Genetics Reference

High-yield reference for genetic disorders and inheritance patterns.

Huntington Disease

Autosomal Dominant
Gene Mutation

HTT (CAG trinucleotide repeat)

Chromosome

4p16.3

Clinical Features

  • Chorea (involuntary movements)
  • Athetosis
  • Progressive dementia and behavioral changes
  • Anticipation (earlier onset in subsequent generations)
  • Caudate nucleus atrophy

Marfan Syndrome

Autosomal Dominant
Gene Mutation

FBN1 (Fibrillin-1)

Chromosome

15q21.1

Clinical Features

  • Tall stature with long extremities (arachnodactyly)
  • Pectus excavatum or carinatum
  • Ectopia lentis (upward and outward subluxation)
  • Aortic root dilation, risk of dissection
  • Mitral valve prolapse

Neurofibromatosis Type 1 (von Recklinghausen)

Autosomal Dominant
Gene Mutation

NF1 (Neurofibromin, a tumor suppressor)

Chromosome

17q11.2

Clinical Features

  • Café-au-lait spots (≥6)
  • Cutaneous neurofibromas
  • Lisch nodules (pigmented iris hamartomas)
  • Optic gliomas
  • Freckling in axillary or inguinal regions

Neurofibromatosis Type 2

Autosomal Dominant
Gene Mutation

NF2 (Merlin)

Chromosome

22q12.2

Clinical Features

  • Bilateral vestibular schwannomas (acoustic neuromas)
  • Meningiomas
  • Ependymomas
  • Juvenile cataracts

Achondroplasia

Autosomal Dominant
Gene Mutation

FGFR3 (Gain of function)

Chromosome

4p16.3

Clinical Features

  • Most common cause of dwarfism
  • Short limbs (rhizomelic shortening) with normal torso
  • Macrocephaly with frontal bossing
  • Midface hypoplasia
  • 80% occur as sporadic new mutations (associated with advanced paternal age)

Familial Hypercholesterolemia (Type IIa)

Autosomal Dominant
Gene Mutation

LDLR (LDL receptor defect)

Chromosome

19p13.2

Clinical Features

  • Severely elevated LDL cholesterol
  • Tendon xanthomas (especially Achilles)
  • Corneal arcus before age 45
  • Premature atherosclerosis and myocardial infarction

Osteogenesis Imperfecta

Autosomal Dominant
Gene Mutation

COL1A1 or COL1A2 (Type I collagen defect)

Chromosome

17q21.33 / 7q21.3

Clinical Features

  • Multiple frequent bone fractures
  • Blue sclerae
  • Hearing loss (ossicle fracture/fixation)
  • Dental imperfections (dentinogenesis imperfecta)

Cystic Fibrosis

Autosomal Recessive
Gene Mutation

CFTR (ΔF508 most common)

Chromosome

7q31.2

Clinical Features

  • Thick, sticky mucus production
  • Recurrent pulmonary infections (Pseudomonas, S. aureus)
  • Pancreatic insufficiency and malabsorption
  • Meconium ileus in newborns
  • Infertility in males (absence of vas deferens)

Sickle Cell Anemia

Autosomal Recessive
Gene Mutation

HBB (Glutamic acid to Valine substitution)

Chromosome

11p15.4

Clinical Features

  • Vaso-occlusive crises (painful crises, dactylitis)
  • Hemolytic anemia
  • Splenic sequestration and autosplenectomy
  • Increased risk of encapsulated bacterial infections
  • Acute chest syndrome

Phenylketonuria (PKU)

Autosomal Recessive
Gene Mutation

PAH (Phenylalanine hydroxylase deficiency)

Chromosome

12q23.2

Clinical Features

  • Intellectual disability (if untreated)
  • Musty body odor
  • Fair skin and hair (decreased melanin)
  • Seizures
  • Requires phenylalanine-restricted diet

Tay-Sachs Disease

Autosomal Recessive
Gene Mutation

HEXA (Hexosaminidase A deficiency)

Chromosome

15q23

Clinical Features

  • Progressive neurodegeneration
  • Cherry-red spot on macula
  • Lysosomes with onion skin appearance
  • No hepatosplenomegaly (unlike Niemann-Pick)
  • Exaggerated startle response

Niemann-Pick Disease (Type A/B)

Autosomal Recessive
Gene Mutation

SMPD1 (Sphingomyelinase deficiency)

Chromosome

11p15.4

Clinical Features

  • Progressive neurodegeneration
  • Cherry-red spot on macula
  • Hepatosplenomegaly
  • Foam cells (lipid-laden macrophages)

Gaucher Disease

Autosomal Recessive
Gene Mutation

GBA (Glucocerebrosidase deficiency)

Chromosome

1q22

Clinical Features

  • Most common lysosomal storage disease
  • Hepatosplenomegaly
  • Pancytopenia
  • Osteoporosis and bone crises (Erlenmeyer flask deformity)
  • Gaucher cells (lipid-laden macrophages resembling crumpled tissue paper)

Wilson Disease

Autosomal Recessive
Gene Mutation

ATP7B (Copper transport defect)

Chromosome

13q14.3

Clinical Features

  • Copper accumulation in liver (cirrhosis)
  • Copper accumulation in brain (parkinsonism, psychiatric symptoms)
  • Kayser-Fleischer rings in the cornea
  • Decreased serum ceruloplasmin

Hemophilia A

X-linked Recessive
Gene Mutation

F8 (Factor VIII deficiency)

Chromosome

Xq28

Clinical Features

  • Hemarthrosis (bleeding into joints)
  • Prolonged PTT, normal PT/Bleeding time
  • Easy bruising and bleeding
  • Primarily affects males

Hemophilia B (Christmas Disease)

X-linked Recessive
Gene Mutation

F9 (Factor IX deficiency)

Chromosome

Xq27.1

Clinical Features

  • Clinically indistinguishable from Hemophilia A
  • Hemarthrosis, prolonged PTT
  • Treated with Factor IX replacement

Duchenne Muscular Dystrophy

X-linked Recessive
Gene Mutation

DMD (Frameshift mutation, truncated dystrophin)

Chromosome

Xp21.2

Clinical Features

  • Progressive myofiber damage
  • Weakness begins in pelvic girdle and ascends
  • Pseudohypertrophy of calf muscles
  • Gowers sign
  • Dilated cardiomyopathy is common cause of death

Lesch-Nyhan Syndrome

X-linked Recessive
Gene Mutation

HPRT1 (HGPRT deficiency)

Chromosome

Xq26.2

Clinical Features

  • Defective purine salvage pathway (excess uric acid)
  • Hyperuricemia and gout
  • Self-mutilation (biting lips/fingers)
  • Intellectual disability
  • Choreoathetosis

Fragile X Syndrome

X-linked Dominant
Gene Mutation

FMR1 (CGG trinucleotide repeat)

Chromosome

Xq27.3

Clinical Features

  • Most common inherited cause of intellectual disability
  • Long face with large jaw and large everted ears
  • Macroorchidism (large testes)
  • Autism spectrum behaviors
  • Mitral valve prolapse

Down Syndrome (Trisomy 21)

Chromosomal
Gene Mutation

N/A

Chromosome

21 (Three copies)

Clinical Features

  • Intellectual disability
  • Flat facial profile, prominent epicanthal folds
  • Single palmar crease
  • Congenital heart defects (Atrioventricular septal defect)
  • Increased risk of early-onset Alzheimer's and ALL/AML

Edwards Syndrome (Trisomy 18)

Chromosomal
Gene Mutation

N/A

Chromosome

18 (Three copies)

Clinical Features

  • Severe intellectual disability
  • Rocker-bottom feet
  • Micrognathia (small jaw)
  • Clenched hands with overlapping fingers
  • Prominent occiput
  • High mortality within first year

Patau Syndrome (Trisomy 13)

Chromosomal
Gene Mutation

N/A

Chromosome

13 (Three copies)

Clinical Features

  • Severe intellectual disability
  • Microphthalmia (small eyes)
  • Cleft lip and palate
  • Holoprosencephaly
  • Polydactyly
  • High mortality within first year

Turner Syndrome

Chromosomal
Gene Mutation

N/A

Chromosome

45, X

Clinical Features

  • Short stature
  • Webbed neck (cystic hygroma)
  • Streak ovaries (primary amenorrhea, premature ovarian failure)
  • Bicuspid aortic valve and coarctation of the aorta
  • Normal intelligence

Klinefelter Syndrome

Chromosomal
Gene Mutation

N/A

Chromosome

47, XXY

Clinical Features

  • Tall stature with disproportionately long limbs
  • Testicular atrophy and infertility
  • Gynecomastia
  • Female hair distribution
  • Presence of inactivated X chromosome (Barr body)

Cri-du-chat Syndrome

Chromosomal
Gene Mutation

N/A

Chromosome

5p- (Microdeletion of short arm of chromosome 5)

Clinical Features

  • High-pitched crying/meowing
  • Microcephaly
  • Severe intellectual disability
  • Epicanthal folds
  • Cardiac abnormalities (VSD)

DiGeorge Syndrome (22q11.2 Deletion)

Chromosomal
Gene Mutation

N/A

Chromosome

22q11.2 (Microdeletion)

Clinical Features

  • Cleft palate
  • Abnormal facies
  • Thymic aplasia (T-cell deficiency)
  • Cardiac defects (Tetralogy of Fallot, truncus arteriosus)
  • Hypocalcemia (parathyroid aplasia)

Alkaptonuria

Autosomal Recessive
Gene Mutation

HGD

Chromosome

3q13.33

Clinical Features

  • Urine turns black on standing
  • Ochronosis (dark connective tissue)
  • Severe early-onset osteoarthritis

Homocystinuria

Autosomal Recessive
Gene Mutation

CBS

Chromosome

21q22.3

Clinical Features

  • Marfanoid habitus
  • Downward lens subluxation
  • Hypercoagulability and thrombosis
  • Intellectual disability

Maple Syrup Urine Disease

Autosomal Recessive
Gene Mutation

BCKDHA/B

Chromosome

19q13.2

Clinical Features

  • Urine smells like maple syrup
  • Severe CNS defects
  • Vomiting and lethargy in infants
  • Blocked degradation of branched amino acids (I, L, V)

Galactosemia

Autosomal Recessive
Gene Mutation

GALT

Chromosome

9p13.3

Clinical Features

  • Infantile cataracts
  • Failure to thrive
  • Jaundice, hepatomegaly
  • E. coli sepsis

Von Gierke Disease (Type I)

Autosomal Recessive
Gene Mutation

G6PC

Chromosome

17q21.31

Clinical Features

  • Severe fasting hypoglycemia
  • Massive hepatomegaly
  • Increased blood lactate
  • Gout

Pompe Disease (Type II)

Autosomal Recessive
Gene Mutation

GAA

Chromosome

17q25.3

Clinical Features

  • Cardiomegaly
  • Hypertrophic cardiomyopathy
  • Exercise intolerance
  • Early death

Cori Disease (Type III)

Autosomal Recessive
Gene Mutation

AGL

Chromosome

1p21.2

Clinical Features

  • Milder form of Von Gierke
  • Normal blood lactate levels
  • Accumulation of limit dextrin-like structures in cytosol

McArdle Disease (Type V)

Autosomal Recessive
Gene Mutation

PYGM

Chromosome

11q13.1

Clinical Features

  • Muscle cramps during exercise
  • Myoglobinuria (red urine) after exercise
  • Second wind phenomenon
  • Normal life expectancy

Fabry Disease

X-linked Recessive
Gene Mutation

GLA

Chromosome

Xq22.1

Clinical Features

  • Episodic peripheral neuropathy
  • Angiokeratomas
  • Hypohidrosis
  • Progressive renal failure
  • Cardiovascular disease

Krabbe Disease

Autosomal Recessive
Gene Mutation

GALC

Chromosome

14q31.3

Clinical Features

  • Peripheral neuropathy
  • Developmental delay
  • Optic atrophy
  • Globoid cells

Metachromatic Leukodystrophy

Autosomal Recessive
Gene Mutation

ARSA

Chromosome

22q13.33

Clinical Features

  • Central and peripheral demyelination
  • Ataxia
  • Dementia

Hurler Syndrome

Autosomal Recessive
Gene Mutation

IDUA

Chromosome

4p16.3

Clinical Features

  • Developmental delay
  • Gargoylism
  • Airway obstruction
  • Corneal clouding
  • Hepatosplenomegaly

Hunter Syndrome

X-linked Recessive
Gene Mutation

IDS

Chromosome

Xq28

Clinical Features

  • Mild Hurler + aggressive behavior
  • No corneal clouding

Friedreich Ataxia

Autosomal Recessive
Gene Mutation

FXN (GAA repeat)

Chromosome

9q21.11

Clinical Features

  • Staggering gait
  • Frequent falling
  • Nystagmus
  • Pes cavus, hammer toes
  • Hypertrophic cardiomyopathy

Myotonic Dystrophy Type 1

Autosomal Dominant
Gene Mutation

DMPK (CTG repeat)

Chromosome

19q13.32

Clinical Features

  • Myotonia (delayed muscle relaxation)
  • Muscle wasting
  • Cataracts
  • Testicular atrophy
  • Frontal balding
  • Arrhythmias

Prader-Willi Syndrome

Chromosomal
Gene Mutation

Imprinting defect (Maternal uniparental disomy)

Chromosome

15q11-q13

Clinical Features

  • Hyperphagia
  • Obesity
  • Intellectual disability
  • Hypogonadism
  • Hypotonia

Angelman Syndrome

Chromosomal
Gene Mutation

UBE3A (Paternal uniparental disomy)

Chromosome

15q11-q13

Clinical Features

  • Inappropriate laughter (happy puppet)
  • Seizures
  • Ataxia
  • Severe intellectual disability

Williams Syndrome

Chromosomal
Gene Mutation

Microdeletion

Chromosome

7q11.23

Clinical Features

  • Elfin facies
  • Extreme friendliness with strangers
  • Hypercalcemia (increased sensitivity to vitamin D)
  • Supravalvular aortic stenosis

Wiskott-Aldrich Syndrome

X-linked Recessive
Gene Mutation

WAS

Chromosome

Xp11.23

Clinical Features

  • WATER: Wiskott-Aldrich, Thrombocytopenia, Eczema, Recurrent infections
  • Increased risk of autoimmune disease and malignancy

Bruton Agammaglobulinemia

X-linked Recessive
Gene Mutation

BTK

Chromosome

Xq22.1

Clinical Features

  • Recurrent bacterial and enteroviral infections after 6 months
  • Absent B cells in peripheral blood
  • Decreased Ig of all classes
  • Absent/scanty lymph nodes and tonsils

Severe Combined Immunodeficiency (SCID)

Autosomal Recessive
Gene Mutation

IL2RG or ADA

Chromosome

Xq13.1 / 20q13.12

Clinical Features

  • Failure to thrive
  • Chronic diarrhea
  • Thrush
  • Recurrent viral, bacterial, fungal, and protozoal infections
  • Absence of thymic shadow

Ataxia-Telangiectasia

Autosomal Recessive
Gene Mutation

ATM

Chromosome

11q22.3

Clinical Features

  • Cerebellar ataxia
  • Telangiectasias (spider angiomas)
  • IgA deficiency
  • Increased risk of lymphoma and leukemia

Chediak-Higashi Syndrome

Autosomal Recessive
Gene Mutation

LYST

Chromosome

1q42.3

Clinical Features

  • Progressive neurodegeneration
  • Oculocutaneous albinism
  • Recurrent pyogenic infections
  • Peripheral neuropathy
  • Giant granules in granulocytes

Chronic Granulomatous Disease

X-linked Recessive
Gene Mutation

CYBB

Chromosome

Xp21.1

Clinical Features

  • Defect in NADPH oxidase
  • Increased susceptibility to catalase-positive organisms (S. aureus, Aspergillus, Nocardia, Serratia)

Familial Adenomatous Polyposis (FAP)

Autosomal Dominant
Gene Mutation

APC

Chromosome

5q22.2

Clinical Features

  • Thousands of colonic polyps arise after puberty
  • 100% progress to colorectal cancer unless colon is resected
  • Always involves the rectum

Lynch Syndrome (HNPCC)

Autosomal Dominant
Gene Mutation

MLH1, MSH2 (Mismatch repair)

Chromosome

3p22.2 / 2p21

Clinical Features

  • High risk of colorectal, endometrial, and ovarian cancer
  • Colorectal cancer arises de novo (not from polyps) at an early age

Li-Fraumeni Syndrome

Autosomal Dominant
Gene Mutation

TP53

Chromosome

17p13.1

Clinical Features

  • Multiple malignancies at an early age
  • SBLA syndrome: Sarcoma, Breast, Leukemia, Adrenal gland

Multiple Endocrine Neoplasia Type 1 (MEN 1)

Autosomal Dominant
Gene Mutation

MEN1

Chromosome

11q13

Clinical Features

  • 3 Ps: Pituitary tumors, Parathyroid adenomas, Pancreatic endocrine tumors (e.g., Zollinger-Ellison)

Multiple Endocrine Neoplasia Type 2A (MEN 2A)

Autosomal Dominant
Gene Mutation

RET

Chromosome

10q11.21

Clinical Features

  • Parathyroid hyperplasia
  • Medullary thyroid carcinoma
  • Pheochromocytoma

Multiple Endocrine Neoplasia Type 2B (MEN 2B)

Autosomal Dominant
Gene Mutation

RET

Chromosome

10q11.21

Clinical Features

  • Medullary thyroid carcinoma
  • Pheochromocytoma
  • Mucosal neuromas (oral/intestinal ganglioneuromatosis)
  • Marfanoid habitus

Peutz-Jeghers Syndrome

Autosomal Dominant
Gene Mutation

STK11

Chromosome

19p13.3

Clinical Features

  • Multiple hamartomatous polyps in GI tract
  • Hyperpigmented macules on lips, oral mucosa, and genitalia
  • Increased risk of breast and GI cancers

Tuberous Sclerosis

Autosomal Dominant
Gene Mutation

TSC1 / TSC2

Chromosome

9q34 / 16p13.3

Clinical Features

  • Hamartomas in CNS and skin
  • Angiofibromas
  • Mitral regurgitation
  • Ash-leaf spots
  • Cardiac rhabdomyoma
  • Autosomal dominant
  • Intellectual disability
  • Renal angiomyolipoma
  • Seizures

Von Hippel-Lindau Disease

Autosomal Dominant
Gene Mutation

VHL

Chromosome

3p25.3

Clinical Features

  • Hemangioblastomas (retina, brain stem, cerebellum, spine)
  • Angiomatosis
  • Bilateral renal cell carcinomas
  • Pheochromocytomas

Polycystic Kidney Disease (ADPKD)

Autosomal Dominant
Gene Mutation

PKD1 / PKD2

Chromosome

16p13.3 / 4q22.1

Clinical Features

  • Bilateral massive enlargement of kidneys due to multiple large cysts
  • Flank pain, hematuria, hypertension
  • Associated with berry aneurysms and mitral valve prolapse

Hereditary Spherocytosis

Autosomal Dominant
Gene Mutation

SPTA1, SPTB, ANK1

Chromosome

Multiple

Clinical Features

  • Defect in RBC cytoskeleton-membrane tethering proteins
  • Extravascular hemolysis in spleen
  • Splenomegaly, jaundice
  • Increased mean corpuscular hemoglobin concentration (MCHC)

Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency

X-linked Recessive
Gene Mutation

G6PD

Chromosome

Xq28

Clinical Features

  • Episodic hemolytic anemia following oxidative stress (e.g., sulfa drugs, antimalarials, fava beans)
  • Heinz bodies and bite cells on blood smear

Thalassemia (Alpha)

Autosomal Recessive
Gene Mutation

HBA1 / HBA2

Chromosome

16p13.3

Clinical Features

  • Microcytic, hypochromic anemia
  • Target cells
  • Hb Barts (hydrops fetalis) if all 4 alleles deleted

Thalassemia (Beta)

Autosomal Recessive
Gene Mutation

HBB

Chromosome

11p15.4

Clinical Features

  • Microcytic, hypochromic anemia
  • Target cells
  • Crew cut on skull x-ray (marrow expansion)
  • Chipmunk facies
  • Requires lifelong blood transfusions

Ehlers-Danlos Syndrome (Classical)

Autosomal Dominant
Gene Mutation

COL5A1 / COL5A2

Chromosome

Multiple

Clinical Features

  • Hyperextensible skin
  • Hypermobile joints
  • Easy bruising
  • Defective Type V collagen

Ehlers-Danlos Syndrome (Vascular)

Autosomal Dominant
Gene Mutation

COL3A1

Chromosome

2q32.2

Clinical Features

  • Fragile tissues
  • Prone to spontaneous rupture of arteries (e.g., aorta) and organs (e.g., intestines, uterus)
  • Defective Type III collagen