Most cases of Prader-Willi syndrome are not inherited, particularly those caused by a deletion in the paternal chromosome 15 or by maternal uniparental disomy. These genetic changes occur as random events during the formation of reproductive cells (eggs and sperm) or in early embryonic development. Affected people typically have no history of the disorder in their family.Rarely, a genetic change responsible for Prader-Willi syndrome can be inherited. For example, it is possible for a genetic change that abnormally inactivates genes on the paternal chromosome 15 to be passed from one generation to the next.Prader-Willi syndrome is a complex genetic condition that affects many parts of the body. In infancy, this condition is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. Beginning in childhood, affected individuals develop an insatiable appetite, which leads to chronic overeating (hyperphagia) and obesity. Some people with Prader-Willi syndrome, particularly those with obesity, also develop type 2 diabetes (the most common form of diabetes).

Turner syndrome (TS) is one of the most common genetic disorders| occurs with an incidence of I: 2,500 female live births. It results from complete or partial chromosome X monosomy. TS is associated with abnormalities of the X chromosome and characteristic clinical features of short stature, gonadal dysgenesis, sexual developmental deficiencies, cardiac and/or renal defects, webbed neck, low-set ears, skeletal deformities including cubitus valgus, a propensity to ear infections and hearing deficits.

CF is inherited in an autosomal recessive manner.This means that to have CF, a person must have a mutation in both copies of the CFTR gene in each cell. People with CF inherit one mutated copy of the gene from each parent, who is referred to as a carrier.CF carriers can pass their copy of the CFTR gene mutation to their children. Each time two CF carriers have a child together, the chances are: 25 percent (1 in 4) the child will have CF50 percent (1 in 2) the child will be a carrier but will not have CF25 percent (1 in 4) the child will not be a carrier of the gene and will not have CFThis male’s parents are obligate carrier because he has a sibling with CFSo the chances he is a carrier too are 2 in 3The risk of having an affected child is the chance of both himself and his partner being carriers: (2/3 × 1/25 = 2/75) × 1/4 = 1/150.

A patient with Down’s syndrome is likely to be subfertile rather than infertile.Down’s syndrome:The clinical features of Down’s syndrome include:- Face: upslanting palpebral fissures, epicanthic folds, Brushfield spots in iris, protruding tongue, small ears, and round/flat face- Flat occiput- Single palmar crease, pronounced ‘sandal gap’ in the first interdigital space of the feet.- Hypotonia- Congenital heart defects (40-50%)- Duodenal atresia- Hirschsprung’s diseaseThe cardiac complications in these patients include:- Endocardial cushion defect (40%)- Ventricular septal defect (30%)- Secundum atrial septal defect (10%)- Tetralogy of Fallot (5%)- Isolated patent ductus arteriosus (5%)The complications that occur later in the life of the patient include:- Subfertility: Males are almost always infertile due to impaired spermatogenesis. Females, however, are usually subfertile and have an increased incidence of problems with pregnancy and labour.- Learning difficulties- Short stature- Repeated respiratory infections (+hearing impairment from glue ear)- Acute lymphoblastic leukaemia- Hypothyroidism- Alzheimer’s disease- Atlantoaxial instability

Cystinosis is a condition characterized by accumulation of the amino acid cystine (a building block of proteins) within cells. This condition is inherited in an autosomal recessive pattern.Excess cystine damages cells and often forms crystals that can build up and cause problems in many organs and tissues. The kidneys and eyes are especially vulnerable to damage| the muscles, thyroid, pancreas, and testes may also be affected.There are three distinct types of cystinosis. In order of decreasing severity, they are nephropathic cystinosis, intermediate cystinosis, and non-nephropathic or ocular cystinosis.Nephropathic cystinosis begins in infancy, causing poor growth and a particular type of kidney damage (renal Fanconi syndrome) in which certain molecules that should be reabsorbed into the bloodstream are instead eliminated in the urine. The kidney problems lead to the loss of important minerals, salts, fluids, and many other nutrients. The loss of nutrients impairs growth and may result in soft, bowed bones (hypophosphatemic rickets), especially in the legs. The nutrient imbalances in the body lead to increased urination, thirst, dehydration, and abnormally acidic blood (acidosis). By about the age of 2, cystine crystals may be present in the clear covering of the eye (cornea). The build-up of these crystals in the eye causes pain and an increased sensitivity to light (photophobia). Untreated children will experience complete kidney failure by about the age of 10. Other signs and symptoms that may occur in untreated people, especially after adolescence, include muscle deterioration, blindness, inability to swallow, diabetes, thyroid and nervous system problems, and an inability to father children (infertility) in affected men.The signs and symptoms of intermediate cystinosis are the same as nephropathic cystinosis, but they occur at a later age.

Cystic fibrosis is a progressive, genetic disease. A defective gene causes a thick, sticky build-up of mucus in the lungs, pancreas, and other organs. In the lungs, the mucus clogs the airways and traps bacteria leading to infections, extensive lung damage, and eventually, respiratory failure. In the pancreas, the mucus prevents the release of digestive enzymes that allow the body to break down food and absorb vital nutrients. Since the digestive enzymes are not being made, the food is not completely digested making them bulky, smelly, and hard to flush away. Finger clubbing is a prominent feature of cystic fibrosis on most patients.

In the pattern of mendelian inheritance, X- linked dominant inheritance means that all who inherit the X chromosome will present with the condition. In the case of maternal x-linked inheritance, sons and daughters have an equal chance of inheriting the condition as there is a 50% chance of inheriting the defective X chromosome from their mother as opposed to a non affected X chromosome from their father. However, in paternal X-linked dominant inheritance, sons will be unaffected as they inherit a Y chromosome from their father while daughters are sure to inherit the defective X-chromosome.

Ataxic gait is not a direct association of Down’s syndrome. All other given responses are associated with Down’s syndrome.

DiGeorge syndrome usually presents at a young age with abnormal faces. Chest x-ray is characterised by an absent thymic shadow and recurrent infections due to an abnormal T-cell mediated immune response. Sometimes it presents by convulsions of the new-born due to hypocalcaemia as a result of a malfunctioning parathyroid gland and low levels of PTH.

Congenital hypertrophy of the retinal pigment epithelium is one of FAP’s extra-intestinal manifestations. It appears in early childhood and affects an estimated 90% of those with FAP.

Angelman Syndrome is a genetic disorder that affects the nervous system. The features of this condition include intellectual disability, a delay in developmental milestones, and movement disorders. The features occur as a result of the deletion or mutation of the maternal copy of the UBE3A gene located on Chromosome 15q. Though individuals usually inherit one copy of this gene from each parent, only the maternal gene remains active in parts of the brain. This phenomenon is known as genetic imprinting, and is also seen in Prader-Willi syndrome.

Penetrance is defined as the percentage of individuals having a particular mutation or genotype who exhibit clinical signs or phenotype of the associated disorder or genotype.Gaucher disease 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.

Neurofibromatosis is a genetic disease caused by the mutation of the neurofibromin gene on Chromosome 17. The diagnostic criteria for Neurofibromatosis type 1 are two or more of the following:-6 or more cafe au lait macules-2 or more cutaneous neurofibroma or one plexiform Neurofibroma-Axillary of groin freckling -Optic pathway glioma -2 or more Lisch nodules (hamartomas of the iris seen on slit lamp examination)-Bony dysplasia (such as sphenoid wing dysplasia, bowing of the long bones, or pseudarthrosis)-First degree relative with neurofibromatosis type 1

Tuberous sclerosis is an autosomal dominant neurocutaneous condition associated with increased psychiatric co-morbidity. It results from the mutation of TSC1 or TSC2 tumour suppressor genes. Multiple benign tumours of the brain and other vital organs are characteristic of this disease. Important findings include subependymal nodules, bone cysts, cardiac rhabdomyoma, and learning difficulties. Lisch nodules of the iris occur in neurofibromatosis.

Familial adenomatous polyposis can have different inheritance patterns.When familial adenomatous polyposis results from mutations in the APC gene, it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition.When familial adenomatous polyposis results from mutations in the MUTYH gene, it is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but do not show signs and symptoms of the condition.

Trisomy 21 (Down’s syndrome)is a genetic disorder characterized by the presence of an extra copy of chromosome 21 in all the body cells, mostly due to non-disjunction during gametogenesis. Robertsonian translocation occurs only in about 2-4% of the cases. A variety of clinical features are found in trisomy 21 due to multi-system involvement but the hallmark is hypotonia, which is present in almost all the cases of trisomy 21. Different types of leukemias are also found in association with down’s syndrome, but they are not the hallmark. Atlantoaxial subluxation is secondary to hypotonia, which induces joint and ligament laxity. Other clinical findings are hypothyroidism, Alzheimer’s disease, Hirschsprung’s disease, and pulmonary hypertension.

The combination of cholestasis, congenital heart disease (mainly affecting the pulmonary vasculature) and anterior-segment abnormalities (primarily posterior embryotoxon) suggests a diagnosis of Alagille syndrome. Clinical features:The facial features are characteristic and include a prominent forehead, deep-set eyes and a pointed chin. The most common skeletal manifestation is butterfly vertebrae, a clefting abnormality of the vertebrae most often seen in the thoracic spine and described in up to 87% of cases. Radio-ulnar synostosis and short phalanges have also been described in Alagille but less frequently. Note: Pectus excavatum is a feature of Noonan syndrome, one of the differential diagnoses of pulmonary valve disease.

Familial/inherited short stature is the most likely and commonest factor resulting in short stature among the children. Klinefelter syndrome is characterised by tall stature, widely spaces nipples and infertility. Other factors include congenital heart disease, maternal deprivation and diabetes mellitus but these are the rare causes.

The trisomy 18 syndrome, also known as Edwards syndrome, is a common chromosomal disorder due to the presence of an extra chromosome 18, either full, mosaic trisomy, or partial trisomy 18q. The condition is the second most common autosomal trisomy syndrome after trisomy 21.Currently, most cases of trisomy 18 are prenatally diagnosed, based on screening by maternal age, maternal serum marker screening, or detection of sonographic abnormalities (e.g., increased nuchal translucency thickness, growth retardation, choroid plexus cyst, overlapping of fingers, and congenital heart defects ).The main clinical features represent the clues for the diagnosis in the perinatal period and include prenatal growth deficiency, characteristic craniofacial features (dolichocephaly, short palpebral fissures, micrognathia external anomalies of the ears, and redundant skin at the back of the neck), distinctive hand posture (overriding fingers: index finger overlapping the third and 5th finger overlapping the 4th), nail hypoplasia, short hallux, underdeveloped thumbs, short sternum, and club feet and major malformations (particularly involving the heart).

Although initially thought to affect only boys, girls with DMD also have an estimated 10% chance of inheriting the condition. In girls, DMD may present with all or some clinical manifestations.