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Smith-McCort dysplasia 2(SMC2)

MedGen UID:
811489
Concept ID:
C3714896
Disease or Syndrome
Synonym: SMC2
 
Gene (location): RAB33B (4q31.1)
 
Monarch Initiative: MONDO:0014087
OMIM®: 615222

Definition

Smith-McCort dysplasia is a rare autosomal recessive osteochondrodysplasia characterized by short trunk dwarfism with a barrel-shaped chest, rhizomelic limb shortening, and specific radiologic features including marked platyspondyly with double-humped end-plates, kyphoscoliosis, metaphyseal irregularities, laterally displaced capital femoral epiphyses, and small pelvis with a lace-like appearance of iliac crests. These clinical and radiologic features are also common to Dyggve-Melchior-Clausen syndrome (DMC; 223800), which is distinguished from SMC by the additional feature of mental retardation (summary by Dupuis et al., 2013). For a discussion of genetic heterogeneity of Smith-McCort dysplasia, see SMC1 (607326). [from OMIM]

Clinical features

From HPO
Pes planus
MedGen UID:
42034
Concept ID:
C0016202
Anatomical Abnormality
A foot where the longitudinal arch of the foot is in contact with the ground or floor when the individual is standing; or, in a patient lying supine, a foot where the arch is in contact with the surface of a flat board pressed against the sole of the foot by the examiner with a pressure similar to that expected from weight bearing; or, the height of the arch is reduced.
Genu valgum
MedGen UID:
154364
Concept ID:
C0576093
Anatomical Abnormality
The legs angle inward, such that the knees are close together and the ankles far apart.
Short phalanx of finger
MedGen UID:
163753
Concept ID:
C0877165
Finding
Short (hypoplastic) phalanx of finger, affecting one or more phalanges.
Short metacarpal
MedGen UID:
323064
Concept ID:
C1837084
Anatomical Abnormality
Diminished length of one or more metacarpal bones in relation to the others of the same hand or to the contralateral metacarpal.
Broad metatarsal
MedGen UID:
330797
Concept ID:
C1842231
Finding
Increased side-to-side width of a metatarsal bone.
Broad femoral neck
MedGen UID:
376496
Concept ID:
C1849016
Finding
An abnormally wide femoral neck (which is the process of bone, connecting the femoral head with the femoral shaft).
Broad phalanx
MedGen UID:
340809
Concept ID:
C1855185
Finding
Increased side-to-side width of one or more phalanges of the fingers or toes.
Flattened femoral head
MedGen UID:
348146
Concept ID:
C1860601
Finding
An abnormally flattened femoral head.
Short stature
MedGen UID:
87607
Concept ID:
C0349588
Finding
A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms).
Decreased body weight
MedGen UID:
375512
Concept ID:
C1844806
Finding
Abnormally low body weight.
Pectus carinatum
MedGen UID:
57643
Concept ID:
C0158731
Finding
A deformity of the chest caused by overgrowth of the ribs and characterized by protrusion of the sternum.
Barrel-shaped chest
MedGen UID:
120497
Concept ID:
C0264172
Finding
A rounded, bulging chest that resembles the shape of a barrel. That is, there is an increased anteroposterior diameter and usually some degree of kyphosis.
Metaphyseal irregularity
MedGen UID:
325478
Concept ID:
C1838662
Finding
Irregularity of the normally smooth surface of the metaphyses.
Platyspondyly
MedGen UID:
335010
Concept ID:
C1844704
Finding
A flattened vertebral body shape with reduced distance between the vertebral endplates.
Disproportionate short-trunk short stature
MedGen UID:
337580
Concept ID:
C1846435
Finding
A type of disproportionate short stature characterized by a short trunk but a average-sized limbs.
Hypoplasia of the odontoid process
MedGen UID:
339524
Concept ID:
C1846439
Finding
The odontoid process, or dens, is a bony projection from the axis (C2) upward into the ring of the atlas (C1) at the top of the spine. During embryogenesis, the body of the odontoid derives from the centrum of the atlas and separates from the atlas, fusing with the superior portion of the axis. If the odontoid is hypoplastic or absent, the attachments for the apical and alar ligaments are missing, allowing for excessive rotation of the atlas, craniocervical instability, and possibly cord compression (summary by Stevens et al., 2009).
Short metatarsal
MedGen UID:
341358
Concept ID:
C1849020
Finding
Diminished length of a metatarsal bone, with resultant proximal displacement of the associated toe.
Flattened epiphysis
MedGen UID:
387844
Concept ID:
C1857527
Finding
Abnormal flatness (decreased height) of epiphyses.
Short neck
MedGen UID:
99267
Concept ID:
C0521525
Finding
Diminished length of the neck.

Recent clinical studies

Etiology

Varshney K, Narayanachar SG, Girisha KM, Bhavani GS, Narayanan D, Phadke S, Nampoothiri S, Udupi GA, Raghupathy P, Nair M, Geetha TS, Bhat M
J Med Genet 2023 Feb;60(2):204-211. Epub 2022 Apr 27 doi: 10.1136/jmedgenet-2021-108098. PMID: 35477554

Diagnosis

Holling T, Bhavani GS, von Elsner L, Shah H, Kausthubham N, Bhattacharyya SS, Shukla A, Mortier GR, Schinke T, Danyukova T, Pohl S, Kutsche K, Girisha KM
Hum Mutat 2022 May;43(5):625-642. Epub 2022 Mar 21 doi: 10.1002/humu.24368. PMID: 35266227
Tüysüz B, Geyik F, Yıldırım T, Alkaya DU, Sharifova S, Kafadar A
Eur J Med Genet 2021 Jul;64(7):104248. Epub 2021 May 14 doi: 10.1016/j.ejmg.2021.104248. PMID: 34000439
Dupuis N, Lebon S, Kumar M, Drunat S, Graul-Neumann LM, Gressens P, El Ghouzzi V
Hum Mutat 2013 Feb;34(2):283-6. Epub 2012 Nov 8 doi: 10.1002/humu.22235. PMID: 23042644

Clinical prediction guides

Tüysüz B, Geyik F, Yıldırım T, Alkaya DU, Sharifova S, Kafadar A
Eur J Med Genet 2021 Jul;64(7):104248. Epub 2021 May 14 doi: 10.1016/j.ejmg.2021.104248. PMID: 34000439

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