The Genetic Disorders: Human Inheritance Anomalies

Introduction

Complex expressions of our genetic code and genetic illnesses tell a story that spans generations. These disorders, which result from mutations in the DNA sequence, cover a wide range of abnormalities that affect anatomical features, metabolic processes, and general health. Genetic illnesses highlight the intricacy of human heredity, from the fusing of digits in syndactyly to the multifarious challenges given by conditions like haemophilia and bipolar disorder. The interaction of environmental factors, mutations, and inheritance results in the observed clinical variation among individuals. Research and diagnostic technology advances enable us to decipher the complex nature of many diseases within this genetic tapestry, opening the door to focused interventions and individualized healthcare. We are going to take a journey that will increase our understanding of human genetics

1. Syndactyly (Greek Syn=together; Dactylos=digit)

The fusing of neighbouring digits during foetal development is known as syndactyly, a genetic disorder affecting the toes/fingers. Genetic mutations in the limb development genes of the HOX gene family cause this webbing.

One of the many forms of syndactyly exhibits X-linked recessive patterns, while the majority follow autosomal dominant inheritance. Two of them exhibit an autosomal recessive pattern.

2. Polydactyly (Poly = many, Dactylos = digits or fingers)

Polydactyly, also known as hyperdactyly is a condition in which there are extra fingers/toes in the hands or feet of an individual. It may result from impaired anterior-posterior patterning of the developing limb. It is inherited as an autosomal dominant character.

Many well-known personalities (like Hrithik Roshan, an Indian film actor) have this genetic condition.

3. Distichiasis (di = two, stichos = row)

The metaplastic transformation of sebaceous glands into the pilosebaceous unit results in an additional row of eyelashes growing out of meibomian gland openings. It can appear as a subsequent symptom of acquired illnesses such as cicatrizing conjunctivitis or trachoma, or it can occur congenitally as in the case of lymphedema distichiasis syndrome.

It is an autosomal dominant disorder, caused by truncating mutations (missense, frameshift, and nonsense) in the Forkhead family gene FOXC2.

4. Heterochromia (hetero = different, chroma = colour)

Heterochromia or heterochromia iridum is a condition in which the colour of the eyes is different. It is due to the differential pigmentation of the iris which provides colour to the eye. It may be complete (both eyes are of different colours) or partial (part of the iris is of different colour than the rest). Olivia Wild American actress and filmmaker has partial heterochromia.

Congenital heterochromia can be inherited in an autosomal dominant pattern. Two genes EYCL1 (gey gene) and EYCL3 (bey2 gene) largely determine the iris (eye) colour.

5. Porphyria variegate

It is a metabolic disorder of the heme biosynthetic pathway. The deficiency of the protoporphyrinogen oxidase (PPOX) enzyme causes this disease.

It is inherited as an autosomal dominant disorder with low penetrance. The symptoms of this disease include constipation, abdominal pain, tachycardia, hypertension, muscle cramps, photosensitivity, and cutaneous blistering. King George III the king of Great Britain and Ireland from 1760 to 1820 had suffered from this disease.

6. Marfan syndrome

The 16th president of America Abraham Lincoln had this disease. It is an autosomal dominant disorder of the connective tissues. The gene FBN1 is located on chromosome number 15 which produces a connective tissue protein fibrillin. It is characterized by disturbances in three major systems: the ocular, skeletal, and cardiovascular.

Individuals having this disorder have a thin, tall build; long arms, legs and fingers; mitral valve prolapse; enlargement of a few bones etc.

7. Hemophilia

One of the most well-known people in British history, Queen Victoria, had hemophilia. Since there was no prior indication of hemophilia in Queen Victoria’s lineage, the mutation that causes hemophilia is thought to have emerged in her germ line. This mutation led to the significant occurrence of haemophilia in her offspring, a genetic condition affecting blood coagulation.

In this disorder, the blood clotting is delayed. It is of several types each caused by the deficiency of blood clotting factors. The most common are haemophilia A and haemophilia B or Christmas disease (less common as compared to A), caused by the deficiency of clotting factors VIII and IX respectively. It is inherited as an X-linked, recessive disorder. It can be treated by injecting the missing blood clotting factor (Replacement therapy).

8. Ehlers-Danlos syndrome (EDS)

It is an autosomal dominant disorder characterized by atrophic scarring (scar that appears flat, thin, and depressed), increased skin extensibility, enhanced joint flexibility etc. It is a disease characterized by malformed collagen fibres formation. It arises due to mutation in the COL gene family. Malformation of different collagen fibres gives rise to a different kind of EDS. There are six types identified. These are: classical, vascular, hypermobile, arthrochalasis, kyphoscoliotic, and dermatosparaxis

The violin maestro of Genoa, Nicolo Paganini (1782–1840) had this disorder.

9. Bipolar (affective) disorder

It is a Manic-depressive illness characterized by chronically occurring episodes of mania or hypomania alternating with depression. The phenomenon appears to result from a confluence of environmental, neurochemical, genetic, and epigenetic factors. It is an autosomal-linked disease with high heritability.

One of the finest Impressionist painters that ever lived Vincent van Gogh had this disorder.

10. Sickle cell disease (SCD)

In 1910, Dr. James Herrick published the first report on sickle-shaped red blood cells in a blood sample from a 20-year-old Grenadan student. Linus Pauling, in 1949, revealed distinct electrical properties of haemoglobin in sickle cell disease (SCD). Neel and Beet documented inheritance patterns in the same year. In 1956, Ingram Vernon used fingerprinting to identify valine replacing glutamine.

Sickle cell anaemia results from the replacement of glutamine with valine in the 6th amino acid of Hb β-chain. It follows an autosomal codominant inheritance, producing both normal and abnormal β-chains in a heterozygous individual with a normal and an abnormal Hb β-gene.

Symptoms range from chronic fatigue, jaundice, and painful crises caused by obstructed blood flow by sickle-shaped cells. Additional symptoms include breathlessness, susceptibility to infections, and organ-related complications in the kidneys and spleen.

References:

You Can join us on telegram for updates and quizzes.  Join Telegram group

“Thank you for using our online study materials. We are a self-sustained group of individuals dedicated to creating quality educational resources for students worldwide. However, we rely on your donations to continue our work. If you have found our materials useful, please consider making a contribution to help support our mission. Your support will allow us to continue providing valuable resources to students in need. To donate, please click the DONATE HERE button. Thank you for your support!”

Leave a Comment

Your email address will not be published. Required fields are marked *