CLINICAL MANIFESTATIONS OF GENETIC MOSAICISM
Transcript of CLINICAL MANIFESTATIONS OF GENETIC MOSAICISM
CLINICAL MANIFESTATIONS OF GENETIC MOSAICISM
RCPA Short course in Medical Genetics and Genetic Pathology
Adjunct Prof Mac GardnerUniv Otago & Northern Regional Genetics, NZ
This word came from the ancient Greek mouseion meaning 'place holy to the Muses‘. This transmutated into the Latin musaeum meaning ‘decoration with small square stones‘, and the decorations may originally have been dedicated to the Muses.
In medieval Latin it was changed to musaicus/mosaicus and passed via Italian mosaicoand French mosaïque into English as mosaic.
DERIVATION OF THE WORD ‘MOSAICISM’
The starting position:
Mosaicism is common
Indeed, are we all mosaics?
Consider the mathematics:
A person ≈ 10,000,000,000,000 cells
This needed 9,999,999,999,999 mitoses
No QA system could get it right that many times!
MOSAICISM:
2 or more genetically different cell lineages in the constitution of one individual, derived from a single original zygote (one cell
line usually normal)
Mendelian: Some cells/tissues carry a classic gene mutation
Chromosomal: 2 (or more) karyotypically different cell lines*:
Epigenetic: Some cells/tissues have a different imprinting state (cf. David Amor re somatic UPD11)
Immunogenetic: All that rearranging of immunogenes
CNVs: May be rather frequent
Mitochondrial: The whole question of heteroplasmy
* k i l id
Excluding:
Cancer:
Many/practically all cancers are chromosomally ‘mosaic’, but these arise post‐constitutionally in 46,XY and 46,XX people (a.k.a. normal men and women)
Example of highly complex cytogenetic aberrations in a case of high‐grade myxofibrosarcoma
Willems SM, Debiec‐Rychter M, Szuhai K, Hogendoorn PC, Sciot R. Local recurrence of myxofibrosarcoma is associated with increase in tumour grade and cytogenetic aberrations, suggesting a multistep tumour progression model. Mod Pathol. 2006 Mar;19(3):407‐16.
Excluding:
Chromosomal loss with ageing:
• The quite common finding of loss of an X or a Y chromosome in an occasional cell in an older female or male population (and more notably in centenarians) may reflect “normal” age‐related anaphase lag.
Excluding:
X Chromosome inactivation in females:
• Every 46,XX female is mosaic with respect to X chromosome activation
• An epigenetic form of mosaicism
• Each cell makes its own autonomous decision about which X – maternal or paternal – remains the active one, at a very early stage of embryonic existence
Excluding:
X Chromosome inactivation in females:
• Every 46,XX female is mosaic with respect to X chromosome activation
• An epigenetic form of mosaicism
• Each cell makes its own autonomous decision about which X – maternal or paternal – remains the active one, at a very early stage of embryonic existence
Excluding:
Chimerism:
The existence of 2 cell lines of different origins:
(1) Fusion of 2 DZ twin embryos
(2) Iatrogenic engraftment
(3) Maternal residuum of fetal cells post partum, 46,XX//46,XY: A cause of maternal auto‐immune disease (systemic sclerosis/scleroderma)
Rak JM, et al. Male microchimerism and HLA compatibility in French women with sclerodema: a different profile in limited and diffuse subset. Rheumatology 2009 48(4):363‐6.
Excluding:
Chimerism:
The existence of 2 cell lines of different origins:
(1) Fusion of 2 DZ twin embryos
(2) Iatrogenic engraftment
(3) Maternal residuum of fetal cells post partum, 46,XX//46,XY: A cause of maternal auto‐immune disease (systemic sclerosis/scleroderma)
Rak JM, et al. Male microchimerism and HLA compatibility in French women with sclerodema: a different profile in limited and diffuse subset. Rheumatology 2009 48(4):363‐6.
MOSAICISM CAN BE:
• SOMATIC,
• GONADAL, or
• SOMATIC‐GONADAL
and
• MENDELIAN, or
• CHROMOSOMAL
Distribution
Genetic type
MENDELIAN SOMATIC MOSAICISM:
The genetic error arises
• post‐zygotically, after initial differentiation of embryonic cell types
• in a cell destined to form a body lineage other than gonadal tissue.
Four examples:
• Neurofibromatosis type 1 (gene is neurofibromin)
• Neurofibromatosis type 2 (gene is NF2, a.k.a. merlin)
• Periventricular nodular heterotopia (one gene is FLNA)
• Atrial fibrillation (one gene may be GJA5)
NF1, a.k.a. VON RECKLINGHAUSEN’S DISEASE
Somatic mosaicism, also called ‘segmental’ mosaicism
Cutaneous signs confined to one region of the body
Tinschert S, Naumann I, Stegmann E, Buske A, Kaufmann D, Thiel G, Jenne DE. Segmental neurofibromatosis is caused by somatic mutation of the neurofibromatosis type 1 (NF1) gene. Eur J Hum Genet. 2000 8:455-9.
Tinschert S, Naumann I, Stegmann E, Buske A, Kaufmann D, Thiel G, Jenne DE. Segmental neurofibromatosis is caused by somatic mutation of the neurofibromatosis type 1 (NF1) gene. Eur J Hum Genet. 2000 8:455-9.
NF1, a.k.a. VON RECKLINGHAUSEN’S DISEASE
Somatic mosaicism, also called ‘segmental’ mosaicism
Cutaneous signs confined to one region of the body
Skin fibroblasts from café au lait macule deletion of the NF1 gene
Fibroblasts from skin elsewhere, and blood, normal
Tinschert S, Naumann I, Stegmann E, Buske A, Kaufmann D, Thiel G, Jenne DE. Segmental neurofibromatosis is caused by somatic mutation of the neurofibromatosis type 1 (NF1) gene. Eur J Hum Genet. 2000 8:455-9.
Mutation happened in this cell?
Cardiac tube
Mutation happened in this cell?
What he (and we) looked like at 3 weeks of age:
• 29 y/o female, quite sudden onset lower limb weakness and loss of bladder control
• Hearing grossly intact
• MRI showed spinal and intracranial tumours:
Neurofibromatosis type 2 (NF2)
a.k.a. Bilateral Vestibular Schwannoma
Tumour
Post-opPre-op
Schwannoma
Vestibular schwannoma
Question:
Will our children get this? What if we have another child?
NF2
NF2 and the neural crest ...
and Schwann cells
What she (and we) looked like at 3 weeks of age:
Cardiac tube
Neural tube
Neural crest cells
Neural
tube
At day 20 of life: genetically perfect
Neural crest cells
At day 21 of life: one (somatic) cell mutates
“First hit”
“First hit”
Orange cells = progeny cells from “first hit”
Orange cells = progeny cells from “first hit”
Cell can cross the midline
Orange cells = progeny cells from “first hit”
Purple cell = cell having “second hit”
Orange cells = progeny cells from “first hit”
Purple, blue cells = cells having “second hits”
Orange cells = progeny cells from “first hit”
Purple, blue, red = cells having “second hits”
Orange cells = progeny cells from “first hit”
Purple, blue, red = cells having “second hits”, whose progeny, being homozygous (or cpd het), can form aschwannoma
(Hypothetical) first & second hits at molecular level
gln320stop448 –1 g>a
methylation
How this knowledge, along with a basic understanding of embryology, can inform genetic counselling .....
Neural crest cells
Precursor yolk sac cells, which will ⇒blood, gametocytes
Neural crest cells
BILATERAL TUMOURS
Precursor yolk sac cells, which will ⇒gametocytes
Neural crest cells
BILATERAL TUMOURS
Precursor yolk sac cells, which will ⇒gametocytes
Blood cells
Neural crest cells
UNILATERAL TUMOURS
Precursor yolk sac cells, which will ⇒gametocytes
MINIMUM ESTIMATES OF MOSAICISM IN SPORADIC (-ve fam hx) CASES OF NF2
Bilateral vestib schwannoma: 33% +
Unilat “ “ : 60% +
But what fraction of the mosaicism includes the gonad?
Transmission risks to offspring for isolated cases of NF2, after negative mutation testing on peripheral blood
Age at dx Risk (cf. baseline risk = 50% in nonmosaic)____________________________________
VESTIBULAR SCHWANNOMA IS
____________BILAT________UNILAT____
< 20 30% 11% 20–29 16% 8%30–39 11% 6%40+ 9% 5%____________________________________
Mosaicism in neurofibromatosis type 2: an update of risk based on uni/bilaterality of vestibular schwannoma at presentation and sensitive mutation analysis including multiple ligation‐dependent probe amplification. D Gareth R Evans, R T Ramsden, A Shenton, C Gokhale, N L Bowers, S M Huson, G Pichert, A Wallace J. Med. Genet. 2007;44;424‐428.
Neurofibromatosis type 2 (NF2): a clinical and molecular review. Evans DGR. Orphanet J Rare Dis. 2009 19:16.
N.
Question:
Will our children get this? What if we have another child?
Answer:
Probably, no
NF2
• Periventricular nodular heterotopia ‐‐ a cause of epilepsy in females
Might some, mutation‐negative on blood, be due to localised (periventricular neurone) mutation in FLNA (filamin‐A)?
• Atrial fibrillation
Some may be due to localised (cardiac myocyte) mutation in ‘gap junction protein’ gene GJA5 (connexin‐40)
Gollob MH et al. Somatic mutations in the connexin 40 gene (GJA5) in atrial fibrillation. New Engl J Med 354: 2677-2688, 2006.
Immune dysfunction Adenosine deaminase deficiencyWiskott–Aldrich syndrome
Clotting disordersHaemophilia AHaemophilia B
Skeletal disorders AchondroplasiaOsteogenesis imperfectaMarfan syndromePseudoachondroplasia
Muscle disorders Duchenne muscular dystrophyCongenital myotonic dystrophy
Chromosomal instability Bloom syndromeFanconi anaemia
Tumour suppressor Neurofibromatosis type INeurofibromatosis type IITuberous sclerosis
Skin disorders Bullous ichthysiform erythrodermaIncontinentia pigmenti
Endocrine disorders Androgen insensitivity
Nervous-system Friedreich ataxia
Metabolic disordersTyrosinaemia type ILesch–Nyhan
Youssoufian & Pyeritz 2002
Recognition of somatic mosaicism: representative monogenic disorders
How much rare variation?
“The total somatic mutational load must be enormous. For example, theintestinal epithelium contains approximately 106 independent stem cells,each of which generates transient daughter cells every week or two. Thus,the intestinal epithelium of a 60-y-old is expected to harbor >109
independent mutations. This implies that, not far beyond the age of60y, nearly every genomic site is likely to have acquired a mutation inat least one cell in this single organ.”
SOMATIC ‘REVERTANT’ MOSAICISM OF LATER ORIGIN
The genetic ‘correction’ arises
• post‐zygotically
• well into embryonic/fetal development
• in a differentiated cell, destined to form just one body lineage
One example:
• Epidermolysis bullosa ‐‐ a blistering/dystrophic skin disorder
SOMATIC ‘MOSAICISM’ OF VERY EARLY ORIGIN:MZ TWIN DISCORDANCE
The genetic error arises
• post‐zygotically
• at or before the blastocyst/inner cell mass stage
• after splitting of embryo into 2
• in a cell destined to form all or almost all body lineages
Three examples:
• Dravet syndrome of severe epilepsy (gene is sodium channel SCN1A)
• NF1 (gene is neurofibromin)
• Trisomy 21 (may be ‘correction’, rather than an error)
Mendelian
Chromosomal
MZ
MZ
Twin with epilepsy →
(Dravet syndrome)
SCN1A mutation in all these tested tissues
← Unaffected twin
Normal SCN1A gene in all these tested tissues
Timing of de novo mutagenesis‐‐a twin study of sodium‐channel mutations. Vadlamudi L, Dibbens LM, Lawrence KM, Iona X, McMahon JM, Murrell W, Mackay‐Sim A, Scheffer IE, Berkovic SF. N Engl J Med 2010 363:1335‐40.
MZ
Normal allele mutates to an SCN1A allele
Zygote is normal at SCN1A locus
ONE TWIN WITH DRAVET SYNDROME
Monozygotic twins discordant for neurofibromatosis type 1 due to a postzygotic NF1 gene mutation.
Vogt J, Kohlhase J, Morlot S, Kluwe L, Mautner VF, Cooper DN, Kehrer-Sawatzki H. Institute of Human Genetics, University of Ulm, Ulm, Germany.
“Whereas DNA sequence analysis indicated somatic mosaicism for the NF1 nonsense mutation, c.4108C>T (p.Q1370X), in the affected twin, this lesion was apparently absent in his unaffected brother. . . . . .
We conclude that the twinning event, which would have taken place within three days post-fertilization, must have preceded the c.4108C>T mutation which is therefore predicted to have occurred during the blastocyst stage, leading to somatic mosaicism with normal cells lacking the mutation.”
MZ
Zygote is normal at NF1 locus
Twining occurs by day 3-4 morula/blastocyst
ONE TWIN WITH NF1
Jansen RPS, Bowman MC, de Boer KA, Leigh DA, Lieberman DB, McArthur SJ. What next for preimplantation genetic screening (PGS)? Experience with blastocyst biopsy and testing for aneuploidy. Hum Reprod 23: 1476-1478, 2008.
Hatching blastocyst →
Hatched blastocyst →
MZ
Normal allele mutates to an NF1 allele, in one cell of day 4 or 5 blastocyst
Zygote is normal at NF1 locus
Twining occurs by day 3-4 morula/blastocyst
ONE TWIN WITH NF1
MZ
‘Third’ chromo 21 lostZygote is
trisomy 21
ONE TWIN WITH TRISOMY 21
47,XX,+21 46,XX
SOMATIC MOSAICISM IN THE EARLY EMBRYO ~ CHROMOSOMAL
The genetic error arises
• post‐zygotically,
• in 1 or more cells in a preimplantation embryo
Four examples:
• Trisomy 21 mosaicism – a classic e.g. (As above, but didn’t twin)
• The concept of ‘chaotic mosaicism’ in the IVF embryo (but in vivo?)
• Fetal Trisomy 3
• ‘Hypomelanosis of Ito’ associated with mosaicism for a structural rearrangement
SOMATIC MOSAICISM IN THE EARLY EMBRYO ~ CHROMOSOMAL
The genetic error arises
• post‐zygotically,
• in 1 or more cells in a preimplantation embryo
Four examples:
• Trisomy 21 mosaicism – a classic e.g. (As above, but didn’t twin)
• The concept of ‘chaotic mosaicism’ in the IVF embryo (but in vivo?)
• Fetal Trisomy 3
• ‘Hypomelanosis of Ito’ associated with mosaicism for a structural rearrangement
PGD -- Preimplantation Genetic Diagnosis
biopsiedblastomere
‘Chaotic mosiaicism’ in a day-3 embryo
Studied blastomeres
Hypothetical derivative
−3+5+13+14+18−19+20+22+X+Y-
+1+3−18+X+Y
3
1,18,X,Y
−1+3+18−X−Y
lysed blastomere
Courtesy: Lucille Voullaire
+3−3
+3−3
N
+3−3
N
To the placenta: ‘confined placental mosaicism’
†
+3−3
N
To the inner cell mass: true mosaicism of the embryo
†
SOMATIC MOSAICISM IN THE EARLY EMBRYO ~ CHROMOSOMAL
The genetic error arises
• post‐zygotically,
• in 1 or more cells in a preimplantation embryo
Four examples:
• Trisomy 21 mosaicism – a classic e.g. (As above, but didn’t twin)
• The concept of ‘chaotic mosaicism’ in the IVF embryo (but in vivo?)
• Fetal mosaic Trisomy 3 (majority of cells trisomic)
• ‘Hypomelanosis of Ito’ associated with mosaicism for a structural rearrangement
FETAL mosaic TRISOMY 3
FETAL mosaic TRISOMY 3
FETAL TRISOMY 3
SOMATIC MOSAICISM IN THE EARLY EMBRYO ~ CHROMOSOMAL
The genetic error arises
• post‐zygotically,
• in 1 or more cells in a preimplantation embryo
Four examples:
• Trisomy 21 mosaicism – a classic e.g. (As above, but didn’t twin)
• The concept of ‘chaotic mosaicism’ in the IVF embryo (but in vivo?)
• Fetal mosaic Trisomy 3 (majority of cells trisomic)
• ‘Hypomelanosis of Ito’ associated with mosaicism for a structural rearrangement
Mosaicism for a duplication of terminal 3q: 3q26.3→3qter
HYPOMELANOSIS OF ITO
SOMATIC‐GONADAL MOSAICISM ~ CHROMOSOMAL
The genetic error arises
• post‐zygotically,
• in a cell destined to form somatic and gonadal tissue.
One example:
• Parental low‐level mosaicism for a deletion of chromosome 1q
blood
GONADAL MOSAICISM
The genetic error arises
• post‐zygotically,
• in a mitotic (pre‐meiotic) gametocyte
• Consider the seminiferous tubule total length of 1 km . . . .
1,000/1,000,000,000 = 1 millionth of the tubule has this abnormality
Close to 1 km of tram track in view
A small ($2) coin comprises 1/50,000 of the distance.
GONADAL MOSAICISM ~ CHROMOSOMAL
One example:
• Parental low‐level mosaicism for a duplication ‐‐ dup(21)
mos dup(21)
• Couple, 3 previous miscarriages, 2 previous failed IVF cycles
• IVF/PGD using FISH, 13 embryos, 2 transfers, 0 pregnancies
• Of 13 embryos, 4 showed apparent dup(21)(q22)
• Of 1002 sperm, 66 showed the same apparent dup(21)
Somprasit et al., RBM Online 9, 225,
Cell from embryo Sperm cells
Reprod Biomed Online 9, 225, 2004
4
26
6% of the track between here and the tram
GONADAL MOSAICISM ~ MENDELIAN:
Two examples:
• Duchenne muscular dystrophy (gene is dystrophin)
• Achondroplasia (gene is FGFR3)
Gonadal mosaicism for Duchenne muscular dystrophy (gene is dystrophin)
Melis MA, Cau M, Congiu R, Puddu R, Muntoni F, Cao A. Germinal mosaicism in a Duchenne muscular dystrophy family: implications for genetic counselling. Clin Genet. 1993 43:247-9.
Natacci F, Baffico M, Cavallari U, Bedeschi MF, Mura I, Paffoni A, Setti PL, Baldi M, Lalatta F. Germline mosaicism in achondroplasia detected in sperm DNA of the father of three affected sibs. Am J Med Genet 2008 146A:784-6.
Gonadal mosaicism for achondroplasia (gene is FGFR3)
Peripheral blood:
Sperm:
PATHOGENIC MOSAICISM CAN BE:
• SOMATIC
e.g. Segmental NF1, Hypomelanosis of Ito
• overtly SOMATIC‐GONADAL
e.g. Father carries deleted no. 1 chromosome
• GONADAL
e.g. grandfather carries Duchenne, father carries abn chromosome 21
END
Arvid Lindau (1892 – 1958), a Swedish pathologist, who described the link between the retinal, cerebellar and visceral components of a disease, which he called “angiomatosis of the central nervous system”.
Eugen von Hippel (1867 ‐ 1939), a German ophthalmologist, first described “angiomatosis retinae” in 1911.
VHL ? Somatic mosaic
• 49 y/o man, onset giddiness, ataxia, vomiting loss of consciousness
• MRI cerebellar tumour
• Histo confirms haemangioblastoma
• Second small lesion in R cerebellar hemisphere
• Renal and pancreatic cysts
Cerebellar haemangioblastoma
P
• No retinal angiomas
• MRI r/v normal adrenal, inner ear anatomy
• Plasma metanephrine normal
VHL:
• Cerebellar/spinal hemangioblastoma
• Retinal angioma
• Pheochromocytoma (incl. extra‐adrenal)
• Renal cancer
• Renal cysts
• Pancreatic cysts
• Epididymal cysts
• Endolymphatic sac tumour
• +ve family hx
• But: on VHL gene sequencing no mutation; andon MLPA, no large deletion/duplication
Note: gene testing has high (97%) detection rate
Why no mutation found?
Possible explanations:
• A VHL‐like ‘phenocopy’ ?
• True VHL, mutation not able to be detected ?
• Somatic (or somatic‐gonadal) mosaicism ?
…… distinction important, in order to be able to advise son
Youssoufian & Pyeritz 2002
a | Asymmetric fibrous dysplasia (non-neoplastic developmental disease of osseous tissue) of bones and irregular skin hyperpigmentation in a female with MCCUNE–ALBRIGHT SYNDROME101. (Reproduced with permission from REF. 131 © (1993) Oxford University Press).
*
b | Regenerating liver nodules (asterisk) that have a reversion of an inherited mutation in the fumarylacetoacetate hydrolase gene, which causes HEREDITARY TYROSINAEMIA TYPE I.(Reproduced with permission from REF. 22 © (1998) Elsevier Science (USA)
Youssoufian & Pyeritz 2002
Cytogenetic abnormalities and fragile-x syndrome in Autism Spectrum DisorderKavita S Reddy Genzyme Genetics, Orange CA 92868, USAauthor email corresponding author email
BMC Medical Genetics 2005, 6:3J Med Genet. 1996 Apr;33(4):338-40.Mosaicism for the fragile X syndrome full mutation and deletions within the CGG repeat of the FMR1 gene.Milà M, Castellví-Bel S, Sánchez A, Lázaro C, Villa M, Estivill X.