cells.

This is caused by the enzyme D-N-acetyl hexosamindase which is normal individuals exists in two forms A and B. The mentally retarded are progressively paralysed child dies in 3 or 4 years. In this disorder the breakdown of fatty acid substance is impaired leading to the accumulation of lipid materials in body tissues and blood.

It caused by the autsomal recessive gene which inhibits the activity of an enzyme glucocerobrosidase. Consequently there is accumulation of cerebroside A sphingolipid. Symptoms: Enlargement of spleen and liver and expansion of some of the limb bones. Sickle Cell Anemia. Mermaid syndrome is a severe and often fatal congenital abnormality involving fused limbs, which have been described as resembling a mermaid's tail.

According to an observational study in , couples, there was a 35 percent increase in the chance of birth defects in newborns if the father…. Krabbe disease is a rare and life threatening disorder of the nervous system. Sturge-Weber syndrome is a rare neurological disorder present at birth. Learn about its symptoms, causes, diagnosis, and treatment. Health Conditions Discover Plan Connect.

Medically reviewed by Alana Biggers, M. What are the symptoms of alkaptonuria? What causes alkaptonuria? How is alkaptonuria diagnosed?

How is alkaptonuria treated? What is the outlook for alkaptonuria? Read this next. Phthisis Bulbi. Medically reviewed by Ann Marie Griff, O. Heart Valve Disorders. Medically reviewed by Gerhard Whitworth, R. Medically reviewed by Dr. Payal Kohli, M. What Is Caudal Regression Syndrome? Medically reviewed by Mia Armstrong, MD. Krabbe Disease. Medically reviewed by Heidi Moawad, M. Alkaptonuria is more common in certain areas of Slovakia where it has an incidence of about 1 in 19, people and in the Dominican Republic.

Mutations in the HGD gene cause alkaptonuria. The HGD gene provides instructions for making an enzyme called homogentisate oxidase. This enzyme helps break down the amino acids phenylalanine and tyrosine, which are important building blocks of proteins.

Mutations in the HGD gene impair the enzyme's role in this process. As a result, a substance called homogentisic acid, which is produced as phenylalanine and tyrosine are broken down, accumulates in the body.

Excess homogentisic acid and related compounds are deposited in connective tissues , which causes cartilage and skin to darken. Over time, a buildup of this substance in the joints leads to arthritis. Homogentisic acid is also excreted in urine, making the urine turn dark when exposed to air.

This condition is inherited in an autosomal recessive pattern , which means both copies of the gene in each cell have mutations.

The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice.