Chediak-Higashi syndrome 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.

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.

Duchenne muscular dystrophy has an X-linked recessive pattern of inheritance. Since the first son is affected by the disease, it means that the mother is a carrier. The male children will inherit the Y chromosome from their father and the X chromosome from their mother, having 50% chances of inheriting the X chromosome with the affected gene.

Types of DNA mutations and their impactpoint mutation:Substitution: One base is incorrectly added during replication and replaces the pair in the corresponding position on the complementary strand as in Sickle cell anaemiaInsertion: One or more extra nucleotides are inserted into replicating DNA, often resulting in a frameshift as in one form of beta-thalassemiaDeletion: One or more nucleotides is skipped during replication or otherwise excised, often resulting in a frameshift as in Cystic fibrosis.Chromosomal mutation:Inversion: One region of a chromosome is flipped and reinserted as in Opitz-Kaveggia syndromeDeletion: A region of a chromosome is lost, resulting in the absence of all the genes in that area as in Cri du chat syndromeDuplication: A region of a chromosome is repeated, resulting in an increase in dosage from the genes in that region as in some cancers and Charcot-Marie toothTranslocation: A region from one chromosome is aberrantly attached to another chromosome as in One form of leukaemiaCopy number variation:Gene amplification: The number of tandem copies of a locus is increased as in Some breast cancersExpanding trinucleotide repeat: The normal number of repeated trinucleotide sequences is expanded as in Fragile X syndrome, Huntington’s disease

Rett syndrome is a disorder that affects the brain and occurs most commonly in girls. It presents with a period of normal development followed by severe problems with language and communication, learning, coordination, and other brain functions.

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).

Neurofibromatosis Type 1 (also known as von Recklinghausen disease) does not present with cataracts.The eye findings in NF1 are Lisch’s nodules, which are pigmentary lesions seen on the iris and constitute one of the major diagnostic features in this condition. Note:Interestingly, in another syndrome closely related to it, Neurofibromatosis type 2 (NF-2), cataracts can occur. Early detection in family members may be made by finding lens opacities (both congenital polar cataracts and posterior lenticular opacities). Other options:- Incontinentia pigmenti is an X-linked dominant disorder with pigmentary skin changes, mental retardation and eye involvement in 40% of cases. – Myotonic dystrophy is a triplet-repeat disorder with neurological symptoms and cataracts. – Lowe syndrome (oculo-cerebro-renal syndrome) is an X-linked recessive condition. Males with this X-linked recessive condition have cataracts, hypotonia, mental retardation, generalised aminoaciduria and renal tubular acidosis with hypophosphatemia. – Wilson disease is an inborn error of copper metabolism. The clinical features include hepatic involvement, progressive neurological features, eye involvement, including Kayser-Fleischer rings and cataracts.

Prader-Willi Syndrome is a genetic disorder that occurs when a chromosome from paternal chromosome 15q is deleted or unexpressed during the formation of the egg or sperm, or in embryonic development. Individuals usually inherit one copy of this gene from each parent, and in this case on the paternal gene remains active in parts of the brain and other organs. This phenomenon is known as genetic imprinting, and is also seen in Angelman’s syndrome. Symptoms seen in Prader-Willi range from poor muscle tone during infancy to developmental and cognitive delays. Many individuals suffer from hypogonadism that affects fertility in both males and females. In Angelman’s syndrome the maternal chromosome 15q is unexpressed. The condition is also called happy puppet syndrome as affected children present with a happy demeanour, ataxic gait, and flapping movements of the limbs.

The autosomal dominant pattern of inheritance involves the presence of at least one of the defected copies of the gene in an individual to develop a specific diseased condition. Examples of this mode of inheritance include myotonic dystrophy, neurofibromatosis, achondroplasia, etc. Still’s disease, also called juvenile idiopathic arthritis, is not a heritable disease. Tay-Sachs disease is an autosomal recessive disease., while spinocerebellar ataxia and Friedreich’s ataxia are caused by trinucleotide repeat expansion.

Cystic fibrosis is an autosomal recessive inherited disorder that affects the lungs or the pancreas. In the case of an affected child whose parents do not have the disorder but carry one copy of the mutated gene, each sibling has a 50% chance of being a carrier of the disease. They can inherit one copy of the gene from each parent. There is a 25 % chance that the child may inherit both mutated genes and be homozygous for the trait.

Advancing paternal age has been linked with lower quality sperm leading to a reduction in overall fertility and an increase in the occurrence of various medical disorders in the fetus. Advanced paternal age has been implicated as a risk factor for diseases like retinoblastoma, achondroplasia, autism spectrum disorders, schizophrenia, and acute lymphoblastic leukaemia. Down’s syndrome is mostly considered a consequence of advanced maternal age, but advanced paternal age has also been implicated as a risk factor.

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.

The most probable diagnosis in this patient is Noonan syndrome.Noonan syndrome is an autosomal dominant condition characterised by short stature, heart defects (mainly pulmonary stenosis) and learning difficulties. An affected foetus can present with a significant increase in the nuchal thickness or a cystic hygroma of the neck. The condition is variable, and an affected parent is often only diagnosed after the diagnosis in the child.

Based on the clinical scenario provided, the most probable diagnosis for this patient would be tuberous sclerosis which is an autosomal dominant condition.Among the options provided, only Neurofibromatosis Type 1 is inherited by an autosomal dominant pattern. Other options:- Beckwith-Wiedemann syndrome is an example of an imprinting disorder and results from abnormalities of inheritance or methylation of chromosome 11p15.- Cystic fibrosis is an autosomal recessive condition.- Duchenne Muscular Dystrophy is an example of an X-linked recessive condition.- Hypophosphataemic (Vitamin D resistant) rickets is an X-linked dominant condition.

The correct answer is triple X syndrome with a genotype of XXX and an almost normal female phenotype. The extra X chromosome is inactive. The final phenotype of an individual is determined after normal sexual and gonadal differentiation, a process that involves several genes located on chromosomes X and Y. Disorders of sexual differentiation result in cases of ambiguous genitalia and are caused by a number of genetic abnormalities. Among these disorders is the turner syndrome with a genotype of 45X0, characterized by gonadal dysgenesis and ovarian failure. DAX-1 gene mutation leads to congenital adrenal hypoplasia and hypogonadotropic hypogonadism, which results in virilization of female external genitalia. Campomelic dysplasia results from mutation of the SOX-9 gene, leading to 46XY sex reversal. Danys-Drash syndrome is characterized by disordered sexual development in affected males due to the mutated WT-1 gene, which also causes Wilm’s tumour.

Cystic fibrosis has an autosomal recessive pattern of inheritance, meaning that a person might be a carrier of the disease without developing it. If the unaffected partner is a carrier, then there is a 50% chance of inheritance and a 50% chance of having a child who is a carrier. However, if the partner is not a carrier, the offspring will not develop the disease but the possibility of being a carrier raises up to 100%.

Haemophilia A has an X-linked recessive pattern of inheritance, meaning that is a 50% chance of having a son with haemophilia and 50% chance of the daughters being carriers of the haemophilia gene.

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 x 1/25 = 2/75) x 1/4 = 1/150.

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.

These cardiovascular findings are suggestive of coarctation of the aorta, which is common among patients with Turner’s syndrome. Physical features of Turner’s syndrome include a short neck with a webbed appearance, a low hairline at the back of the head, low-set ears, and narrow fingernails and toenails that are turned upward.Atrioventricular septal defect is the most common cardiac anomaly in Down’s syndrome. Structural heart defects at birth (i.e., ventricular septal defect, atrial septal defect, patent ductus arteriosus) are common in Edward’s syndrome. Pulmonary stenosis with or without dysplastic pulmonary valve and hypertrophic cardiomyopathy are common in Noonan’s syndrome. Supravalvar aortic stenosis and peripheral pulmonary stenosis are found in William’s syndrome.

Ehlers-Danlos Syndrome (EDS) is a group of genetic connective tissue disorders with over 13 clinical subtypes. Hyper-mobility is common to many of these subtypes. Vascular EDS is identified by thin, translucent skin prone to easy bleeding, as well as the risk of early arterial rupture, gastrointestinal perforation and uterine rupture. Those affected have dysmorphic features including a thin nose and lips, sunken cheeks and large eyes. The other features including; atrophic scars, a dominant family history, hyper extensible skin and kyphoscoliosis are not specific to vascular EDS and overlap in many of the subtypes.

Neurofibromatosis type 2, also known as schwannomin, is an autosomal dominant genetic disease caused by mutation of the merlin gene located on chromosome 22. Merlin is a tumour suppressor protein, which is responsible for controlling cell shape, growth and adhesion, and is predominantly found in nervous tissue. Its mutation increases the risk of tumour development especially bilateral vestibular schwannomas, the hallmark of neurofibromatosis 2.

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).

Hereditary diseases follow specific inheritance patterns according to the type of gene involved. Mutations in the genes which are on the sex chromosome, chromosome X are called X-linked diseases. X-linked recessive conditions result when both the copies of X-chromosomes are defective, which happens in the case of females since males have only one X- chromosome. Thus, these conditions are more common among males, and examples include colour blindness, haemophilia, Lesch-Nyhan syndrome, and hunter’s syndrome, etc. Hunter’s syndrome is a type of lysosomal storage disease which is also known as mucopolysaccharidosis II. Vitamin D resistant rickets is a X-linked dominant disease. Neurofibromatosis type 1 and 2 are autosomal dominant conditions while Wilson’s disease is autosomal recessive.

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

Haemophilia is a X-linked recessive disorder. In X-linked recessive inheritance only males are affected. An exception to this seen in examinations are patients with Turner’s syndrome, who are affected due to only having one X chromosome. X-linked recessive disorders are transmitted by heterozygote females (carriers) and male-to-male transmission is not seen. Affected males can only have unaffected sons and carrier daughters.

Tuberous sclerosis, an autosomal dominant disorder, may present with a variety of symptoms, including seizures, developmental delay, behavioural problems, skin abnormalities, and lung and kidney disease. Hamartomas are often associated.

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

Individuals with Down syndrome are at increased risk for a variety of eye and vision disorders. Fortunately, many of these eye problems can be treated, especially if discovered at an early age. The quality of life can be further enhanced by the proper assessment and correction of eye problems. The most common eye findings include:- Refractive errors – Children with Down syndrome are more likely to need glasses than are other children. This may be due to myopia (near-sightedness), hyperopia (far-sightedness), and/or astigmatism. Refractive error may develop early in life or later on.- Strabismus – Between 20% and 60% of individuals with Down syndrome have eyes that are misaligned (strabismus). Esotropia (eyes that drift in) is most common while exotropia(eyes that drift out) occurs less frequently. Strabismus may be treated with glasses, patching and/or eye muscle surgery.- Keratoconus – A cone shaped distortion of the cornea (front layer of the eye), occurs in up to 30% of those with Down syndrome. Keratoconus is usually diagnosed around puberty and should be monitored regularly. Blurred vision, corneal thinning, or corneal haze may result from keratoconus. Keratoconus is worsened by eye rubbing; therefore, eye rubbing should be discouraged.- Cataracts – There is an increased incidence of congenital cataracts (present at birth) as well as acquired cataracts (develop later). Cataracts may progress slowly and should be monitored regularly, with surgical treatment performed when appropriate.- Glaucoma- There is an increased risk of infantile glaucoma (elevated pressure within the eye).- Blepharitis – Inflammation of the eyelids with redness at the edge of the lids and crusting around the lashes may occur and cause a feeling of dryness or burning. Treatment is with eyelid hygiene and topical antibiotics.- Tearing – Excessive tears or watering of the eyes may occur because the drainage channels are blocked or narrow (nasolacrimal duct obstruction). This may require surgical intervention.- Nystagmus – This is an involuntary back-and-forthť movement or shaking of the eyes. It can affect vision to a mild or severe degree.

The property described in the question is heterogeneity.Heterogeneity is when a single phenotype or genetic disorder can be caused by multiple numbers of genetic mutations.Other options:- Pleiotropy occurs when a single gene influences multiple phenotypic traits. The underlying mechanism is that the gene codes for a product that is used by various cells. A classic example of pleiotropy is the human disease PKU (phenylketonuria).- The penetrance of a disease-causing mutation is the proportion of individuals with the mutation who exhibit clinical symptoms. For example, the gene responsible for a particular autosomal dominant disorder has 70% penetrance, then 70% of those with the mutation will develop the disease, while 30% will not.